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Pressure Relief Valves

ANDERSON GREENWOODflow control

Technical ManualTechnical Manual


Anderson Greenwood Pressure Relief ValvesTechnical Manual

© 1997 Anderson Greenwood reserves the right to change product designs and specifications without notice. 3

Contents


General Information ........................................................................... 1, 2Glossary ............................................................................................ 3, 4

Valve SizingNomenclatures ................................................................................... 5 - 7Valve Data ......................................................................................... 8 - 14Back Pressure and Subsonic Correction............................................ 16 - 21Gas and Vapor.................................................................................... 22 - 24Steam ................................................................................................. 25 - 30Liquid.................................................................................................. 31 - 35Subsonic Flow .................................................................................... 37 - 45Special Applications ........................................................................... 46 - 47Reaction Forces ................................................................................. 48

Conversion Factors........................................................................................................... 49 - 55

Fluid Data........................................................................................................... 56 - 61

ANSI Flange Standards........................................................................................................... 62 - 76

Valve Installations - Handling Procedures........................................................................................................... 77

ASME Code Section I1Excerpts ............................................................................................. 78 - 91

ASME Code Section IV1

Excerpts ............................................................................................. 92 - 97

ASME Code Section VIII1Excerpts ............................................................................................. 98 - 116

API RP 520 Part I1Excerpts ............................................................................................117 - 149

API RP 520 Part II1Excerpts ............................................................................................150 - 158

NACE MR0175-951

Excerpts ............................................................................................159 - 169

API RP 5211

Noise Levels ...................................................................................... 170

API RP 5271

Seat Leakage Requirements..............................................................171 - 173

Section 16Chemical Resistance for Metals ........................................................174 - 180

Section 17Chemical Resistance for Elastomers/Thermoplastics ........................181 - 205

Note

1. Some referenced figures, tables, equations,or paragraphs may not be included. Consultoriginal document for complete text.

Pressure Relief ValveTechnical ManualRevised May 1998Catalog: PRVTM-US.97



IntroAnderson Greenwood is a globally recog-nized leader in the field of pressure reliefdevice technology. Fundamental to ourability to solve the most challenging appli-cation is our belief in understanding allapplication parameters. As a leader in thefield of pressure relief device education, weproudly provide this manual for use as thefinest technical source on our technologyand the specialized area of these safetydevices. The users of this manual will ben-efit from its completeness as a pressurerelief device resource document.

Body MaterialsPressure relief valve standard body mate-rials are ASME SA-216 grade WCB orWCC CS, or ASME SA-351 GR. CF8MSS. Also available at additional costs arebodies of special alloys, such as Hastelloy®

‘C’, Monel®, high temperature alloy, du-plex SS, Titanium, alloy 20 and others.

CastingsValve castings to meet requirements of radiography, magnetic particle, liquid pen-etrant examination and Charpy Impacttests are available on special order. Ourdocumented quality control can providecomplete chemical and physical analysisfor all cast materials on request.

Standard Flanged Connections(a) All steel flange ratings conform to

ANSI B-16.5 – 1977 and are indicatedon each orifice selector chart in the ap-plicable product catalog. Heavier outletflanges are available on application.For back pressure exceeding listedvalues, consult the factory for valvelimitations. Steel raised face flangesare provided with a serrated finish onthe flange face.

(b) Standard Aluminum valves are manu-factured with flat faced flange finish inaccordance with commercial practice.The flanges are designated as Class125 FF, with drilling equal to ANSIClass 150.

(c) All iron flange ratings conform to ANSI B-16.1 – 1977 and to FlangeDimension Table (page 70). Iron flatface flanges are supplied with asmooth surface on flange face.

(d) Bronze flange ratings conform to ANSIB-16.24 and to Flange DimensionTable (page 86). Bronze flat faceflanges are supplied with a smoothsurface on flange face.

(e) All ring joint flange facings comply withANSI B-16.5 – 1977 ring groove. Forring joint facing dimensions, refer tothe Flange Dimension Table (page 73).

(f) Flange facings different from raisedface can be furnished at additional cost.The standard surface finish roughnessis 125-250 AARH. DIN, JIS, or otherflange finishes may be available on aproduct-by-product basis. Contact oursales department for availabilities.

(g) Drilling of both inlet and outlet flangesalways straddles center lines. Offsetdrilling is available with proper appli-cation.

Special FlangesAnderson, Greenwood offers a variety ofnon-standard connection arrangements tomeet the most exacting special flange re-quirement.

Spring MaterialsPressure relief valve standard spring ma-terials are carbon steel aluminum painted.Spring materials of special alloys, such astungsten steel, 316 SS, 302 SS, phosphorbronze, K-Monel® and Inconel® and oth-ers are all available in many models onrequest.

Spring AssemblyCorrosion ProtectionAt additional cost, springs can be fur-nished with protective finishes of phenolic,plastic, epoxy resin, and nickel plate.

Bellows ValvesFor easy field conversion, the convention-al valve – D Series – may be changed to abellows valve – all orifice sizes from F to T– by installing the bellows assembly andgaskets. Standard material for all bellowsis Inconel® 625. KYNAR® coating, Monel®

and other materials available at additionalcost. Bellows conversions in D and E ori-fices require a body adapter, stem, guide,gaskets and bellows.

Bellows CoatingThe standard bellows is Inconel® 625.KYNAR® coating of the bellows for addi-tional corrosion protection is available atadditional cost.

Seating SurfacesArmco 17-4 PH stainless steel hardenedto hardfaced equivalence is an optional D Series disc material. The seating sur-faces for other models with stainless steeltrim can be hardfaced, when specified, atadditional cost.

General Information

Copyright Notes

1. © ASME: the American Society ofMechanical Engineers.

2. © NACE: National Association of CorrosionEngineers.

3. © API: American Petroleum Institute.

Notes

1. Shop test procedure for temperature com-pensation available on request.

2. All shop orders will state 100°F [38°C] un-less customer’s purchase order statesotherwise.

3. Inconel® and Monel® are registered trade-marks of the International Nickel Company.

4. KYNAR® is a registered trademark of thePennwatt Chemical Corporation.

5. Hastelloy® is a registered trademark ofHaynes International.

© 1995 Keystone/Anderson, Greenwood & Co. 2



O-ring Seat SealsAnderson Greenwood offers the mostcomplete line of pressure relief valves withO-ring seat seals. All valves are available– up to the maximum pressure limits – in a variety of O-ring materials. See O-ringSeals Section for complete details andspecifications.

Trim or Wetted PartsTrim refers to the nozzle or base and thedisc in direct spring valves. Consult eachproduct catalog for available materials.

Operating and SetPressure DifferentialsOptimum performance of a direct springpressure relief valve protected system isavailable at operating pressures up to90% of valve set pressure. Pump andcompressor discharge pulsations are off-set by the greatest allowable valve setpressure differentials. System pressurepulsations can cause valve malfunctions.Therefore, the pressure relief valve shouldbe set as high as possible above the discharge line pressure. Applications re-quiring closer system-to-valve pressuredifferentials may be accommodated bysoft seat seal, or Anderson, Greenwoodhigh performance Series 80 or PilotOperated Valves.

Cold Differential Test Pressure RecommendationsWhen pressure relief valves for high tem-perature service are tested at roomtemperature, a compensating adjustmentis made in the set pressure. High temper-ature reduces set pressure – lessensspring load – via thermal expansion ofspring, body and bonnet. Cold differentialtest pressure adjustments are also required on unbalanced valves when constant applied back pressure conditionsexist. Cold differential test pressure adjustments are indicated on the valvenameplate, and are recorded on the func-tional test report.

Set Pressure Lower LimitsMinimum set pressure per valve series is listed in the applicable product catalog.

Seat TightnessAll metal seated pressure relief valves aretested for seat leakage per API STD 527and ANSI B147.1.

The Anderson Greenwood tightness standard for Series 80 and Pilot Operatedpressure relief valves soft seated valvesis: ‘no leakage at 95% of set pressure forset pressures of 60 psig [4.13 barg] andhigher, or no leakage at 3 psig [.21 barg]below the set pressure for set pressuresbelow 60 psig [4.13 barg].’ For all other di-rect spring, soft-seated pressure reliefvalves, seat tightness is: ‘no leakage at90% of set pressure for set pressures 15psig [1.03 barg], or no leakage at 3 psig[.21 barg] below the set pressure for setpressures below 15 psig [1.03 barg].’

Special ApplicationsMany exacting process applications re-quire specially built valves. When yourvalve requirements exceed catalog de-scriptions, Anderson Greenwood invitesyou to submit the specifications. Designdata and quotations will be furnished.

Valves for Corrosive ServiceA design advantage frequently overlookedin corrosive application is the full nozzleinlet option on many of our valve models.Until a valve discharges – an infrequentoccurrence – the only contact surfacesare the wetted parts – nozzle and disc.Where standard materials are susceptibleto attack, corrosion resistant alloys arerecommended.

Valves for Low TemperatureServiceAnderson Greenwood has a wide range ofpressure relief devices to meet servicetemperatures to -450°F [-267°C].

Steam Jacketed ValvesTo keep viscous fluids flowing or to pre-vent lading fluids from becoming solidified,heat is often applied to the valves. Appli-cation of heat, to the valves and piping,however, is often a problem. Steam tracing lines and insulation are frequentlyrequired, in addition to heating coils.Removal and reinstallation of a valve isexpensive, time consuming and can cre-ate costly delays in a process application.

Proper heat transfer to keep viscous fluidsin their correct flowing state can be ob-tained by integrally jacketing the housingof the valve. Piping can be simplified, thusreducing maintenance time and permittingthe use of many standard replacementparts.

Contact your Anderson Greenwood representative or the factory for more in-formation on Steam Jacketed Valves.Steam Jackets are available in integrallycast or bolt on type for the D and L Seriesonly.

Installation and MaintenanceComplete installation and maintenancetraining manuals are available on request.

Replacement Valvesand Repair PartsSubmit valve serial number for exact replacement. Anderson Greenwood willsupply a valve with correct materials anddimensions. The serial number for mostvalves is located on the nameplate andstamped on the perimeter of the outlet or body flange. Proper replacement will be made for valves which have becomeobsolete. Iron and bronze valves may re-quire the complete model number, locatedon the nameplate.

Repair ToolsFor proper maintenance of AndersonGreenwood Pressure Relief Valves, noz-zle wrenches, lapping discs and lappingplates are available, as are complete operating, installation and maintenancemanuals.

General Information

Glossary

Accumulation is the pressure increaseover the maximum allowable workingpressure of the vessel during dischargethrough the pressure relief device, ex-pressed in pressure units or as a percent.Maximum allowable accumulations areestablished by applicable codes for oper-ating and fire contingencies.

Actual Discharge Area is the measuredminimum net area that determines theflow through a valve.

Back Pressure is the pressure that exists at the outlet of a pressure relief device as a result of the pressure in thedischarge system.

Balanced Pressure Relief Valve is aspring-loaded pressure relief valve that in-corporates a means for minimizing theeffect of back pressure on the perfor-mance characteristics.

Blowdown is the difference between theset pressure and the closing pressure of apressure relief valve, expressed as a per-cent of the set pressure or in pressureunits.

Built-up Back Pressure is the increase inpressure in the discharge header that de-velops as a result of flow after thepressure relief device opens.

Closing Pressure is the value of de-creasing inlet static pressure at which thevalve disc re-establishes contact with theseat or at which lift becomes zero.

Cold Differential Test Pressure is thepressure at which the pressure relief valveis adjusted to open on the test stand. Thecold differential test pressure includes cor-rections for the service conditions of backpressure or temperature or both.

Conventional Pressure Relief Valve is aspring-loaded pressure relief valve whoseperformance characteristics are directlyaffected by changes in the back pressureon the valve.

Curtain Area is the area of the cylindricalor conical discharge opening between theseating surfaces above the nozzle seatcreated by the lift of the disc.

Design Gauge Pressure refers to at leastthe most severe conditions of coincidenttemperature and pressure expected duringoperation. This pressure may be used inplace of the maximum allowable workingpressure in all cases where the MAWP hasnot been established. The design pressureis equal to or less than the MAWP.

Effective Discharge Area or EquivalentFlow Area is a nominal or computed areaof a pressure relief valve used in recog-nized flow formulas to determine the sizeof the valve. It will be less than the actualdischarge area.

Huddling Chamber is an annular pres-sure chamber in a pressure relief valvelocated beyond the seat for the purpose of generating a rapid opening.

Inlet Size is the nominal pipe size (NPS)of the valve at the inlet connection, unlessotherwise designated.

Leak-test Pressure is the specified inletstatic pressure at which a seat leak test isperformed.

Lift is the actual travel of the disc awayfrom the closed position when a valve isrelieving.

Maximum Allowable Working Pressure(MAWP) is the maximum gauge pressurepermissible at the top of a completed vessel in its operating position for a desig-nated temperature. The pressure is basedon calculations for each element in a ves-sel using nominal thicknesses, exclusiveof additional metal thicknesses allowed forcorrosion and loadings other than pres-sure. The maximum allowable workingpressure is the basis for the pressure set-ting of the pressure relief devices thatprotect the vessel.

Maximum Operating Pressure is themaximum pressure expected during sys-tem operation.

Nozzle Area is the cross-sectional flowarea of a nozzle at the minimum nozzle diameter.





Glossary

Opening Pressure is the value of in-creasing inlet static pressure at whichthere is a measurable lift of the disc or atwhich discharge of the fluid becomes con-tinuous.

Outlet Size is the nominal pipe size(NPS) of the valve at the discharge con-nection, unless otherwise designated.

Overpressure is the pressure increaseover the set pressure of the relieving de-vice, expressed in pressure units or as apercent. It is the same as accumulationwhen the relieving device is set at themaximum allowable working pressure of the vessel, and the inlet pipe pressureloss is zero.

Pilot Operated Pressure Relief Valve isa pressure relief valve in which the mainvalve is combined with and controlled byan auxiliary pressure relief device.

Pressure Relief Device is actuated by inlet static pressure and designed to openduring an emergency or abnormal condi-tions to prevent a rise of internal fluidpressure in excess of a specified value.The device also may be designed to pre-vent excessive internal vacuum. Thedevice may be a pressure relief valve, a nonreclosing pressure relief device, or a vacuum relief valve.

Rated Relieving Capacity is that portionof the measured relieving capacity permit-ted by the applicable code or regulation tobe used as a basis for the application of apressure relief device.

Relief Valve is a spring-loaded pressurerelief valve actuated by the static pressureupstream of the valve. The valve opensnormally in proportion to the pressure in-crease over the opening pressure. A reliefvalve is used primarily with incompress-ible fluids.

Relieving Conditions is the term used toindicate the inlet pressure and tempera-ture on a pressure relief device at aspecific overpressure. The relieving pres-sure is equal to the valve set pressure (orrupture disc burst pressure) plus the over-pressure. (The temperature of the flowingfluid at relieving conditions may be higheror lower than the operating temperature.)

Rupture Disc Device is a nonreclosingdifferential pressure relief device actuatedby inlet static pressure and designed tofunction by bursting the pressure-contain-ing rupture disc. A rupture disc deviceincludes a rupture disc and a rupture discholder.

Safety Relief Valve is a spring-loadedpressure relief valve that may be used aseither a safety or relief valve dependingon the application.

Safety Valve is a spring-loaded pressurerelief valve actuated by the static pressureupstream of the valve and characterizedby rapid opening or pop action. A safetyvalve is normally used with compressiblefluids.

Set Pressure is the inlet gauge pressureat which the pressure relief valve is set toopen under service conditions.

Simmer is the audible or visible escape ofcompressible fluid between the seat anddisc at an inlet static pressure below the setpressure and at no measurable capacity.

Spring-loaded Pressure Relief Valve isa pressure relief device designed to auto-matically reclose and prevent the furtherflow of fluid.

Stamped Capacity is the rated relievingcapacity that appears on the devicenameplate. The stamped capacity isbased on the set pressure or burst pres-sure plus the allowable overpressure forcompressible fluids and the differentialpressure for incompressible fluids.

Superimposed Back Pressure is the static pressure that exists at the outlet of a pressure relief device before it actuates.It is the result of pressure in the dischargesystem coming from other sources andmay be constant or variable.



A Orifice area or equivalent flow area.

C The gas constant of gas, derived fromthe specific heat ratio, k. If C is un-known, use C = 315, a conservativevalue. Refer also to Physical Propertiesof Selected Gases.

F´ Subsonic flow factor, based on the ratioof specific heats and pressure drop (dif-ferential) across the valve or nozzle.

k The ratio of specific heats of gas, wherek = Cp/Cv. When the value of k is un-known, use k = 1.001, a conservativevalue. Refer also to Physical Propertiesof Selected Gases.

K The valve coefficient to be used whereset pressure is 15 psig [1.03 barg] andgreater, and in accordance with the re-quirements of Section VIII, Division 1 ofthe ASME Boiler and Pressure VesselCode, ASME I, and ASME III. Valve co-efficient K includes the required deratingto 90% of actual average measured noz-zle coefficient, KD, as required by theASME Code. Please note that safetyvalve models available for gas and liq-uid applications will have differingnozzle coefficients.

Kb A back pressure correction factor forgas, used when the flow becomes sub-sonic, occurring when the pressure ratioacross the valve nozzle exceeds thecritical pressure, PCF/P1.

KN Steam flow correction factor, from theNapier equation.

KSH Superheat correction factor for use inthe steam formulas.

M Molecular weight of the flowing gas.Refer to Physical Properties of SelectedGases, or other resources, for listing of M.

P Set pressure in gauge units. All formulasherein are based on barg or psig.

Pb Back pressure, under relieving condi-tions, at valve outlet in gauge pressureunits.

square inch square centimeter(in2) [cm2]

— —

— —

— —

— —

— —

— —

— —

— —

lb/in2 gauge bar gauge(psig) [barg]


Gas and Steam Flow

Symbol Description Inch MetricPounds Units

Valve Sizing – Nomenclature



P1 Absolute pressure at valve inlet con-nection under relieving conditionsand equal to set pressure, p + over-pressure + atmospheric pressure.Atmospheric pressure will be equalto standard sea level pressure, 14.7 psia [1.013 bara], unless other-wise specified. When a local plantsite barometric pressure is men-tioned, sizing for orifice area shouldbe made with the stated local baro-metric pressure.

P2 Absolute pressure at valve outlet under relieving conditions; equal toback pressure, pb + atmosphericpressure (as expressed in previousparagraph).

PCF/P1 Critical pressure ratio. The critical pres-sure ratio is used to determine if theback pressure correction factor Kbshall be applied to the sizing formula.

t Relieving temperature, to be evaluat-ed at the valve inlet, under relievingcondition.

T Absolute relieving temperature,equal to relieving temperature plusbase temperature, where:

T [°Rankin] = t [°F] + 460 andT [Kelvin] = t [°C] + 273

V Gas flow capacity expressed in volumetric units per time unit. Theformulas in this section are based on a sea level atmospheric pressureof 14.7 psia [1.013 bars] and a temperature base of 60°F or 0°C, respectively for metric and inch-pound systems. Refer to Gas FlowConversions for other pressure andtemperature bases as well as otherunits of measure.

W Gas flow capacity expressed inweight units per time unit. Refer toGas Flow Conversions for otherunits of measure.

Z Compressibility factor, correcting forthe difference between the physicalcharacteristics of a theoretical gasand the actual gas under considera-tion. If Z is unknown, use Z = 1.00.

lb/in2 absolute bar absolute(psia) [bara]



— —

degrees Fahrenheit degrees Celsius(°F) [°C]

degrees Rankin degrees Kelvin(°R) [°K]

standard cubic feet normal cubic metersper minute per hour

(scfm) [Nm3/h]

pounds per hour kilograms per hour(lb/h) [kg/h]

— —

Gas and Steam Flow



Note

1. The formulas using this pseudo pressureratio are valid only for the specified pres-sure units to the right and for the Series 90low pressure pilot operated safety valves.

P

P

2

1

P2

P1

Set pressure = 15 psig[1.03 barg] and higher

Set pressure is less than 15 psig [1.03 barg]



A Orifice area

G Relative density of liquid at flowing tem-perature, referred to water at 68°F [20°C].Gwater = 1.00.

K Effective or certified nozzle coefficient. Thecertified nozzle coefficients, when given,are in accordance with the requirements ofSection VIII, Division 1 of the ASME Boilerand Pressure Vessel Code, ASME I, andASME III and include a derating to 90% ofactual, as required by the Code. The effec-tive nozzle coefficients, when given, alsoassume the same derating, but are not cer-tified by the National Board of Boiler andPressure Vessel Inspectors. Please notethat safety valve models available for gasand liquid applications will have differingnozzle coefficients.

Kp Capacity correction factor due to lift charac-teristics of conventional and balanced springoperated valves, in liquid service, where fulllift is achieved at 25% overpressure. Use Kp= 0.60 for sizing these valve types at 10%overpressure, and Kp = 1.00 for 25% andgreater overpressure.1

Kv Capacity correction factor due to viscosity.For most applications, viscosity may not besignificant, in which case use Kv = 1.00.

Kw Capacity correction factor for balanced bel-lows safety valves due to back pressure.Use Kw = 1.00 for conventional (unbal-anced) and pilot operated safety valves.

p1 Upstream pressure under relieving condi-tions. This is set pressure, plusoverpressure.2

p2 Total back pressure, under relieving con-ditions, at valve outlet.

R Reynolds Number. A dimensionless ex-pression for the flow behavior of fluidsand is used to determine the viscositycorrection factor Kv.

µ Absolute viscosity of the liquid at the re-lieving temperature. Kinematic viscosityand/or viscosity expressed in other unitsof measure must be converted to ab-solute viscosity in centipoise. Most liquidapplications need not consider viscosityand should therefore use a Kv = 1.00.The approximate viscosity of water undermost conditions is 1 centipoise. When vis-cosity is given, it should be considered.

W Liquid flow rate.

square inch square centimeter (in2) [cm2]— —

— —

— —

— —

— —



— —

centipoise centipoise

US gallons cubic metersper min per hour

(US gpm) [m3/h]

Liquid Flow



Notes

1. Relief valves certified for liquid applica-tions with full lift at 10% overpressure,shall use Kp = 1.00 at 10% and greateroverpressure. The 1985 revision to ASMEVIII required all liquid relief valves to havecertified capacities at 10% overpressure.Therefore, the use of Kp in the sizing for-mula would apply to non-ASME Codevalves only.

2. The maximum permitted values of over-pressure for various types of liquid safetyvalves in this manual are as follows:

Maximum Liquid Safety Overpressure Valve Type

10% Pilot operated.

10% Conventional and bal-anced direct springoperated, with certified fulllift at 10% overpressure.

25% Conventional and balanced direct spring op-erated valves not meetingthe above requirements. Note: Sizing may be doneat 10% overpressure whenthe correction factor Kp ismade equal to 0.60.



Valve Sizing – Nozzle Coefficients

ASME Nozzle Coefficients – Direct Spring PRVs

Valve ASME I ASME III ASME IV ASME VIIISteam Hot Water Steam Gas, Vapor Liquids Steam Steam Gas, Vapor Liquids

A Series .975 .878 .878 .710

D Series .878 .878 .700 .878 .878 .700

F Series .798 .878 .878

G Series .840 .878 .878

K Series .878 .878

L Series .874 .874 .475 .874 .874 .475

Y Series .840 .878 .878

15W .975

Model 61 .877

Model 63B .877

Model 83F .847

Model 81, 83 .988

Model 86 .816 .816

Model 81P .720

API Nozzle Coefficients – Direct Spring PRVs

Valve ASME I ASME III ASME IV ASME VIIISteam Hot Water Steam Gas, Vapor Liquids Steam Steam Gas, Vapor Liquids

A Series .878

D Series .971 .971 .776 .971 .971 .776

F Series .876 .910 .910

G Series .876 .910 .910

K Series .878 .878

L Series .971 .971 .528 .971 .971 .528

Y Series .876

15W .975

Model 61 .877

Model 63B .847

Model 83F .998

Model 81, 83 .816

Model 86 .816

Model 81P .720

1. ASME nozzle coefficient is the actual coeffi-cient recorded by the National Board ofBoiler and Pressure Vessel Inspectors. Itdiffers from the API nozzle coefficient.When sizing PRVs using the ASME coeffi-cient, the ASME area must be used.

The API nozzle coefficient is an effective coefficient to be used when sizing PRVs using API 526 orifice areas.

Note



Valve Sizing – Nozzle Coefficients

ASME Nozzle Coefficients – Pilot Operated PRVs

Valve ASME VIIISteam Gas, Vapor Liquids

223, 233 .830

423, 433 .830 .650

623, 633 .830 .650

823, 833 .830 .650

923, 933 .830 .650

226 .833

526 .833 .833 .650

576 .809 .809

727 .788 .788

273, 473, 673, 873, 973 .809

91/94 .770

93/93T .845

95 .852

9300 .629

API Nozzle Coefficients – Pilot Operated PRVs

Valve ASME VIIISteam Gas, Vapor Liquids

223, 233 .860

423, 433 .860 .670

623, 633 .860 .670

823, 833 .860 .670

923, 933 .860 .670

226 .860

526 .860 .860

576 .860 .860

727 .975 .975

273, 473, 673, 873, 973 .860

91/94 .770

93/93T .845

95 .852

9300 .629



Valve Sizing – Orifice Areas

Orifice Areas – Direct Spring PRVs

Valve Orifice ASME Area API AreaDesignation (in2) [cm2] (in2) [cm2]

A Series D .1213 .783 .110 .710

A Series E .2157 1.392 .196 1.265

A Series F .3369 2.174 .307 1.981

A Series G .553 3.568 .503 3.245

A Series H .864 5.574 .785 5.065

A Series J 1.415 9.129 1.287 8.303

D Series D .1219 .786 .110 .710

D Series E .2173 1.402 .196 1.265

D Series F .340 2.194 .307 1.981

D Series G .558 3.600 .503 3.245

D Series H .869 5.606 .785 5.065

D Series J 1.427 9.206 1.287 8.303

D Series K 2.036 13.135 1.838 11.858

D Series L 3.160 20.380 2.853 18.406

D Series M 3.987 25.720 3.600 23.230

D Series N 4.807 31.010 4.340 28.030

D Series P 7.070 45.610 6.380 41.160

D Series Q 12.240 73.970 11.050 71.290

D Series R 17.720 114.320 16.000 103.230

D Series T 28.800 185.810 26.000 167.740

Note

1. The ASME area is the actual flow area certi-fied by the National Board of Boiler andPressure Vessel Inspectors. The API area isthe flow area defined per API 526. Whensizing PRVs, care should be exercised tonot mix API and ASME values.




Orifice Areas – Direct Spring PRVs

Valve Orifice ASME Area API AreaDesignation (in2) [cm2] (in2) [cm2]

K Series F .307 1.981 .307 1.981

K Series G .503 3.245 .503 3.245

K Series H .785 5.065 .785 5.065

K Series J 1.287 8.303 1.287 8.303

K Series K 1.838 11.858 1.838 11.858

K Series L 2.853 18.406 2.853 18.406

K Series M 3.597 23.200 3.600 23.230

K Series N 4.340 28.030 4.340 28.030

K Series P 6.380 41.160 6.380 41.160

K Series Q 11.045 71.260 11.050 71.290

L Series — .0767 .495 .069 .445

L Series C .150 .968 .135 .871

L Series V .248 1.600 .223 1.439

L Series G .559 3.606 .503 3.245

Model 61 .110 .710 .110 .710

Model 63B 5 .150 .968 .150 .968

Model 63B 7 .437 2.819 .437 2.819

Model 81, 83, 81P -4 .049 .316 .049 .316

Model 81, 83 -6 .110 .710 .110 .710

Model 81, 83, 81P -8 .196 1.265 .196 1.265

Model 81, 83 F .307 1.981 .307 1.981

Model 81, 83, 81P G .503 3.245 .503 3.245

Model 81, 83 H .785 5.065 .785 5.065

Model 81, 83, 81P J 1.287 8.303 1.287 8.303




ASME Orifice Areas – Pilot Operated PRVs

Valve Size Orifice Area, in2 [cm2]Type X331 Type X231 Type X731 Type 226/526 Type 576 Type 727

1” x 2” 0.152 (‘D’) [0.98]20.318 (‘F’) [2.05] — — — —

11/2” x 2” 0.265 (‘E’) [1.71]

11/2” x 2” 0.599 (‘G’) [3.86]3 0.817 (‘H’) [5.27]3 1.336 [8.62] — 1.336 [8.62] —

11/2” x 3” 0.599 (‘G’) [3.86] 0.817 (‘H’) [5.27] — 0.817 (‘H’) [5.27] — —

0.629 (‘G’) [4.06]2” x 3”

0.631 (‘G’) [4.07]1.336 (‘J’) [8.62] 2.530 [16.32] 1.336 (‘J’) [8.62] 2.530 [16.32] 0.981 (‘H’) [6.33]

0.973 (‘H’) [6.28]1.635 (‘J’) [10.55]

1.635 (‘J’) [10.55]3” x 4” 1.448 (‘J’) [9.34] 2.985 (‘L’) [19.26] 6.651 [42.91] 2.985 (‘L’) [19.26] 6.651 [42.91] 2.298 (‘K’) [14.82]

2.162 (‘K’) [13.95] 3.557 (‘L’) [22.95]

3.557 (‘L’) [22.95]3.512 (‘L’) [22.66]

4.505 (‘M’) [29.06]4” x 6” 4.369 (‘M’) [28.19] 6.651 (‘P’) [42.91] 9.629 [62.12] 6.651 (‘P’) [42.91] 9.629 [62.12]

5.425 (‘N’) [35.00]5.054 (‘N’) [32.61]

7.911 (‘P’) [51.04]

—13.813 (‘Q’) [89.12]

6” x 8” 12.350 (‘Q’) [79.68] 16.655 (‘R’) [107.45] 16.655 (‘R’) [107.45] 21.520 [138.84] 20.000 (‘R’) [129.03]22.990 (‘RR’) [148.32]

6” x Dual 8” — — 21.520 [138.84] — — —

8” x 10” — 27.109 (‘T’) [174.90] — 27.109 (‘T’) [174.90] 44.180 [285.03] 32.500 (‘T’) [209.68]

8” x Dual 8” — — 29.420 [189.81] — — —

8” x Dual 10”— — 44.180 [285.03] — 44.180 [285.03] —

8” x Single 10”

Notes

1. Series 200/300/400/600/800/900.

2. Except for liquid service.

3. Threaded body only.




API Orifice Areas – Pilot Operated PRVs

Valve Size Orifice Area, in2 [cm2]Type X331 Type X231 Type X731 Type 226/526 Type 576 Type 727

1” x 2” 0.110 (‘D’) [0.71]20.307 (‘F’) [1.98] — — — —

11/2” x 2” 0.196 (‘E’) [1.26]

11/2” x 2” 0.503 (‘G’) [3.24]3 0.785 (‘H’) [5.06]3 1.257 [8.11] — 1.257 [8.11] —

11/2” x 3” 0.503 (‘G’) [3.24] 0.785 (‘H’) [5.06] — 0.785 (‘H’) [5.06] — —

0.503 (‘G’) [3.24]2” x 3”

0.503 (‘G’) [3.24]1.287 (‘J’) [8.30] 2.380 [15.35] 1.287 (‘J’) [8.30] 2.380 [15.35] 0.785 (‘H’) [5.06]

0.785 (‘H’) [5.06]1.287 (‘J’) [8.30]

1.287 (‘J’) [8.30]3” x 4”

1.287 (‘J’) [8.30]2.853 (‘L’) [18.41] 6.257 [40.37] 2.853 (‘L’) [18.41] 6.257 [40.37] 1.838 (‘K’) [11.86]

1.838 (‘K’) [11.86]2.853 (‘L’) [18.41]

2.853 (‘L’) [18.41]2.853 (‘L’) [18.41]

3.60 (‘M’) [23.22]4” x 6” 3.60 (‘M’) [23.22] 6.38 (‘P’) [41.16] 9.058 [58.44] 6.38 (‘P’) [41.16] 9.058 [58.44]

4.34 (‘N’) [28.00]4.34 (‘N’) [28.00]

6.38 (‘P’) [41.16]

6” x 8” 11.05 (‘Q’) [71.29] 16.00 (‘R’) [103.22] — 16.00 (‘R’) [103.22] —11.05 (‘Q’) [71.29]16.00 (‘R’) [103.22]

6” x Dual 8” — — 20.244 [130.61] — — —

8” x 10” — 26.00 (‘T’) [167.74] — 26.00 (‘T’) [167.74] 41.56 [268.13] 26.00 (‘T’) [167.74]

8” x Dual 8” — — 27.675 [178.55] — — —

8” x Dual 10”— — 41.56 [268.13] — 41.56 [268.13] —

8” x Single 10”

Notes

1. Series 200/300/400/600/800/900.

2. Except for liquid service.

3. Threaded body only.



Orifice Areas - Types 93/93T

Valve ASME APISize (in2) [cm2] (in2) [cm2]

2” 2.29 14.77 2.29 14.77

3” 5.16 33.29 5.16 33.29

4” 8.74 56.38 8.74 56.38

6” 19.56 126.93 19.56 126.93

8” 36.40 234.84 36.40 234.84

10” 51.00 329.03 51.00 329.03

12” 84.00 541.93 84.00 541.93

Orifice Areas - Type 95


2” 2.92 18.84 2.92 18.84

3” 6.25 40.32 6.25 40.32

4” 10.32 66.58 10.32 66.58

6” 22.15 142.90 22.15 142.90

Orifice Areas - Series 9000


2” 3.356 21.65 3.356 21.65

3” 7.393 47.69 7.393 47.69

4” 12.73 82.12 12.73 82.12

6” 28.89 186.38 28.89 186.38

8” 50.027 322.71 50.027 322.71

10” 78.854 508.73 78.854 508.73

12” 113.097 729.66 113.097 729.66

Orifice Areas - Types 91/94


2” 2.92 18.84 2.92 18.84

3” 6.24 40.26 6.24 40.26

4” 10.33 66.65 10.33 66.65

6” 22.22 143.35 22.22 143.35

8” 39.57 255.29 39.57 255.29

10” 56.75 366.12 56.75 366.12

12” 89.87 579.80 89.87 579.80

Orifice Areas - Type 96A


2” 11.70 75.48 11.70 75.48

3” 23.89 154.12 23.89 154.12

4” 36.80 237.42 36.80 237.42

6” 80.93 522.12 80.93 522.12




Back Pressure and Subsonic Flow Correction Factorfor Section I and Section VIII Sizing Formulas for Gas,Steam and Liquid



Valve Sizing – Evaluating Back Pressure Correction

Kb Factor for Gas and SteamWhen any back pressure exists, a test forsubsonic flow should be made. If the ab-solute outlet-to-inlet flowing pressure ratio(P2/P1) is greater than 0.30 a back pres-sure correction factor Kb may be requiredsubject to the additional commentary below.

The required values of Kb as a function ofP outlet/P inlet are determined from thecurves presented in this section for bothconventional spring operated and pilot op-erated pressure relief valves.

GeneralWhenever flow through a pressure reliefvalve occurs under sonic conditions, thevalue of Kb is 1.00. When a pressure reliefvalve discharges directly to the atmos-phere and the set pressure is 15 psig[1.03 barg] or greater, flow is consideredto be sonic, therefore Kb remains equal to1.00. If the pressure relief valve dis-charges into any piping where the backpressure at the valve outlet under reliev-ing conditions exceeds a definitive limit,flow will be subsonic. The orifice area cal-culation of a pressure relief valve, flowingunder these conditions, must be mathe-matically adjusted using the backpressure correction factor Kb.

Kw Factor for LiquidsWhenever back pressure is encounteredin bellows and pressure balanced springoperated liquid relief valves, a reduction inflow capacity due to reduced valve lift canresult. A Kw factor to correct for this reduc-tion is included in the liquid capacityequation. The required values of Kwbased upon P2/P1 are determined fromthe curves at the back of this section.

Sources of Back PressureA pressure relief valve whose outlet is dis-charging into vent piping or to anotherpressure vessel or system will encounterone or two types of back pressure: super-imposed and/or built-up.

Superimposed back pressure may comefrom the vent system due to the dischargeof other pressure relief valves into a com-mon manifold or due to the nature of otherprocesses that affect the downstreampressure. The presence of superimposedback pressure may not necessarily createsubsonic flow. However the outlet pres-sure may rise further, due to flow from thepressure relief valve, and may be suffi-cient to cause subsonic flow.

Built-up back pressure occurs as a resultof the discharge of fluid through a flowingpressure relief valve with connecteddownstream piping or equipment. In someinstances, relatively short sections of pip-ing connected by the outlet of a pressurerelief valve and venting to the atmospherewill be sufficient to create back pressureduring a relieving cycle that will cause flowto be subsonic.

The result will be a reduction of flow capacity. If this is less than the requiredrelieving capacity, the inlet pressure mayrise sufficiently to exceed the permissibleaccumulation for the application. The prob-lem is compounded when there is alsosome superimposed back pressure, sincebuilt-up back pressure will be additive.

Conventional Direct SpringOperated Pressure Relief ValvesIf a conventional, direct spring operatedpressure relief valve is to be appliedwhere any built-up back pressure will bedeveloped, the maximum permissiblebuilt-up back pressure shall not exceed10% of set pressure. Under this limit, noback pressure correction factor need beapplied, except as follows:

• When a conventional pressure reliefvalve is set to open with a superim-posed back pressure sufficiently high tocreate subsonic flow, the back pressurecorrection factor may be applied (as-suming that the pressure ratio exceedsthe critical ratio).

• If the valve is known to be tolerant to agreater amount, the back pressure cor-rection factor may be applied.

Balanced Pressure Relief ValvesThe balanced bellows valve is balancedagainst superimposed back pressure. It is also resistant to a moderate amount of built-up back pressure. Apply the backpressure correction factor Kb. When balanced bellows valves are used, themaximum permissible built-up back pres-sure should not exceed 40%.

Pilot Operated Pressure Relief ValvesA properly selected and installed pilot op-erated pressure relief valve will operateeffectively under all combinations of su-perimposed and built-up back pressure,limited only by the valve pressure ratingand practical considerations. Apply theback pressure correction factor Kb, if ap-plicable.

Solving for Kb

The critical pressure ratio is a function ofthe value of k, the specific heat ratio of thegas. The value of PCF/P1 varies from0.444 to 0.607 for a range of k between1.00 and 2.00. When sizing valve designsfor set pressures below 15 psig coveredunder API 2000, the P outlet/P inlet ratiomay be calculated and compared directlyto the correct P critical for the gas or va-por k value. The k values for selectedgases, the P critical vs. k equation and aset of P critical vs. k curves for frequentlyencountered k values are presented in the‘Fluid Data’ section of this manual.



Valve Sizing – Superimposed Back PressureCorrection Factors

Direct Spring PRVs/Vapor and Gases ASME Section VIII

Example:Set pressure = 200 psig [13.79 barg]

Constant back pressure = 160 psig [11.03 barg]160 + 14.7

Back pressure percentage (absolute) = –––––––––––––– x 100 = 74% or 200 + 20 + 14.7

11.03 + 1.013–––––––––––––––––– = 74% 13.79 + 1.38 + 1.013

Factor Kb = 0.91 (follow dotted line from curve)

Capacity with back pressure = 0.91 x rated capacity without back pressure

▲

0▲

10▲

20▲

30▲

40▲

50▲

60▲

70▲

80▲

90▲

100

1.00

.90

.80

.70

.60

.50

.40

.30

.20

.10

0

Constant Back Pressure Correction Factor Kb

Back

Pre

ssur

e Co

rrec

tion

Fact

or K

b

Back Pressure Percentage =Back pressure, psia or bara

Flowing pressure, psia or barax 100



Direct Spring PRVs - Model Designations - Bellows Valves Only/Vapors and Gases ASME Section VIII

Valve Sizing – Superimposed and Built Up BackPressure/Subsonic Flow Correction Factors

Back pressure percentage =

Back pressure, psig or bargSet pressure, psig or barg

x 100


Back pressure = 0 to 35 psig [2.41 barg]35

Back pressure percentage (gauge) = ––– x 100 = 35% max. 100

Factor Kb = 0.94 (follow dotted line fromcurve)

Capacity with back pressure = 0.94 x ratedcapacity without back pressure



x 100




Factor Kb = 0.99 (follow dotted line fromcurve)

Capacity with back pressure = 0.99 x ratedcapacity without back pressure

▲0

▲5

▲10

▲15

▲20

▲25

▲30

▲35

▲40

▲45

▲50

1.00

.90

.80

.70

.60

Variable Back Pressure Correction Factor Kb

Capa

city

with

bac

k pr

essu

re

Rate

d ca

paci

ty w

ithou

t bac

k pr

essu

reK b

=

10% Overpressure

15 psig[1.013 barg]

50 psig [3.44 barg]and over

▲0

▲10

▲15

▲20

▲25

▲30

▲35

▲40

▲45

▲50

1.00

.90

.80▲5

Variable Back Pressure Correction Factor Kb

Capa

city

with

bac

k pr

essu

re

Rate

d ca

paci

ty w

ithou

t bac

k pr

essu

reK b

=

20% Overpressure

15 psig[1.013 barg]

50 psig [3.44 barg]and over



Valve Sizing – Superimposed and Built Up BackPressure/Subsonic Flow Correction Factor (Kb)

0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

P2

P1

= Absolute Pressure Ratio at Valve Inlet

Back

Pre

ssur

e Fa

ctor

, Kb

k = 1.0

k = 1.2

k = 1.4

k = 1.6

k = 1.8

k = 2.0

Back Pressure Correction Factor for Piston Pilot Operated PRVs - Gas, Vapor, or Steam

The above curves are applicable for allpressure ranges and overpressures andaccurately predict the reduction on capaci-

ty for full lift, API orifice valves. For fullbore valves, multiply above ‘Kb’ values by0.95.



Valve Sizing - Back Pressure Correction Factor for Type 727 – Gas, Vapor or Steam

1.0

0.98

0.96

0.94

0.92

0.90

0.88

0.860.40 0.45 0.50 0.55 0.60 0.65 0.70

P /P = Absolute Pressure Ratio at Orifice2 1

k = 1.0

k = 1.2

k = 1.4

k = 1.6

k = 1.8

k = 2.0

Bac

k P

ress

ure

Fac

tor,

Kb





x 100




Factor Kw = 0.95 (follow dotted line fromcurve)

Capacity with variable back pressure =0.95 x rated capacity

Based on differential pressure Fd

Direct Spring PRVs - Model Designation - Bellows Valves Only/Liquid Service

1.00

.90

.80

.70

.60

▲0

▲5

▲10

▲15

▲20

▲25

▲30

▲35

▲40

▲45

▲50

Variable or Constant Back Pressure Correction Factor Kw

Capa

city

with

var

iabl

e ba

ck p

ress

ure

Rate

d ca

paci

ty b

ased

on

F dK w

=

Valve Sizing - Liquid Flow

K w =

Bac

k Pr

essu

re C

orre

ctio

n Fa

ctor

Base

d on

10%

Ove

rpre

ssur

e

Correction Curvefor Types 81P - 4

and 81P - 8

Correction Curvefor Types 81P - G

and 81P - J

▲0

▲5

▲10

▲15

▲20

▲25

▲30

▲35

▲40

▲45

▲50

▲55

▲60

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

Percentage Back Pressure = Back Pressure, psig [barg]Set Pressure, psig [barg]

x 100

Curve to Evaluate Liquid Back Pressure for Series 81PCorrection Factor kw



ASME VIII Gas Flow (Set Pressure ≥ 15 psig [1.03 barg])

U.S. Weight Flow (lb/h) Metric Weight Flow [kg/h]Formula 1 Formula 1M

U.S. Volumetric Flow (scfm) Metric Volumetric Flow [Nm3/h]Formula 2 Formula 2M

Valve Sizing – Gas and Vapor Equations

Sizing InformationASME Section I and VIIIAfter system capacity has been deter-mined, a properly sized pressure reliefvalve is determined by the followingmethod.

A. From the formulas in this section calculate required orifice area as afunction of capacity. The orifice sizesfor steam, air, or water may be ob-tained from the capacity tablescatalog.

B. Identify the required orifice letter des-ignation, such as D, E, F, etc. Alwayschoose an orifice which is equal to, orgreater than the required orifice area.

C. Specifications exceeding AndersonGreenwood standard catalog descrip-tions should be referred to our salesdepartment.

D. When selecting orifice areas and nozzle coefficients, either select theASME area and nozzle coefficient, or the equivalent API area and nozzlecoefficient.

Mixing ASME and API values is incor-rect and may result in a dangeroussizing error.

––––

A =W TZ

––––––– –––CK P1Kb √ M

––––

A =1.316 W TZ––––––– –––CK P1Kb √ M

––––

A =V√MTZ

––––––––––––6.32 CK P1Kb

––––

A =V√MTZ

–––––––––––––17.02 CK P1Kb



Solution:Use Formula 1

–––––

A =V √ MTZ

––––––––––––6.32 CK P1Kb

––––––––––––––

A =16,999 √ (58.12)(520)(1) 12.108 ––––––––––––––––––––– = ––––––

6.32 (326)(111.5) K Kb K Kb

For the bellows valve, the correct orifice selection would be an 8T10 (26.0 in2). For thecase of selecting a POSRV, the correct orifice selection would be 6R8 (16.00 in2).

Case 1 - Select a DB Series with K = 0.971, Kb = 0.77, A = 16.19 in2.

Case 2 - Select a POSRV with K = 0.86, Kb = 0.98, A = 14.36 in2.

Example 1 - ASME VIII GasGiven: Butane, with a required flow rate of

16,000 scfm, set at 88 psig, 10%overpressure, gas temperature of 60°F, discharging to a closedheader system. The back pressure(maximum) is 40 psig.

Find: The required orifice area.

Valve Sizing – Gas and Vapor Flow (English Units)

Examples for Steam and Gas Applications

V = 16,000

M = 58.12

C = 326

T = 60 + 460 = 520

Z = 1.0

P1 = 88 (1.1) + 14.7 = 111.5

Kb = 40 = 45%88

Bellows Valve – Kb = 0.77

Pilot Valve – 40 + 14.7 = 49%111.5

Kb = 0.98



Solution:Use formula 1M and the physical properties found on pages 51-63.

P1 = 5 x (1.1) + 1.013 = 6.513 baraT = 15 + 273 = 288°KM = 58.12, C = 326Z = 1.00 (used when no value is given)Kb = 1.00 (when back pressure equals atmospheric)

––––––––––––––––

A9,000 √ 58.12 x 288 x 1.00 32.22 cm2

[cm2] = ––––––––––––––––––––––––– = –––––––––17.02 x 326 x K x 6.513 x 1.00 K

A = 32.22 = 33.18 cm2.971

Selecting a valve with a K = 0.971, the orifice to be selected is a 4P6 (41.16 cm2).

Solution:The same data is used as in example 2, except use a nozzle coefficient K = 0.809 (frompage 9) in formula 2M.

––––––––––––––––

A9,000 √ 58.12 x 288 x 1.00

[cm2] = –––––––––––––––––––––––––––– = 39.83 cm2

17.02 x 326 x 0.809 x 6.513 x 1.00

From page 12, the next larger available orifice is 42.91 cm2 corresponding to a ‘full-bore,’ 3-inch x 4-inch valve, Series 273 or 473. Note in this example, ASME not APIcoefficients are used.

Solution:The back pressure represents 44% of the set pressure (2.2/5.0).

For a Direct Spring SRV, Kb = 0.78, for a 200 Series Pilot Operated PRV, the back pres-sure represents 49% of the absolute pressure ratio: 2.2 + 1.03

5.0 x 1.1 + 1.03

Therefore, the Kb for the Series 200 = 0.985 (from page 19).

Again using formula 2M, for the Direct Spring Valve: –––––––––––––––

A9,000 √ 58.12 x 288 x 1.0

= ––––––––––––––––––––––––––– = 42.54 cm2

17.02 x 326 x 971x 6.513 x .78

Selecting a direct spring would result in a 6Q8 (71.29 cm2).

For the POSRV:

–––––––––––––––

A9,000 √ 58.12 x 288 x 1.0 32.71 cm2

= ––––––––––––––––––––––––––– = ––––––––17.02 x 326 x K x 6.513 x .985 K

Case 1 - Select a Type 223, K = 0.830, A = 39.40 cm2.

Case 2 - Select a Type 273, K = 0.809, A = 40.43 cm2.

Selecting a pilot valve could either be a 4P6 (42.91 cm2) or a full bore 3 x 4 (42.91 cm2).

Example 2Given: Butane, with a required flow rate

of 9,000 Nm3/h, set at 5 barg, 10% overpressure, relieving tem-perature of 15°C, discharging toatmosphere.

Find: The required orifice area for a typi-cal conventional safety valve andthe orifice selected.

Example 3Given: Same as example 2.

Find: The appropriate size valve for apiston type (Series 200, 300, etc.),pilot operated safety valve.

Example 4Given: The same as example 2, except

with a built-up back pressure of2.2 barg.

Find: The appropriate size to meet therelieving conditions.

Valve Sizing – Gas and Vapor Flow - [Metric Units]

Examples for Gas and Steam Applications



Valve Sizing – Steam Flow

Sizing InformationASME Section I and VIIIAfter system capacity has been deter-mined, a properly sized pressure reliefvalve is determined by the followingmethod.

A. From the formulas in this section calculate required orifice area as afunction of capacity. The orifice sizesfor steam, air, or water may be ob-tained from the capacity tablescatalog.

B. Identify the required orifice letter des-ignation, such as D, E, F, etc. Alwayschoose an orifice which is equal to, orgreater than the required orifice area.

C. Specifications exceeding AndersonGreenwood standard catalog descrip-tions should be referred to our salesdepartment.

D. When selecting orifice areas and noz-zle coefficients, either select the ASMEarea and nozzle coefficient, or theequivalent API area and nozzle coeffi-cient.

Mixing ASME and API values is incor-rect and may result in a dangeroussizing error.

ASME I Sonic Steam Flow (Set Pressure ≥ 15 psig [1.03 barg])

U.S. Units (lb/h) Metric Units [kg/h]Formula 3 Formula 3M

ASME VIII Sonic Steam Flow (Set Pressure ≥ 15 psig [1.03 barg])

U.S. Units (lb/h) Metric Units [kg/h]Formula 4 Formula 4M

A = W

–––––––––––––––––51.45 K P1KSHKNKb

KN = 1.00 for P ≤ 1500 psig

KN =0.1906 P - 1000–––––––––––––0.2292 P - 1061

where 1500 psig < P < 3200 psig

A = W

–––––––––––––––––52.45 K P1KSHKNKb

KN = 1.00 for P ≤ 103.4 barg

KN =2.764 P - 1000

–––––––––––––3.323 P - 1061

where 103.4 barg < P < 220.7 barg

A = W

––––––––––––––––51.5 K P1KSHKNKb

KN = 1.00 for P ≤ 1500 psig

KN =0.1906 P - 1000–––––––––––––0.2292 P - 1061


A = W

––––––––––––––––52.5 K P1KSHKNKb

KN = 1.00 for P ≤ 103.4 barg

KN =2.764 P - 1000

–––––––––––––3.323 P - 1061





A = W

51.45 K P1KSHKNKb

A =4050 2.388

–––––––––––––––––––– = ––––––51.45 K (.97)(1)(34.7)(1) K

Selecting a valve with a K = 0.878 (K Series), A = 2.66 in2.

This orifice corresponds to an L orifice (2.853 in2). Note the overpressure for set pressures between 15 psig and 70 psig is 3% or 2 psig minimum.


A = W

51.5 K P1KSHKNKb

A =84,000 3.587

–––––––––––––––––––– = ––––––51.5 (K)(1)(1)(454.7)(1) K

Selecting a valve with a K = 0.971 (D Series), A = 3.69 in2.

This orifice corresponds to a 4N6 orifice (4.34 in2).

The approximate flowing capacity can be estimated from the ratio of actual area to required area as follows:

W = 84,000 x4.34

= 98,796 lb/hr3.69

Example 5 - ASME I SteamGiven: Steam, with a required flow rate

of 4,050 lb/h, set at 18 psig, is required for an ASME I boiler application. Steam temperature is 420°F.


= 2.338

K

Example 6 - ASME VIII SteamGiven: Steam, with a required flow rate

of 84,000 lb/h, set at 400 psig, is required for an unfired pressurevessel application. Steam temper-ature is 448°F.

Find: The required orifice area and approximate valve capacity.

Valve Sizing – Steam (English Units)

Examples for Steam Applications

W = 4050

KSH = 0.97

KN = 1.00

Kb = 1.00

P1 = 18 + 2 + 14.7 = 34.7

W = 84,000

KSH = 1.00

KN = 1.00

Kb = 1.00

P1 = 400 (1.1) + 14.7 = 454.7



Valve Sizing – Sonic Flow (English Units)

Curve to Evaluate Napier Correction Factor KN for High PressureDry Saturated Steam

Steam Relieving Pressure, P1 (psig)

Napi

er C

orre

ctio

n Fa

ctor

, KN

▲1500

▲1700

▲1900

▲2100

▲2300

▲2500

▲2700

▲2900

▲3100

▲3300

1.200

1.190

1.180

1.170

1.160

1.150

1.140

1.130

1.120

1.110

1.100

1.090

1.080

1.070

1.060

1.050

1.040

1.030

1.020

1.010

1.000

KN =KN =0.1906 P - 1000

0.2292 P - 1061(10a)




▲100

▲110

▲120

▲130

▲140

▲150

▲160

▲170

▲180

▲190

▲200

▲210

▲220

▲230

KN =KN =2.764 P - 1000

3.323 P - 1061(10)


1.210

1.200

1.190

1.180

1.170

1.160

1.150

1.140

1.130

1.120

1.110

1.000

1.090

1.080

1.070

1.060

1.050

1.040

1.030

1.020

1.010

Steam Relieving Pressure, P1 (barg)

Napi

er C

orre

ctio

n Fa

ctor

, KN

Curve to Evaluate Napier Correction Factor KN for High Pressure Dry Saturated Steam

Valve Sizing – Sonic Flow [Metric Units]



Valve Sizing – Steam – Superheat Correction

Relieving Total Steam Temperature °F [°C]Pressure 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200

psia [bara] [204] [232] [260] [288] [316] [343] [371] [399] [427] [454] [482] [510] [538] [566] [593] [621] [649]

50 [3.4] .987 .957 .930 .905 .882 .861 .841 .823 .805 .789 .774 .759 .745 .732 .719 .708 .696

100 [6.9] .998 .963 .935 .909 .885 .864 .843 .825 .807 .790 .775 .760 .746 .733 .720 .708 .697

150 [10.3] .984 .970 .940 .913 .888 .866 .846 .826 .808 .792 .776 .761 .747 .733 .721 .709 .697

200 [13.8] .979 .977 .945 .917 .892 .869 .848 .828 .810 .793 .777 .762 .748 .734 .721 .709 .698

250 [17.2] .972 .951 .921 .895 .871 .850 .830 .812 .794 .778 .763 .749 .735 .722 .710 .698

300 [20.7] .968 .957 .926 .898 .874 .852 .832 .813 .796 .780 .764 .750 .736 .723 .710 .699

350 [24.1] .968 .963 .930 .902 .877 .854 .834 .815 .797 .781 .765 .750 .736 .723 .711 .699

400 [27.6] .963 .935 .906 .880 .857 .836 .816 .798 .782 .766 .751 .737 .724 .712 .700

450 [31.0] .961 .940 .909 .883 .859 .838 .818 .800 .783 .767 .752 .738 .725 .712 .700

500 [34.5] .961 .946 .914 .886 .862 .840 .820 .801 .784 .768 .753 .739 .725 .713 .701

550 [37.9] .962 .952 .918 .889 .864 .842 .822 .803 .785 .769 .754 .740 .726 .713 .701

600 [41.4] .964 .958 .922 .892 .867 .844 .823 .804 .787 .770 .755 .740 .727 .714 .702

650 [44.8] .968 .958 .927 .896 .869 .846 .825 .806 .788 .771 .756 .741 .728 .715 .702

700 [48.3] .958 .931 .899 .872 .848 .827 .807 .789 .772 .757 .742 .728 .715 .703

750 [51.7] .958 .936 .903 .875 .850 .828 .809 .790 .774 .758 .743 .729 .716 .703

800 [55.2] .960 .942 .906 .878 .852 .830 .810 .792 .774 .759 .744 .730 .716 .704

850 [58.6] .962 .947 .910 .880 .855 .832 .812 .793 .776 .760 .744 .730 .717 .704

900 [62.1] .965 .953 .914 .883 .857 .834 .813 .794 .777 .760 .745 .731 .718 .705

950 [65.5] .969 .958 .918 .886 .860 .836 .815 .796 .778 .761 .746 .732 .718 .705

1000 [69.0] .974 .959 .923 .890 .862 .838 .816 .797 .779 .762 .747 .732 .719 .706

1050 [72.4] .960 .927 .893 .864 .840 .818 .798 .780 .763 .748 .733 .719 .707

1100 [75.9] .962 .931 .896 .867 .842 .820 .800 .781 .764 .749 .734 .720 .707

1150 [79.3] .964 .936 .899 .870 .844 .821 .801 .782 .765 .749 .735 .721 .708

1200 [82.8] .966 .941 .903 .872 .846 .823 .802 .784 .766 .750 .735 .721 .708

1250 [86.2] .969 .946 .906 .875 .848 .825 .804 .785 .767 .751 .736 .722 .709

1300 [89.7] .973 .952 .910 .878 .850 .826 .805 .786 .768 .752 .737 .723 .709

1350 [93.1] .977 .958 .914 .880 .852 .828 .807 .787 .769 .753 .737 .723 .710

1400 [96.6] .982 .963 .918 .883 .854 .830 .808 .788 .770 .754 .738 .724 .710

1450 [100.0] .987 .968 .922 .886 .857 .832 .809 .790 .771 .754 .739 .724 .711

1500 [103.4] .993 .970 .926 .889 .859 .833 .811 .791 .772 .755 .740 .725 .711

1550 [106.9] .972 .930 .892 .861 .835 .812 .792 .773 .756 .740 .726 .712

1600 [110.3] .973 .934 .894 .863 .836 .813 .792 .774 .756 .740 .726 .712

Superheat Correction Factor (KSH) for Superheated Steam



Valve Sizing – Steam – Superheat Correction

Relieving Total Steam Temperature °F [°C]Pressure 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200

psia [bara] [204] [232] [260] [288] [316] [343] [371] [399] [427] [454] [482] [510] [538] [566] [593] [621] [649]

1650 [113.8] .973 .936 .895 .863 .836 .812 .791 .772 .755 .739 .724 .710

1700 [117.2] .973 .938 .895 .863 .835 .811 .790 .771 .754 .738 .723 .709

1750 [120.7] .974 .940 .896 .862 .835 .810 .789 .770 .752 .736 .721 .707

1800 [124.1] .975 .942 .897 .862 .834 .810 .788 .768 .751 .735 .720 .705

1850 [127.6] .976 .944 .897 .862 .833 .809 .787 .767 .749 .733 .718 .704

1900 [131.0] .977 .946 .898 .862 .832 .807 .785 .766 .748 .731 .716 .702

1950 [134.5] .979 .949 .898 .861 .832 .806 .784 .764 .746 .729 .714 .700

2000 [137.9] .982 .952 .899 .861 .831 .805 .782 .762 .744 .728 .712 .698

2050 [141.4] .985 .954 .899 .860 .830 .804 .781 .761 .742 .726 .710 .696

2100 [144.8] .988 .956 .900 .860 .828 .802 .779 .759 .740 .724 .708 .694

2150 [148.3] .956 .900 .859 .827 .801 .778 .757 .738 .722 .706 .692

2200 [151.7] .955 .901 .859 .826 .799 .776 .755 .736 .720 .704 .690

2250 [155.2] .954 .901 .858 .825 .797 .774 .753 .734 .717 .702 .687

2300 [158.6] .953 .901 .857 .823 .795 .772 .751 .732 .715 .699 .685

2350 [162.1] .952 .902 .856 .822 .794 .769 .748 .729 .712 .697 .682

2400 [165.5] .952 .902 .855 .820 .791 .767 .746 .727 .710 .694 .679

2450 [169.0] .951 .902 .854 .818 .789 .765 .743 .724 .707 .691 .677

2500 [172.4] .951 .902 .852 .816 .787 .762 .740 .721 .704 .688 .674

2550 [175.9] .951 .902 .851 .814 .784 .759 .738 .718 .701 .685 .671

2600 [179.3] .951 .903 .849 .812 .782 .756 .735 .715 .698 .682 .664

2650 [182.8] .952 .903 .848 .809 .779 .754 .731 .712 .695 .679 .664

2700 [186.2] .952 .903 .846 .807 .776 .750 .728 .708 .691 .675 .661

2750 [189.7] .953 .903 .844 .804 .773 .747 .724 .705 .687 .671 .657

2800 [193.1] .956 .903 .842 .801 .769 .743 .721 .701 .684 .668 .653

2850 [196.6] .959 .902 .839 .798 .766 .739 .717 .697 .679 .663 .649

2900 [200.0] .963 .902 .836 .794 .762 .735 .713 .693 .675 .659 .645

2950 [203.4] .902 .834 .790 .758 .731 .708 .688 .671 .655 .640

3000 [206.9] .901 .831 .786 .753 .726 .704 .684 .666 .650 .635

3050 [210.3] .899 .827 .782 .749 .722 .699 .679 .661 .645 .630

3100 [213.8] .896 .823 .777 .744 .716 .693 .673 .656 .640 .625

3150 [217.2] .894 .819 .772 .738 .711 .688 .668 .650 .634 .620

3200 [220.7] .889 .815 .767 .733 .705 .682 .662 .644 .628 .614

Superheat Correction Factor (KSH) for Superheated Steam



ASME VIII Liquids (Set Pressure ≥ 15 psig [1.03 barg])

U.S. Volumetric Flow Metric Volumetric Flow (gpm @ 10% overpressure) [m3/h @ 10% overpressure]

Formula 5 Formula 5M

Liquids (Non ASME Certified)

U.S. Volumetric Flow (gpm) Metric Volumetric Flow [m3/h]Formula 6 Formula 6M

Valve Sizing – Liquid Flow

–––

A =W √ G

–––––––––––––––––––––––––––––––38 K KvKw √1.10 P - P2

–––

A =0.19631 W √ G

–––––––––––––––––––––––––––K KvKw √1.10 P - P2

–––

A =W √ G

––––––––––––––––––––––––38 K KpKvKw √ P - P2

–––

A =0.19631 W√ G

–––––––––––––––––––––K KpKvKw √ P - P2

Reynolds Number Calculation

U.S. Volumetric Flow (gpm) Metric Volumetric Flow [m3/h]Formula 7 Formula 7M

R =12,700 W

–––––––––––U √A

R =31,313 WG

–––––––––––––µ √A



Example 7

When a relief valve is sized for viscous liq-uid service, it is suggested that it be sizedfirst as for nonviscous-type application inorder to obtain a preliminary required dis-charged area, A. From manufacturers’standard orifice sizes, the next larger ori-fice size should be used in determiningthe Reynold’s number, R, from the follow-ing relationship:

R =12,700 W

––––––––––––µ √A1

Where:W = required flow rate at the flowing tem-

perature, in U.S. gallons per minute.

A1 = effective discharge area, insquare inches

U = viscosity at the flowing temperature,in Saybolt Universal seconds.

After the value of R is determined, thefactor Kv is obtained from page 33. Kv isapplied to correct the ‘preliminary re-quired discharge area.’ If the correctedarea exceeds the ‘chosen standard orificearea,’ the above calculations should berepeated using the next larger standardorifice size.

Example:

Viscosity - SSU .......10,000 SSU @ 100°F

Required Capacity ......................300 GPM

Set Pressure.................................100 psig

Constant Back Pressure.................15 psig

Allowable Overpressure......................10%

Specific Gravity......................1.0 @ 100°F

Relieving Temperature .....................100°F

Step 1–––

A =W √ G

–––––––––––––––––––––––––––––––38 K KvKw √1.10 P - P2

–––

A =300 √1.0

–––––––––––––––––––––––––––––38 (.776)(1) √1.10 - 15

A = 1.043

Preliminary Required Discharge Area

A1, Select Standard Orifice Area = 1.287 -‘J ’ Orifice

Step 2

R =12,700 x 300

–––––––––––––––––––––10,000 √ 1.287

R = 335.8

Step 3R = 335.8 correction factor from chart

Kv = 0.815

Step 4Corrected ‘Preliminary RequiredDischarge Area’ = A––––

Kv

= 1.043––––––.815

= 1.279 in2

If corrected ‘Preliminary RequiredDischarge Area’ is greater than selectedstandard orifice area, select next orificesize and repeat steps 2, 3, and 4. In thisexample, the corrected orifice area is stillwithin the ‘J’ orifice and therefore is thecorrect selection.

Valve Sizing – Liquid Flow Viscosity Correction(English)



Curve to Evaluate Liquid Viscosity Correction Factor Kv

▲0.20

▲0.30

▲0.40

▲0.50

▲0.60

▲0.70

▲0.80

▲0.90

▲1.00

100,000

50,00040,00030,000

20,000

10,000

5,0004,0003,000

2,000

1,000

500400300

200

100

50403020

Rey

no

lds

Nu

mb

er, R

Liquid Viscosity Correction Factor, KV

Valve Sizing – Liquid Flow




–––

A =69 √ G

–––––––––––––––––––––––––––38 KKvKw √1.1 P - P2

––––––

A =69 √ 1.115 .3865

––––––––––––––––––––––– = –––––––––––––– 38 K x 1 x 1 x √1.1(26) - 4 K

For Direct Spring D Series: K = .776

For POSRV: K = .670

For AGCO D Series: A = .3865 = 0.498, Select 11/2G21/2 (0.503 in2).776

For AGCO 400 Series POSRV: A = .3865 = 0.576, Select 11/2H3 (0.785 in2).67

Solution:ASME API

K for D Series = .700 K for D Series = .776

K for 400 Series = .650 K for 400 Series = .670

For D Series:

A = .3865

= .552, Select 11/2G21/2 (0.558 in2) = same orifice selection.700

For 400 Series:

A = .3865

= .594, Select 11/2G3 (0.599 in2) = smaller orifice may be selected.650

Example 8 - ASME VIII LiquidsGiven: Ethylene Glycol, with a required

flow rate of 69 GPM, set at 26psig, 10% overpressure, built-upback pressure of 4 psig.

Find: The required orifice area and theorifice area to be selected.

Valve Sizing – Liquid Flow (English Units)

Examples for Liquid Applications

W = 69

G = 1.115

P = 26

P2 = 4

KV = 1

KW = 1

Example 9 Compare the ASME vs API sizing coeffi-cients for the data used in example 8.

This example illustrates two importantpoints to consider in valve sizing.

1. Either ASME or API coefficients may beused, but they may not be mixed. Anerror results if the ASME area is usedwith the API coefficient, and vice versa.

2. Consider the selection of the 400Series Pilot Operated PRV. Using aver-aged API coefficients actually wouldresult in specifying a larger orifice thanusing the ASME actual data. When acalculated orifice (using API data) isvery close to an orifice area selection, a check using ASME actual data mayresult in a smaller orifice.



Example 10Given: Water with a required flow rate

of 50.0 m3/h, set at 10.0 barg,10% overpressure, built-up back pressure of 2.0 barg.

Find: The required orifice area for aType 81P balanced pressure reliefvalve and the orifice area selected.

Example 11Given: Same as example 10.

Find: The appropriate size valve for a D Series pressure relief valve,suitable for liquid service.

Example 12Given: A liquid with a required flow rate

of 72 m3/h, set at 6.5 barg, 10%overpressure, a relative density of0.95, viscosity of 450 centipoise, aback pressure of 0.75 barg.

Find: The required valve size for aSeries 400 pilot operated pressurerelief valve. Use API coefficients.

Valve Sizing – Liquid Flow [Metric Units]

Examples for Liquid Applications

Solution:Use formula 5M and the physical properties found on pages 51-63.

P = 10 barg p2 = 2 barg

G = 1.00 K = 0.720

Kp = 1.00 Kv = 1.00

Kw = 1.00 –––––

A[cm2] =0.19631 x 50 x √ 1.00

–––––––––––––––––––––––––––––––––– = 4.54 cm2–––––––––

0.720 x 1.00 x 1.00 x 1.00 x √1.1(10) - 2

From page 11, the next available orifice, greater than this is 8.303 cm2, corresponding toa ‘J’ orifice.

Solution:The same data is used as in example 10, except use a nozzle coefficient K = 0.776 (frompage 8), in formula 5M. The values of Kp, Kv and Kw = 1.00 for this application.

–––––

A[cm2] =0.19631 x 50 x √ 1.00

–––––––––––––––––––––––––––––– = 4.216 cm2–––––

.776 x 1.00 x 1.00 x 1.00 x √11 - 2

From page 10, the next available larger area is 5.065 cm2, corresponding to an ‘H’ orifice.

Solution:Use formula 5M and make any adjustment for the effect of viscosity if necessary.

P = 6.5 barg p2 = 0.75 barg

K = 0.650 Kp = 1.00

Kw = 1.00 Kv = 1.00 for initial sizing calculation, thenevaluated in subsequent calculation as ex-plained on page 28.

–––––

A[cm2] =0.19631 x 72 x √ 0.95

––––––––––––––––––––––––––––––––––––– = x 8.127 cm2–––––––––––

0.670 x 1.00 x 1.00 x 1.00 x √1.1(6.5) - .75

From page 13, the next larger, available orifice area is 8.30 cm2.This preliminary orifice area is then used to determine a value for Kv. Calculate R fromformula 7M on page 31.

R =31,313 x 72 x 0.95

––––––––––––––––– = 1652––––– 450 √ 8.30

From page 33, Kv = 0.925

Atrial =8.127

–––––– = 8.78 cm2

0.915

This is larger than the preliminary orifice A therefore the next larger orifice must be selectedand re-evaluated. The new preliminary orifice is 11.86 cm2. Calculate a new R.

R =31,313 x 72 x 0.95 –––––––––––––––– = 1382–––––

450 √ 11.86

From page 33, Kv = 0.925

Atrial =8.127

–––––– = 8.88 cm2 which confirms the selection of a type 423 3K4 size.0.925

This result is smaller than our last preliminary orifice area of 11.86 cm2, which therefore issatisfactory for the application. Orifice designation ‘K’ is the appropriate choice.





Subsonic Flow API 2000 and Open Discharge ValvesWithout Kb Factor



U.S. Weight Flow (lb/h) Metric Weight Flow [kg/h]Formula 8 Formula 8M

U.S. Volumetric Flow (scfm) Metric Volumetric Flow [Nm3/h]Formula 9 Formula 9M

Valve Sizing – Subsonic Flow per API RP 520

Note

1. Applicable for conventional valves set atpressures below 15 psig [1.03 barg], orwhen the ratio of back pressure to inletpressure (P2/P1) exceeds the critical pres-sure ratio (PCF/P1). For balanced bellowsvalves that operate in the subsonic flow region, the sonic flow equations should beused with a back pressure correction factor(Kb) particular to this application.

Gas Flow - Direct Spring Valves with ASME K coefficient1

(Set Pressure < 15 psig [1.03 barg])

––––––––––––

A(in2) =W ZT

––––––– ––––––––––––735 F2K √ MP1(P1 - P2)

––––

A(in2) =V √MTZ

––––––––––––––––––––––––––––––––4645.2 F2K √ P1(P1 - P2)

–––––––––––––––––––––––

F2 = k

2

1 - r(k - 1)

(–––) r (––)[––––––––√ k - 1

k

1 - rk ]

k = ratio of specific heats

r =P2P1

––––

A[cm2] =W √ TZ

––––––––––––––––––––––––––––––––––2087 F2K √ MP1(P1 - P2)

–––––

A[cm2] =V √ MTZ

–––––––––––––––––––––––––––––––––4892 F2K √ P1 (P1 - P2)



Solution:Using formula 9 from page 38:

Solution:Using formula 9M from page 38:

Example 13 (English Units)Given: Methane, with a required flow

rate of 1500 scfm, set at 19 psig,flows into a header where the back pressure is 9 psig. The gastemperature is 120°F.


Valve Sizing – Subsonic Flow per API RP 520

Examples for Gas Applications

V = 1500

M = 16.04

k = 1.31

T = 120 + 460 = 580°R

Z = 1.00

K = 0.971 (AGCO D Series)

V = 195

M = 29

T = -15 + 273 = 258

Z = 1

K = 0.971

Example 14 (Metric Units)Given: Air, at .78 barg and -15°C, with a

required flow rate of 195 Nm3/h,requires a pressure relief valve forprotection. The valve is to be in-stalled at 2,000 meters above sealevel.

Find: The required valve size. Also, determine the error using the stan-dard sonic formula for the sameconditions given.

––––

A =W √MTZ

––––––––––––––––––––––––––––––––4645.2 F2K √ P1(P1 - P2)

P1 = 19 (3 + 14.7) = 36.7

P2 = 9 + 14.7 = 23.7

r = P2/P1 = 23.7/36.7 = 0.6457

––––––––––––––––––––––––––––––––––––

F2 = 1.31

2

1 - .6457(.31 )(––––) 0.6457 (–––)[––––––––––––√ .31

1.31

1 -.65471.31 ]

–––––––––––––––––––––––––––

F2 = 1 - .9016

4.2258 x .5128 [–––––––– √ .3543 ]F2 = .7757

–––––––––––––

A =1500 √ 16.04 x 580 x 1

––––––––––––––––––––––––––––––––––– = 1.893 in2–––––––––––––––

4645.2 x .7757 x .971 √ 36.7 (36.7 - 23.7)

––––

A =V √MTZ

–––––––––––––––––––––––––––––––4892 F2K √ P1(P1 - P2)

At 2000 M above sea level, the barometric pressure is 0.793 bara.

P1 = .78 + .2069 + .793 = 1.779 bara

P2 = 0.793

r = P2/P1 = .793/1.779 = .5227–––––––––––––––––––––––––––––

F2 = 1.4

2

1 - r(.4 )(––– ) .5227

(––)[–––––––√ .4 1.4

1 - r1.4 ]

––––––––––––––––––––––––

F2 = 1 - .8308

3.5 x .3958 [–––––––– √ 1 - .5227 ]F2 = .7007

–––––––––––

A =195 √ 29 x 258 x 1

–––––––––––––––––––––––––––––––––––– = 3.826 cm2–––––––––––––––––

4892 x .7007 x .971 √ 1.779 (1.779 - .793)

Therefore, the correct valve size would be 11/2H3 (5.064 cm2). Had the standard sonicsizing formula been used, the orifice calculation would have been as follows:

–––– ––––––––––

A =V √MTZ 195 √29 x 258 x 1

––––––––––––––– A = –––––––––––––––––––––––––––– = 1.603 cm2

17.02 CKdP1Kb 17.02 x 356 x 971 x 1.779 x 1.00

The resultant error would be the selection of an undersized valve (11/2 F2, with 1.98 cm2).This would create a condition where the pressure relief valve could not control the designoverpressure transients.



Valve Sizing1 – Subsonic Flow per API RP 2000

Pilot Operated PRV Types 91, 93, 94, 95, 9200 and 9300(Set Pressure < 15 psig [1.03 barg])

Note

1. A computer sizing program is available.Consult your local representative.

U.S. Weight Flow (lb/h)Formula 10

–––

A(in2) =W√ TZ

––––––––––––––––––735 KdP1F √M

U.S. Volumetric Flow (SCFM)Formula 11–––––

A(in2) =V√MTZ

–––––––––––4645 KdP1F

Metric Weight Flow [kg/h]Formula 10M

–––

A[cm2] =W√ TZ

––––––––––––––––––́558 KdP1F √M

Metric Volumetric Flow [Nm3/h]Formula 11M

–––––

A[cm2] =V√MTZ

––––––––––––12510 KdP1F

where:

–––––––––––––––––––––––––––––––

F = k P2

2 P2k + 1

–––– [ (–––– )–– – ( ––– ) ––––] √ k - 1 P1

kP1

k

Coefficients of Discharge

For Type 9200 Kd = 0.756 (P1)0.0517

US units. See page 42.

For Type 9200, Kd = 0.8681 (P1)0.0517

Metric units. See page 42.

For Type 9300 Kd = 0.650 (P2/P1)-0.349

See page 42.

For Type 9200 Vacuum Kd = 0.667.

For Type 9300 Vacuum Kd = 0.55.

For Types 91, 94, 95 Kd = 0.678 (P2/P1)-0.285

For Type 93 Kd = 0.700 (P2/P1)-0.265



F

F

.100

.095

.090

.085

.080

.075

.070

.065

.060

.055

.050

.045

.040

.035

.030

1.00

0

.950

.900

.850

.800

.750

.700

.650

.600

.550

.500

.450

.400

.550

.525

.500

.475

.450

.425

.400

.375

.350

.325

.300

.275

.250

.225

.200

.175

.150

.125

.100

1.00

0

.995

.990

1.90

1.70

1.601.50

1.40

1.301.20

1.10

1.00

k =

1.90

k =

1.00

k =

1.0

0 th

ru 1

.90

k =

1.0

0 th

ru 1

.90

.990

Absolute Pressure Ratio PP

2

1( )

Flow Correction Factor F (For use in subsonic sizing page 39)

Sizing - Series 90 and 9000



Valve Sizing – Subsonic Flow

psig0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5

0 .05 1 .15 2 .25 .3 .35

.60

.70

.80

.90

Flowing Pressure (P)

Val

ve C

oef

fici

ent

(K ) d

barg

English Units = K = 0.756 (P)Metric Units = K = 0.756 (P x 14.50)

dd

.0517 1

.0517 2

.65

.75

.85

Type 9200 Valve Coefficient (Kd) vs. Relief Pressure Notes (Type 9200 only)

1. P = set pressure + overpressure - inlet pip-ing loss + atmospheric pressure (psia).

2. P = set pressure + overpressure - inlet pip-ing loss + atmospheric pressure (barg).

Absolute Pressure Ratio

K = 0.650P

P

-.3492

.50 .55 .60 .65 .70 .75 .80 .85 .90 .95 1.00.60

.70

.80

.90

Val

ve C

oef

fici

ent

(K ) d

d1

( )

PP

2

1( )

.85

.75

.65

Type 9300 Valve Coefficient (Kd) vs. Absolute Pressure Ratio

.85

.83

.81

.79

.77

.75

.73

.71

.69

.67

.65.50 .55 .60 .65 .70 .75 .80 .85 .90 .95 1.00

Val

ve C

oef

fici

ent

(Kd)


Kd = .678 -.285P

P2

1)(

P

P2

1)(

Types 91 and 94 Valve Coefficient (Kd) vs. Absolute Pressure Ratio



Valve Sizing – Subsonic Flow

.85

.83

.81

.79

.77

.75

.73

.71

.69

.67

.65.50 .55 .60 .65 .70 .75 .80 .85 .90 .95 1.00

Val

ve C

oef

fici

ent

(Kd)


Kd = .700 -.265P

P2

1)(

P

P2

1)(

Type 93 Valve Coefficient (Kd) vs. Absolute Pressure Ratio



Solution:Using formula 11 from page 40:

––––

A =V√MTZ

–––––––––––– 4645 Kd P1F

P2___ = 0.6458P1

F =______________

2 k +1___ ____k P2 k P2 k√ ____ [(___) – (___) ]k - 1 P1 P1

F =_____________

2 2.27___ ____1.27 1.31 1.31√ ___ [(.6458) – (.6458) ].31

F = 0.4616

Kd = 0.650

K = 0.7572

–––––––––––––

A =1500 √16.04 x 580 x 1

––––––––––––––––––––– (4645) (.7572) (36.7) (.4616)

A = 2.4282 in2

Example 15Find: Using the same conditions as stat-

ed in Example 13, size for a Type9300 pilot operated pressure reliefvalve.

Valve Sizing – Subsonic Flow (English)

Examples for Gas Applications



Valve Sizing – Special Applications

Thermal Relief, Fire and Special Water

Detailed requirements for fire siz-ing of pressure relief devices arecontained in API RP520 Part I. Asummary of sizing equations isgiven below.

Heat absorption (Q) into a vessel is deter-mined by equation (13).

(13) Q = 21,000 FA 0.82

Where:

A = wetted surface area of the vessel, insquare feet.

F = an insulation factor. F = 1.0 for anuninsulated vessel corresponding to aheat conductance of 13.33 BTU/h x ft 2 x°F with a 1600°F temperature difference.

F = Actual Conductance (BTU/h x ft2 x °F)

13.33

For horizontal pressure vessels, use totalarea in square feet. For vertical vessels,use the area up to 25 feet above ground.For spherical vessels, use height aboveground of maximum diameter or 25 feet,whichever is greater.

Once the heat input (Q) is determined – inBTU/h from equation (13) – gas flow ratemust be determined from the latent heatof the fluid medium. The rate of changefrom liquid to vapor, or vaporization rate,is a function of both the fluid’s physical/chemical properties and the relievingpressure value. The vapor mass flow rate,lbs/hr, (Wp) is derived from equation (14).

(14) Wp =Q

(lbs/h)–––L

Where:

Wp = the flow rate in lbs/h

Q = the maximum heat input in BTU/hfrom equation (13).

L = minimum latent heat of vaporization1,BTU/lb, at the absolute relievingpressure (psia).

Example:

What is the total heat input, in BTU/h, to a vertical distillation column 8 feet in diameter by 50 feet long with flat ends,mounted 4 feet above ground and insulated to provide 6 BTU/h x ft x °F conductance with a 1600°F temperaturedifference?2

Step 1Q = 21,000 FA 0.82

F =6

= 0.45–––––13.33

A = π

D2 + (h x πD)––( 4 )Where: h equals 25 ft max. minus theheight above the ground.

A = 3.1416

82 + (25 - 4) 3.1416 x 8( –––––– )4

A = 50.27 ft2 + 527.79 ft2

A = 578.06 ft2

Q = 21,000 (0.45) (578.06)0.82

Q = 21,000 (0.45) (184)

Q = 1,738,800 BTU/h

Example:

If the vessel contains a liquid with a latentheat of 120 BTU/lb at 70 psia, 400°F andmolecular weight of 60, what is the re-quired valve capacity and set pressure?

Step 2From equation (14)

Wp =Q 1,738,800

= 14,490 lbs/h––– = –––––––––L 120

Step 3P = 70 psia

Where: P = relieving pressure =

(Set Pressure x 1.10) + 14.7

Set Pressure = (70 – 14.7)

50 psig–––––––––1.10

Determine required orifice area (A) as follows:

Step 4

––––A = Wp Z

––––––– ––CKdPFp √ T

––––––––––––A =

14,490 1 x (400 + 460)–––––––––––––––– –––––––––––315 x 0.971 x (70) x 1√ 60

A = 2.562 in2

Step 5

Select orifice just in excess of 2.562 in2,orifice L at 2.853 in2.

Notes

1. Thermal properties of the specific fluidshould be obtained from appropriatesources.

2. For vessels with other than flat ends, use theappropriate equations for surface area of theends.



Valve Sizing for Saturated HighTemperature Liquids which Flashto Vapor at Relief Conditions.As a hot liquid suddenly increases in volume, such as in flow through a pres-sure relief valve, part of it expands tovapor or ‘flashes.’ Under these conditionsthe required flow area for the pressure re-lief valve is greater than that required forliquid alone. Since enthalpy, or total ener-gy, in the fluid remains constant, andsince fluid properties1 are available at sat-urated liquid and saturated vaporconditions, the amount of liquid whichflashes to vapor can be calculated usingequation (15).

(15) % of Flash =H1 - H2

x (100%)–––––––HFg

Where:

H1 is the maximum enthalpy at the reliev-ing absolute pressure;

H2 is the enthalpy of saturated liquid atsonic flow conditions occurring in the nozzle; and HFg is the latent heat of vaporization, or the difference in enthalpybetween vapor and liquid states. SeeEnthalpy graph on page 46.

The set pressure (P1) is the accumulatedabsolute pressure plus the overpressure.

The sonic flow pressure, also called thecritical pressure, is obtained by using thefluid’s specific heat ratio (k)1 as a term inthe following equation.

Pcp = P12

k

––––– ––––( k + 1 ) k - 1

P1If k is not known, Pcp = ––––

2

From the required flow rate, derive the vapor flow and liquid flow from equationsas follows:

Vapor flow:

(16) Wp =% Flash

x Reg. Capacity2 (lbs/h)–––––––100

Liquid flow:

(17) W =(Required Capacity - Wp)

gpm–––––––––––––––––––––500 x G

G is the specific gravity of the liquid.

Combine the required flow area values forvapor and liquid and use that value in thearea equations on pages 7 and 8. Selectthe valve orifice area which just exceedsthe required combined area.

Example of sizing or flashing service conditions:

Set Pressure P = 250 psig

Required Capacity W = 74,000 lbs/h

Temperature T = 380°F

Accumulation = 10%

P1= 250 x 1.1 + 14.7 = 289.7 psia

Pcp = 289.7 x 0.58 = 168 psia

H1 (380°F liquid) = 353.6 BTU/lb

H2 (sat. liquid @ 168 psia) = 340.2 BTU/lb

HFg (latent heat @ 168 psia) = 855.6 BTU/lb

G (specific gravity) @168 psia = .892

W - liquid capacity

H1 - H2% of Flash = –––––––– x (100%)

HFg

353.6 - 340.2––––––––––– x (100%) = 1.57%

855.6

WP = 0.0157 x 174000 = 2731 lbs/h, steam

WG = 174000 - 2731 = 171269 lbs/h, water

lbs/h, water 171269WG = –––––––––– = –––––––– = 384 gpm

500 x G 500 x 0.892

Determine As and Aw required area forsteam and water, respectively.

WpAs = –––––––––––

51.5 KP1Ksh

2731As = ––––––––––––––––––– = 0.188 in2

51.5 x 0.971 x 289.7 x 1

–––

Aw =W√ G

––––––––––––––––––––––––––––––––38K Kv Kw √1.1 P1 - P2

–––––

Aw =384√0.892

––––––––––––––––––––––––––––––––––––––38 x .776 x 1 x 1 x √1.1 (250) - 0

Aw = .7416 in2

Thus, total required area, A, is:

A = As + Aw = 0.188 + 0.742 = 0.930 in2

Select orifice 1.287 in2, orifice J .

Notes

1. Thermal properties of the specific fluidshould be obtained form appropriatesources.

2. The required capacity is given for the application by process requirements.

Valve Sizing – Special Applications



Terminology for pressure relief devices:ANSI B95. 1-1977

Sample pressure relief valve specificationsheet:

API–STD-526

Guide for operating differentials:ASME Section VIII, APP. M

Fire Sizing:API-RP-520, Part INFPA No. 58

Overpressure Boilers:Pressure Vessels:

ASME Section I, Par. PG-72ASME Section VIII, Par. UG - 125

Installation Boiler:Pressure Vessels:

ASME Section I, Par. PG-71ASME Section VIII, Par. UG-135And Appendix M. API-RP-520, Part II

Commercial Seat Tightness:API-STD-527

Notes

ANSI American National StandardsInstitute

API American Petroleum Institute

ASME American Society of MechanicalEngineers

NFPA National Fire ProtectionAssociation

Standards – Sources

Valve Sizing – Special ApplicationsReference Specifications

P1

P2

Critical Point

HpgH2

T2H1

T1

Liqui

d

Satu

rate

d Saturated

Vapor

P –

Pres

sure

, PSI

A

H (Enthalpy), BTU/Lb.

Special Water Sizing Enthalpy Graph



The discharge from a pressure relief valveexerts a reaction force on the valve or outlet piping. If the discharge piping is unsupported, this force is transmitted tothe valve inlet and associated piping. Thefollowing formula or chart may be used to determine the reaction force. It is as-sumed that critical flow of the gas or vaporis obtained at the valve outlet. Under con-ditions of sub-critical flow, the reactionforce will be less than that calculated.

The chart is based on a value of k = 1.4.This will provide a conservative value forthe reaction force for most applications.However, if more accurate results are desired, the reaction forces can be deter-mined by the following formula (18):

–––––––––

(18) F =

k T–––––––

W√ (k + 1)M + (Ao x P2)–––––––––––––––

366

Reference: API RP 520, Part II

F = reaction force at the point of dis-charge to the atmosphere, inpounds (newtons)

W = flow of any gas or vapor, in poundsper hour (kilograms per second)

k = ratio of specific heats (Cp/Cv)

Cp = specific heat at constant pressure

Cv = specific heat at constant volume

T = temperature at inlet, in degreesRankine (degrees Fahrenheit + 460)

M = molecular weight of the process fluid

Ao = area of the outlet at the point of dis-charge, in square inches (squaremillimeters)

P2 = static pressure at the point of dis-charge, in pounds per square inchgauge (bar gauge)

Reaction Forces – Vapors and Gases

Valve Sizing – Reaction Forces



Conversion Factors

Equivalents and Conversion Factors

A B CMultiply By To Obtain

Atmospheres 14.697 Pounds per in2

Atmospheres 1.033 Kilograms per cm2

Atmospheres 29.92 Inches of mercury

Atmospheres 760 Millimeters of mercury

Atmospheres 407 Inches of water

Atmospheres 33.90 Feet of water

Barrels (petroleum) 42 Gallons

Barrels per day 0.0292 Gallons per minute

Bars-G 14.5 Pounds per in2

Centimeters 0.3937 Inches

Centimeters 0.03281 Feet

Centimeters 0.01 Meters

Centimeters 0.01094 Yards

Cubic centimeters 0.06102 Cubic inches

Cubic feet 7.48055 Gallons

Cubic feet 0.17812 Barrels

Cubic feet per second 448.833 Gallons per minute

Cubic inches 16.39 Cubic centimeters

Cubic inches 0.004329 Gallons

Cubic meters 264.17 Gallons

Cubic meters per hour 4.4 Gallons per minute

Feet 0.3048 Meters

Feet 0.3333 Yards

Feet 30.48 Centimeters

Feet of water 0.882 Inches of mercury

Feet of water 0.433 Pounds per in2

Gallons (U.S.) 3785 Cubic centimeters

Gallons (U.S.) 0.13368 Cubic feet

Gallons (U.S.) 231 Cubic inches

Gallons (Imperial) 277.4 Cubic inches

Gallons (U.S.) 0.833 Gallons (Imperial)

Gallons (U.S.) 3.785 Liters

Gallons of water 8.328 Pounds (at 70°F)

Gallons of liquid per minute 500 x Sp. Gr. Pounds per hr. liquid (at 70°F)

Gallons per minute 0.002228 Cubic feet per second

Horsepower (boiler) 34.5 Pounds water per hr. evaporation

Notes

This table may be used in two ways:

1. Multiply the unit under column A by the figure under column B; the result is the unit under column C.

2. Divide the unit under column C by the figureunder column B; the result is the unit undercolumn A.



Conversion Factors



Horsepower (boiler) 33479 BTU per hour

Inches 2.54 Centimeters

Inches 0.0833 Feet

Inches 0.0254 Meters

Inches 0.02778 Yards

Inches of mercury 1.133 Feet of water

Inches of mercury 0.4912 Pounds per in2

Inches of mercury 0.0345 Kilograms per cm2

Inches of water 0.03613 Pounds per in2

Inches of water 0.07355 Inches of mercury

Kilograms 2.205 Pounds

Kilograms 0.001102 Short tons (2000 lbs.)

Kilograms per minute 132.3 Pounds per hour

Kilograms per cm2 14.22 Pounds per in2

Kilograms per cm2 0.9678 Atmospheres

Kilograms per cm2 28.96 Inches of mercury

Kilopascals .145 Pounds per in2

Liters 1000 Cubic centimeters

Liters 0.2642 Gallons

Liters per hour 0.0044 Gallons per minute

Meters 3.281 Feet

Meters 1.0936 Yards

Meters 100 Centimeters

Meters 39.37 Inches

Megapascals 145 Pounds per in2

Metric Ton 1000 Kilogram

Pounds 0.0005 Short tons (2000 lbs.)

Pounds 0.4536 Kilograms

Pounds 0.000454 Metric tons

Pounds 16 Ounces

Pounds per hour 6.32/M.W. Cubic feet per minute

Pounds per hour liquid 0.002/Sq. Gr. Gallons per minute liquid (at 70°F)

Pounds per in2 27.684 Inches of water

Pounds per in2 2.307 Feet of water

Pounds per in2 2.036 Inches of mercury

Pounds per in2 0.0703 Kilograms per cm2

Pounds per in2 51.71 Millimeters of mercury

Notes

This table may be used in two ways:

1. Multiply the unit under column A by the figure under column B; the result is the unit under column C.

2. Divide the unit under column C by the figureunder column B; the result is the unit undercolumn A.



Conversion Factors



Pounds per in2 0.7037 Meters of water

Specific Gravity (of gas or vapors) 28.97 Molecular wt. (of gas or vapors)

Square centimeters 0.1550 Square inches

Square inches 6.452 Square centimeters

Tons (short ton, 2000 lbs) 907.2 Kilograms

Tons (short ton, 2000 lbs.) 1.102 Metric tons

Tons (metric) per day 91.8 Pounds per hour

Water (cubic feet) 62.3 Pounds (at 70°F)

Yards 0.9144 Meters

Yards 91.44 Centimeters



Pressure Conversions1

Given To Find (To find desired value, multiply ‘Given’ value by factor below)

mm wc mb mm Hg in wc oz kPa in Hg psig kg/cm2 bars

mm wc(mm water column) ––– 0.0980 0.735 0.0394 0.0227 0.00980 0.00290 0.001421

1 1

(60°F or 15.6°C)10010 10207

mb (millibars) 10.21 –––– 0.750 0.4019 0.2320 0.1000 0.0296 0.01450 0.00102 0.00100

mm Hg2

(mm Mercury) 13.61 1.333 –––– 0.5358 0.3094 0.1333 0.03948 0.01934 0.00136 0.00133(32°F or 0°C)

in wc(in. water column) 25.40 2.488 1.866 –––– 0.5775 0.2488 0.0737 0.03609 0.00254 0.00249(60°F or 15.6°C)

oz (oz/in2) 43.99 4.309 3.232 1.732 –––– 0.4309 0.12760.0625

0.00439 0.00431or 1/16

kPa (kilopascal) 102.1 10.00 7.501 4.019 2.321 –––– 0.2961 0.1450 0.0102 0.0100

in Hg (in. Mercury)344.7 33.77 25.33 13.57 7.836 3.377 –––– 0.4898 0.0344 0.0338

(60°F or 15.6°C)

psig (lbs/in2) 703.8 68.95 51.72 27.71 16.00 6.895 2.042 –––– 0.0703 0.0689

kg/cm23 (kg/cm2) 10010 980.7 735.6 394.1 227.6 98.07 29.04 14.22 –––– 0.9807

bars 10207 1000 750.1 401.9 232.1 100.0 29.61 14.50 1.020 ––––

Conversion Factors

1. When pressure is stated in liquid columnheight, conversions are valid only for listedtemperature.

2. Also expressed as torr.

3. Also expressed as kp/cm2 and kgf/cm2.

4. Normal Temperature and Pressure, (NTP)conditions, are at sea level, equal to 1.013bars (absolute) or 1.033 kg/cm2 a (kilogramsforce per square centimeter absolute) atbase temperature of 32°F [0°C]. This differsslightly from Metric Standard conditions,(MSC), which uses 15°C for the base tem-perature.

Inch-Pound Standard Conditions are at sea level,equal to 14.7 psia (pounds force per squareinch absolute), rounded from 14.696 psia, at abase temperature of 60°F [15.6°C].

Temperature conversion:

If °F is known, to find °C: °C = (°F/1.8)-17.78

If °C is known, to find °F: °F = (°C+17.78)1.8

Example: Temperature is -20°C, find °F: F = (-20+17.78)1.8 = -2.22 x 1.8 = -4°F

Notes



Conversion Factors

Notes

M = molecular weight of gas.

1. Volumetric flow (per time unit of hour orminute as shown) in standard cubic feet per minute at 14.7 psia, 60°F.

2. Weight flow in pounds per hour.

3. Weight flow in kilograms per hour.

4. Volumetric flow (per time unit of hour orminute as shown) at 1.013 bars absolute,0°C. This represents the commercial stan-dard, known as the Normal Temperature and Pressure (NTP).

Inch-Pound Units

Metric Units

scfm = (cfm or acfm) x14.7 + p

x520

––––––– ––––––14.7 460 + t

Where: p = gauge pressure of gas in psig

t = temperature of gas in °F

cfm or acfm = displacement or swept volume in cubic feet or actual cubic feet per minute

Conversions from volumetric to volumetricor to weight flow (and vice versa) mayonly be done when the volumetric flow isexpressed in the standard conditionsshown above. If flows are expressed attemperature or pressure bases that differfrom those listed above, they must first beconverted to the standard base.

If flow is expressed in actual volume, suchas cfm (cubic feet per minute) or acfm (ac-tual cfm) as is often done for compressors,where the flow is described as displace-ment or swept volume, the flow may beconverted to scfm as follows (or from flowexpressed in m3/h to Nm3/h).

Nm3/h = m3/h x 1.013 + p

x273

–––––––– ––––––1.013 460 + 1

Where: p = gauge pressure of gas in barg

t = temperature of gas in °C

m3/h = displacement or swept volume in cubic meters/hour

Gas Flow Conversions


scfm scfh lb/h kg/h Nm3/h Nm3/min

scfm1 –––– 60M M

1.608 0.02686.32 13.93

M Mscfh1 0.01677 ––––

379.2 836.10.0268 0.000447

lb/h26.32 379.2

–––– 0.453610.17 0.1695

M M M M

13.93 836.1 22.40 0.3733kg/h3

M M2.205 ––––

M M

Nm3/h4 0.6216 37.30M M

–––– 0.0166710.17 22.40

Nm3/min4 37.30 2238 5.901 M 2.676 M 60 ––––



Note

G = relative density of liquid at its relieving temperature to that of water at 68°F [20°C],where Gwater = 1.00.

Conversion Factors

Liquid Flow Conversions


l/h gpm (US) gpm(Imp) barrels/day m3/h

l/h–––– 0.00440 0.003666 0.1510 0.0010

liters/hour

gpm (US)US gallons per 227.1 ––––

––––0.8327 34.29 0.2271

minute

gpm (Imp)Imperial gallons 272.8 1.201 –––– 41.18 0.2728per minute

barrels/day(petroleum) 6.624 0.02917 0.02429 –––– 0.006624(42 US gallons)

m3/hcubic meters per hour

1000 4.403 3.666 151.0 ––––

m3/scubic meters per second

3.6 x 106 15.850 13.200 543.400 3600

kg/h 1 1 1 0.151 1kilograms per hour G 227.1G 272.8G G 1000G

lb/h 1 1 1 1 1pounds per hour 2.205G 500.8G 601.5G 14.61G 2205G



Viscosity Conversion Table

Seconds Seconds Seconds Seconds SecondsViscosity Saybolt Saybolt Redwood1 Redwood2

Centistokes Universal Furol (standard) (Admiralty)ν ssu ssf

1.00 31 29.0

2.56 35 32.1

4.30 40 36.2 5.10

7.40 50 44.3 5.83

10.3 60 52.3 6.77

13.1 70 12.95 60.9 7.60

15.7 80 13.70 69.2 8.44

18.2 90 14.4 77.6 9.30

20.6 100 15.24 85.6 10.12

32.1 150 19.30 128.0 14.48

43.2 200 23.5 170.0 18.90

54.0 250 28.0 212.0 23.45

65.0 300 32.5 254.0 28.0

87.60 400 41.9 338.0 37.1

110.0 500 51.6 423.0 46.2

132.0 600 61.4 508.0 55.4

154.0 700 71.1 592.0 64.6

176.0 800 81.0 677.0 73.8

198.0 900 91.0 462.0 83.0

220.0 1000 100.7 896.0 92.1

330.0 1500 150.0 1270.0 138.2

440.0 2000 200.0 1690.0 184.2

550.0 2500 250.0 2120.0 230.0

660.0 3000 300.0 2540.0 276.0

880.0 4000 400.0 3380.0 368.0

1100.0 5000 500.0 4230.0 461.0

1320.0 6000 600.0 5080.0 553.0

1540.0 7000 700.0 5920.0 645.0

1760.0 8000 800.0 6770.0 737.0

1980.0 9000 900.0 7620.0 829.0

2200.0 10000 1000.0 8460.0 921.0

3300.0 15000 1500.0 13700.0

4400.0 20000 2000.0 18400.0

Viscosity Units and TheirConversionWhen a correction for the effects of viscosity in the liquid orifice sizing formula is needed, the value of viscosity,expressed in centipoise, is required. Sincemost liquid data for viscosity uses otherexpressions, a convenient method forconversion is presented below.

The viscosity, µ (Greek mu), in centipoise,is correctly known as absolute or dynamicviscosity. This is related to the kinematicviscosity expression, ν (Greek nu), in cen-tistokes as follows:

µ (absolute viscosity, centipoise) = ν (kinematic viscosity, centistokes) x

ρ (density, grams/cm3)

The liquid sizing formula uses the relative density, G, where G = ρliquid/ρwater andwhere the density of water is accepted (forthis manual) as 1g/cm3. The value of Gthen becomes the density in g/cm3.

Substituting G for ρ (Greek rho) in the for-mula above, gives:

µ = ν x G (22),where:

µ = absolute viscosity, centipoiseν = kinematic viscosity, centistokesG = relative density (water = 1.00)

Most other viscosity units in common usage are also kinematic units and can berelated to the kinematic viscosity in centis-tokes, via the accompanying table. To usethis table, obtain the viscosity from datafurnished. Convert this to ν, in centistokes,then convert to absolute viscosity µ, incentipoise.

The conversions are approximate but satisfactory for viscosity correction in liquid safety valve sizing.

Conversion Factors



Curve to Evaluate Gas Constant C and Gas Specific Heat Ratio k

Fluid Data

▲1.00

▲1.10

▲1.20

▲1.30

▲1.40

▲1.50

▲1.60

▲1.70

▲1.80

▲1.90

▲2.00

400

390

380

370

360

350

340

330

320

310

Gas

Co

nst

ant,

C

C = 520 k 2k + 1( (

k + 1k - 1

Gas Specific Heat Ratio, k



Curve to Evaluate Critical Pressure RatioPCF

P1

Fluid Data

▲

1.00▲

1.10▲

1.20▲

1.30▲

1.40▲

1.50▲

1.60▲

1.70▲

1.80▲

1.90▲

2.00

0.610

0.600

0.590

0.580

0.570

0.560

0.550

0.540

0.530

0.520

0.510

0.500

0.490

0.480

0.470

0.460

0.450

0.440

PCF

P1

=2

k + 1)(k

k - 1

Gas Specific Heat Ratio, k

Cri

tica

l Pre

ssu

re R

atio

,P

CF

P1



Physical Properties for Selected Gases

Gas Empirical Molecular Specific Gas CriticalFormula Weight Heat Constant Pressure

M Ratio C Ratiok PCF/P1

Acetone C3H6O 58.08 1.12 329 0.581

Acetylene (Ethyne) C2H2 26.04 1.26 343 0.553

Air — 28.97 1.40 356 0.528

Ammonia, Anhydrous NH3 17.03 1.31 348 0.544

Argon Ar 39.95 1.67 378 0.487

Benzene (Benzol or Benzole) C6H6 78.11 1.12 329 0.581

Boron Trifluoride BF3 67.82 1.2 337 0.564

Butadiene-1,3 (Divinyl) C4H6 54.09 1.12 329 0.581

Butane (Normal Butane) C4H10 58.12 1.09 326 0.587

Butylene (1-Butene) C4H8 56.11 1.11 328 0.583

Carbon Dioxide CO2 44.01 1.29 346 0.548

Carbon Disulfide (C. Bisulfide) CS2 76.13 1.21 338 0.563

Carbon Monoxide CO 28.01 1.40 356 0.528

Carbon Tetrachloride CCI4 153.82 1.11 328 0.583

Chlorine Cl2 70.91 1.36 353 0.535

Chloromethane (Methyl Chloride) CH3Cl 50.49 1.28 345 0.549

Cyclohexane C6H12 84.16 1.09 326 0.587

Cyclopropane (Trimethylene) C3H6 42.08 1.11 328 0.583

Decane-n C10H22 142.29 1.04 320 0.598

Diethylene Glycol (DEG) C4H10O3 106.17 1.07 323 0.591

Diethyl Ether (Methyl Ether) C2H6O 46.07 1.11 328 0.583

Dowtherm A — 165.00 1.05 321 0.595

Dowtherm E — 147.00 1.00 315 0.607

Ethane C2H6 30.07 1.19 336 0.566

Ethyl Alcohol (Ethanol) C2H6O 46.07 1.13 330 0.578

Ethylene (Ethene) C2H4 28.05 1.24 341 0.557

Ethylene Glycol C2H6O2 62.07 1.09 326 0.587

Ethylene Oxide C2H4O 44.05 1.21 338 0.563

Fluorocarbons:12, Dichlorodifluoromethane CCI2F2 120.93 1.14 331 0.576

13, Chlorotrifluoromethane CCIF3 104.47 1.17 334 0.570

13B1, Bromotrifluoromethane CBrF3 148.93 1.14 331 0.576

22, Chlorodifluoromethane CHCIF2 86.48 1.18 335 0.568

115, Chloropentafluoroethane C2CIF5 154.48 1.08 324 0.589

Glycerine (Glycerin or Glycerol) C3H8O3 92.10 1.06 322 0.593

The specific heat ratios listed herein havebeen obtained from numerous sources. Theymay vary from values available to the reader.

Exercise caution when selecting the specificheat ratio. Please note that the values for Cand PCF/P1 are derived from the listed k.

Fluid Data



Physical Properties for Selected Gases, continued

Gas Empirical Molecular Specific Gas CriticalFormula Weight Heat Constant Pressure

M Ratio C Ratiok PCF/P1

Helium He 4.00 1.67 378 0.487

Heptane C7H16 100.21 1.05 321 0.595

Hexane C6H14 86.18 1.06 322 0.593

Hydrogen H2 2.02 1.41 357 0.527

Hydrogen Chloride, Anhydrous HCl 36.46 1.41 357 0.527

Hydrogen Sulfide H2S 34.08 1.32 349 0.542

Isobutane (2-Methylpropane) C4H10 58.12 1.10 327 0.585

Isobutane (2-Methyl-1,3butadiene) C5H8 68.12 1.09 326 0.587

Isopropyl Alcohol (Isopropanol) C3H8O 60.10 1.09 326 0.587

Krypton Kr 83.80 1.71 380 0.481

Methane CH4 16.04 1.31 348 0.544

Methyl Alcohol (Methanol) CH4O 32.04 1.20 337 0.564

Methylanmines, Anhydrous:Monomethylamine (Methylamine) CH5N 31.06 1.02 317 0.602

Dimethylamine C2H7N 45.08 1.15 332 0.574

Triethylamine C3H9N 59.11 1.18 335 0.568

Methyl Mercapton (Methylamine) CH4S 48.11 1.20 337 0.564

Naphthalene (Naphthaline) C10H8 128.17 1.07 323 0.591

Natural Gas (Relative Density = 0.60) — 17.40 1.27 344 0.551

Neon Ne 20.18 1.64 375 0.491

Nitrogen N2 28.01 1.40 356 0.528

Nitrous Oxide N2O 44.01 1.30 347 0.546

Octane C8H18 114.23 1.05 321 0.595

Oxygen O2 32.00 1.40 356 0.528

Pentane C5H12 72.15 1.07 323 0.591

Propadiene (Allene) C3H4 40.07 1.69 379 0.484

Propane C3H8 44.10 1.13 330 0.578

Propylene (Propene) C3H6 42.08 1.15 332 0.574

Propylene Oxide C3H6O 58.08 1.13 330 0.578

Styrene C8H8 104.15 1.07 323 0.591

Sulfur Dioxide SO2 64.06 1.28 345 0.549

Sulfur Hexafluoride SF6 146.05 1.09 326 0.587

Steam H2O 18.02 1.31 348 0.544

Toluene (Toluol or Methylbenzene) C7H8 92.14 1.09 326 0.587

Triethylene Glycol (TEG) C6H14O4 150.18 1.04 320 0.598

Vinyl Chloride Monomer (VCM) C2H3Cl 62.50 1.19 336 0.566

Xenon Xe 131.30 1.65 376 0.490

Xylene (p-Xylene) C8H10 106.17 1.07 323 0.591

Fluid Data



Physical Properties for Selected Liquids

Fluid Empirical Relative FluidFormula Density G: Temperature

Water = 1 ˚C ˚F

Acetaldehyde C2H4 0.779 20 68

Acetic Acid C2H4O2 1.051 20 68

Acetone C3H6O 0.792 20 68

Ammonia, Anhydrous NH3 0.666 20 68

Automotive Crankcase and Gear Oils:SAE-5W Through SAE 150 — 0.88-0.94 15.6 60

Beer — 1.01 15.6 60

Benzene (Benzol) C6H6 0.880 20 68

Boron Trifluoride BF3 1.57 -100 -148

Butadiene-1,3 C4H6 0.622 20 68

Butane-n (Normal Butane) C4H10 0.579 20 68

Butylene (1-Butene) C4H8 0.600 20 68

Carbon Dioxide CO2 1.03 -20 -4

Carbon Disulphide (C. Bisulphide) CS2 1.27 20 68

Carbon Tetrachloride CCl4 1.60 20 68

Chlorine Cl2 1.42 20 68

Chloromethane (Methyl Chloride) CH3Cl 0.921 20 68

Crude Oils:32.6 Deg API — 0.862 15.6 60

35.6 Deg API — 0.847 15.6 60

40 Deg API — 0.825 15.6 60

48 Deg API — 0.79 15.6 60

Cyclohexane C6H12 0.780 20 68

Cyclopropane (Trimethylene) C3H6 0.621 20 68

Decane-n C10H22 0.731 20 68

Diesel Fuel Oils — 0.82-0.95 15.6 60

Diethylene Glycol (DEG) C4H10O3 1.12 20 68

Dimethyl Ether (Methyl Ether) C2H6O 0.663 20 68

Dowtherm A — 0.998 20 68

Dowtherm E — 1.087 20 68

Ethane C2H6 0.336 20 68

Ethyl Alcohol (Ethanol) C2H6O 0.79 20 68

Ethylene (Ethene) C2H4 0.569 -104 -155

Ethylene Glycol C2H6O2 1.115 20 68

Ethylene Oxide C2H4O 0.901 20 68

Fluorocarbons:R12, Dichlorodifluoromethane CCl2F2 1.34 20 68

R13, Chlorotrifluoromethane CClF3 0.916 20 68

R13B1, Bromtrifluoromethane CBrF3 1.58 20 68

R22, Chlorodifluoromethane CHClF2 1.21 20 68

R115, Chloropentafluoroethane C2ClF5 1.31 20 68

Fluid Data



Fuel Oils, Nos. 1, 2, 3, 5 and 6 — 0.82-0.95 15.6 60

Gasolines — 0.68-0.74 15.6 60

Glycerine (Glycerin or Glycerol) C3H8O3 1.26 20 68

Heptane C7H16 0.685 20 68

Hexane C6H14 0.660 20 68

Hydrochloric Acid HCl 1.64 15.6 60

Hydrogen Sulphide H2S 0.78 20 68

Isobutane (2-Methylpropane) C4H10 0.558 20 68

Isoprene (2-Methyl-1,3-Butadiene) C5H8 0.682 20 68

Isopropyl Alcohol (Isopropanol) C3H8O 0.786 20 68

Jet Fuel (average) — 0.82 15.6 60

Kerosene — 0.78-0.82 15.6 60

Methyl Alcohol (Methanol) CH4O 0.792 20 68

Methylamines, Anhydrous:Monomethylamine (Methylamine) CH5N 0.663 20 68

Dimethylamine C2H7N 0.656 20 68

Trimethylamine C3H9N 0.634 20 68

Methyl Mercapton (Methanethiol) CH4S 0.870 20 68

Nitric Acid HNO3 1.5 15.6 60

Nitrous Oxide N2O 1.23 -88.5 -127

Octane C8H18 0.703 20 68

Pentane C5H12 0.627 20 68

Propadiene (Allene) C3H4 0.659 -34.4 -30

Propane C3H8 0.501 20 68

Propylene (Propene) C3H6 0.514 20 68

Propylene Oxide C3H6O 0.830 20 68

Styrene C8H8 0.908 20 68

Sulfur Dioxide SO2 1.43 20 68

Sulphur Hexafluoride SF6 1.37 20 68

Sulphur Acid: H2SO4

95-100% — 1.839 20 68

60% — 1.50 20 68

20% — 1.14 20 68

Toluene (Toluol or Methylbenzene) C7H8 0.868 20 68

Triethylene Glycol (TEG) C6H12O4 1.126 20 68

Vinyl Chloride Monomer (VCM) C2H3Cl 0.985 -20 -4

Water, fresh H2O 1.00 20 68

Water, sea — 1.03 20 68

Xylene (p-Xylene) C8H10 0.862 20 68

Fluid Data

Physical Properties for Selected Liquids, continued

Fluid Empirical Relative FluidFormula Density G: Temperature

Water = 1 ˚C ˚F



ANSI Flange Standards



Pressure and Temperature Ratings

WCB

6 0 0

3 0 0

1 5 0

Pressure - psig [barg]

Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0 200[13.8]

400[27.6]

600[41.3]

800[55.1]

1000[69.0]

1200[82.7]

1400[96.5]

1600[110.2]

2500

1500

900

1000[538]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0 800[55.1]

1600[110.2]

2400[165.4]

3200[220.5]

4000[275.6]

4800[330.7]

5600[385.8]

6400[441.0]




WC6

6 0 0

3 0 0

1 5 0

1000[538]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0 200[13.8]

400[27.6]

600[41.3]

800[55.1]

1000[69.0]

1200[82.7]

1400[96.5]

1600[110.2]

2500

1500

900

1000[538]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0 800[55.1]

1600[110.2]

2400[165.4]

3200[220.5]

4000[275.6]

4800[330.7]

5600[385.8]

6400[441.0]




Monel

6 0 0

3 0 0

1 5 0

1000[538]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0 200[13.8]

400[27.6]

600[41.3]

800[55.1]

1000[69.0]

1200[82.7]

1400[96.5]

1600[110.2]

2500

1500

900

1000[538]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0 800[55.1]

1600[110.2]

2400[165.4]

3200[220.5]

4000[275.6]

4800[330.7]

5600[385.8]

6400[441.0]




Hastelloy

6 0 0

3 0 0

1 5 0

1000[538]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0 200[13.8]

400[27.6]

600[41.3]

800[55.1]

1000[69.0]

1200[82.7]

1400[96.5]

1600[110.2]

2500

1500

900

1000[538]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0 800[55.1]

1600[110.2]

2400[165.4]

3200[220.5]

4000[275.6]

4800[330.7]

5600[385.8]

6400[441.0]




CF8M

6 0 0

3 0 0

1 5 0

1000[538]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0

1200[649]

200[13.8]

400[27.6]

600[41.3]

800[55.1]

1000[69.0]

1200[82.7]

1400[96.5]

1600[110.2]

2500

1500

900

1000[538]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0

1200[649]

800[55.1]

1600[110.2]

2400[165.4]

3200[220.5]

4000[275.6]

4800[330.7]

5600[385.8]

6400[441.0]



6 0 0

3 0 0

1 5 0

1000[538]

200[13.8]

400[27.6]

600[41.3]

800[55.1]

1000[69.0]

1200[82.7]

1400[96.5]

1600[110.2]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0

1200[649]

2500

1500

900

1000[538]

800[55.1]

1600[110.2]

2400[165.4]

3200[220.5]

4000[275.6]

4800[330.7]

5600[385.8]

6400[441.0]


Tem

pera

ture

˚F

[˚C]

800[427]

600[316]

400[204]

200[93]

0

1200[649]


WC9




Types of FlangesAll flange faces and ratings conform toANSI B16.5-1977. Steel, full nozzle valveinlet flange thickness is equal to orgreater than ANSI minimum thickness.The raised face thickness is also equal toor greater than ANSI standard, and inletthickness ‘D’ dimension should be usedfor calculating length of stud for inlet bolt-ing on the various available flange faces.

Refer to the next two following pages forANSI dimensions for raised face and ringjoint.

The drilling of inlet and outlet flangesstraddle the centerlines of the valves.

For ring joint outlet face and other avail-able similar faces with projections ordepressions, the centerline of inlet to faceof outlet dimension is increased by the

amount of the projection or depressionover the ANSI total flange thickness.

For outlets furnished with heavier thanstandard flanges, the centerline of inlet to face of outlet dimension increases bythe difference in the ANSI total flangethickness.

Raised Face Ring Joint Large Tongue

Large Groove Small Male Small Female

Small Tongue Small Groove Large Female




Specifications

Pipe Diam. of Min. Thk. Diam. of Diam. of Number Diam. ofSize Flange of Flange Raised Face Bolt Circle of Bolts Bolts

in [mm] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm]

125 lb. Iron Flange

11/2 [40] 5 [127] 9/16 [14] — — 37/8 [98] 4 [102] 1/2 [13]

2 [50] 6 [152] 5/8 [16] — — 43/4 [121] 4 [102] 5/8 [16]

21/2 [65] 7 [178] 11/16 [17] — — 51/2 [140] 4 [102] 5/8 [16]

3 [80] 71/2 [191] 3/4 [19] — — 6 [152] 4 [102] 5/8 [16]

4 [100] 9 [229] 15/16 [24] — — 71/2 [178] 8 [203] 5/8 [16]

6 [150] 11 [279] 1 [25] — — 91/2 [241] 8 [203] 3/4 [19]

8 [200] 131/2 [343] 11/8 [29] — — 113/4 [298] 8 [203] 3/4 [19]

250 lb. Iron Flange

11/2 [40] 61/8 [156] 13/16 [21] 39/16 [90] 41/2 [114] 4 [102] 3/4 [19]

2 [50] 61/2 [165] 7/8 [22] 43/16 [106] 5 [127] 8 [203] 5/8 [16]

21/2 [65] 71/2 [191] 1 [25] 415/16 [125] 57/8 [149] 8 [203] 3/4 [19]

3 [80] 81/4 [210] 11/8 [29] 511/16 [144] 65/8 [168] 8 [203] 3/4 [19]

4 [100] 10 [254] 11/4 [32] 615/16 [176] 77/8 [200] 8 [203] 3/4 [19]

6 [150] 121/2 [318] 17/16 [37] 911/16 [246] 105/8 [270] 12 [305] 3/4 [19]

8 [200] 15 [381] 15/8 [41] 1115/16 [303] 13 [330] 12 [305] 7/8 [22]

Pipe Diam. of Min. Thk. Diam. of Diam. of Number Diam. of D-Dim E-DimSize Flange of Flange Raised Bolt of Bolts Thk. Thk.

Face Circle Bolts D Series D Seriesin [mm] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm]

150 lb. Steel Flange

1 [25] 41/4 [108] 7/16 [11] 2 [51] 31/8 [79] 4 [102] 1/2 [13] 13/16 [30] 1/2 [13]

11/2 [40] 5 [127] 9/16 [14] 27/8 [73] 37/8 [98] 4 [102] 1/2 [13] 15/16 [33] 11/16 [17]

2 [50] 6 [152] 5/8 [16] 35/8 [92] 43/4 [121] 4 [102] 5/8 [16] 13/8 [35] 11/16 [17]

21/2 [65] 7 [178] 11/16 [17] 41/8 [105] 51/2 [140] 4 [102] 5/8 [16] — — — —

3 [80] 71/2 [191] 3/4 [19] 5 [127] 6 [152] 4 [102] 5/8 [16] 11/2 [38] 11/16 [17]

4 [100] 9 [229] 15/16 [24] 63/16 [157] 71/2 [178] 8 [203] 5/8 [16] 111/16 [43] 11/16 [17]

6 [150] 11 [279] 1 [25] 81/2 [216] 91/2 [241] 8 [203] 3/4 [19] 17/8 [48] 13/16 [21]

8 [200] 131/2 [343] 11/8 [29] 105/8 [270] 113/4 [298] 8 [203] 3/4 [19] 2 [51] 13/16 [21]

10 [250] 16 [406] 13/16 [30] 123/4 [324] 141/4 [362] 12 [305] 7/8 [22] — — — —

Semi-Nozzle

Body

ASA Raised Face

Full Nozzle

Body

Inlet Iron Semi-Nozzle ANSI B16.1 Inlet Iron Full Nozzle ANSI B16.5

D

E



Specifications

Pipe Diam. of Min. Thk. Diam. of Diam. of Number Diam. of D-Dim E-DimSize Flange of Flange Raised Bolt of Bolts D Series D Series

Face Circle Boltsin [mm] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm]


1 [25] 47/8 [124] 11/16 [17] 2 [51] 31/2 [89] 4 [102] 5/8 [16] 17/16 [37] 1/2 [13]

11/2 [40] 61/8 [156] 13/16 [21] 27/8 [73] 41/2 [114] 4 [102] 3/4 [19] 15/8 [41] 11/16 [17]

2 [50] 61/2 [165] 7/8 [22] 35/8 [92] 5 [127] 8 [203] 5/8 [16] 13/4 [44] 11/16 [17]

21/2 [65] 71/2 [191] 1 [25] 41/8 [105] 57/8 [149] 8 [203] 3/4 [19] 17/8 [48] 11/16 [17]

3 [80] 81/4 [210] 11/8 [29] 5 [127] 65/8 [168] 8 [203] 3/4 [19] 2 [51] 11/16 [17]

4 [100] 10 [254] 11/4 [32] 63/16 [157] 77/8 [200] 8 [203] 3/4 [19] 21/16 [52] 11/16 [17]

6 [150] 121/2 [318] 17/16 [37] 81/2 [216] 105/8 [270] 12 [305] 3/4 [19] 25/16 [59] 13/16 [19]

8 [200] 15 [381] 15/8 [41] 105/8 [270] 13 [330] 12 [305] 7/8 [22] 21/2 [64] 13/16 [19]


1 [25] 47/8 [124] 11/16 [17] 2 [51] 31/2 [89] 4 [102] 5/8 [16] 17/16 [37] 1/2 [13]

11/2 [40] 61/8 [156] 7/8 [22] 27/8 [73] 41/2 [114] 4 [102] 3/4 [19] 15/8 [41] 11/16 [17]

2 [50] 61/2 [165] 1 [25] 35/8 [92] 5 [127] 8 [203] 5/8 [16] 13/4 [44] 11/16 [17]

21/2 [65] 71/2 [191] 11/8 [29] 41/8 [105] 57/8 [149] 8 [203] 3/4 [19] 17/8 [48] 11/16 [17]

3 [80] 81/4 [210] 11/4 [32] 5 [127] 65/8 [168] 8 [203] 3/4 [19] 2 [51] 11/16 [17]

4 [100] 103/4 [273] 11/2 [38] 63/16 [157] 81/2 [216] 8 [203] 7/8 [22] 21/4 [57] 11/16 [17]

6 [150] 14 [356] 17/8 [48] 81/2 [216] 111/2 [292] 12 [305] 1 [25] 23/4 [70] 13/16 [19]


11/2 [40] 7 [178] 11/4 [32] 27/8 [73] 47/8 [124] 4 [102] 1 [25] 2 [51] 11/16 [17]

2 [50] 81/2 [216] 11/2 [38] 35/8 [92] 61/2 [165] 8 [203] 7/8 [22] 21/4 [57] 11/16 [17]

21/2 [65] 95/8 [244] 15/8 [41] 41/8 [105] 71/2 [191] 8 [203] 1 [25] 23/8 [60] 11/16 [17]

3 [80] 91/2 [241] 11/2 [38] 5 [127] 71/2 [191] 8 [203] 7/8 [22] 21/4 [57] 11/16 [17]

4 [100] 111/2 [292] 13/4 [44] 63/16 [157] 91/4 [235] 8 [203] 11/8 [29] 21/2 [64] 11/16 [17]


11/2 [40] 7 [178] 11/4 [32] 27/8 [73] 47/8 [124] 4 [102] 1 [25] 2 [51] 11/16 [17]

2 [50] 81/2 [216] 11/2 [38] 35/8 [92] 61/2 [165] 8 [203] 7/8 [22] 25/16 [59] 11/16 [17]

3 [80] 101/2 [267] 17/8 [48] 5 [127] 8 [203] 8 [203] 11/8 [29] 25/8 [67] 11/16 [17]

4 [100] 121/4 [311] 21/8 [54] 63/16 [157] 91/2 [241] 8 [203] 11/4 [32] 27/8 [73] 11/16 [17]


11/2 [40] 8 [203] 13/4 [44] 27/8 [73] 53/4 [146] 4 [102] 11/8 [29] 21/2 [64] 11/16 [17]

2 [50] 91/4 [235] 2 [51] 35/8 [92] 63/4 [171] 8 [203] 1 [25] 213/16 [71] 11/16 [17]

Note

1. Inlet Thickness = Flange Thickness plusRaised Face Thickness.




Specifications

Pipe Diam. of Min. Thk. Diam. of Diam. of Number Diam. ofSize Flange of Flange Raised Face Bolt Circle of Bolts Bolts

in [mm] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm]

150 lb. Bronze Flange, ANSI B16.24

1/2 [15] 31/2 [89] 5/16 [8] — — 23/8 [60] 4 [102] 1/2 [13]

3/4 [20] 37/8 [98] 11/32 [9] — — 23/4 [70] 4 [102] 1/2 [13]

1 [25] 41/4 [108] 3/8 [10] — — 31/8 [79] 4 [102] 1/2 [13]

11/4 [32] 45/8 [117] 13/32 [10] — — 31/2 [89] 4 [102] 1/2 [13]

11/2 [40] 5 [127] 7/16 [11] — — 37/8 [98] 4 [102] 1/2 [13]

2 [50] 6 [152] 1/2 [13] — — 43/4 [121] 4 [102] 5/8 [16]

21/2 [65] 7 [178] 9/16 [14] — — 51/2 [140] 4 [102] 5/8 [16]

3 [80] 71/2 [191] 5/8 [16] — — 6 [152] 8 [203] 5/8 [16]

4 [100] 9 [229] 11/16 [17] — — 71/2 [191] 8 [203] 5/8 [16]

5 [125] 10 [254] 3/4 [19] — — 81/2 [216] 8 [203] 3/4 [19]

6 [150] 11 [279] 13/16 [21] — — 91/2 [241] 8 [203] 3/4 [19]

8 [200] 131/2 [343] 15/16 [24] — — 113/4 [298] 12 [305] 3/4 [19]

10 [250] 16 [406] 1 [25] — — 141/4 [362] 12 [305] 7/8 [22]

300 lb. Bronze Flange, ANSI B16.24

1/2 [15] 33/4 [95] 1/2 [13] — — 25/8 [67] 4 [102] 1/2 [13]

3/4 [20] 45/8 [117] 17/32 [13] — — 31/4 [83] 4 [102] 5/8 [16]

1 [25] 47/8 [124] 19/32 [15] — — 31/2 [89] 4 [102] 5/8 [16]

11/4 [32] 51/4 [133] 5/8 [16] — — 37/8 [98] 4 [102] 5/8 [16]

11/2 [40] 61/8 [156] 11/16 [17] — — 41/2 [114] 4 [102] 3/4 [19]

2 [50] 61/2 [165] 3/4 [19] — — 5 [127] 8 [203] 5/8 [16]

21/2 [65] 71/2 [191] 13/16 [21] — — 57/8 [149] 8 [203] 3/4 [19]

3 [80] 81/4 [210] 29/32 [23] — — 65/8 [168] 8 [203] 3/4 [19]

4 [100] 10 [254] 11/16 [27] — — 77/8 [200] 8 [203] 3/4 [19]

5 [125] 11 [279] 11/8 [29] — — 91/4 [235] 8 [203] 3/4 [19]

6 [150] 121/2 [318] 13/16 [30] — — 105/8 [270] 12 [305] 3/4 [19]

8 [200] 15 [381] 13/8 [35] — — 13 [330] 12 [305] 7/8 [22]




Ring Joint Facings

Nominal Pipe Size Groove Groove Dimensions Diameter of Raised Face ‘K’ANSI Flange Class Pitch ANSI Flange Class

Number Dia. Depth Width Radius 300150 300 600 900 1500 2500 P E F R 150 600 900 1500 2500

in[mm] in[mm] in[mm] in[mm] in[mm] in[mm] in[mm] in[mm] in[mm] in[mm]

1 [25] R-15 17/8 [48] 1/4 [6] 11/32 [9] 1/32 [1]

1 [25] 1 [25] 1 [25] 3/4 [20] R-16 2 [51] 1/4 [6] 11/32 [9] 1/32 [1]

11/2 [40] R-19 29/16 [65] 1/4 [6] 11/32 [9] 1/32 [1]

11/2 [40] 11/2 [40] 11/2 [40] R-20 211/16 [68] 1/4 [6] 11/32 [9] 1/32 [1]

2 [50] R-22 31/4 [83] 1/4 [6] 11/32 [9] 1/32 [1]

2 [50] 2 [50] 11/2 [40] R-23 31/4 [83] 5/16 [8] 15/32 [12] 1/32 [1]

2 [50] R-24 33/4 [95] 5/16 [8] 15/32 [12] 1/32 [1]

21/2 [65] R-25 4 [102] 1/4 [6] 11/32 [9] 1/32 [1]

21/2 [65] 21/2 [65] 2 [50] R-26 4 [102] 5/16 [8] 15/32 [12] 1/32 [1]

21/2 [65] R-27 41/4 [108] 5/16 [8] 15/32 [12] 1/32 [1]

3 [80] R-29 41/2 [114] 1/4 [6] 11/32 [9] 1/32 [1]

3 [80] 3 [80] 3 [80] R-31 47/8 [124] 5/16 [8] 15/32 [12] 1/32 [1]

3 [80] R-35 53/8 [137] 5/16 [8] 15/32 [12] 1/32 [1]

4 [100] R-36 57/8 [149] 1/4 [6] 11/32 [9] 1/32 [1]

4 [100] 4 [100] 4 [100] R-37 57/8 [149] 5/16 [8] 15/32 [12] 1/32 [1]

4 [100] R-39 63/8 [162] 5/16 [8] 15/32 [12] 1/32 [1]

6 [150] R-43 75/8 [194] 1/4 [6] 11/32 [9] 1/32 [1]

6 [150] 6 [150] R-45 85/16 [211] 5/16 [8] 15/32 [12] 1/32 [1]

8 [200] R-48 93/4 [248] 1/4 [6] 11/32 [9] 1/32 [1]

8 [200] R-49 105/8 [270] 5/16 [8] 15/32 [12] 1/32 [1]

10 [250] R-52 12 [305] 1/4 [6] 11/32 [9] 1/32 [1]

Note

Use 1500 psig in sizes 1 to 21/2 for 900 lbs.pressure. The depth of groove is added to mini-mum thickness of the flange increasing thecenter line of inlet to face of outlet. Ring Jointinlet Face and other flange facings have thesame dimension from center line of outlet toface of inlet as raised inlet flange. Diameter ofraised face is stamped with groove number. Alldimensions conform to ANSI B16.5-1977.


E

F

P

K

R23°± 1/2°

± .005

Minimum

± .008

± 1/64 -0

in [mm] in [mm] in [mm] in [mm] in[mm]

21/2 [64]

23/4 [70] 213/16 [71] 27/8 [73]

31/4 [83]

39/16 [90] 35/8 [92]

4 [102]

41/4 [108] 41/2 [114]

47/8 [124]

43/4 [121]

5 [127] 51/4 [133]

53/8 [137]

51/4 [133]

53/4 [146] 61/8 [156]

65/8 [168]

63/4 [171]

67/8 [175] 71/8 [181]

75/8 [194]

85/8 [219]

91/2 [241] 91/2 [241]

103/4 [273]

117/8 [302]

13 [330]




Raised Facing and Ring Joint Facing

ANSI Flange ClassTemperature 150 300 600 900 1500 2500

°F [°C] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm]

SS (A351 Gr CF8M) Maximum Pressure psig [barg]

100 [38] 275 [19.0] 720 [49.7] 1440 [99.3] 2160 [149.0] 3600 [248.3] 6000 [413.8]

200 [93] 240 [16.6] 620 [42.8] 1240 [85.5] 1860 [128.3] 3095 [213.4] 5160 [355.9]

300 [149] 215 [14.8] 560 [38.6] 1120 [77.2] 1680 [115.9] 2795 [192.8] 4660 [321.4]

400 [204] 195 [13.4] 515 [35.5] 1030 [71.0] 1540 [106.2] 2570 [177.2] 4280 [295.2]

500 [260] 170 [11.7] 480 [33.1] 955 [65.9] 435 [99.0] 390 [164.8] 3980 [274.5]

600 [316] 140 [9.7] 450 [31.0] 905 [62.4] 1355 [93.4] 2255 [155.5] 3760 [259.3]

700 [371] 110 [7.6] 430 [29.7] 865 [59.7] 1295 [89.3] 2160 [149.0] 3600 [248.3]

800 [427] 80 [5.5] 415 [28.6] 830 [57.2] 1245 [85.9] 2075 [143.1] 3460 [238.6]

900 [482] 50 [3.4] 395 [27.2] 790 [54.5] 1180 [81.4] 1970 [135.9] 3280 [226.2]

1000 [538] 20 [1.4] 365 [25.2] 725 [50.0] 1090 [75.2] 1820 [125.5] 3030 [209.0]

1100 [593] — — 325 [22.4] 645 [44.5] 965 [66.6] 1610 [111.0] 2685 [185.2]

1200 [649] — — 205 [14.1] 410 [28.3] 620 [42.8] 1030 [71.0] 1715 [118.3]

Monel® (A494 Gr M-35-2)

100 [38] 230 [15.9] 600 [41.4] 1200 [82.8] 1800 [124.1] 3000 [206.9] 5000 [344.8]

200 [93] 200 [13.8] 530 [36.6] 1055 [72.8] 1585 [109.3] 2640 [182.1] 4400 [303.4]

300 [149] 190 [13.1] 495 [34.1] 990 [68.3] 1485 [102.4] 2470 [170.3] 4120 [284.1]

400 [204] 185 [12.8] 480 [33.1] 955 [65.9] 1435 [99.0] 2390 [164.8] 3980 [274.5]

500 [260] 170 [11.7] 475 [32.8] 950 [65.5] 1435 [99.0] 2375 [163.8] 3960 [273.1]

600 [316] 140 [9.7] 475 [32.8] 950 [65.5] 1435 [99.0] 2375 [163.8] 3960 [273.1]

700 [371] 110 [7.6] 475 [32.8] 950 [65.5] 1435 [99.0] 2375 [163.8] 3960 [273.1]

750 [399] 95 [6.6] 470 [32.4] 935 [64.5] 1405 [96.9] 2340 [161.4] 3900 [269.0]

Hastelloy® C (A494 CW-N12MW)

100 [38] 290 [20.0] 750 [51.7] 1500 [103.4] 2250 [155.2] 3750 [258.6] 6250 [431.0]

200 [93] 260 [17.9] 750 [51.7] 1500 [103.4] 2250 [155.2] 3750 [258.6] 6250 [431.0]

300 [149] 230 [15.9] 730 [50.3] 1455 [100.3] 2185 [150.7] 3640 [251.0] 6070 [418.6]

400 [204] 200 [13.8] 705 [48.6] 1410 [97.2] 2115 [145.9] 3530 [243.4] 5880 [405.5]

500 [260] 170 [11.7] 665 [45.9] 1230 [84.8] 1915 [132.1] 3325 [229.3] 5540 [382.1]

600 [316] 140 [9.7] 605 [41.7] 1210 [83.4] 1815 [125.2] 3025 [208.6] 5040 [347.6]

700 [371] 110 [7.6] 570 [39.3] 1135 [78.3] 1705 [117.6] 2840 [195.9] 4730 [326.2]

750 [399] 95 [6.6] 530 [36.6] 1065 [73.4] 1595 [110.0] 2660 [183.4] 4430 [305.5]





ANSI Flange ClassTemperature 150 300 600 900 1500 2500

°F [°C] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm]

CS (A216 Grade WCB) Maximum Pressure psig [barg]

100 [38] 285 [19.7] 740 [51.0] 1480 [102.1] 2220 [153.1] 3705 [255.5] 6170 [425.5]

200 [93] 260 [17.9] 675 [46.6] 1350 [93.1] 2025 [139.7] 3375 [232.8] 5625 [387.9]

300 [149] 230 [15.9] 655 [45.2] 1315 [90.7] 1970 [135.9] 3280 [226.2] 5470 [377.2]

400 [204] 200 [13.8] 635 [43.8] 1270 [87.6] 1900 [131.0] 3170 [218.6] 5280 [364.1]

500 [260] 170 [11.7] 600 [41.4] 1200 [82.8] 1795 [123.8] 2995 [206.6] 4990 [344.1]

600 [316] 140 [9.7] 550 [37.9] 1095 [75.5] 1640 [113.1] 2735 [188.6] 4560 [314.5]

650 [343] 125 [8.6] 535 [36.9] 1075 [74.1] 1610 [111.0] 2685 [185.2] 4475 [308.6]

700 [371] 110 [7.6] 535 [36.9] 1065 [73.4] 1600 [110.3] 2665 [183.8] 4440 [306.2]

750 [399] 95 [6.6] 505 [34.8] 1010 [69.7] 1510 [104.1] 2520 [173.8] 4200 [289.7]

800 [427] 80 [5.5] 410 [28.3] 825 [56.9] 1235 [85.2] 2060 [142.1] 3430 [236.6]


ANSI Flange ClassTemperature 150 300 400 600 900 1500 2500

°F [°C] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm] in [mm]

Chrome-Moly Steel (A217 Grade WC6) Maximum Pressure psig [barg]

100 [38] 290 [20.0] 750 [51.7] 1000 [69.0] 1500 [103.4] 2250 [155.2] 3750 [258.6] 6250 [431.0]

200 [93] 260 [17.9] 710 [49.0] 950 [65.5] 1425 [98.3] 2135 [147.2] 3560 [245.5] 5930 [409.0]

300 [149] 230 [15.9] 675 [46.6] 895 [61.7] 1345 [92.8] 2020 [139.3] 3365 [232.1] 5605 [386.6]

400 [204] 200 [13.8] 660 [45.5] 880 [60.7] 1315 [90.7] 1975 [136.2] 3290 [226.9] 5485 [378.3]

500 [260] 170 [11.7] 640 [44.1] 855 [59.0] 1285 [88.6] 1925 [132.8] 3210 [221.4] 5350 [369.0]

600 [316] 140 [9.7] 605 [41.7] 805 [55.5] 1210 [83.4] 1815 [125.2] 3025 [208.6] 5040 [347.6]

650 [343] 125 [8.6] 590 [40.7] 785 [54.1] 1175 [81.0] 1765 [121.7] 2940 [202.8] 4905 [338.3]

700 [371] 110 [7.6] 570 [39.3] 755 [52.1] 1135 [78.3] 1705 [117.6] 2840 [195.9] 4730 [326.2]

750 [399] 95 [6.6] 530 [36.6] 710 [49.0] 1065 [73.4] 1595 [110.0] 2660 [183.4] 4430 [305.5]

800 [427] 80 [5.5] 510 [35.2] 675 [46.6] 1015 [70.0] 1525 [105.2] 2540 [175.2] 4230 [291.7]

850 [454] 65 [4.5] 485 [33.4] 650 [44.8] 975 [67.2] 1460 [100.7] 2435 [167.9] 4060 [280.0]

900 [482] 50 [3.4] 450 [31.0] 600 [41.4] 900 [62.1] 1350 [93.1] 2245 [154.8] 3745 [258.3]

950 [510] 35 [2.4] 380 [26.2] 505 [34.8] 755 [52.1] 1130 [77.9] 1885 [130.0] 3145 [216.9]

1000 [538] 20 [1.4] 225 [15.5] 300 [20.7] 445 [30.7] 670 [46.2] 1115 [76.9] 1860 [128.3]



Bronze Flange Ratings ANSI B16.24 1971

ANSI Flange Class Temperature 150 300°F [°C] in [mm] in [mm]

Bronze (B62) Maximum Pressure psig [barg]

0 to 150 [-18 to +66] 225 [15.5] 500 [34.5]

175 [79] 220 [15.2] 480 [33.1]

200 [93] 210 [14.5] 465 [32.1]

225 [107] 205 [14.1] 445 [30.7]

250 [121] 195 [13.4] 425 [29.3]

275 [135] 190 [13.1] 410 [28.3]

300 [149] 180 [12.4] 390 [26.9]

350 [177] 165 [11.4] 350 [24.1]

400 [204] — — 315 [21.7]

406 [208] 150 [10.3] — —

422 [217] — — 300 [20.7]

Iron Flange Ratings ANSI B16.1ANSI Flange Class

Temperature 150 300°F [°C] in [mm] in [mm]

Iron (A126) Maximum Pressure psig [barg]

0 to 150 [-18 to +66] 175 [12.1] 400 [27.6]

200 [93] 165 [11.4] 370 [25.5]

225 [107] 155 [10.7] 355 [24.5]

250 [121] 150 [10.3] 340 [23.4]

275 [135] 145 [10.0] 325 [22.4]

300 [149] 140 [9.7] 310 [21.4]

350 [177] 130 [9.0] 295 [20.3]

375 [191] 125 [8.6] 280 [19.3]

400 [208] — — 265 [18.3]

— — 250 [17.2]




Valve Installations

Valve Installation Precautions1. No intervening stop valve is permitted

between the system and/or piping andits protective relieving valve or valves,except per ASME SEC. VIII UG-135 (E).

2. No intervening stop valve is permittedbetween the protective relieving valveand discharge port, except per ASMESEC. VIII UG-135 (E).

3. No valve discharge media is permittedto strike other piping, or other equip-ment, when discharge is to atmosphere.Also, discharge media must be aimedaway from personnel platforms and alltraffic areas.

4. All set pressure adjustments must beverified as falling within the designrange for that valve spring. Consultfactory. State laws dictate that valveseals be broken only by persons authorized to do so by ASME andAnderson Greenwood and Co. Other-wise, valve warranties are void andlaws breached. Consult factory.

5. When discharging more than onevalve into a common header, exces-sive back pressure must be avoided.See ASME SEC. VIII Appx. M-8

6. The capacity of the relieving valve willalways be increased or decreasedproportionally with increase or de-crease of set pressure.

7. Test Gags Must Be Removed. Failureto do so renders the valve inoperableand, due to overpressure, may dam-age either the relieving valve or thesystem, or both.

8. Bonnet vents on all bellows or bal-anced pressure relief valves must beleft open – the shipping plugs must beremoved.

9. Pressure relief valves should bemounted in a vertical position. Installinga pressure relief valve in other than a vertical position will adversely affectoperation in varying degrees as a result of consequent misalignment of moving parts. Also, warranties maybe voided. Upside-down mountedvalves should be provided with ampledrainage of accumulated liquids fromall sections of the valve.

10.Prior to all installations, inlet connec-tions – flanged or threaded – must becleared of foreign matter. Any dirt entering the valve may damage valveseats. Use only wrench flats when securing threaded valves.

11. Should leakage be detected from anewly installed valve, first assume thecause to be from shipping and han-dling or installation procedures. Applypressure to the inlet side equal to 75%of operating pressure so that the liftlever can be manually activated, thusoperating the valve. For valves withoutlift levers, system pressure may be allowed to rise to the point of valve operation. In most instances, the valvewill properly reseat and the leakagewill stop.

12.Absolute tightness at seat surfaces isdifficult to achieve. Valve manufacturersadhere to a commercial seat tightnessstandard – API Standard 527.

13.Chatter may result when improper piping at valve inlet or outlet exists, or oversizing the valve.

14.Temperature and corrosion effects onvalve materials are very important toany pressure relief valve application.Disregard of these critical considera-tions may damage or cause malfunctionof the pressure relief valve.

15. Minimum differential between operat-ing pressure and set pressure: 5 psigto 70 psig; set 10% from 71 to 1000psig; 7% over 1000 psig. See ASMESEC. VIII Appx. M-M11C.

16. ASME-type pressure valves must beequipped with lift levers for all air,steam and hot water (above 140°F[60°C]) service.

17. Upon installation or after repair, theproper valve set pressure must be ver-ified. Also, pressure gauges should becalibrated periodically, insuring propersystem readout.

18. Any water leg between the valve and gauge must be compensated for.Otherwise, incorrect pressure readoutwill result.

19. Pressure relief valves left on-line during extended shutdowns should beinspected and tested before resumingservice. Certain conditions or actswhich often occur during long, unat-tended idle periods, such as corrosion,fouling or tampering, may prevent thedevice from performing properly. Wherea change in operating conditions fol-lows a shutdown, the inspectioninterval must be reviewed.



Following is an Excerpt from ASME Code Section I,Section IV, and Section VIII (1995 Addenda)



1. Safety Valve: An automatic pressure reliev-ing device actuated by the static pressureupstream of the valve and characterized byfull opening pop action. It is used for gas orvapor service.

Relief Valve: An automatic pressure reliev-ing device actuated by the static pressureupstream of the valve which opens furtherwith the increase in pressure over the open-ing pressure. It is used primarily for liquidservice.

Safety Relief Valve: An automatic pressure-actuated relieving device suitable for useeither as a safety valve or relief valve, de-pending on application.

Unless otherwise defined, the definitions re-lating to pressure relief devices in AppendixI of ASME/ANSI PTC 25.3, Safety andRelief Valves, shall apply.

2. Safety relief valves in hot water service aremore susceptible to damage and subse-quent leakage, than safety valves relievingsteam. It is recommended that the maximumallowable working pressure of the boiler andthe safety relief valve setting for high-tem-perature water boilers be selectedsubstantially higher than the desired operat-ing pressure so as to minimize the times thesafety relief valve must lift.

Notes

ASME Code Section I, Power Boilers - (1995 Addenda)

Safety Valves and Safety ReliefValves1

PG-67 Boiler Safety Valve Requirements

A93PG-67.1 Each boiler shall have at leastone safety valve or safety relief valve andif it has more than 500 sq ft of bare tubewater-heating surface, or if an electricboiler has a power input more than 1100kW, it shall have two or more safetyvalves or safety relief valves. For a boilerwith combined bare tube and extendedwater-heating surface exceeding 500 sqft, two or more safety valves or safety re-lief valves are required only if the designsteam generating capacity of the boilerexceeds 4000 lb/hr. Organic fluid vaporiz-er generators require specialconsideration as given in Part PVG.

A93PG-67.2 The safety valve or safety reliefvalve capacity for each boiler (except asnoted in PG-67.4) shall be such that thesafety valve, or valves, will discharge allthe steam that can be generated by theboiler without allowing the pressure to risemore than 6% above the highest pressureat which any valve is set and in no case tomore than 6% above the maximum allow-able working pressure.

A93PG-67.2.1 The minimum required reliev-ing capacity of the safety valves or safetyrelief valves for all types of boilers shallnot be less than the maximum designed

steaming capacity as determined by theManufacturer and shall be based on thecapacity of all the fuel burning equipmentas limited by other boiler functions.

A93PG-67.2.2 The minimum required reliev-ing capacity for a waste heat boiler shallbe determined by the Manufacturer. Whenauxiliary firing is to be used in combinationwith waste heat recovery, the maximumoutput as determined by the boilerManufacturer shall include the effect ofsuch firing in the total required capacity.When auxiliary firing is to be used in placeof waste heat recovery, the minimum re-quired relieving capacity shall be basedon auxiliary firing or waste heat recovery,whichever is higher.

A93PG-67.2.3 The minimum required relieving capacity for electric boilers shallbe in accordance with PEB-15.

A93PG-67.2.4 The minimum required relieving capacity in lb/hr for a high-tem-perature water boiler shall be determinedby dividing the maximum output in Btu/hrat the boiler nozzle, produced by the high-est heating valve fuel for which the boileris designed, by 1000.

A93PG-67.2.5 The minimum required reliev-ing capacity for organic fluid vaporizersshall be in accordance with PVG-12.

A93PG-67.2.6 Any economizer which may beshut off from the boiler, thereby permittingthe economizer to become a fired pres-sure vessel, shall have one or more safetyrelief valves with a total discharge capaci-ty, in lbs/hr, calculated from the maximumexpected heat absorption in Btu/hr, as de-termined by the Manufacturer, divided by1000. This absorption shall be stated inthe stamping (PG-106.4).

PG-67.3 One or more safety valves onthe boiler proper shall be set at or belowthe maximum allowable working pressure(except as noted in PG-67.4). If additionalvalves are used the highest pressure set-ting shall not exceed the maximumallowable working pressure by more than3%. The complete range of pressure set-tings of all the saturated-steam safetyvalves on a boiler shall not exceed 10% ofthe highest pressure to which any valve isset. Pressure setting of safety relief valveson high-temperature water boilers2 mayexceed this 10% range.

PG-67.4 For a forced-flow steam genera-tor with no fixed steam and waterline,equipped with automatic controls and pro-tective interlocks responsive to steampressure, safety valves may be providedin accordance with the above paragraphsor the following protection against over-pressure shall be provided:



3. The power-actuated pressure relieving valveis one of whose movements to open or closeare fully controlled by a source of power(electricity, air, steam, or hydraulic). Thevalve may discharge to atmosphere or to acontainer at lower pressure. The dischargecapacity may be affected by the downstreamconditions, and such effects shall be takeninto account . If the power-actuated pressurerelieving valves are also positioned in re-sponse other control signals, the controlimpulse to prevent overpressure shall be re-sponsive only to pressure and shall overrideany other control function.

4. ‘Fail-safe’ shall mean a circuitry arranged aseither of the following:

(1) Energize to trip: There shall be at leasttwo separate and independent trip cir-cuits served by two power sources, toinitiate and perform the trip action. Onepower source shall be a continuouslycharged dc battery. The second sourceshall be an ac-to-dc converter connectedto the dc system to charge the batteryand capable of performing the trip ac-tion. The trip circuits shall becontinuously monitored for availability.

It is not mandatory to duplicate themechanism that actually stops the flow offuel and feedwater.

(2) De-energize to trip: If the circuits arearranged in such a way that a continu-ous supply of power is required to keepthe circuits closed and operating andsuch that any interruption of power supply will actuate the trip mechanism,then a single trip circuit and single powersupply will be enough to meet the requirements of this subparagraph.

PG-67.4.1 One or more power-actuatedpressure relieving valves3 shall be providedin direct communication with the boiler whenthe boiler is under pressure and shall re-ceive a control impulse to open when themaximum allowable working pressure at thesuperheater outlet, as shown in the masterstamping (PG-106.3), is exceeded. The totalcombined relieving capacity of the power-actuated relieving valves shall be not lessthan 10% of the maximum design steamingcapacity of the boiler under any operatingcondition as determined by the Manufacturer.The valve or valves shall be located in thepressure part system where they will relievethe overpressure.

An isolating stop valve of the outside-screw-and-yoke type may be installedbetween the power-actuated pressure relieving valve and the boiler to permit repairs provided an alternate power-actuated pressure relieving valve of thesame capacity is so installed as to be in direct communication with the boiler in accordance with the requirements ofthis paragraph.

Power-actuated pressure relieving valvesdischarging to intermediate pressure andincorporated into bypass and/or startupcircuits by the boiler Manufacturer neednot be capacity certified. Instead, theyshall be marked by the valve manufacturerwith a capacity rating at a set of specifiedinlet pressure and temperature conditions.Power-actuated pressure relieving valvesdischarging directly to atmosphere shallbe capacity certified. This capacity certifi-cation shall be conducted in accordancewith the provisions of PG-69.3. The valvesshall be marked in accordance with theprovisions of PG.69.4 and PG-69.5.

PG-67.4.2 Spring-loaded safety valvesshall be provided, having a total combinedrelieving capacity, including that of thepower-actuated pressure relieving capaci-ty installed under PG-67.4.1, of not lessthan 100% of the maximum designedsteaming capacity of the boiler, as deter-mined by the Manufacturer, except thealternate provisions of PG-67.4.3 are sat-isfied. In this total, no credit in excess of30% of the total required relieving capaci-ty shall be allowed for the power-actuatedpressure relieving valves actually in-stalled. Any or all of the spring-loadedsafety valves may be set above the maxi-mum allowable working pressure of theparts to which they are connected, but theset pressures shall be such that when allof these valves (together with the power-actuated pressure relieving valves) are inoperation the pressure will not rise morethan 20% above the maximum allowableworking pressure of any part of the boiler,except for the steam piping between theboiler and the prime mover.

PG-67.4.3 The total installed capacity ofspring-loaded safety valves may be lessthan the requirements of PG-67.4.2 provid-ed all of the following conditions are met.

PG-67.4.3.1 The boiler shall be of no lesssteaming capacity than 1,000,000 lb/hrand installed in a unit system for powergeneration (i.e., a single boiler supplying asingle turbine-generator unit).

PG-67.4.3.2 The boiler shall be providedwith automatic devices, responsive to vari-ations in steam pressure, which include noless than all the following:

PG-67.4.3.2.1 A control capable of main-taining steam pressure at the desired

operating level and of modulating firingrates and feedwater flow in proportion to avariable steam output; and

PG-67.4.3.2.2 A control which overridesPG-67.4.3.2.1 by reducing the fuel rateand feedwater flow when the steam pres-sure exceeds the maximum allowableworking pressure as shown in the masterstamping (PG-106.3) by 10%; and

PG-67.4.3.2.3 A direct-acting overpres-sure-trip-actuating mechanism, using anindependent pressure sensing device, thatwill stop the flow of fuel and feedwater tothe boiler, at a pressure higher than theset pressure of PG-67.4.3.2.2, but lessthan 20% above the maximum allowableworking pressure as shown in the masterstamping (PG-106.3).

PG-67.4.3.3 There shall be not less thantwo spring-loaded safety valves and thetotal rated relieving capacity of the spring-loaded safety valves shall be not less than10% of the maximum designed steamingcapacity of the boiler as determined by theManufacturer. These spring-loaded safetyvalves may be set above the maximum al-lowable working pressure of the parts towhich they are connected but shall be setsuch that the valves will lift at a pressureno higher than 20% above the maximumallowable working pressure as shown inthe master stamping (PG-106.3).

PG-67.4.3.4 At least two of these spring-loaded safety valves shall be equipped witha device that directly transmits the valvestem lift action to controls that will stop theflow of fuel and feedwater to the boiler.The control circuitry to accomplish thisshall be arrange in a ‘fail-safe’ manner.4

Notes




PG-67.4.3.5 The power supply for all con-trols and devices required by PG-67.4.3shall include at least one source containedwithin the same plant as the boiler andwhich is arranged to actuate the controlsand devices continuously in the event offailure or interruption of any other powersources.

PG-67.4.4 When stop valves are installed in the water-steam flow path be-tween any two sections of a forced-flowsteam generator with no fixed steam andwaterline:

PG-67.4.4.1 The power-actuated pres-sure relieving valve(s) required byPG-67.4.1 shall also receive a control im-pulse to open when the maximumallowable working pressure of the compo-nent, having the lowest pressure levelupstream to the stop valve, is exceeded;and

PG-67.4.4.2 The spring-loaded safetyvalves shall be located to provide thepressure protection requirements in PG-67.4.2 or PG-67.4.3.

PG-67.4.5 A reliable pressure-recordingdevice shall always be in service andrecords kept to provide evidence of con-formity to the above requirements.

PG-67.5 All safety valves or safety reliefvalves shall be so constructed that thefailure of any part cannot obstruct the freeand full discharge of steam and waterfrom the valve. Safety valves shall be ofthe direct spring-loaded pop type, withseat inclined at any angle between 45 degrees and 90 degrees, inclusive, to thecenter line of the spindle. The coefficientof discharge of safety valves shall be determined by actual steam flow mea-surements at a pressure not more than3% above the pressure at which the valveis set to blow and when adjusted for blow-down in accordance with PG-72. Thevalves shall be credited with capacities asdetermined by the provisions of PG-69.2

Safety valves or safety relief valves maybe used which give any opening up to thefull discharge capacity of the area of theopening of the inlet of the valve (see PG-69.5), provided the movement of thesteam safety valve is such as not to in-duce lifting of water in the boiler.

Deadweight or weighted lever safetyvalves or safety relief valves shall not beused.

For high-temperature water boilers safetyrelief valves shall be used. Such valvesshall have a closed bonnet. For purposesof selection the capacity rating of suchsafety relief valves shall be expressed interms of actual steam flow determined onthe same basis as for safety valves. In ad-dition the safety relief valves shall becapable of satisfactory operation when re-lieving water at the saturation temperaturecorresponding to the pressure at whichthe valve is set to blow.

PG-67.6 A safety valve or safety reliefvalve over 3-inch in size, used for pres-sures greater than 15 psig, shall have aflanged inlet connection or weld-end inletconnection. The dimensions of flangessubjected to boiler pressure shall conformto the applicable American NationalStandards as given in PG-42. The facingshall be similar to those illustrated in theStandard.

PG-67.7 Safety valves or safety reliefvalves may have bronze parts complyingwith either SB-61 or SB-62, provided themaximum allowable stresses and temper-atures do not exceed the values given inTable 1B of Section II, Part D, and shall be marked to indicate the class of materialused. Such valves shall not be used onsuperheaters delivering steam at a temper-ature over 450°F and 306°F respectively,and shall not be used for high-temperaturewater boilers.

PG-68 Superheater Safety ValveRequirements

PG-68.1 Except as permitted in PG-58.3.1, every attached superheater shallhave one or more safety valves in thesteam flow path between the superheateroutlet and first stop valve. The locationshall be suitable for the service intendedand shall provide the overpressure protec-tion required. The pressure drop upstreamof each safety valve shall be considered inthe determination of set pressure and re-lieving capacity of that valve. If thesuperheater outlet header has a full, freesteam passage from end to end and is so

constructed that steam is supplied to it atpractically equal intervals throughout itslength so that there is a uniform flow ofsteam through the superheater tubes andthe header, the safety valve, or valves,may be located anywhere in the length ofthe header.

PG-68.2 The discharge capacity of thesafety valve, or valves, on an attached superheater may be included in determin-ing the number and size of the safetyvalves for the boiler, provided there are no intervening valves between the super-heater safety valve and the boiler, andprovided the discharge capacity of thesafety valve, or valves, on the boiler, asdistinct from the superheater is at least75% of the aggregate valve capacity required.

PG-68.3 Every independently fired super-heater which may be shut off from theboiler and permit the superheater to be-come a fired pressure vessel shall haveone or more safety valves having a dis-charge capacity equal to 6 lb of steam perhour per square foot of superheater sur-face measured on the side exposed to thehot gases. In the case of electrically heat-ed superheaters, the safety valve capacityshall be based upon 31/2 lb/hr/kW input.The number of safety valves installedshall be such that the total capacity is atleast equal to that required.

PG-68.4 Every reheater shall have one ormore safety valves, such that the total re-lieving capacity is at least equal to themaximum steam flow for which the re-heater is designed. At least one valveshall be located in the stamp flow path be-tween the reheater outlet and the first stopvalve. The location shall be suitable forthe service intended and shall provide theoverpressure protection required. Thepressure drop upstream of each safetyvalve shall be considered in the determi-nation of set pressure and relievingcapacity of that valve. The relieving ca-pacity of that valve shall be not less than15% of the required total. The capacity ofreheater safety valves shall not be includ-ed in the required relieving capacity forthe boiler and superheater.




PG-68.5 A soot blower connection maybe attached to the same outlet from thesuperheater or reheater that is used forthe safety valve connection.

PG-68.6 Every safety valve used on asuperheater or reheater discharging superheated steam at a temperature over450°F shall have a casing, including thebase, body, and bonnet and spindle, ofsteel, steel alloy, or equivalent heat-resist-ing material.

The valve shall have a flanged inlet con-nection, or a weld-end inlet connection. It shall have the seat and disk of suitableheat erosive and corrosive resisting mate-rial, and the spring fully exposed outsideof the valve casing so that it shall be pro-tected from contact with the escapingsteam.

PG-69 Certification of Capacity ofSafety and Safety Relief Valves

PG-69.1 Before the Code symbol is ap-plied to any safety or safety relief valve,the valve manufacturer shall have the re-lieving capacity of his valves certified inaccordance with the provisions of thisparagraph.

PG-69.1.1 Capacity certification testsshall be conducted using dry saturatedsteam. The limits for test purposes shallbe 98% minimum quality and 20°F maxi-mum superheat. Correction from withinthese limits may be made to the dry satu-rated condition.

PG-69.1.2 Tests shall be conducted at aplace which meets the requirements ofAppendix A-312.

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PG-69.1.3 Capacity test data reports foreach valve design and size, signed by themanufacturer and Authorized Observerwitnessing the tests, together with draw-ings showing the valve construction, shallbe submitted to the ASME designee forreview and acceptance.5

PG-69.1.4 Capacity certification testsshall be conducted at a pressure whichdoes not exceed the set pressure by 3%or 2 psi, whichever is greater. Safety andsafety relief valves shall be adjusted sothat the blowdown does not exceed 4% of the set pressure. For valves set at orbelow 100 psi, the blowdown shall be ad-justed so as not to exceed 4 psi. Safetyvalves used on forced-flow steam genera-tors with no fixed steam and waterline,and safety relief valves used on high-tem-perature water boilers shall be adjustedso that the blowdown does not exceed10% of the set pressure. The reseatingpressure shall be noted and recorded.

PG-69.2 Relieving capacities shall be determined using one of the followingmethods.

PG-69.2.1 Three Valve Method.A capacity certification test is required ona set of three valves for each combinationof size, design and pressure setting. Thecapacity of each valve of the set shall fallwithin a range of ±5% of the average ca-pacity. If one of the three valves testedfalls outside this range, it shall be re-placed by two valves, and a new averageshall be calculated based on all fourvalves, excluding the replaced valve.Failure of any of the four capacities to fallwithin a range of ±5% of the new averageshall be cause to refuse certification ofthat particular valve design.

The rated relieving capacity for each com-bination of design, size, and test pressureshall be 90% of the average capacity.

PG-69.2.2 Four Valve Method.Four valves of each combination of valveinlet size and orifice size shall be tested.These four valves shall be set at pressurescovering the range for which the valves willbe used or the range available at the certi-fied test facility where tests are conducted.

The slope of the actual measured capaci-ty versus the absolute flow rating pressurefor each test point shall be calculated andaveraged:

measured capacitySlope =absolute flow rating pressure, psia

All values derived from the testing mustfall within ±5% of the average slope.

If all slopes derived from the testing do not fall within ±5% of the average slope,the Authorized Observer shall require twoadditional valves to be tested as replace-ments for each valve having a slopeoutside this range, with a limit of four addi-tional valves. Failure of any slope to fallwithin ±5% of the new average slope, ex-cluding the replaced valve(s), shall because to refuse certification of that partic-ular valve design.

The rated relieving capacity to bestamped on the valve shall be determinedas follows:

rated relieving capacity = 0.90 x average slope x (1.03 x set

pressure + 14.7)

or

= 0.90 x average slope x (set pressure+ 2 psi + 14.7)

whichever is greater.

PG-69.2.3 Coefficient of DischargeMethod.

A coefficient of discharge for the design,K, may be established for a specific valvedesign according to the following proce-dure.

A. For each design, the safety or safetyrelief valve manufacturer shall submit fortest at least three valves for each of threedifferent sizes (a total of nine valves).Each valve of a given size shall be set at a different pressure, covering the rangeof pressures for which the valve will beused or the range available at the facilitywhere the tests are conducted.

B. Tests shall be made on each safetyor safety relief valve to determine its lift atcapacity, popping, and blowdown pres-sures, and actual relieving capacity.


Notes

5. Valve capacities are published in ‘PressureRelief Device Certifications.’ This publica-tion may be obtained from the NationalBoard of Boiler and Pressure VesselInspectors, 1055 Crupper Ave., Columbus,OH 43229.



An individual coefficient, KD, shall be established for each valve as follows:

Actual flow Individual coeffi-KD = = Theoretical flow cient of discharge

Where actual flow is determined by testand theoretical flow, WT is calculated byone of the following equations:

For 45 degree seatWT = 51.45 x πDLP x 0.707

For flat seatWT = 51.45 x πDLP

For nozzleWT = 51.45 AP

where:WT = theoretical flow, lb/hr

A = nozzle throat area, in2

P = (1.03 x set pressure + 14.7), or

= (set pressure + 2 + 14.7), whichever is greater, psia

L = lift pressure at P, in.

D = seat diameter, in.

The coefficient of discharge for the design,K, shall be the average of the nine individualcoefficients, KD. All individual coefficientsof discharge, KD, shall fall within a rangeof ±5% of the coefficient, K. If a valve failsto meet this requirement, the AuthorizedObserver shall require two additionalvalves to be tested as replacements foreach valve having an individual coeffi-cient, KD, outside the ±5% range, with alimit of four additional valves. Failure of a coefficient, KD, to fall within ±5% of thenew average value, excluding the re-placed valve(s), shall be cause to refusecertification of that particular valve design.

The rated relieving capacity of all sizesand set pressures of a given design, forwhich K has been established under theprovision of this paragraph, shall be deter-mined by the equation:

W = WT x K x 0.9

where:W = rated relieving capacity, lb/hr

WT = theoretical flow, defined by the sameequation used to determine KD, lb/hr

K = coefficient of discharge for the design

The coefficient of discharge for the de-sign, K, shall not be greater than 0.975.The coefficient shall not be applied tovalves whose beta ratio (ratio of valvethroat to inlet diameter) lies outside therange of 0.15 to 0.75, unless tests havedemonstrated that the individual coeffi-cient of discharge, KD, for valves at theextreme ends of a larger range, is within±5% of the coefficient, K.

For designs where the lift is used to deter-mine the flow area, all valves shall have thesame nominal lift to seat diameter ratio (L/D).

For pressures over 1500 psig and up to3200 psig, the value of W shall be multi-plied by the correction factor:

0.1906P - 1000

0.2292P - 1061

PG-69.3 If a manufacturer wishes to ap-ply the Code symbol to a power-actuatedpressure relieving valve under PG-67.4.1,one valve of each combination of inletpipe size and orifice size to be used withthat inlet pipe size shall be tested. Thevalve shall be capacity tested at four dif-ferent pressures approximately coveringthe range of the certified test facility onwhich the tests are conducted. The capac-ities, as determined by these four tests,shall be plotted against the absolute flowtest pressure and a line drawn throughthese four test points. All points must liewithin ±5% in capacity value of the plottedline and must pass through 0-0. From theplotted line, the slope of the line dW/dPshall be determined and a factor of(0.90/51.45) x (dW/dP) shall be applied tocapacity computations in the supercriticalregion at elevated pressures by means ofthe isentropic flow equation.6

––––––W =

0.90 dW P1135.8 ––––––– x ––– –––

51.45 dP √ ν

where:W = capacity, lb of steam/hr

P = absolute inlet pressure, psia

ν = inlet specific volume, cu ft/lb

dW/dP = rate of change of measured capacity with respect to absolutepressure

A92

PG-69.4 Power-actuated pressure relieving valves, having capacities certi-fied in accordance with the provision ofPG-69.3 and computed in accordancewith the formula contained therein, shallbe marked as required by PG-110 with thecomputed capacity, corresponding to 3%above the full load operating pressure andtemperature conditions at the valve inletwhen the valve is operated by the con-troller, and they shall also be stampedwith the set pressure of the controller.When the valve is marked as required bythis paragraph, it shall be the guaranteeby the manufacturer that the valve alsoconforms to the details of constructionherein specified.

A92

PG-69.6 When changes are made in thedesign of a safety or safety relief valve insuch a manner as to affect the flow path,lift, or performance characteristics of thevalve, new tests in accordance with thisSection shall be performed.

PG-70 Capacity of Safety Valves

A93

PG-70.1 Subject to the minimum numberrequired by PG-67.1, the number of safetyvalves or safety relief valves required shallbe determined on the basis of the maxi-mum designed steaming capacity, asdetermined by the boiler Manufacturer,and the relieving capacity marked on thevalves by the manufacturer.

In many cases a greater relieving capacityof safety valves or safety relief valves willhave to be provided than the minimumspecified by this rule, and in every casethe requirements of PG-67.2 shall be met.

6. The constant 1135.8 is based on a γ factorof 1.30 which is accurate for superheatedsteam at temperature above approximately800°F. In interest of accuracy, other meth-

ods of capacity computations must be usedat temperatures below 800°F at supercriticalpressures.


Notes



PG-71 Mounting

PG-71.1 When two or more safety valvesare used on a boiler, they may be mount-ed either separately or as twin valvesmade by placing individual valves on Y-bases, or duplex valves having twovalves in the same body casing. Twinvalves made by placing individual valveson Y-bases, or duplex valves having twovalves in the same body, shall be of approximately equal capacity.

When not more than two valves of differ-ent sizes are mounted singly the relievingcapacity of the smaller valve shall be notless than 50% of that of the larger valve.

PG-71.2 The safety valve or safety reliefvalve or valves shall be connected to theboiler independent of any other connec-tion, and attached as close as possible tothe boiler or the normal steam flow path,without any unnecessary intervening pipeor fitting. Such intervening pipe or fittingshall be not longer than the face-to-facedimension of the corresponding tee fittingof the same diameter and pressure underthe applicable American NationalStandard listed in PG-42 and shall alsocomply with PG-8 and PG-39. Every safe-ty valve or safety relief valve shall beconnected so as to stand in an upright position, with spindle vertical. On high-temperature water boilers of thewatertube forced-circulation type, thevalve shall be located at the boiler outlet.

PG-71.3 The opening or connection be-tween the boiler and the safety relief valveshall have at least the area of the valve in-let. No valve of any description shall beplaced between the required safety valveor safety relief valve or valves and theboiler, nor on the discharge pipe betweenthe safety valve or safety relief valve andthe atmosphere. When a discharge pipe isused, the cross-sectional area shall be notless than the full area of the valve outletor of the total of the areas of the valveoutlets, discharging thereinto. It shall beas short and straight as possible and soarranged as to avoid undue stresses onthe valve or valves.

All safety valve or safety relief valve dis-charges shall be so located or piped as

to be carried clear from running boards or platforms. Ample provision for gravitydrain shall be made in the discharge pipeat or near each safety valve or safety relief valve, and where water of conden-sation may collect. Each valve shall have an open gravity drain through the casingbelow the level of the valve seat. For iron- and steel-bodied valves exceeding 21/2-inch size, the drain hole shall betapped not less than 3/8-inch pipe size.

Discharge piping from safety relief valveson high-temperature water boilers shall beprovided with adequate provisions for wa-ter drainage as well as the steam venting.

The installation of cast iron bodied safetyrelief valves for high-temperature waterboilers is prohibited.

PG-71.4 If a muffler is used on a safetyvalve or safety relief valve, it shall havesufficient outlet area to prevent back pressure from interfering with the properoperation and discharge capacity of thevalve. The muffler plates or other devicesshall be so constructed as to avoid a possibility of restriction of the steam pas-sages due to deposit. Mufflers shall not be used on high-temperature water boilersafety relief valves.

When a safety valve or safety relief valveis exposed to outdoor elements which mayaffect operation of the valve, it is permissi-ble to shield the valve with a satisfactorycover. The shield or cover shall be proper-ly vented and arranged to permit servicingand normal operation of the valve.

PG-71.5 When a boiler is fitted with twoor more safety relief valves on one con-nection, this connection to the boiler shallhave a cross-sectional area not less thanthe combined areas of inlet connections ofall the safety valves or safety relief valveswith which it connects and shall also meetthe requirements of PG-71.3.

PG-71.6 Safety valves may be attachedto drums or headers by welding providedthe welding is done in accordance withCode requirements.

PG-71.7 Every boiler shall have properoutlet connections for the required safetyvalve, or safety relief valve, or valves, in-

dependent of any other outside steamconnection, the area of opening to be atleast equal to the aggregate areas of inletconnections of all of the safety valves orsafety relief valves to be attached thereto.An internal collecting pipe, splash plate, orpan may be used, provided the total areafor inlet of steam thereto is not less thantwice the aggregate areas of the inlet con-nections of the attached safety valves.The holes in such collecting pipes shall beat least 1/4-inch in diameter and the leastdimension in any other form of opening forinlet of steam shall be 1/4-inch.

Such dimensional limitations to operationfor steam need not apply to steam scrub-bers or driers provided the net free steaminlet area of the scrubber or drier is atleast 10 times the total area of the boileroutlets for the safety valves.

PG-71.8 If safety valves are attached to a separate steam drum or dome, theopening between the boiler proper and the steam drum or dome shall be not lessthan required by PG-71.7.

PG-72 OperationPG-72.1 Safety valves shall be designedand constructed to operate without chatter-ing and to attain full lift at a pressure nogreater than 3% above their set pressure.After blowing down, all valves shall closeat a pressure not lower than 96% of theirset pressure, except that all drum valvesinstalled on a single boiler may be set toreseat at a pressure not lower than 96% ofthe set pressure of the lowest set drumvalve. The minimum blowdown for spring-loaded safety or safety relief valves shall be2% of the set pressure, except that for boil-ers whose maximum allowable workingpressure is less than 100 psi, the valvesmay be set to reseat between 2 and 4 psibelow their set pressure.

Safety valves used on forced-flow steamgenerators with no fixed steam and water-line, and safety relief valves used onhigh-temperature water boilers may be set and adjusted to close after blowingdown not more than 10% of the set pres-sure. The valves for these special usesmust be so adjusted and marked by themanufacturer.




PG-72.2 The popping point toleranceplus or minus shall not exceed the follow-ing: 2 psi for pressures up to andincluding 70 psi, 3% for pressures over 70psi up to and including 300 psi, 10 psi forpressures over 300 psi up to and includ-ing 1000 psi, and 1% for pressures over1000 psi.

PG-72.3 The spring in a safety valve orsafety relief valve shall not be reset for anypressure more than 5% above or below thatfor which the valve is marked unless thenew setting is within the spring design rangeestablished by the manufacturer or is deter-mined to be acceptable to the manufacturer.

If the set pressure is to be adjusted withinthe limits specified above, the adjustmentshall be performed by the manufacturer, hisauthorized representative, or an assembler.An additional valve data tag identifying thenew set pressure, capacity, and date shallbe furnished and installed, and the valvedshall be resealed.

PG-72.4 If the set pressure of a valve ischanged so as to require a new spring,the spring shall be acceptable to the man-ufacturer. The spring installation and valveadjustment shall be performed by themanufacturer, his authorized representa-tive, or an assembler. A new nameplate asdescribed in PG-110 shall be furnishedand installed, and the valve shall be re-sealed.

PG-73 Minimum Requirements forSafety and Safety Relief ValvesPG-73.1 Mechanical Requirements

PG-73.1.1 The design shall incorporateguiding arrangements necessary to insureconsistent operation and tightness.

PG-73.1.2 The spring shall be designed so that the full lift spring com-pression shall be no greater than 80% of the nominal solid deflection. The per-manent set of the spring (defined as thedifference between the free height andheight measured 10 min after the springhas been compressed solid three addi-tional times after presetting at roomtemperature) shall not exceed 0.5% of thefree height.

PG-73.1.3 To provide a means for verify-ing whether it is free, each safety valveor safety relief valve shall have a sub-stantial lifting device, which whenactivated will release the seating force onthe disk when the valve is subject topressure of at least 75% of the set pres-sure. The lifting device shall be such thatit cannot lock or hold the valve disk in lift-ed position when the exterior lifting forceis released. Disks of safety relief valvesused on high-temperature water boilersshall not be lifted while the temperatureof the water exceeds 200°F. If it is de-sired to lift the valve disk to assure that itis free, this shall be done when the valveis subjected to a pressure of at least 75%of the set pressure. For high-temperaturewater boilers, the lifting mechanism shallbe sealed against leakage.

PG-73.1.4 The seat of a safety valveshall be fastened to the body of the valvein such a way that there is no possibility ofthe seat lifting.

PG-73.1.5 A body drain below seat levelshall be provided in the valve and thisdrain shall not be plugged during or afterfield installation. For valves exceeding21/2-inch pipe size, the drain hole or holesshall be tapped not less than 3/8-inch pipesize. For valves of 21/2-inch pipe size orsmaller, the drain hole shall not be lessthan 1/4-inch in diameter.

PG-73.1.6 In the design of the body ofthe valve, consideration shall be given tominimizing the effects of water deposits.

PG-73.1.7 Valves having screwed inlet or outlet connections shall be provid-ed with wrenching surfaces to allow fornormal installation without damaging op-erating parts.

A92PG-73.1.8 Means shall be provided in thedesign of all valves for use under thisSection, for sealing all external adjust-ments. Seals shall be installed by themanufacturer, his authorized representa-tive, or an assembler at the time of theinitial adjustment. After spring replace-ment and/or subsequent adjustment, thevalve shall be resealed. Seals shall be in-

stalled in such a manner as to preventchanging the adjustment without breakingthe seal and, in addition, shall serve as ameans of identifying the manufacturer, hisauthorized representative, or the assem-bler making the adjustment.

PG-73.2 Material Selections

PG-73.2.1 Cast iron seats and disks arenot permitted.

PG-73.2.2 Adjacent sliding surfaces suchas guides and disks or disk holders shallboth be of corrosion resistant material.Springs of corrosion resistant material orhaving a corrosion resistant coating arerequired. The seats and disks of safetyvalves or safety relief valves shall be ofsuitable material to resist corrosion by thelading fluid.7

PG-73.2.3 Materials used in bodies andbonnets or yokes shall be listed in SectionII, Parts A and B, and identified in Tables1A and 1B of Section II, Part D, as permit-ted for Section I construction. Materialsused in nozzles, disks, and other parts con-tained within the external structure of thesafety or safety relief valves shall be one ofthe following categories:

1. listed in ASME Section II;

2. listed in ASTM Specifications;8

3. controlled by the manufacturer of thesafety or safety relief valve by a specifica-tion insuring control of chemical andphysical properties and quality at leastequivalent to ASTM Standards.8

Notes

7. The degree of corrosion resistance, appro-priate to the intended service, shall be amatter of agreement between the manufac-turer and purchaser.

8. It shall be the manufacturer’s responsibilityto insure that the allowable stressed at tem-perature meet the requirements of SectionII, Part D, Appendix 1, Nonmandatory Basisfor Establishing Stress Values in Table 1Aand 1B.




PG-73.3 Inspection of Manufacturingand/or Assembly

A92/A93PG-73.3.1 A manufacturer shall demon-strate to the satisfaction of an ASMEdesignee that his manufacturing, produc-tion, and test facilities and quality controlprocedures will insure close agreementbetween the performance of random pro-duction samples and the performance ofthose valves submitted for capacity certifi-cation.

A93PG-73.3.2 Manufacturing, assembly,inspection, and test operations includingcapacity, are subject to inspections at anytime by an ASME designee.

A92/A93PG-73.3.3 A Manufacturer or assemblermay be granted permission to apply the VCode Symbol to production pressure reliefvalves capacity-certified in accordancewith PG-69, provided the following testsare successfully completed. This permis-sion shall expire on the fifth anniversary ofthe date it is initially granted. This permis-sion may be extended for 5 year periods ifthe following tests are successfully repeat-ed within the 6 month period beforeexpiration.

1. Two sample production pressure reliefvalves of a size and capacity within thecapability of an ASME accepted labora-tory shall be selected by an ASMEdesignee.

2. Operational and capacity tests shall beconducted in the presence of an ASMEdesignee at an ASME accepted labora-tory. The valve manufacturer orassembler shall be notified of the timeof the test and may have representa-tives present to witness the test.

3. Should any valve fail to relieve at orabove its certified capacity or should itfail to meet performance requirementsof this Section, the test shall be repeat-ed at the rate of two replacementvalves, selected in accordance withPG-73.3.3(1), for each valve that failed.

4. Failure of any of the replacement valvesto meet the capacity or the performancerequirements of this Section shall because for revocation within 60 days ofthe authorization to use the Code sym-bol on that particular type of valve.During this period, the Manufacturer orassembler shall demonstrate the causeof such deficiency and the action takento guard against future occurrence, andthe requirements of PG-73.3.3 aboveshall apply.

A93PG-73.3.4 Use of the Code SymbolStamp by an assembler indicates the useof original unmodified parts in strict accor-dance with the instructions of themanufacturer of the valve.

A93PG-73.3.5 In addition to the requirementsof PG-110, the same plate marking shallinclude the name of the Manufacturer andthe assembler. The Code Symbol Stampshall be that of the assembler.9

PG-73.4 Testing by Manufacturers orAssemblers

PG-73.4.1 Valves exceeding 1-inch inletsize or 300 psig set pressure shall meetthe following requirements. Primary pres-sure containing cast and welded parts ofpressure relief valves shall be tested at apressure at 1.5 times the design pressureof the parts. These tests shall be conduct-ed after all machining operations to theparts have been completed. There shallbe no visible signs of leakage.

Closed bonnet pressure relief valves de-signed for discharge to a closed systemshall be tested with a minimum of 30 psigair or other gas in the secondary pressurezone. There shall be no visible signs ofleakage.

PG-73.4.2 Every valve shall be testedwith steam by the manufacturer or assem-bler to demonstrate the popping point,blowdown, tightness, and pressure con-taining integrity. Valves beyond thecapability of production test facilities maybe shop tested with air, provided requiredfield tests and applicable adjustments aremade.

PG-73.4.3 A seat tightness test shall beconducted at maximum expected operat-ing pressure, but at a pressure notexceeding the reseating pressure of thevalve. When being tested, a valve exhibit-ing no visible signs of leakage shall beconsidered adequately tight.

A92PG-73.4.4 A manufacturer or assemblershall have a documented program for theapplication, calibration, and maintenanceof test gauges.

PG-73.4.5 Testing time on steam valvesshall be sufficient to assure that test re-sults are repeatable and representative offield performance.

A92PG-73.4.6 Test fixtures and test drums,where applicable, shall be of adequatesize and capacity to assure that the ob-served set pressure is consistent with thestamped set pressure within the tolerancerequired by PG-72.2.

PG-73.5 Design RequirementsAt the time of submission of valves for capacity certification or testing in accor-dance with PG-69, the ASME designeehas the authority to review design for con-formity with the requirements of thisSection and to reject or require modifica-tion of designs which do not conform, priorto capacity testing.

9. Within the requirements of PG-73.3 and PG-73.4, a manufacturer is defined as a personor organization who is completely responsi-ble for design, material selection, capacitycertification, manufacture of all componentparts, assembly, testing, sealing, and ship-ping of safety and safety relief valvescertified under this Section.

An assembler is defined a person or organi-zation who purchases or receives from amanufacturer the necessary componentparts or valves and assembles, adjusts,tests, seals, and ships safety or safety reliefvalves certified under this Section at a geo-graphical location other than and usingfacilities other than those used by the manu-facturer.


Notes




PFT-44 Opening Between Boilerand Safety ValveThe opening or connection between theboiler and the safety valve shall have atleast the area of the valve inlet. In thecase of firetube boilers, the openings inthe boilers for safety valves or safety reliefvalves shall be not less than given inTable PFT-44, except firetube boilers usedfor waste heat purposes only, notequipped for direct firing, need not meetthe requirements of Table PFT-44 provid-

ed the rated steaming capacity is stampedon the boiler and safety valves or safetyrelief valves of the required relieving ca-pacity are supplied such that theprovisions of PG-67.2 are satisfied.

After the boiler Manufacturer provides forthe opening required by the Code, a bush-ing may be inserted in the opening in theshell to suit a safety valve that will havethe capacity to relieve all the steam thatcan be generated in the boiler and whichwill meet the Code requirements.

No valve of any description shall beplaced between the required safety valveor safety relief valve or valves and theboiler, or on the discharge pipe betweenthe safety valve or safety relief valve andthe atmosphere. When a discharge pipe isused, the cross-sectional area shall be notless than the full area of the valve outlet orof the total of the areas of the valve out-lets discharging thereinto and shall be asshort and straight as possible and soarranged as to avoid undue stresses onthe valve or valves.

Table PFT-44

Minimum Total Areas of Openings (in2) in Firetube Boilers for Safety Valve Connections1, 2

Gauge Boiler Heating Surface, sq. ft.Press.psi 100 200 300 400 500 600 800 1000 1200 1400 1600 1800 2000 2500 3000 V

16 3.174 6.348 9.522 12.696 15.869 19.043 25.392 31.739 38.086 44.435 50.783 57.130 63.478 79.347 95.216 13.330

25 2.500 5.000 7.499 10.000 12.498 15.000 20.000 24.996 30.000 35.000 40.000 44.992 49.992 62.489 74.987 10.498

50 1.584 3.168 4.752 6.338 7.920 9.504 12.677 15.839 19.007 22.175 25.354 28.510 31.678 39.599 47.517 6.655

75 1.166 2.331 3.497 4.663 5.828 6.995 9.326 11.657 13.989 16.320 18.652 20.983 23.314 29.143 34.972 4.896

100 0.924 1.849 2.773 3.697 4.621 5.546 7.394 9.243 11.092 12.940 14.789 16.637 18.486 23.106 27.729 3.882

125 0.767 1.533 2.300 3.067 3.834 4.600 6.134 7.667 9.201 10.734 12.267 13.800 15.334 19.166 23.000 3.220

150 0.655 1.311 1.966 2.621 3.276 3.932 5.242 6.553 7.863 9.174 10.484 11.795 13.106 16.382 19.658 2.752

175 0.572 1.145 1.718 2.289 2.862 3.435 4.579 5.725 6.870 8.015 9.158 10.305 11.450 14.312 17.175 2.404

200 0.508 1.016 1.525 2.033 2.541 3.049 4.066 5.082 6.099 7.115 8.132 9.148 10.164 12.706 15.247 2.1345

225 0.457 0.913 1.370 1.827 2.284 2.740 3.654 4.567 5.481 6.394 7.308 8.221 9.134 11.417 13.702 1.9183

250 0.415 0.830 1.244 1.659 2.074 2.489 3.318 4.148 4.978 5.807 6.637 7.466 8.296 10.370 12.444 1.7422

Nominal Pipe Internal Internal Nominal Pipe Internal Internal Nominal Pipe Internal InternalSize, Inch Diameter Area, in2 Size, inch Diameter Area, in2 Size, inch Diameter Area, in2

1/2 0.622 0.304 2 2.067 3.355 4 4.026 12.7303/4 0.824 0.533 21/2 2.469 4.788 5 5.047 20.006

1 1.049 0.864 3 3.068 7.393 6 6.065 28.891

11/4 1.380 1.495 31/2 3.548 9.886 8 8.071 51.161

11/2 1.610 2.036

1. Based on formula A = HV/420where

A = total area of openings, in2

H = boiler heating surface, ft2

V = specific volume of steam in cu. ft/lb at maximum allowable working pressure.

2. Number and size of openings shall providefor not less than the area given.Intermediate values may be interpolated.With flanged openings, use internal area fordetermining diameter.

Notes



ASME Code Section I, Electric Boilers - (1995 Addenda)

PEB-15 Safety ValvesPEB-15.1 Each electric boiler shall haveat least one safety valve or safety

relief valve, and if it has a power inputmore than 1100 kW, it shall have two ormore safety valves or safety relief valves.

PEB-15.2 The minimum safety valve orsafety relief valve relieving capacity forelectric boilers shall be 31/2 lb/hr/kW input.

ASME Code Section I, Miniature Boilers - (1995 Addenda)

PMB-15 Safety ValvesEach miniature boiler shall be equippedwith a sealed spring loaded safety valveof not less than NPS 1/2.

The minimum relieving capacity of thesafety valve shall be determined in accor-dance with PG-70. In addition to theserequirements, the safety valve shall havesufficient capacity to discharge all thesteam that can be generated by the boiler

without allowing the pressure to rise morethan 6% above the maximum allowableworking pressure.

All other provisions for safety valves inthis Section shall be complied with.

PVG-12 Safety ValvesPVG-12.1 Safety valves shall be of a to-tally enclosed type so designed thatvapors escaping beyond the valve seatshall not discharge into the atmosphere,except through an escape pipe that willcarry such vapors to a safe point of dis-charge outside of the building. A suitablecondenser that will condense all the va-pors discharged from the safety valvemay be used in lieu of piping the vapors tothe atmosphere. The safety valve shall nothave a lifting lever. The vaporizer shall bedesigned in accordance with the rules inthis Code for a working pressure of atleast 40 psi above the operating pressureat which it will be used. Valve body drainsare not mandatory.

PVG-12.2 Safety valves shall be discon-nected from the vaporizer at least onceyearly, when they shall be inspected, re-paired if necessary, tested, and thenreplaced on the vaporizer.

PVG-12.3 In order to minimize the lossby leakage of material through the safetyvalve, a rupture disk may be installed be-tween the safety valve and the vaporizerprovided the following requirements aremet.

PVG-12.3.1 The cross-sectional area ofthe connection to a vaporizer shall be notless than the required relief area of therupture disk.

PVG-12.3.2 Every rupture disk shallhave a specified bursting pressure at aspecified temperature, shall be markedwith a lot number, and shall be guaran-teed by its manufacturer to burst within

5% (plus or minus) of its specified burst-ing pressure.

PVG-12.3.3 The specified bursting pressure at the coincident operating tem-perature shall be determined by burstingtwo or more specimens from a lot of thesame material and of the same size asthose to be used. The tests shall be madein a holder of the same form and pressurearea dimensions as that with which thedisk is to be used.

PVG-12.3.4 A rupture disk may be installed between a safety valve and thevaporizer provided:

PVG-12.3.4.1 The maximum pressure ofthe range for which the disk is designed torupture does not exceed the openingpressure for which the safety valve is setor the maximum allowable working pres-sure of the vessel.

ASME Code Section I, Organic Vapor Generator - (1995 Addenda)

Figure PVG-12

Constant C For Vapor Related to Ratio of Specific Heats (k = Cp/Cv)

▲1.0

▲1.2

▲1.4

▲1.6

▲1.8

▲2.0

400

390

380

370

360

350

340

330

320

k

Cons

tant

, C

C = 520

Flow Formula Calculations

W = K (CAP M/T)

k 2k + 1

k + 1k - 1( (



PVG-12.3.4.2 The opening providedthrough the rupture disk, after breakage, issufficient to permit a flow equal to the ca-pacity of the attached valve and there isno chance of interference with the properfunctioning of the valve; but in no caseshall this area be less than the inlet areaof the valve.

PVG-12.3.4.3 The space between a rup-ture disk and the valve should be providedwith a pressure gauge, try cock, free vent,or a suitable telltale indicator. Thisarrangement permits the detection of diskrupture or leakage.1

PVG-12.4 Safety valve discharge capacityshall be determined from the formula:

––––W = (0.90)CKAP √M/T

where:

W = flow of vapor, lb/hr

C = constant for vapor which is a functionof the ratio of Specific Heats k = Cp/Cv (see Fig. PVG-12) Note:Where k is not known, k = 1.001.

K = average coefficient of discharge

A = discharge area of safety valve, in2

P = (set pressure x 1.03) + Atmosphere Pressure, psia

M = molecular weight

T = absolute temperature at inlet, °F + 460

PVG-12.5 Safety valves for organic fluidvaporizers shall be tested and certified un-der PG-69, and they shall be stampedwith the rated relieving capacity in poundsper hour at coincident temperature as determined in PVG-12.4 The fluid identifi-cation shall be stamped on the nameplate.

PVG-12.6 The required minimum safetyvalve relieving capacity shall be deter-mined from the formula:

W = C x H x 0.75

h

where:

h = latent heat of heat transfer fluid at relieving pressure, BTU/lb

W = weight of organic fluid vapor generated per hour, lb

C = maximum total weight or volume of fuel burned per hour, lb or cu ft

H = heat of combustion of fuel, BTU/lb or BTU/cu ft (see A-17)

The sum of the safety valve capacitiesmarked on the valves shall be equal to or greater than W.

Note

1. Users are warned that a rupture disc willnot burst at its designed pressure if backpressure builds up in the space betweenthe disc and the safety valve which will oc-cur should leakage develop in the rupturedisc due to corrosion or other cause.

ASME Code Section I, Organic Vapor Generator -(1995 Addenda)



ASME Code Section I, Mandatory Appendix A - (1995 Addenda)Safety Valves for Power Boilers

A93

A-44The safety valve capacity of each boilershall be such that the safety valve orvalves will discharge all the steam thatcan be generated by the boiler without al-lowing the pressure to rise more than 6%above the maximum allowable workingpressure, or more than 6% above the high-est pressure to which any valve is set.

The minimum safety valve or safety reliefvalve relieving capacity for other thanelectric boilers, waste heat boilers, organicfluid vaporizers, and forced-flow steamgenerators with no fixed steam and water-line, when provided in accordance withPG-67.4.3, shall be determined on the ba-sis of the pounds of steam generated perhour per square foot of boiler heating sur-face and waterwall heating surface, asgiven in Table A-44.

The minimum safety valve or safety reliefvalve relieving capacity for electric boilersshall be 31/2 lb/hr/kW input.

In many cases, a greater relieving capacityof safety valves or safety relief valves willhave to be provided than the minimumspecified in Table A-44, in order to meet therequirements of the first paragraph of A-44.

A-45One or more safety valves on every boilershall be set at or below the maximum

allowable working pressure. The remainingvalves may be set within a range of 3%above the maximum allowable workingpressure, but the range of setting of all ofthe saturated steam valves on a boilershall not exceed 10% of the highest pres-sure to which any saturated steam valve is set.

When boilers of different maximum allow-able working pressures with minimumsafety valve settings varying more than 6% are so connected that steam can flowtoward the lower pressure units, the lattershall be protected by additional safetyvalve capacity, if necessary, on the lowerpressure side of the system. The additionalsafety valve capacity shall be based uponthe maximum amount of steam which canflow into the lower pressure system. Theadditional safety valves shall have at leastone valve set at a pressure not to exceedthe lowest allowable pressure and the oth-er valves shall be set within a range not toexceed 3% above that pressure.

A93

A-46If the safety valve or safety relief valve capacity cannot be determined or if it isdesirable to verify the computations, thecapacity may be checked in one of thethree following ways, and if found insuffi-cient, additional capacity shall be provided.

A-46.1 By making an accumulation test,that is, by shutting off all other steam-dis-charge outlets from the boiler and forcingthe fires to the maximum. The safety valveequipment shall be sufficient to prevent anexcess pressure beyond that specified inPG-67.2. This method should not be usedon a boiler with a superheater or reheateror on a high-temperature water boiler.

A-46.2 By measuring the maximumamount of fuel that can be burned andcomputing the corresponding evaporativecapacity upon the basis of the heating val-ue of the fuel (see A-12 through A-17).

A93A-46.3 By determining the maximumevaporative capacity by measuring thefeedwater. The sum of the safety valve capacities marked on the valves shall beequal to or greater than the maximumevaporative capacity of the boiler. Thismethod shall not be used on high-temper-ature water boilers.

A93

A-48When operating conditions are changed,or additional heating surface such as wa-ter screens or waterwalls is connected tothe boiler circulation, the safety valve orsafety relief valve capacity shall be in-creased, if necessary, to meet the newconditions and be in accordance with PG-67.2. The additional valves required onaccount of changed conditions may be

Note

When a boiler is fired only by a gas having aheat value not in excess of 200 BTU/cu ft, theminimum safety valve or safety relief valve re-lieving capacity may be based on the valuesgiven for hand-fired boilers above.

Table A-44

Minimum Pounds of Steam Per Hour Per Square Foot of Surface

Firetube Boilers Watertube Boilers

Boiler heating surface:

Hand fired 5 6

Stoker fired 7 8

Oil, gas or pulverized fuel fired 8 10

Waterwall heating surface

Hand fired 8 8

Stoker fired 10 12

Oil, gas, or pulverized fuel fired 14 16



ASME Code Section I,Mandatory Appendix A - (1995 Addenda)installed on the piping between the boilerand the main stop valve except when theboiler is equipped with a superheater orother piece of apparatus. In the latter casethey may be installed on the piping be-tween the boiler drum and the inlet to thesuperheater or other apparatus, providedthat the piping between the boiler andsafety valve (or valves) connection has across-sectional area of at least three timesthe combined areas of the inlet connec-tions to the safety valves applied to it.

A-49No valve of any description shall be placebetween the safety valve and the boiler, oron the discharge pipe between the safetyvalve and the atmosphere. When a dis-charge pipe is used, it shall be not lessthan the full size of the valve, and the dis-

charge pipe shall be fitted with an opendrain to prevent water lodging in the upperpart of the safety valve or in the pipe. If amuffler is used on a safety valve it shallhave sufficient outlet area to prevent backpressure from interfering with the properoperation and discharge capacity of thevalve. The muffler plates or other devicesshall be so constructed as to avoid any pos-sibility of restriction of the steam passagesdue to deposit. When an elbow is placed ona safety valve discharge pipe, it shall be lo-cated close to the safety valve outlet or thepipe shall be securely anchored and sup-ported. All safety valve discharges shall beso located or piped as to be carried clearfrom running boards or working platformsused in controlling the main stop valves ofboilers or steam headers.



ASME Code Section IV – Heating Boiler Code (1995 Addenda)

Pressure Relieving Devices

HG-400 Pressure Relieving ValveRequirementsHG-400.1 Safety Valve Requirementsfor Steam BoilersA. Each steam boiler shall have one or

more officially rated safety valves thatare identified with the V or HV Symbolof the spring pop type adjusted andsealed to discharge at a pressure not toexceed 15 psi. Seals shall be attachedin a manner to prevent the valve frombeing taken apart without breaking theseal. The safety valves shall bearranged so that they cannot be resetto relieve at a higher pressure than themaximum allowable working pressureof the boiler. Drain holes are not re-quired for valves 3/4-inch and smaller,when the seating surface of the valve isabove the lowest portion of the insidediameter of the discharge piping. Meansshall be provided for complete drainageof the discharge piping.

B. No safety valve for a steam boiler shallbe smaller than 1/2-inch. No safetyvalve shall be larger than 41/2-inch. Theinlet opening shall have an inside diam-eter equal to, or greater than, the seatdiameter.

C. The minimum relieving capacity of valveor valves shall be governed by the capaci-ty marking on the boiler called for inHG-530.

D. The minimum valve capacity in poundsper hour shall be the greater of that de-termined by dividing the maximum BTU

output at the boiler nozzle obtained bythe firing of any fuel for which the unitis installed by 1000, or shall be deter-mined on the basis of the pounds ofsteam generated per hour per squarefoot of boiler heating surface as givenin Table HG-400.1. For cast iron boilersconstructed to the requirements of PartHC, the minimum valve capacity shallbe determined by the maximum outputmethod. In many cases a greater re-lieving capacity of valves will have tobe provided than the minimum speci-fied by these rules. In every case, therequirement of HG-400.1(E) shall bemet.

E. The safety valve capacity for eachsteam boiler shall be such that with thefuel burning equipment installed, andoperated at maximum capacity, thepressure cannot rise more than 5 psiabove the maximum allowable workingpressure.

F. When operating conditions arechanged, or additional boiler heatingsurface is installed, the valve capacityshall be increased, if necessary, tomeet the new conditions and be in ac-cordance with HG-400.1(E). Theadditional valves required, on accountof changed conditions, may be installedon the outlet piping provided there is nointervening valve.

HG-400.2 Safety Relief ValveRequirements for Hot Water BoilersA. Each hot water heating or supply boiler

shall have at least one officially ratedsafety relief valve, of the automatic re-

seating type, identified with the V or HVSymbol, and set to relieve at or belowthe maximum allowable working pres-sure of the boiler. Safety relief valvesofficially rated as to capacity shall havepop action when tested by steam.When more than one safety relief valveis used on either hot water heating orhot water supply boilers, the additionalvalve or valves shall be officially ratedand may have a set pressure within arange not to exceed 6 psi above themaximum allowable working pressureof the boiler up to and including 60 psi,and 5% for those having a maximumallowable working pressure exceeding60 psi. Safety relief valves shall bespring loaded. Safety relief valves shallbe set and sealed so that they cannotbe reset without breaking the seal.

B. No materials liable to fail due to deterioration or vulcanization whensubjected to saturated steam tempera-ture corresponding to capacity testpressure shall be used for any part.

C. No safety relief valve shall be smallerthan 3/4-inch nor larger than 41/2-inchstandard pipe size except that boilershaving a heat input not greater than15,000 BTU/hr may be equipped with arated safety relief valve of 1/2-inch stan-dard pipe size. The inlet opening shallhave an inside diameter approximatelyequal to, or greater than, the seat di-ameter. In no case shall the minimumopening through any part of the valvebe less than 1/4-inch in diameter or itsequivalent area.

Table HG-400.1

Minimum Pounds of Steam Per Hour Per Square Foot of Heating Surface

Firetube Boilers Watertube Boilers

Boiler heating surface

Hand fired 5 6

Stoker fired 7 8

Oil, gas or pulverized fuel fired 8 10

Waterwall heating surface

Hand fired 8 8

Stoker fired 10 12

Oil, gas, or pulverized fuel fired 14 16

Notes

1. When a boiler is fired only by a gas havinga heat value not in excess of 200 BTU/cu ft,the minimum safety valve or safety reliefvalve relieving capacity may be based onthe values given for hand fired boilersabove.

2. The minimum safety valve or safety reliefvalve relieving capacity for electric boilersshall be 31/2 lb/hr/kW input.

3. For heating surface determination, see HG-403.



D. The required steam relieving capacity,in pounds per hour, of the pressure re-lieving device or devices on a boilershall be the greater of that determinedby dividing the maximum output in BTUat the boiler nozzle obtained by the fir-ing of any fuel for which the unit isinstalled by 1000, or shall be deter-mined on the basis of pounds of steamgenerated per hour per square foot ofboiler heating surface as given in TableHG-400.1. For cast iron boilers con-structed to the requirements of PartHC, the minimum valve capacity shallbe determined by the maximum outputmethod. In many cases a greater re-lieving capacity of valves will have tobe provided than the minimum speci-fied by these rules. In every case, therequirements of HG-400.2(F) shall be met.

E. When operating conditions arechanged, or additional boiler heatingsurface is installed, the valve capacityshall be increased, if necessary, tomeet the new conditions and shall be inaccordance with HG-400.2(F). The ad-ditional valves required, on account ofchanged conditions, may be installedon the outlet piping provided there is nointervening valve.

F. Safety relief valve capacity for eachboiler with a single safety relief valveshall be such that, with the fuel burningequipment installed and operated atmaximum capacity, the pressure cannotrise more than 10% above the maxi-mum allowable working pressure. Whenmore than one safety relief valve isused, the overpressure shall be limitedto 10% above the set pressure of thehighest set valve allowed by HG-400.2(A).

HG-400.3 Safety and Safety ReliefValves for Tanks and Heat ExchangersA. Steam to Hot Water Supply. When a

hot water supply is heated indirectly bysteam in a coil or pipe within the ser-vice limitations set forth in HG-101, thepressure of the steam used shall notexceed the safe working pressure ofthe hot water tank, and a safety reliefvalve at least 1-inch in diameter, set torelieve at or below the maximum allow-able working pressure of the tank, shallbe applied on the tank.

B. High Temperature Water to Water HeatExchanger.1 When high temperaturewater is circulated through the coils ortubes of a heat exchanger to warm wa-ter for space heating or hot watersupply, within the service limitations setforth in HG-101, the heat exchangershall be equipped with one or more offi-cially rated safety relief valves that areidentified with the V or HV Symbol, setto relieve at or below the maximum al-lowable working pressure of the heatexchanger, and of sufficient rated ca-pacity to prevent the heat exchangerpressure from rising more than 10%above the maximum allowable workingpressure of the vessel.

C. High Temperature Water to Steam HeatExchanger.1 When high temperaturewater is circulated through the coils ortubes of a heat exchanger to generatelow pressure steam, within the servicelimitations set forth in HG-101, the heatexchanger shall be equipped with oneor more officially rated safety valvesthat are identified with the V or HVSymbol, set to relieve at a pressure notto exceed 15 psi, and of sufficient ratedcapacity to prevent the heat exchangerpressure from rising more than 5 psiabove the maximum allowable workingpressure of the vessel. For heat ex-changers requiring steam pressuresgreater than 15 psi, refer to Section I orSection VIII, Division 1.

HG-401 Minimum Requirements forSafety and Safety Relief ValvesHG-401.1 Mechanical RequirementsA. Bottom guided designs are not permit-

ted on hot water valves.

B. Synthetic disk inserts of O-ring or other types if used shall be compatiblewith the maximum design temperatureestablished for the valve.

C. O-rings or other packing devices whenused on the stems of hot water safetyrelief valves shall be so arranged as notto affect their operation or capacity.

D. The design shall incorporate guidingarrangements necessary to insure con-sistent operation and tightness.Excessive lengths of guiding surfacesshould be avoided.

E. Steam valves shall have a controlledblowdown of 2 psi to 4 psi and thisblowdown need not be adjustable.

F. The spring shall be designed so that thefull lift spring compression shall be nograter than 80% of the nominal solid de-flection. The permanent set of the spring(defined as the difference between thefree height and height measured 10 minafter the spring has been compressedsolid three additional times after pre-set-ting at room temperature) shall notexceed 0.5% of the free height.

G. There shall be a lifting device and amechanical connection between thelifting device and the disk capable oflifting the disk from the seat a distanceof at least 1/16-inch with no pressure onthe boiler.

A-92H. A body drain below seat level shall be

provided by the Manufacturer for allsafety valves and safety relief valves,except that the body drain may beomitted when the valve seat is abovethe bottom of the inside diameter of thedischarge piping. For valves exceedingNPS 21/2 the drain hole or holes shallbe tapped not less than NPS 3/8. Forvalves NPS 21/2 or smaller, the drainhole shall not be less than 1/4-inch indiameter. Body drain connections shallnot be plugged during or after field in-stallation. In hot water relief valves ofthe diaphragm type, the space abovethe diaphragm shall be vented to pre-vent a buildup of pressure above the diaphragm. Hot water relief valves ofthe diaphragm type shall be so de-signed that failure or deterioration of thediaphragm material will not impair theability of the valve to relieve at the ratedcapacity.

I. In the design of the body of the valveconsideration shall be given to minimiz-ing the effects of water deposits.

J. Valves shall be provided with wrenchingsurfaces to allow for normal installationwithout damaging operating parts.

Note

1. Suggested installation practices for the secondary side of heat exchangers.





K. The set pressure tolerances, plus or mi-nus, of steam safety valves shall notexceed 2 psi, and for safety reliefvalves shall not exceed 3 psi for pres-sures up to and including 60 psi and5% for pressures above 60 psi.

HG-401.2 Material SelectionA. Cast iron seats and disks are not per-

mitted.

B. Adjacent sliding surfaces such asguides and disks shall both be of corro-sion resistant material.

C. Springs of corrosion resistant materialor having a corrosion resistant coatingare required.

D. Material for seats and disks should besuch as to provide a reasonable degreeof resistance to steam cutting.

E. Material for valve bodies and bonnetsor their corresponding metallic pressurecontaining parts shall be listed inSection II, except that in cases where amanufacturer desires to make use ofmaterials other than those listed inSection II, he shall establish and main-tain specifications requiring equivalentcontrol of chemical and physical prop-erties and quality.

A-93

HG-401.3 Manufacture and InspectionA. A Manufacturer shall demonstrate to

the satisfaction of an ASME designeethat his manufacturing, production, andtesting facilities and quality control pro-cedures will insure close agreementbetween the performance of randomproduction samples and the perfor-mance of those valves submitted forcapacity certification.

B. Manufacturing, inspection, and test op-erations including capacity are subjectto inspection at any time by an ASMEdesignee.

C. A Manufacturer may be granted per-mission to apply the HV Code Symbolto production pressure relief valves ca-pacity certified in accordance withHG-402.3 provided the following testsare successfully completed. This per-mission shall expire on the fifthanniversary of the date it is initially

granted. The permission may be ex-tended for 5 year periods if thefollowing tests are successfully repeat-ed within the 6 month period beforeexpiration.

1. Two sample production pressure reliefvalves of a size and capacity within thecapability of an ASME accepted labora-tory shall be selected by an ASMEdesignee.

2. Operational and capacity tests shall beconducted in the presence of an ASMEdesignee at an ASME accepted labora-tory. The valve Manufacturer shall benotified of the time of the test and mayhave representatives present to wit-ness the test.

3. Should the valve fail to relieve at orabove its certified capacity or should itfail to meet performance requirementsof this Section, the test shall be repeat-ed at the rate of two replacementvalves, selected in accordance withHG-401.3(C)(1), for each valve thatfailed.

4. Failure of any of the replacementvalves to meet the capacity or the per-formance requirements of this Sectionshall be cause for revocation within 60days of the authorization to use theCode Symbol on that particular type of valve. During this period, theManufacturer shall demonstrate thecause of such deficiency and the actiontaken to guard against future occur-rence, and the requirements ofHG-401.3(C) above shall apply.

HG-401.4 Manufacturer’s Testing

A. Every steam valve shall be tested todemonstrate its popping point, blow-down, and tightness. Every hot watervalve shall be tested to demonstrate itsopening point and tightness. Steamvalves shall be tested on steam or airand hot water valves on water, steam, orair. When the blowdown is nonad-justable, the blowdown test may beperformed on a sampling basis.

B. A Manufacturer shall have a well-estab-lished program for the application,calibration, and maintenance of testgauges.

C. Testing time on steam valves shall besufficient, depending on size and de-sign, to insure that test results arerepeatable and representative of fieldperformance.

D. Test fixtures and test drums shall be ofadequate size and capacity to assurerepresentative pop action and accuracyof blowdown adjustment.

E. A tightness test shall be conducted atmaximum expected operating pressure,but not at a pressure exceeding the re-seating pressure of the valve.

HG-401.5 Design Requirements. At thetime of the submission of valves for ca-pacity certification, or testing inaccordance with this Section, the ASMEDesignee has the authority to review thedesign for conformity with the require-ments of this Section, and to reject orrequire modification of designs which donot conform, prior to capacity testing.

HG-402 Discharge Capacities ofSafety and Safety Relief ValvesHG-402.1 Valve Markings. Each safety orsafety relief valve shall be plainly markedwith the required data by the Manufacturerin such a way that the markings will not beobliterated in service. The markings shallbe stamped, etched, impressed, or caston the valve or on a nameplate whichshall be securely fastened to the valve.The markings shall include the following:

A. the name or an acceptable abbrevia-tion of the Manufacturer;

B. Manufacturer’s design or type number;

C. NPS size _____ inch (the nominal pipesize of the valve inlet);

D. set pressure ________psi;

E. capacity _________lb/hr, or capacity_________ BTU/hr in accordance with HG-402.3;

F. year built or, alternatively, a coding maybe marked on the valves such that thevalve Manufacturer can identify the yearthe valve was assembled and tested;

G. ASME Symbol as shown in Figure HG-402.



HG-402.2 Authorization to Use ASMEStamp. Each safety valve to which theCode Symbol (Figure HG-402) is to be ap-plied shall be produced by a Manufacturerand/or Assembler who is in possession ofa valid Certificate of Authorization. (SeeHG-540)

HG-402.3 Determination of Capacity toBe Stamped on Valves. The Manufacturerof the valves that are to be stamped withthe Code symbol shall submit valves fortesting to a place where adequate equip-ment and personnel are available toconduct pressure and relieving-capacitytests which shall be made in the presenceof and certified by an authorized observer.The place, personnel, and authorized ob-server shall be approved by the Boiler andPressure Vessel Committee. The valvesshall be tested in one of the followingthree methods.

A. Coefficient Method.1 Tests shall bemade to determine the lift, popping,and blowdown pressures, and the ca-pacity of at least three valves each ofthree representative sizes (a total ofnine valves). Each valve of a given size

shall be set at a different pressure.However, safety valves for steam boil-ers shall have all nine valves set at 15psig. A coefficient shall be establishedfor each test as follows:

Actual steam flow Coefficient ofKD = =Theoretical steam flow discharge

The average coefficient of the tests re-quired shall be taken as the coefficientK of the design, and the stamped ca-pacity for all sizes and pressures of thedesign shall not exceed the value de-termined from the following formulas:

For 45 degree seat, W = (51.45 πDLP x 0.707K ) 0.90

For flat seat, W = (51.45 πDLPK ) 0.90

For nozzle,W = (51.45 APK ) 0.90

Where:

W = weight of steam/hr, lb

D = seat diameter, inch

L = lift, inch

P = absolute pressure, psi (accumulated)

KD = coefficient of discharge for a single test

K = average coefficient of discharge

A = nozzle-throat area, in2

B. Slope Method. If a Manufacturer wish-es to apply the Code Symbol to adesign of pressure relief valves, fourvalves of each combination of pipe andorifice size shall be tested. These fourvalves shall be set at pressures thatcover the approximate range of pres-sures for which the valve will be used,or that cover the range available at thecertified test facility that shall conduct

the tests. The capacities shall be basedon these four tests as follows.

1. The slope (dW/dP ) of the actual mea-sured relieving capacity versus the flowpressure for each test point shall becalculated and averaged:

Slope = dW/dP = measured capacity/absolute flow pressure (psia)

All values derived from the testingmust fall within ± 5% of the averagevalue:

Minimum slope = average slope x 0.95

Maximum slope = average slope x 1.05

If slope values derived from the test donot fall between the minimum and maxi-mum slope values, the authorizedobserver shall require that additionalvalves be tested at the rate of two foreach value beyond the maximum andminimum values with a limit of four ad-ditional valves.

2. The relieving capacity to be stampedon the valve shall not exceed 90% ofthe average slope times the absoluteflow pressure:

W ≤ average slope [(stamped set pressure x 1.10) + 14.7] 0.90

C. Three-Value Method. If a Manufacturerwishes to apply the Code Symbol tosteam safety valves or safety reliefvalves of one or more sizes of a designset at one pressure, he shall submitthree valves of each size of each de-sign set at one pressure for testing andthe stamped capacity of each size shallnot exceed 90% of the average capaci-ty of the three valves tested.2

1. The maximum and minimum coefficient de-termined by the tests of a valve design shallnot vary more than ±5% from the average. Ifone or more tests are outside the accept-able limits, one valve of the Manufacturer’schoice shall be replaced with another valveof the same size and pressure setting or bya modification of the original valve.

Following this test a new average coefficientshall be calculated, excluding the replacedvalve test. If one or more tests are now out-

side the acceptable limits, as determined bythe new average coefficient, a valve of theManufacturer’s choice must be replaced bytwo valves of the same size and pressureas the rejected valve. A new average coeffi-cient, including the replacement valves,shall be calculated. If any valve, excludingthe two replaced valves, now falls outsidethe acceptable limits, the tests shall be con-sidered unsatisfactory.

2. The discharge capacity as determined bythe test of each valve tested shall not varyby more than ±5% of the average capacityof the three valves tested. If one of the threevalve tests falls outside of the limits, it maybe replaced by two valves and a new aver-age calculated based on all four valves,excluding the replaced valve.


Figure HG-402Official Symbol For Stamp to Denote The

American Society of MechanicalEngineers’ Standard

Notes




HG-402.4 Pressures at Which CapacityTests Shall Be Conducted. Safety valvesfor steam boilers shall be tested for capac-ity at 5 psi over the set pressure for whichthe valve is set to operate. Capacity certifi-cation tests of safety relief valves for hotwater heating and hot water supply boilersshall be conducted at 110% of the pres-sure for which the valve is set to operate.

HG-402.5 Opening Tests of Pressure-Temperature Relief Valves. For thepurpose of determining the set (opening)pressure, the test medium shall be roomtemperature water. The actual set pres-sure is defined as the pressure at thevalve inlet when the flow rate through thevalve is 40 cm3/min. Capacity tests shallbe conducted with steam (see HG-402.7)at a pressure 10% above the actual wa-ter set pressure. For production capacitycheck tests, the rated capacity shall bebased on the actual water set pressure.

HG-402.6 Capacity Tests of Pressure-Temperature Relief Valves. For thepurpose of determining the capacity ofpressure-temperature relief valves, dum-my elements of the same size and shapeas the regularly applied thermal elementshall be substituted and the relieving capacity shall be based on the pressureelement only. Valves selected to meet therequirements of production testing, HG-401.3, shall have their temperatureelements deactivated by the Manufacturerprior to or at the time of capacity testing.

HG-402.7 Fluid Medium for CapacityTests. The tests shall be made with drysaturated steam. For test purposes the limits of 98% minimum quality and 20°Fmaximum superheat shall apply. Correction

from within these limits may be made to the dry saturated condition. The relievingcapacity shall be measured by condensingthe steam or with a calibrated steamflowmeter.

A. To determine the discharge capacity ofsafety relief valves in terms of BTU, therelieving capacity in pounds for steamper hour W is multiplied by 1000.

A92HG-402.8 Where and by WhomCapacity Tests Shall Be Conducted.A. Tests shall be conducted at a place

where the testing facilities, methods,procedures, and person supervising thetests (Authorized Observer) meet theapplicable requirements of ASME/ANSIPTC 25.3. The tests shall be made un-der the supervision of and certified byan Authorized Observer. The testing fa-cilities, methods, procedures, andqualifications of the AuthorizedObserver shall be subject to the accep-tance of ASME on recommendation ofan ASME Designee. Acceptance of thetesting facility is subject to review withineach 5 year period.

B. Capacity test data reports for eachvalve model, type, and size, signed by the Manufacturer and the AuthorizedObserver witnessing the tests, shall besubmitted to the ASME Designee for review and acceptance.1,2

HG-402.9 Test Record Data Sheet. A data sheet for each valve shall be filledout and signed by the authorized observerwitnessing the test. Such data sheet willbe the manufacturer’s authority to buildand stamp valves of corresponding design

and construction. When changes are madein the design of a safety or safety reliefvalve in such a manner as to affect theflow path, lift, or performance characteris-tics of the valve, new tests in accordancewith this Section shall be performed.3

HG-405 Thermal Elements forPressure-Temperature Relief ValvesThe thermal elements for pressure-tem-perature relief valves shall be so designedand constructed that they will not fail inany manner which could obstruct flowpassages or reduce capacities of thevalves when the elements are subjectedto steam temperatures.4

HG-512 Safety and Safety ReliefValve Accumulation TestsIf the safety valve or safety relief valve capacity cannot be computed or if it is de-sirable to prove the computations, it maybe checked in any one of the followingways and, if found insufficient, additionalcapacity shall be provided:

A. by making an accumulation test, that is,by shutting off all discharge outletsfrom the boiler and forcing the fires tothe maximum, the safety valve equip-ment shall be sufficient to prevent anexcess pressure beyond that specifiedin HG-400.1(F) and HG-400.2(F);

B. by measuring the maximum amount offuel that can be burned, and computingthe corresponding evaporative capacityupon the basis of the heating value ofthe fuel. (See B-100, B-101, and B-102.)

1. When changes are made in the design, ca-pacity certification tests shall be repeated.

2. Valve capacities are published in ‘PressureRelief Device Certifications.’ This publica-tion may be obtained from The NationalBoard of Boiler and Pressure VesselInspectors, 1055 Crupper Avenue,Columbus, Ohio, 43229.

3. See HG-512 for safety and safety reliefvalve accumulation test requirements. SeeHG-701 for safety and safety relief valve in-stallation requirements.

4. Since the temperature elements are de-signed for temperatures up to only 250°F,they will fail when subjected to steam pres-sures with corresponding saturationtemperatures in excess of 250°F.

Notes



Installation Requirements

HG-700 Installation Requirements,All boilers

HG-701 Mounting Safety andSafety Relief ValvesHG-701.1 Permissible Mounting. Safetyvalves and safety relief valves shall be lo-cated in the top or side1 of the boiler. Theyshall be connected directly to a tapped orflanged opening in the boiler, to a fittingconnected to the boiler by a short nipple,to a Y-base, or to a valveless header con-necting steam or water outlets on thesame boiler. Coil or header type boilersshall have the safety valve or safety reliefvalve located on the steam or hot wateroutlet end. Safety valves and safety reliefvalves shall be installed with their spindlesvertical. The opening or connection be-tween the boiler and any safety valve orsafety relief valve shall have at least thearea of the valve inlet.

HG-701.2 Requirements for CommonConnections for Two or More ValvesA. When a boiler is fitted with two or more

safety valves on one connection, thisconnection shall have a cross-sectionalarea not less than the combined areasof inlet connections of all the safetyvalves with which it connects.

B. When a Y-base is used, the inlet areashall be not less than the combinedoutlet areas. When the size of the boil-er requires a safety valve or safetyrelief valve larger than 41/2-inch in di-ameter, two or more valves having therequired combined capacity shall beused. When two or more valves areused on a boiler, they may be single,directly attached, or mounted on a Y-base.

HG-701.3 Threaded Connections. Athreaded connection may be used for at-taching a valve.

HG-701.4 Prohibited Mountings. Safetyand safety relief valves shall not be con-nected to an internal pipe in the boiler.

HG-701.5 Use of Shutoff ValvesProhibited. No shutoff of any descriptionshall be place between the safety or safety relief valve and the boiler, or on discharge pipes between such valves andthe atmosphere.

A92HG-701.6 Safety and Safety ReliefValve Discharge PipingA. A discharge pipe shall be used. Its in-

ternal cross-sectional area shall be notless than the full area of the valve out-let or of the total of the valve outletsdischarging thereinto and shall be asshort and straight as possible and soarranged as to avoid undue stress onthe valve or valves. A union may be in-stalled in the discharge piping close tothe valve outlet. When an elbow isplaced on a safety or safety relief valvedischarge pipe, it shall be located closeto the valve outlet downstream of theunion.

B. The discharge from safety or safety re-lief valves shall be so arranged thatthere will be no danger of scalding at-tendants. The safety or safety reliefvalve discharge shall be piped awayfrom the boiler to the point of dis-charge, and there shall be provisionsmade for properly draining the piping.The size and arrangement of dischargepiping shall be independent of otherdischarge piping and shall be such thatany pressure that may exist or developwill not reduce the relieving capacity ofthe relieving devices below that re-quired to protect the boiler.

Note

1. The top or side of the boiler shall mean thehighest practicable part of the boiler properbut in no case shall the safety valve be locat-ed below the normal operating level and inno case shall the safety relief valve be locat-ed below the water level.

ASME Code Section IV –Heating Boiler Code (1995 Addenda)



Pressure Relief Devices

UG-125 GeneralA. All vessels within the Scope of this

Division, irrespective of size or pres-sure, shall be provided1 with protectivedevices in accordance with the require-ments of UG-125 through UG-136.Unless otherwise defined in thisDivision, the definitions relating to pres-sure relief devices in Appendix I ofASME/ANSI PTC 25.3 Safety andRelief Valves shall apply.

B. An unfired steam boiler, as defined inU-1(G), shall be equipped with pres-sure relief devices required by Section Iinsofar as they are applicable to theservice of the particular installation.

C. All pressure vessels other than unfiredsteam boilers shall be protected by apressure relieving device that shall pre-vent the pressure from rising more than10% or 3 psi, whichever is greater,above the maximum allowable workingpressure except as permitted in (1) and(2) below. (See UG-134 for pressuresettings.)

1. When multiple pressure relieving devicesare provided and set in accordance withUG-134(A), they shall prevent the pres-sure from rising more than 16% or 4 psi,whichever is greater, above the maxi-mum allowable working pressure.

2. Where an additional hazard can becreated by exposure of a pressure ves-sel to fire or other unexpected sourcesof external heat, supplemental pres-sure relieving devices shall be installedto protect against excessive pressure.

Such supplemental pressure relievingdevices shall be capable of preventingthe pressure from rising more than21% above the maximum allowableworking pressure. The same pressurerelieving devices may be used to satisfythe capacity requirements of (C) or(C)(1) above and this paragraph provid-ed the pressure setting requirements ofUG-134(A) are met.

3. Pressure relief devices, intended primar-ily for protection against exposure of apressure vessel to fire or other unex-pected sources of external heat installedon vessels having no permanent supplyconnection and used for storage at am-bient temperatures of nonrefrigeratedliquefied compressed gases,2 are ex-cluded from the requirements of (C)(1)and (C)(2) above, provided:

(a) the relief devices are capable of pre-venting the pressure from rising morethan 20% above the maximum allowableworking pressure of the vessels;

(b) the set pressure of these devicesshall not exceed the maximum allowablepressure of the vessels;

(c) the vessels have sufficient ullage toavoid a liquid full condition;

(d)the maximum allowable working pres-sure of the vessels on which thesedevices are installed is greater than thevapor pressure of the stored liquefiedcompressed gas at the maximum antici-pated temperature3 that the gas willreach under atmospheric conditions; and

(e) pressure relief valves used to satisfy

these provisions also comply with the re-quirements of UG-129(A)(5),UG-131(C)(2), and UG-134(D)(2).

D. Pressure relieving devices shall be con-structed, located, and installed so thatthey are readily accessible for inspec-tion and repair and so that they cannotbe readily rendered inoperative (seeAppendix M), and should be selectedon the basis of their intended service.

E. Pressure relief valves or nonreclosingpressure relief devices4 may be usedas protective devices. Nonreclosingpressure relief devices may be used either alone or, if applicable, in combi-nation with safety or safety relief valveson vessels.5

F. Vessels that are to operate completelyfilled with liquid shall be equipped withliquid relief valves, unless otherwiseprotected against overpressure.

G. The protective devices required in (A)above need not be installed directly ona pressure vessel when the source ofpressure is external to the vessel andis under such positive control that thepressure in the vessel cannot exceedthe maximum allowable working pres-sure at the operating temperature exceptas permitted in (C) above (see UG-98).6

H. Safety and safety relief valves forsteam service shall meet the require-ments of UG-131(B).

UG-126 Pressure Relief Valves7

A. Safety, safety relief, and relief valvesshall be of the direct spring loaded type.

1. Safety devices need not be provided by thevessel manufacturer, but overpressure pro-tection shall be provided prior to placing thevessel in service.

2. For the purpose of these rules, gases areconsidered to be substances having a vaporpressure greater than 40 psia at 100°F.

3. Normally this temperature should not beless than 115°F.

4. A pressure relief valve is a pressure reliefdevice which is designed to reclose andprevent the further flow of fluid after normalconditions have been restored. A nonreclos-ing pressure relief device is a pressure reliefdevice designed to remain open after operation.

5. Use of nonreclosing devices of some typesmay be advisable on vessels containingsubstances that may render a safety orsafety relief valve inoperative, where a lossof valuable material by leakage should beavoided, or where contamination of the at-mosphere by leakage of noxious fluids mustbe avoided. The use of rupture disc devicesmay also be advisable when very rapidrates of pressure rise may be encountered.

6. Pressure reducing valves and similar me-chanical or electrical control instruments,except for pilot operated valves as permit-ted in UG-126(B), are not considered assufficiently positive in action to prevent ex-cess pressures from being developed.

7. A safety valve is a pressure relief valve actuated by inlet static pressure and char-acterized by rapid opening or pop action. Arelief valve is a pressure relief valve actuat-ed by inlet static pressure which opens inproportion to the increase in pressure overthe opening pressure. A safety relief valve isa pressure relief valve characterized byrapid opening or pop action, or by openingin proportion to the increase in pressureover the opening pressure, depending onapplication. A pilot operated pressure reliefvalve is a pressure relief valve in which themajor relieving device is combined with andis controlled by a self-actuated auxiliarypressure relief valve.

ASME Code Section VIII – Division I (1995 Addenda)

Notes



B. Pilot operated pressure relief valvesmay be used, provided that the pilot isself-actuated and the main valve willopen automatically at not over the setpressure and will discharge its full ratedcapacity if some essential part of the pilot should fail.

C. The spring in a safety valve or safety relief valve shall not be set for any pressure more than 5% above or belowthat for which the valve is marked, un-less the setting is within the springdesign range established by the valvemanufacturer or is determined to be ac-ceptable to the manufacturer. The initialadjustment shall be performed by themanufacturer, his authorized represen-tative, or an assembler, and a valvedata tag shall be provided that identifiesthe set pressure capacity and date. Thevalve shall be sealed with a seal identi-fying the manufacturer, his authorizedrepresentative, or the assembler per-forming the adjustment.

D. The set pressure tolerance, plus or mi-nus, of pressure relief valves shall notexceed 2 psi for pressures up to and in-cluding 70 psi and 3% for pressuresabove 70 psi.

UG-127 Nonreclosing PressureRelief DevicesA. Rupture Disk Devices8

1. General

(a) Every rupture disk shall have stampedburst pressure established by rules of

(A)(1)(b) below with a manufacturingdesign range9 at a specified disk tem-perature10 and shall be marked with alot number. The burst pressure toleranceat the specific disk temperature shall notexceed ±2 psi for stamped burst pres-sure up to and including 40 psi and ±5%for stamped burst pressure above 40psi.

(b) The stamped bursting pressure with-in the manufacturing design range at thecoincident disk temperature shall be de-rived by one of the following methods.All the tests of disks for a given lot shallbe made in a holder of the same formand dimensions as that with which thedisk is to be used.

(1) At least two sample rupture disksfrom each lot of rupture disks, madefrom the same materials and of thesame size as those to be used, shall beburst to verify that the stamped burstingpressure falls within the manufacturingdesign range at the coincident disk tem-perature. At least one disk shall beburst at room temperature. Thestamped rating at specified disk temper-ature shall be the average of the burstsat coincident disk temperature.

(2) At least four sample rupture disks,but not less than 5%, from each lot ofrupture disks, made from the same ma-terial and of the same size as those tobe used, shall be burst at four differenttemperatures, distributed over the ap-plicable temperature range for whichthe disk will be used. These data shall

be used to establish a curve of burstingpressure versus temperature for the lotof disks. The stamped rating at the coin-cident disk temperature shall beinterpolated from this curve.

(3) For prebulged, solid metal disks orgraphite disks only, a curve of percentageratio at temperatures other than ambientmay be establish as in (2) above, usingone size of disk for each lot of material.At least four bursts at four different tem-peratures shall be used to establish theabove curve over the applicable tempera-ture range. At least two disks from eachlot of disks, made from this lot of materialand of the same size as those to beused, shall be burst at ambient tempera-ture to establish the room temperaturerating of the lot of disks.

The percent change of bursting pres-sure taken from the above curve shallbe used to establish the stamped ratingat the coincident disk temperature forthe lot of disks.

2. Capacity Rating

(a) The calculated capacity rating of arupture disk device shall not exceed avalue based on the applicable theoreticalformula (UG-131) for the various mediamultiplied by K = coefficient = 0.62. Thearea A (square inches) in the theoreticalformula shall be the minimum net areaexisting after disk burst.11,12

(b) In lieu of the method of capacity rat-ing in (a) above, a Manufacturer mayhave the capacity of a given rupture disk

8. A rupture disc device is a nonreclosingpressure relief device actuated by inlet stat-ic pressure and designed to function by thebursting of a pressure containing disc. Arupture disc is the pressure containing andpressure sensitive element of a rupture discdevice. A rupture disc holder is the structurewhich encloses and clamps the rupture discin position. Rupture discs may be designedin several configurations, such as plain flat,prebulged or reverse buckling, and may bemade of either ductile or brittle material;rupture disc material is not required to con-form to an ASME specification. The materialof the rupture disc holder shall be listed inSection II and be permitted for use in thisDivision.

9. The manufacturing design range is a rangeof pressure within which the average burstpressure of test discs must fall to be accept-able for a particular requirement as agreedupon between the rupture disc Manufacturerand the user or his agent. The disc shall bemarked at the average burst pressure of alltest discs.

10. The specified disc temperature supplied tothe rupture disc Manufacturer shall be thetemperature of the disc when the disc is ex-pected to burst.

11. The minimum net flow area is the calculatednet area after a complete burst of the discwith appropriate allowance for any structuralmembers which may reduce the net flow

area through the rupture disc device. Thenet flow area for sizing purposes shall notexceed the nominal pipe size area of therupture disc device.

12. When rupture disc devices are used, it isrecommended that the design pressure ofthe vessel be sufficiently above the intend-ed operating pressure to provide sufficientmargin between operating pressure andrupture disc due to fatigue or creep.

Application of rupture disc devices to liquidservice should be carefully evaluated to as-sure that the design of the rupture discdevice and the dynamic energy of the sys-tem on which it is installed will result insufficient opening of the rupture disc.


Notes



device design determined for the KDcoefficient in general accordance withthe procedures of UG-131, as applicable.

3. Application of Rupture Disks

(a) A rupture disk device may be used asthe sole pressure relieving device on a ves-sel.

(b) A rupture disk device may be installedbetween a pressure relief valve13 and thevessel provided:

(1) the combination of the spring loadedsafety or safety relief valve and the rup-ture disk device is ample in capacity tomeet the requirements of UG-133(A)and (B);

(2) the stamped capacity of a springloaded safety or safety relief valve (noz-zle type) when installed with a rupturedisk device between the inlet of thevalve and the vessel shall be multipliedby a factor of 0.90 of the rated relievingcapacity of the valve alone, or alterna-tively, the capacity of such acombination shall be established in ac-cordance with (3) below;

(3) the capacity of the combination ofthe rupture disk device and the springloaded safety or safety relief valve maybe established in accordance with theappropriate paragraphs of UG-132,Certification of Capacity of Safety andSafety Relief Valves in Combination withnonreclosing Pressure Relief Devices;

(4) the space between a rupture disk de-vice and a safety or safety relief valveshall be provided with a pressure gauge,a try cock, free vent, or suitable telltale

indicator. This arrangement permits de-tection of disk rupture or leakage.14

(5) the opening12 provided through therupture disk, after burst, is sufficient topermit a flow equal to the capacity of thevalve [(2) and (3) above], and there is nochance of interference with proper func-tioning of the valve; but in no case shallthis area be less than the area of the in-let of the valve unless the capacity andfunctioning of the specific combination ofrupture disk and valve have been estab-lished by test in accordance with UG-132.

(c) A rupture disk device may be installedon the outlet side15 of a spring loadedsafety relief valve which is opened by di-rect action of the pressure in the vesselprovided:

(1) the valve is so designed that it will notfail to open at its proper pressure settingregardless of any back pressure that canaccumulate between the valve disk andthe rupture disk. The space between thevalue disk and the rupture disk shall bevented or drained to prevent accumula-tion of pressure due to a small amount ofleakage from the valve.16

(2) the valve is ample in capacity tomeet the requirements of UG-133(A)and (B);

(3) the stamped bursting pressure of therupture disk at the coincident disk tem-perature plus any pressure in the outletpiping shall not exceed the design pres-sure of the outlet portion of the safety orsafety relief valve and any pipe or fittingbetween the valve and the rupture diskdevice. However, in no case shall the

stamped bursting pressure of the rup-ture disk at the coincident operatingtemperature plus any pressure in theoutlet piping exceed the maximum al-lowable working pressure of the vesselor the set pressure of the safety or safe-ty relief valve.

(4) the opening provided through therupture disk device after breakage issufficient to permit a flow equal to therated capacity of the attached safety orsafety relief valve without exceeding theallowable overpressure;

(5) any piping beyond the rupture diskcannot be obstructed by the rupture diskor fragment;

(6) the contents of the vessel are cleanfluids, free from gumming or cloggingmatter, so that accumulation in thespace between the valve inlet and therupture disk (or in any other outlet thatmay be provided) will not clog the outlet;

(7) the bonnet of the safety relief valveshall be vented to prevent accumulationof pressure.

B. Breaking Pin Device17

1. Breaking pin devices shall not be usedas single devices but only in combina-tion between the safety or safety reliefvalve and the vessel.

2. The space between a breaking pin de-vice and a safety or safety relief valveshall be provided with a pressuregauge, a try cock, a free vent, or suit-able telltale indicator. This arrangementpermits detection of breaking pin deviceoperation or leakage.

13. Use of a rupture disc device in combinationwith a safety relief valve shall be carefullyevaluated to ensure that the media beinghandled and the valve operational charac-teristics will result in pop action of the valvecoincident with the bursting of the rupturedisc.

14. Users are warned that a rupture disc will notburst at its design pressure if back pressurebuilds up in the space between the disc andthe safety or safety relief valve which willoccur should leakage develop in the rupturedisc due to corrosion or other cause.

15. This use of a rupture disc device in serieswith the safety or safety relief valve is per-

mitted to minimize the loss by leakagethrough the valve of valuable or of noxiousor otherwise hazardous materials, andwhere a rupture disc alone or disc locatedon the inlet side of the valve is impractica-ble, or to prevent corrosive gases from acommon discharge line from reaching thevalve internals.

16. Users are warned that an ordinary springloaded safety relief valve will not open at itsset pressure if back pressure builds up inthe space between the valve and rupturedisc. A specially designed valve is required,such as a diaphragm valve or a valveequipped with a bellows above the disc.

17. A breaking pin device is a nonreclosingpressure relief device actuated by inlet stat-ic pressure and designed to function by thebreakage of a load-carrying section of a pinwhich supports a pressure containing mem-ber. A breaking pin is the load-carryingelement of a breaking pin device. A breakingpin housing is the structure which enclosesthe breaking pin mechanism. The materialof the housing shall be listed in Section IIand be permitted for use in this Division.


Notes



3. Each breaking pin device shall have arated pressure and temperature atwhich the pin will break. The breakingpin shall be identified to a lot numberand shall be guaranteed by theManufacturer to break when the ratedpressure, within the following toler-ances, is applied to the device:

Rated Pressure, psi Tolerance, Plus Minimum Maximum or Minus, psi

30 150 5

151 275 10

276 375 15

4. The rated pressure of the breaking pinplus the tolerance in psi shall not ex-ceed 105% of the maximum allowableworking pressure of the vessel to whichit is applied.

5. The rated pressure at the coincidentoperating temperature18 shall be veri-fied by breaking two or more samplebreaking pins from each lot of the samematerial and the same size as those tobe used. The lot size shall not exceed25. The test shall be made in a deviceof the same form and pressure dimen-sions as that in which the breaking pinis to be used.

C. Spring Loaded NonreclosingPressure Relief Device

1. A spring loaded nonreclosing pressurerelief device, pressure actuated bymeans which permit the spring loadedportion of the device to open at thespecified set pressure and remain openuntil manually reset, may be used pro-vided the design of the spring loadednonreclosing device will achieve fullopening at or below its set pressure.Such a device may not be used in com-bination with any other pressure reliefdevice. The tolerance on opening pointshall not exceed ±5%.

2. The calculated capacity rating of a springloaded nonreclosing pressure relief de-vice shall not exceed a value based onthe applicable theoretical formula (seeUG-131) for the various media, multipliedby: K = coefficient = 0.62.

The area A (square inches) in the the-oretical formula shall be the flow areathrough the minimum opening of thenonreclosing pressure relief device.

3. In lieu of the method of capacity rating(2) above, a Manufacturer may havethe capacity of a spring loaded nonre-closing pressure relief device designcertified in general accordance with theprocedures of UG-131, as applicable.

UG-128 Liquid Relief ValveAny liquid relief valve used shall be atleast NPS 1/2.

UG-129 MarkingA. Safety, Safety Relief, Liquid Relief, and

Pilot Operated Pressure Relief Valves.Each safety, safety relief, liquid reliefand pilot operated valve NPS 1/2 andlarger shall be plainly marked by themanufacturer or assembler with the re-quired data in such a way that themarking may be placed on the valve oron a plate or plates that satisfy the re-quirements of UG-119:

1. the name, or an acceptable abbreviation,of Manufacturer and the Assembler;

2. Manufacturer’s design or type number;

3. NPS size _______ (the nominal pipesize of the valve inlet);

4. set pressure ________ psi;

5. certified capacity (as applicable);

(a) lb/hr of saturated steam at an over-pressure of 10% or 3 psi, whichever isgreater for valves certified on steamcomplying with UG-131(B); or

(b) gal/min of water at 70°F at an over-pressure of 10% or 3 psi, whichever isgreater for valves certified on water; or

(c) SCFM (standard cubic feet perminute at 60°F and 14.7 psia), or lb/min,of air at an overpressure of 10% or 3psi, whichever is greater. Valves that arecapacity certified in accordance withUG-131(C)(2) shall be marked ‘at 20%overpressure.’

(d) In addition to one of the fluids speci-fied above, the Manufacturer mayindicate the capacity in other fluids (seeAppendix 11).

6. year built, or alternatively, a coding maybe marked on the valve such that thevalve Manufacturer or Assembler canidentify the year the valve was assem-bled or tested;

7. ASME Symbol as shown in Fig. UG-129. The pilot of a pilot operatedpressure relief valve shall be plainlymarked by the Manufacturer orAssembler showing the name of theManufacturer; the Manufacturer’s de-sign or the type number, the setpressure in pounds per square inch,and the year built, or alternately a cod-ing that the Manufacturer can use toidentify the year built.

On valves smaller than NPS 1/2, themarkings may be made on a metal tag at-tached by wire or adhesive meeting therequirements of UG-119 or other meanssuitable for the service conditions.

Figure UG-129 Official Symbol for Stampto denote the American Society ofMechanical Engineers’ Standard


Notes

18. The specified temperature supplied to thebreaking pin manufacturer shall be the tem-perature of the breaking pin when anemergency condition exists and the pin isexpected to break.



B. Safety and safety relief valves certifiedfor a steam discharging capacity underthe provisions of Section I and bearingthe official Code Symbol Stamp ofSection I for safety valves may be usedon pressure vessels. The rated capaci-ty in term of other fluids shall bedetermined by the method of conver-sion given in Appendix 11. [SeeUG-131(H).]

C. Pressure Relief Valves in CombinationWith Rupture Disk Devices. Pressurerelief valves in combination with rupturedisk devices shall be marked with thecapacity as established in accordancewith UG-127(A)(3)(b)(2) (using 0.90 fac-tor) or the combination capacity factorestablished by test in accordance withUG-132(A) or (B), in addition to themarking of UG-129(A) and (F) below.The marking may be placed on thevalve or rupture disk device or on aplate or plates that satisfy the require-ments of UG-119 or rupture disk device.The marking shall include the following:

1. name of Manufacturer of valve;

2. design or type number of valve;

3. name of Manufacturer of rupture diskdevice;

4. design or type number of rupture diskdevice;

5. capacity or combination capacity factor;

6. name of organization responsible forthis marking. This shall be either thevessel user, vessel Manufacturer,rupture disk Manufacturer, or pres-sure relief valve Manufacturer.

D. Pressure Relief Valves in CombinationWith Breaking Pin Devices. Pressurerelief valves in combination with break-ing pin devices shall be marked inaccordance with (A) above. In addition,the rated pressure shall be marked onthe breaking pin and the breaking pinhousing.

E. Rupture Disk Devices. Every rupturedisk shall be plainly marked by theManufacturer in such a way that themarking will not be obliterated in ser-vice. The rupture disk marking may beplaced on the flange of the disk or on ametal tab that satisfies the require-ments of UG-119. The marking shallinclude the following:

1. the name or identifying trademark ofthe Manufacturer;

2. Manufacturer’s design or type number;

3. lot number;

4. disk material;

5. size ________ (NPS designator at valve inlet);

6. stamped bursting pressure _____psi;

7. coincident disk temperature _____°F;

8. capacity _______ lb of saturatedsteam/hr, or _______ cu ft of air/min(60°F and 14.7 psia).19

Items (1), (2), and (5) above shall also bemarked on the rupture disk holder.

F. Spring Loaded nonreclosing PressureRelief Devices. Spring loadednonreclosing pressure relief devicesshall be marked in accordance with (A)above except that the Code SymbolStamp is to be applied only when thecapacity has been established and cer-tified in accordance with UG-127(C)(3)and all other requirements of UG-130have been met.

UG-130 Use of Code Symbol StampEach pressure relief valve20 to which theCode Symbol (see Fig. UG-129) will beapplied shall have been fabricated or as-sembled by a Manufacturer or Assemblerholding a valid Certificate of Authorization(UG-117) and capacity certified in accor-dance with the requirements of thisDivision.

UG-131 Certification of Capacity ofPressure Relief ValvesA. Before the Code Symbol is applied

to any pressure relief valve, the valveManufacturer shall have the capacity ofhis valves certified in accordance withprovisions of this paragraph.

B. 1. Capacity certification tests for pres-sure relief valves for compressiblefluids shall be conducted on dry satu-rated steam, or air, or natural gas.When dry saturated steam is used, thelimits for test purposes shall be 98%minimum quality and 20°F maximumsuperheat. Correction from within theselimits may be made to the dry saturatedcondition. Valves for steam service maybe rated as above, but at least onevalve of each series shall be tested onsteam to demonstrate the steam ca-pacity and performance.

2. Capacity certification tests for pres-sure relief valves for incompressiblefluids shall be conducted on water at atemperature between 40°F and 125°F.

C. 1. Capacity certification tests shall beconducted at a pressure which doesnot exceed the pressure for which thepressure relief valve is set to operateby more than 10% or 3 psi, whicheveris greater, except as provided in (C)(2)below. Minimum pressure for capacitycertification tests shall be at least 3 psiabove set pressure. The reseatingpressure shall be noted and recorded.

2. Capacity certification tests of pres-sure relief valves for use in accordancewith UG-125(C)(3) may be conductedat a pressure not to exceed 120% ofthe stamped set pressure of the valve.

3. (a) Pressure relief valves for com-pressible fluids having an adjustableblowdown construction shall be adjustedprior to testing so that the blowdowndoes not exceed 5% of the set pressureor 3 psi, whichever is greater.

19. In addition, the Manufacturer may indicatethe capacity in other fluids (see Appendix11).

20. Vacuum relief valves are not covered byCode Symbol Stamp requirements.


Notes



(b) The blowdown of pressure reliefvalves for incompressible fluids andpressure relief valves for compressiblefluids having nonadjustable blowdownshall be noted and recorded.

4. Capacity certification of pilot operat-ed pressure relief valves may be based on tests without the pilot valve installed,provided prior to capacity tests it hasbeen demonstrated by test to the satis-faction of the Authorized Observer thatthe pilot valve will cause the main valveto open fully at a pressure which doesnot exceed the set pressure by morethan 10% or 3 psi, whichever is greater,and that the pilot valve in combinationwith the main valve will meet all the re-quirements of this Division.

D. 1. A capacity certification test is re-quired on a set of three valves for eachcombination of size, design, and pres-sure setting. The stamped capacityrating for each combination of design,size, and test pressure shall not ex-ceed 90% of the average capacity ofthe three valves tested. The capacityfor each set of three valves shall fallwithin a range of ±5% of the averagecapacity. Failure to meet this require-ment shall be cause to refuse certificationof that particular safety valve design.

2. If a Manufacturer wishes to apply theCode Symbol to a design of pressure relief valves, four valves of each combi-nation of pipe size and orifice size shallbe tested. These four valves shall beset at pressures which cover the ap-proximate range of pressures for whichthe valve will be used or covering therange available at the certified test facil-ity that shall conduct the tests. The

capacities based on these four testsshall be as follows:

(a) For compressible fluids, the slopeW/P of the actual measured capacityversus the flow pressure for each testpoint shall be calculated and averaged:

W measured capacityslope = ––– = ––––––––––––––––––––––

P absolute flow pressure, psia

All values derived from the testing mustfall within ±5% of the average value:

minimum slope = 0.95 x average slope

maximum slope = 1.05 x average slope

If the values derived from the testingdo not fall between the minimum andmaximum slope values, the AuthorizedObserver shall require that additionalvalves be tested at the rate of two foreach valve beyond the maximum andminimum values with a limit of four addi-tional valves.

The relieving capacity to be stampedon the valve shall not exceed 90% ofthe average slope times the absoluteaccumulation pressure:

rated slope = 0.90 x average slopestamped capacity ≤ rated slope (1.10 xset pressure + 14.7)

or (set pressure + 3 psi + 14.7),whichever is greater

For valves certified in accordance with(C)(2) above,

stamped capacity ≤ rated slope (1.20 x set pressure + 14.7)or (set pressure + 3 psi + 14.7),whichever is greater

(b) For incompressible fluids, the ca-pacities shall be plotted on log-logpaper against the differential (inlet mi-

nus discharge pressure) test pressureand a straight line drawn through thesefour points. If the four points do not es-tablish a straight line, two additionalvalves shall be tested for each unsatis-factory point, with a limit of twounsatisfactory points. Any point that de-parts from the straight line by more than5% should be considered an unsatis-factory point. The relieving capacityshall be determined from this line. Thecertified capacity shall not exceed 90%of the capacity taken from the line.

E. Instead of individual capacity certifica-tion as provided in (D) above, acoefficient of discharge K may be established for specific safety valve design according to the following procedure.

1. For each design, the pressure reliefvalve manufacturer shall submit for testat least three valves for each of threedifferent sizes (a total of nine valves) to-gether with detailed drawings showingthe valve construction. Each valve of agiven size shall be set at a differentpressure.

2. Tests shall be made on each pres-sure or relief valve to determine itscapacity-lift, popping and blowdownpressures, and actual capacity in termsof the fluid used in the test. A coefficientKD shall be established for each test runas follows:

Actual flow coefficientKD = =Theoretical flow of discharge




where actual flow is determined quanti-tatively by test, and theoretical flow iscalculated by the appropriate formulawhich follows:

For tests with dry saturated steam,21

WT = 51.5 AP

For tests with air,–––––

MWT = 356 AP –––√ T

For tests with natural gas,–––––

MWT = CAP –––√ ZT

For tests with water,–––––––––

WT = 2407A √(P-Pd)w

where:WT = theoretical flow, lb/hr

A = actual discharge area throughthe valve at developed lift, in2

P = (set pressure x 1.10) plus atmosphere, psia, or set pres-sure plus atmospheric pressureplus 3 psi, whichever is greater

Pd = pressure at discharge fromvalve, psia


T = absolute temperature at inlet,°F + 460°F

C = constant for gas or vapor basedon the ratio of specific heats

k = Cp /Cv (see Fig.11-1, pg.99)

Z = compressibility factor corre-sponding to P and T

w = specific weight of water at valve inlet conditions

The average of the coefficients KD ofthe nine tests required shall be multi-plied by 0.90, and this product shall betaken as the coefficient K of that de-sign. The coefficient of the design shall

not be greater than 0.878 (the productof 0.9 x 0.975).22

To convert lb/hr of water to gal/min ofwater, multiply the capacity in lb/hr by1/500.

3. The official relieving capacity of allsizes and pressures of given design, forwhich K has been established underthe provisions of (E)(2) above, that aremanufactured subsequently shall notexceed the value calculated by the ap-propriate formula in (E)(2) abovemultiplied by the coefficient K (seeAppendix 11).

4. The coefficient shall not be applied tovalves whose beta ratio (ratio of valvethroat to inlet diameter) lies outside therange of 0.15 to 0.75, unless tests havedemonstrated that the individual coeffi-cient of discharge KD for valves at theextreme ends of a larger range is within±5% of the average coefficient K. Fordesigns where the lift is used to deter-mine the flow area, all valves shall havethe same nominal lift-to-seat diameterratio (L/D).

F. Tests shall be conducted at a placewhere the testing facilities, methods,procedures, and person supervisingthe tests (Authorized Observer) meetthe applicable requirements ofASME/ANSI PTC 25.3. The tests shallbe made under the supervision of andcertified by an Authorized Observer.The testing facilities, methods, proce-dures, and qualifications of theAuthorized Observer shall be subject tothe acceptance of the ASME on recom-mendation of an ASME Designee.Acceptance of the testing facility is sub-ject to review within each 5 year period.

G. Capacity test data reports for eachvalve model, type, and size, signed bythe manufacturer and the AuthorizedObserver witnessing the tests shall besubmitted to the ASME Designee for

review and acceptance.23 Wherechanges are made in the design, ca-pacity certification tests shall berepeated.

H. For absolute pressures up to 1500psia, it is permissible to rate safetyvalves under PG-69.1.2 of Section Iwith capacity ratings at a flow pressureof 103% of the set pressure, for use onpressure vessels, without further test.In such instances, the capacity rating ofthe valve may be increased to allow forthe flow pressure permitted in (C)(1)and (C)(3) above, namely, 110% of theset pressure, by the multiplier:

1.10p + 14.7

1.03p + 14.7

where:p = set pressure, psi

Such valves shall be marked in accor-dance with UG-129. This multiplier shallnot be used as a divisor to transformtest ratings from a higher to a lowerflow.

For steam pressures above 1500 psi,the above multiplier is not acceptable.For steam valves with relieving pres-sures between 1500 psi and 3200 psi,the capacity shall be determined by us-ing the equation for steam and thecorrection factor for high pressuresteam in (E)(2) above with the permit-ted absolute relieving pressure (1.10p +14.7) and the coefficient K for that valvedesign.

I. Rating of nozzle type pressure reliefvalves, i.e., coefficient KD, greater than0.90 and nozzle construction, for satu-rated water shall be according to 11-2.

J. When changes are made in the designof a pressure relief valve in such a man-ner as to affect the flow path, lift, orperformance characteristics of thevalve, new tests in accordance with thisDivision shall be performed.


21. For dry saturated steam pressures over1500 psig and up to 3200 psig, the value of WT, calculated by the above equa-tion, shall be corrected by being multipliedby the following factors:

( 0.1906P –1000)0.2292P –1061

22. All experimentally determined coefficientsKD shall fall within a range of ±5% of the average KD found. Failure to meet this requirement shall be cause to refuse certifi-cation of that particular valve design.

23. Valve capacities are published in ‘PressureRelief Device Certification.’ This publicationmay be obtained from the National Board ofBoiler and Pressure Vessel Inspectors, 1055Crupper Avenue, Columbus, Ohio 43229.

Notes



UG-132 Certification of Capacity ofSafety Relief Valves in Combinationwith Nonreclosing Pressure ReliefDevicesA. Capacity of Safety or Safety Relief

Valves in Combination With a RuptureDisk Device at the Inlet

1. For each combination of safety orsafety relief valve design and rupturedisk device design, the safety valvemanufacturer or the rupture disk devicemanufacturer may have the capacity ofthe combination certified as prescribedin (3) and (4) below.

2. Capacity certification tests shall beconducted on saturated steam, air ornatural gas. When saturated steam isused, corrections for moisture contentof the steam shall be made.

3. The valve manufacturer or the rup-ture disk device manufacturer maysubmit for tests the smallest rupturedisk device size with the equivalent sizeof safety or safety relief valve that is in-tended to be used as a combinationdevice. The safety or safety relief valveto be tested shall have the largest ori-fice used in the particular inlet size.

4. Tests may be performed in accor-dance with the following subparagraphs.The rupture disk device and safety orsafety relief valve combination to betested shall be arranged to duplicatethe combination assembly design.

(a) The test shall embody the mini-mum burst pressure of the rupture diskdevice design which is to be used incombination with safety or safety reliefvalve design. The stamped burstingpressure shall be between 90% and100% of the stamped set pressure ofthe valve.

(b) The test procedure to be usedshall be as follows.

The safety or safety relief valve (onevalve) shall be tested for capacity as anindividual valve, without the rupture diskdevice at a pressure 10% above thevalve set pressure.

The rupture disk device shall then beinstalled ahead of the safety or safety

relief valve and the disk burst to oper-ate the valve. The capacity test shall beperformed on the combination at 10%above the valve set pressure duplicat-ing the individual safety or safety reliefvalve capacity test.

(c) Tests shall be repeated with twoadditional rupture disks of the samenominal rating for a total of three rup-ture disks to be tested with the singlevalve. The results of the test capacityshall fall within a range of 10% of theaverage capacity of the three tests.Failure to meet this requirement shallbe cause to require retest for determi-nation of cause of the discrepancies.

(d) From the results of the tests, aCombination Capacity Factor shall bedetermined. The Combination CapacityFactor is the ratio of the average capac-ity determined by the combination teststo the capacity determined on the indi-vidual valve.

The Combination Capacity Factor shallbe used as a multiplier to make appro-priate changes in the ASME ratedrelieving capacity of the safety or safetyrelief valve in all sizes of the design.The value of the Combination CapacityFactor shall not be greater than one.The Combination Capacity Factor shallapply only to combinations of the samedesign of safety or safety relief valveand the same design of rupture disk de-vice as those tested.

(e) The test laboratory shall submit thetest results to the ASME Designee foracceptance of the CombinationCapacity Factor.

B. Optional Testing of Rupture DiskDevices and Safety or Safety ReliefValves

1. If desired, a valve manufacturer or arupture disk manufacturer may conducttests in the same manner as outlined in(A)(4)(c) and (A)(4)(d) above using thenext two larger sizes of the design ofrupture disk device and safety or safetyrelief valve to determine a CombinationCapacity Factor applicable to largersizes. If a greater CombinationCapacity Factor is established and canbe certified, it may be used for all larger

sizes of the combination, but shall notbe greater than one.

2. If desired, additional tests may beconducted at higher pressures in accor-dance with (A)(4)(c) and (A)(4)(d)above to establish a maximumCombination Capacity Factor to beused at all pressures higher than thehighest tested, but shall not be greaterthan one.

C. Capacity of Breaking Pin Devices inCombination With Safety Relief Valves

1. Breaking pin devices in combinationwith safety relief valves shall be capaci-ty tested in compliance with UG-131(D)or UG-131(E) as a combination.

2. Capacity certification and CodeSymbol stamping shall be based on thecapacity established in accordance withthese paragraphs.

UG-133 Determination of PressureRelieving RequirementsA. Except as permitted in (B) below, the

aggregate capacity of the pressure re-lieving devices connected to any vesselor system of vessels for the release ofa liquid, air, steam, or other vapor shallbe sufficient to carry off the maximumquantity that can be generated or sup-plied to the attached equipment withoutpermitting a rise in pressure within thevessel of more than 16% above themaximum allowable working pressurewhen the pressure relieving devicesare blowing.

B. Protective devices as permitted in UG-125(C)(2), as protection againstexcessive pressure caused by expo-sure to fire or other sources of externalheat, shall have a relieving capacitysufficient to prevent the pressure fromrising more than 21% above the maxi-mum allowable working pressure of thevessel when all pressure relieving de-vices are blowing.

C. Vessels connected together by a sys-tem of adequate piping not containingvalves which can isolate any vesselmay be considered as one unit in figur-ing the required relieving capacity of




pressure relieving safety devices to befurnished.

D. Heat exchangers and similar vesselsshall be protected with a relieving deviceof sufficient capacity to avoid overpres-sure in case of an internal failure.

E. The official rated capacity of a pressurerelieving safety device shall be thatwhich is stamped on the device andguaranteed by the manufacturer.

F. The rated pressure relieving capacity ofa pressure relief valve for other thansteam or air shall be determined by themethod of conversion given in Appendix11.

G. To prorate the relieving capacity at anyrelieving pressure greater than 1.10p,as permitted under UG-125, a multipliermay be applied to the official relieving capacity of a pressure relieving deviceas follows:

P + 14.71.10p + 14.7

where:P = relieving pressure, psip = set pressure, psi

For steam pressures above 1500 psi,the above multiplier is not acceptable.For steam valves with relieving pres-sures greater than 1500 psi and lessthan or equal to 3200 psi, the capacityat relieving pressures greater than1.10p shall be determined using theequation for steam and the correctionfactor for high pressure steam in UG-131 (E)(2) with the permitted absoluterelieving pressure and the coefficient Kfor that valve design.

UG-134 Pressure Setting ofPressure Relief DevicesA. When a single pressure relieving de-

vice is used, it shall be set to operate24

at a pressure not exceeding the maxi-mum allowable working pressure of thevessel. When the required capacity isprovided in more than one pressure re-lieving device, only one device need beset at or below the maximum allowable

working pressure, and the additionaldevices may be set to open at higherpressures but in no case at a pressurehigher than 105% of the maximum al-lowable working pressure, except asprovided in (B) below.

B. Protective devices permitted in UG-125(C)(2) as protection againstexcessive pressure caused by expo-sure to fire or other sources of externalheat shall be set to operate at a pres-sure not in excess of 110% of themaximum allowable working pressureof the vessel. If such a device is usedto meet the requirements of both UG-125(C) and UG-125(C)(2), it shall beset to operate at not over the maximumallowable working pressure.

C. The pressure at which any device is setto operate shall include the effects ofstatic head and constant back pressure.

D. 1. The set pressure tolerance for pres-sure relief valves shall not exceed ±2 psi for pressures up to and including70 psi and ±3% for pressures above 70psi, except as covered in (D)(2) below.

2.The set pressure tolerance of pressurerelief valves which comply with UG-125(C)(3) shall be within -0%, +10%.

UG-135 InstallationA. Pressure relief devices for vapor appli-

cation shall be connected to the vesselin the vapor space above any containedliquid or to piping connected to the va-por space in the vessel which is to beprotected.

B. The opening through all pipe and fit-tings between a pressure vessel and itspressure relieving device shall have atleast the area of the pressure relievingdevice inlet, and the flow characteristicsof this upstream system shall be suchthat the pressure drop will not reducethe relieving capacity below that re-quired or adversely affect the properoperation of the pressure relieving de-vice. The opening in the vessel wallshall be designed to provide direct andunobstructed flow between the vessel

and its pressure relieving device. (SeeAppendix M.)

C. When two or more required pressurerelieving devices are placed on oneconnection, the inlet internal cross-sec-tional area of this connection shall beeither sized to avoid restricting flow tothe pressure relief devices or made atleast equal to the combined inlet areasof the safety devices connected to it.The flow characteristics of the up-stream system shall satisfy therequirements of (B) above. (SeeAppendix M.)

D. Pressure relief devices for liquid ser-vice applications shall be connectedbelow the normal liquid level.

E. There shall be no intervening stopvalves between the vessel and its pro-tective device or devices, or betweenthe protective device or devices and thepoint of discharge, except:

1. when these stop valves are so con-structed or positively controlled that theclosing of the maximum number ofblock valves possible at one time willnot reduce the pressure relieving ca-pacity provided by the unaffectedrelieving devices below the required re-lieving capacity; or

2. under conditions set forth in Appen-dix M.

F. The safety devices on all vessels shallbe so installed that their proper func-tioning will not be hindered by thenature of the vessel’s contents.

G.Discharge lines from pressure relievingsafety devices shall be designed to fa-cilitate drainage or shall be fitted withdrains to prevent liquid from lodging inthe discharge side of the safety device,and such lines shall lead to a safe placeof discharge. The size of the dischargelines shall be such that any pressurethat may exist or develop will not re-duce the relieving capacity of the


Notes

24. Set to operate means the set pressure of apressure relief valve or a spring loaded non-reclosing device; the bursting pressure of arupture disc device; or, the breaking pres-sure of a breaking pin device.



relieving devices below that required toproperly protect the vessel. [See UG-136(A)(8) and Appendix M.]

UG-136 Minimum Requirementsfor Pressure Relief ValvesA. Mechanical Requirements

1. The design shall incorporate guidingarrangements necessary to ensure con-sistent operation and tightness.

2. The spring shall be designed so thatthe full lift spring compression shall beno greater than 80% of the nominal sol-id deflection. The permanent set of thespring (defined as the difference be-tween the free height and heightmeasured 10 min after the spring hasbeen compressed solid three additionaltimes after presetting at room tempera-ture) shall not exceed 0.5% of the freeheight.

3. Each pressure relief valve on air, wa-ter over 140°F, or steam service shallhave a substantial lifting device whichwhen activated will release the seatingforce on the disk when the valve is sub-jected to a pressure of at least 75% ofthe set pressure of the valve. Pilot oper-ated pressure relief valves used onthese services shall be provided with ei-ther a lifting device as described aboveor means for connecting and applyingpressure to the pilot adequate to verifythat the moving parts critical to properoperation are free to move.

4. The seat of a pressure relief valveshall be fastened to the body of thevalve in such a way that there is nopossibility of the seat lifting.

5. In the design of the body of thevalve, consideration shall be given to minimizing the effects of deposits.

6. Valves having screwed inlet or outlet

connections shall be provided withwrenching surfaces to allow for normal installation without damaging operatingparts.

7. Means shall be provided in the design of all valves for use under thisDivision for sealing all initial adjust-ments which can be made withoutdisassembly of the valve. Seals shall beinstalled by the manufacturer or assem-bler at the time of initial adjustment.Seals shall be installed in a manner toprevent changing the adjustment with-out breaking the seal. For valves largerthan NPS 1/2, the seal shall serve as ameans of identifying the manufactureror assembler making the initial adjust-ment.

8. If the design of a pressure reliefvalve is such that liquid can collect onthe discharge side of the disk, the valveshall be equipped with a drain at thelowest point where liquid can collect (forinstallation, see UG-135).

9. For pressure relief valves of the di-aphragm type, the space above thediaphragm shall be vented to prevent abuildup of pressure above the di-aphragm. Pressure relief valves of thediaphragm type shall be designed sothat failure or deterioration of the di-aphragm material will not impair theability of the valve to relieve at the ratedcapacity.

B. Material Selections

1. Cast iron seats and disks are notpermitted.

2. Adjacent sliding surfaces such asguides and disks or disk holders shallboth be of corrosion resistant material.Springs of corrosion resistant materialor having a corrosion resistant coatingare required. The seats and disks ofpressure relief valves shall be of suit-able material to resist corrosion by the

fluid to be contained.25

3. Materials used in bodies and bonnetsor yokes shall be listed in Section Il andthis Division. Carbon and low alloy steelbodies, bonnets, yokes and bolting(UG-20) subject to in-service tempera-tures colder than -20°F shall meet therequirements of UCS-66, unless ex-empted by the following.

(a) The coincident Ratio defined inFig. UCS-66.1 is 0.4 or less

(b) The material(s) is exempted fromimpact testing per Fig. UCS-66.

4. Materials used in nozzles, disks, andother parts contained within the exter-nal structure of the pressure reliefvalves shall be one of the following cat-egories:

(a) listed in Section II;

(b) listed in ASTM Specifications;

(c) controlled by the manufacturer ofthe pressure relief valve by a specifica-tion insuring control of chemical andphysical properties and quality at leastequivalent to ASTM Standards.

C. Inspection of Manufacturing and/orAssembly of Pressure Relief Valves

1. A Manufacturer or assembler shalldemonstrate to the satisfaction of adesignated representative of the ASMEthat his manufacturing, production, andtesting facilities and quality control pro-cedures will insure close agreementbetween the performance of randomproduction samples and the perfor-mance of those valves submitted forCapacity Certification.

2. Manufacturing, assembly, inspection,and test operations including capacityare subject to inspections at any timeby an ASME designee.

3. The following schedule of tests ap-


Notes

25. The degree of corrosion resistance, appro-priate to the intended service, shall be amatter of agreement between the manufac-turer and the purchaser.



plies to production pressure reliefvalves certified under this Division, pro-duced, assembled, tested, sealed, andshipped by the Manufacturer and hav-ing a normal scope of size and capacitywithin the capability of ASME acceptedlaboratories. Production valves for ca-pacity and operational testing shall beselected by a designated representativeof the ASME and the testing shall becarried out in the presence of a repre-sentative of the same organization atan ASME accepted laboratory in accor-dance with the following.

(a) Initial capacity certification shall bevalid for 1-year during which time twoproduction valves shall be tested for|operation and stamped capacity verifi-cation. Should any of these valves failto relieve at or above its stamped capacity, or should it fail to meet perfor-mance requirements, the test shall berepeated at the rate of two valves foreach valve that failed. Initial capacityverification may be extended for 1-yearintervals until the valve is in production.Valves having an adjustable blowdownconstruction shall be adjusted by theManufacturer following successful test-ing for operation but prior to flow testingso that the blowdown does not exceed7% of the set pressure or 3 psi,whichever is greater. This adjustmentmay be made on the flow test facility.

(b) Thereafter, two valves shall betested within each 5-year period oftime. The valve manufacturer shall benotified of the time of the test and mayhave a witness present during the test.Should any of these valves fail to re-lieve at or above its stamped capacityor should it fail to meet performance re-quirements of this Division, the testshall be repeated at the rate of twovalves for each valve that failed. Valveshaving an adjustable blowdown con-struction shall be adjusted by themanufacturer following successful test-

ing for operation but prior to flow testingso that the blowdown does not exceed7% of the set pressure or 3 psi, whichev-er is greater. This adjustment may bemade on the flow test facility. Thesevalves shall be furnished by the manu-facturer or assembler. Failure of any ofthese valves to meet the stamped ca-pacity or the performance requirementsof this Division shall be cause for revoca-tion within 60 days of the authorization touse the Code Symbol on that particulartype of valve. During this period, themanufacturer shall demonstrate thecause of such deficiency and the actiontaken to guard against future occur-rence, and the requirements of (C)(3)(a)above shall apply.

4. An assembler may be granted per-mission to use a Code Symbol Stampafter demonstrating to the satisfactionof a designated representative of theASME that his quality control proce-dures will insure that the assembledvalves meet the requirements of thisDivision, including the following.

(a) Initially, two valves of each type orseries to which the Code stamp is to beapplied and which have been assem-bled, tested, and sealed by theassembler shall be selected by a desig-nated representative of the ASME andtested for operation and stamped ca-pacity verification. Should any valve failto relieve at or above its stamped ca-pacity, or should it fail to meetperformance requirements, the testshall be repeated at the rate of twovalves for each valve that failed. Valveshaving an adjustable blowdown con-struction shall be adjusted by theassembler following successful testingfor operation but prior to flow testing sothat the blowdown does not exceed 7%of the set pressure or 3 psi, whicheveris greater. This adjustment may bemade on the flow test facility.

(b) Thereafter, within each 5-year peri-od of time, two valves of each type orseries shall be selected by a designat-ed representative of the ASME andtested for operation and stamped ca-pacity verification. The assembler shallbe notified of the time of the test andmay have a witness present during thetest. Should any valve fail to relieve ator above its stamped capacity or shouldit fail to meet performance requirementsof this Division, the test shall be repeat-ed at the rate of two valves for eachvalve that failed. Valves having an ad-justable blowdown construction shall beadjusted by the manufacturer followingsuccessful testing for operation but pri-or to flow testing so that the blowdowndoes not exceed 7% of the set pressureor 3 psi, whichever is greater. This ad-justment may be made on the flow testfacility. These valves shall be furnishedby the assembler. Failure of any valveto meet the performance requirementsof this Division shall be cause for revo-cation within 60 days of the assembler’sauthorization to use the Code Symbolon that particular type or series ofvalve. During this period, the assemblershall demonstrate the cause of suchdeficiency and the action taken to guardagainst future occurrence.

(c) All tests shall be carried out in thepresence of a designated representa-tive of the ASME at an ASME acceptedlaboratory.

(d) Use of the Code Symbol Stamp by an assembler indicates the use oforiginal, unmodified parts in strict accor-dance with the instructions of themanufacturer of the valve.

(e) In addition to the requirements ofUG-129, the nameplate marking shallinclude the name of the manufacturerand the assembler. The Code SymbolStamp shall be that of the assembler.26


26. Within the requirements of UG-136(C) andUG-136(D): A manufacturer is defined as aperson or organization who is completelyresponsible for design material selection capacity certification, manufacture of allcomponent parts, assembly, testing, seal-ing, and shipping of pressure relief valves

certified under this Division. An assembler isdefined as a person or organization whopurchases or receives from a manufacturerthe necessary component parts or valvesand assembles, adjusts, tests, seals, andships pressure relief valves certified underthis Division, at a geographical location

other than and using facilities other thanthose used by the manufacturer. An assem-bler may be organizationally independent ofa manufacturer or may be wholly or partlyowned by a manufacturer.

Notes




D. Production Testing by Manufacturersand Assemblers

1. Each pressure relief valve to whichthe Code Symbol Stamp is to be appliedshall be subjected to the following testsby the manufacturer or assembler. Amanufacturer or assembler shall have adocumented program for the application,calibration, and maintenance of gaugesand instruments used during thesetests.

2. The primary pressure parts of eachvalve exceeding NPS 1 inlet size or 300psig set pressure where the materialsused are either cast or welded shall betested at a pressure of at least 1.5 timesthe design pressure of the parts. Thesetests shall be conducted after all ma-chining operations on the parts havebeen completed. There shall be no visi-ble sign of leakage.

3. The secondary pressure zone of eachclosed bonnet valve exceeding NPS 1inlet size when such valves are de-signed for discharge to a closed systemshall be tested with air or other gas at apressure of at least 30 psig. There shallbe no visible sign of leakage.

4. Each valve shall be tested to demon-strate its popping or set pressure. Valvesmarked for steam service or having spe-cial internal parts for steam service shallbe tested with steam, except that valvesbeyond the capability of the productionsteam test facility either because of sizeor set pressure may be tested on air.Necessary corrections for differentials inpopping pressure between steam and airshall be established by the manufacturerand applied to the popping point on air.Valves marked for gas or vapor may be

tested with air. Valves marked for liquidservice shall be tested with water or oth-er suitable liquid. Test fixtures and testdrums where applicable shall be of ade-quate size and capacity to ensure thatvalve action is consistent with thestamped set pressure within the toler-ances required by UG-134(E).

5. A seat tightness test shall be conduct-ed at a maximum expected operatingpressure, but at a pressure not exceed-ing the reseating pressure of the valve.When testing with either water or steam,a valve exhibiting no visible signs ofleakage shall be considered adequatelytight. Leakage tests conducted with airshall be in accordance with industry ac-cepted standards.

6. Testing time on steam valves shall besufficient, depending on size and de-sign, to insure that test results arerepeatable and representative of fieldperformance.

E. Design Requirements. At the time ofthe submission of valves for capacitycertification, or testing in accordancewith (C)(3) above, the ASME Designeehas the authority to review the designfor conformity with the requirements ofUG-136(A) and UG-136(B) and to re-ject or require modification of designswhich do not conform, prior to capacitytesting.

F. Welding and Other Requirements. Allwelding, brazing, heat treatment, andnondestructive examination used in theconstruction of bodies, bonnets, andyokes shall be performed in accordancewith the applicable requirements of thisDivision.



11.1The capacity of a safety or relief valve interms of a gas or vapor other than themedium for which the valve was officiallyrated shall be determined by application ofthe following formulas:1

For steam,

Ws = 51.5KAP

For air,–––––

MWa = CKAP –––√ T

C = 356

M = 28.97

T = 520 when Wa is the rated capacity

For any gas or vapor,–––––

MW = CKAP –––√ T

where:

Ws = rated capacity, lb/hr of steam

Wa = rated capacity, converted to lb/hr of air at 60°F, inlet temperature

W = flow of any gas or vapor, lb/hr

C = constant for gas or vapor which is a function of the ratio of specificheats, k = Cp/Cv (see Fig. 11-1)

K = coefficient of discharge [see UG-131(D) and (E)]

A = actual discharge area of the safetyvalve, in2

P = (set pressure x 1.10) plus atmos-pheric pressure, psia


T = absolute temperature at inlet (°F + 460)

These formulas may also be used whenthe required flow of any gas or vapor isknown and it is necessary to compute therated capacity of steam or air.

Molecular weights of some of the commongases and vapors are given in Table 11-1.

For hydrocarbon vapors, where the actualvalue of k is not known, the conservativevalue, k = 1.001 has been commonly usedand the formula becomes

––––– M

W = 315 KAP –––√ TWhen desired, as in the case of light hy-drocarbons, the compressibility factor Zmay be included in the formulas for gasesand vapors as follows:

––––– M

W = CKAP –––√ ZT

Example 1Given: A safety valve bears a certified ca-pacity rating of 3020 lb/hr of steam for apressure setting of 200 psi.

Problem: What is the relieving capacity ofthat valve in terms of air at 100°F for thesame pressure setting?

Solution:

For steam,

Ws = 51.5KAP

3020 = 51.5KAP

KAP =3020

= 58.551.5

For air,

––––– M

Wa = CKAP –––√ T–––––––––

28.97 = 356 KAP ––––––––√ 460 + 100

––––––– 28.97

= (356) (58.5) ––––––√ 560

= 4750 lb/hr

Example 2Given: It is required to relieve 5000 lb/hrof propane from a pressure vesselthrough a safety valve set to relieve at apressure of Ps, psi, and with an inlet tem-perature of 125°F.

Problem: What total capacity in pounds ofsteam per hour in safety valves must befurnished?

Solution:

For propane,

––––– M

W = CKAP –––√ T

The value of C is not definitely known.Use the conservative value, C = 315.

–––––––––––– 44.09

5000 = 315AP ––––––––√ 460 + 125KAP = 57.7

For steam,

Ws = 51.5 KAP = (51.5)(57.7)

= 2970 lb/hr set to relieve at Ps, psi

1. Knowing the official rating capacity of asafety valve which is stamped on the valve,it is possible to determine the overall valueof KA in either of the following formulas incases where the value of these individualterms is not known:

Official Rating in Steam:

KA =Ws

51.5P

Official Rating in Air:

––––– Wa T

KA = –––– –––CP √ M

This value for KA is then substituted in theabove formulas to determine the capacity of thesafety valve in terms of the new gas or vapor.

ASME Code Section VIII – Division I (1995 Addenda)Capacity Conversions For Safety Valves

Notes



Example 3Given: It is required to relieve 1000 lb/hr ofammonia from a pressure vessel at 150°F.

Problem: What is the required total capac-ity in pounds of steam per hour at thesame pressure setting?

Solution:

For ammonia,–––––

MW = CKAP –––√ T

Manufacturer and user agree to use k = 1.33; from Fig. 11-1, C = 350.

–––––––––– 17.03

1000 = 350 CKAP –––––––––√ 460 + 150

KAP = 17.10

For steam,

Ws = 51.5 KAP = 51.5 x 17.10

= 880 lb/hr

Example 4Given: A safety valve bearing a certifiedrating of 10,000 cu ft/min of air at 60°Fand 14.7 psia (atmospheric pressure).

Problem: What is the flow capacity of thissafety valve in pounds of saturated steamper hour for the same pressure setting?

Solution:

For air: Weight of dry air at 60°F and 14.7 psia is 0.0766 lb/cu ft.

Wa = 10,000 x 0.0766 x 60 = 45,960 lb/hr

–––––––– 28.97

45,960 = 356 KAP –––––––√460 + 60KAP = 546

For steam,2

Ws = 51.5 KAP = (51.5)(546)

= 28,200 lb/hr

k Constant k Constant C C

1.00 315 1.38 354

1.02 318 1.40 356

1.04 320 1.42 358

1.06 322 1.44 359

1.08 324 1.46 361

1.10 327 1.48 363

1.12 329 1.50 364

1.14 331 1.52 366

1.16 333 1.54 368

1.18 335 1.56 369

1.20 337 1.58 371

1.22 339 1.60 372

1.24 341 1.62 374

1.26 343 1.64 376

1.28 345 1.66 377

1.30 347 1.68 379

1.32 349 1.70 380

1.34 351 2.00 400

1.36 352 2.20 412

Notes

2. Before converting the capacity of a safetyvalve from any gas to steam, the require-ments of UG-131(B) must be met.

ASME Code Section VIII – Division I (1995 Addenda)Capacity Conversions For Safety Valves

Constant C for Gas or Vapor Related to Ratio of Specific Heats (k = Cp/Cv)

Figure 11-1

▲1.0

▲1.2

▲1.4

▲1.6

▲1.8

▲2.0

400

390

380

370

360

350

340

330

320

k

Cons

tant

, C

C = 520

Flow Formula Calculations

W = K (CAP M/T)

k 2k + 1

k + 1k - 1( (




Figure 11-2

Flow Capacity Curve for Rating Nozzle Type Safety Valves on SaturatedWater (Based on 10% Overpressure)

▲0

▲400

▲800

▲1200

▲1600

▲2000

▲2400

▲2800

▲3200

Saturated water

24

20

16

12

8

4

0

Set pressure, psig

Flo

w c

apac

ity

x 10

-4 (

lb/h

r/in

2 )

Table 11-1

Molecular Weights of Gases and Vapors

Air 28.97 Freon 22 86.48

Acetylene 26.04 Freon 114 170.90

Ammonia 17.03 Hydrogen 2.02

Butane 58.12 Hydrogen Sulfide 34.08

Carbon Dioxide 44.01 Methane 16.04

Chlorine 70.91 Methyl Chloride 50.48

Ethane 30.07 Nitrogen 28.02

Ethylene 28.05 Oxygen 32.00

Freon 11 137.371 Propane 44.09

Freon 12 120.9 Sulfur Dioxide 64.06

11.2A. Since it is realized that the saturated

water capacity is configuration sensi-tive, the following applies only to thosesafety valves that have a nozzle typeconstruction (throat to inlet diameter ra-tio of 0.25 to 0.80 with a continuously contouredchange and have exhibited a coefficientKD in excess of 0.90). No saturated wa-ter rating shall apply to other types ofconstruction.3

B. To determine the saturated water capacity of a valve currently rated under UG-131 and meeting the require-ments of (A) above, refer to Fig. 11-2.Enter the graph at the set pressure ofthe valve, move vertically upward to thesaturated water line and read horizontal-ly the relieving capacity. This capacity isthe theoretical, isentropic value arrivedat by assuming equilibrium flow andcalculated values for the critical pres-sure ratio.

Notes

3. The manufacturer, user, and inspector areall cautioned that for the following rating toapply, the valve shall be continuously sub-jected to saturated water. If, after initial reliefthe flow media changes to quality steam,the valve shall be rated as per dry saturatedsteam. Valves installed on vessels or linescontaining steam-water mixture shall be rated on dry saturated steam.



M-1IntroductionA. The rules in this Appendix are for gener-

al information only, because they pertainto the installation and operation of pres-sure vessels, which are the prerogativeand responsibility of the law enforce-ment authorities in those states andmunicipalities which have made provi-sion for the enforcement of Section VIII.

B. It is permissible to use any departuressuggested herein from provisions in themandatory parts of this Division whengranted by the authority having legal jurisdiction over the installation of pres-sure vessels.

M-2CorrosionA. Vessels subject to external corrosion

shall be so installed that there is suffi-cient access to all parts of the exteriorto permit proper inspection of the exte-rior, unless adequate protection againstcorrosion is provided or unless the ves-sel is of such size and is so connectedthat it may readily be removed from itspermanent location for inspection.

B. Vessels having manholes, handholes,or cover plates to permit inspection ofthe interior shall be so installed thatthese openings are accessible.

C. In vertical cylindrical vessels subject tocorrosion, to insure complete drainage,the bottom head, if dished, shouldpreferably be concave to pressure.

M-3Marking on the VesselThe marking required by this Division shallbe so located that it will be accessible afterinstallation and when installed shall not becovered with insulation or other material thatis not readily removable [see UG-116(J)].

M-4Pressure Relieving Safety DevicesThe general provisions for the installationof pressure relieving devices are fully cov-ered in UG-135. The following paragraphscontain details in arrangement of stopvalves for shutoff control of safety pres-

sure relief devices which are sometimesnecessary to the continuous operation ofprocessing equipment of such a complexnature that the shutdown of any part of itis not feasible. There are also rules withregard to the design of inlet and dischargepiping to and from safety and relief valves,which can only be general in nature be-cause the design engineer must fit thearrangement and proportions of such asystem to the particular requirements inthe operation of the equipment involved.

M-5Stop Valves Between PressureRelieving Device and VesselA. A vessel, in which pressure can be

generated because of service condi-tions, may have a full-area stop valvebetween it and its pressure relievingdevice for inspection and repair purpos-es only. When such a stop valve isprovided, it shall be so arranged that itcan be locked or sealed open, and itshall not be closed except by an autho-rized person who shall remain stationedthere during that period of the vessel’soperation within which the valve re-mains closed, and who shall again lockor seal the stop valve in the open posi-tion before leaving the station.

B. A vessel or system [see UG-133(C)] forwhich the pressure originates from anoutside source exclusively may haveindividual pressure relieving devices oneach vessel, or connected to any pointon the connecting piping, or on any oneof the vessels to be protected. Undersuch an arrangement, there may be astop valve between any vessel and thepressure relieving devices, and thisstop valve need not be locked open,provided it also closes off that vesselfrom the source of pressure.

M-6Stop Valves on the Discharge Sideof a Pressure Relieving Device[See UG-135(E)]A full-area stop valve may be placed onthe discharge side of a pressure relievingdevice when its discharge is connected toa common header with other discharge

lines from other pressure relieving deviceson nearby vessels that are in operation,so that this stop valve when closed willprevent a discharge from any connectedoperating vessels from backing up beyondthe valve so closed. Such a stop valveshall be so arranged that it can be lockedor sealed in either the open or closed po-sition, and it shall be locked or sealed ineither position only by an authorized per-son. When it is to be closed while thevessel is in operation, an authorized per-son shall be present, and he shall remainstationed there; he shall again lock or sealthe stop valve in the open position beforeleaving the station. Under no conditionshould this valve be closed while the ves-sel is in operation except when a stopvalve on the inlet side of the safety reliev-ing device is installed and is first closed.

M-7Inlet Pressure Drop for High Lift,Top Guided Safety, Safety Relief,and Pilot Operated Pressure ReliefValves in Compressible FluidServiceA. The nominal pipe size of all piping,

valves and fittings, and vessel compo-nents between a pressure vessel andits safety, safety relief, or pilot operatedpressure relief valves shall be at leastas large as the nominal size of the de-vice inlet, and the flow characteristicsof the upstream system shall be suchthat the cumulative total of all nonre-coverable inlet losses shall not exceed3% of the valve set pressure. The inletpressure losses will be based on thevalve nameplate capacity corrected forthe characteristics of the flowing fluid.

B. When two or more required safety, safe-ty relief, or pilot operated pressure reliefvalves are placed on one connection,the inlet internal cross-sectional area ofthis connection shall be either sized toavoid restricting flow to the pressure re-lief valves or made at least equal to thecombined inlet areas of the safetyvalves connected to it. The flow charac-teristics of the upstream system shallmeet the requirements of (A) above withall valves relieving simultaneously.

Appendix M Installation and Operation – ASME VIII Division I - (1995 Addenda)



M-8 Discharge Lines from Safety DevicesA. Where it is feasible, the use of a short

discharge pipe or vertical riser, connect-ed through long-radius elbows from eachindividual device, blowing directly to theatmosphere, is recommended. Such dis-charge pipes shall be at least of thesame size as the valve outlet. Where thenature of the discharge permits, tele-scopic (sometimes called ‘broken’)discharge lines, whereby condensed va-por in the discharge line, or rain, iscollected in a drip pan and piped to adrain, are recommended.1

B. When discharge lines are long, orwhere outlets of two or more valveshaving set pressures within a compara-ble range are connected into acommon line, the effect of the backpressure that may be developed there-in when certain valves operate must be considered [see UG-135(G)]. Thesizing of any section of a common-dis-charge header downstream from eachof the two or more pressure relievingdevices that may reasonably be ex-pected to discharge simultaneouslyshall be based on the total of their out-let areas, with due allowance for thepressure drop in all downstream sec-tions. Use of specially designed valvessuitable for use on high or variableback pressure service should be considered.

C. The flow characteristics of the dischargesystem of high lift, top guided safety, safe-ty relief, or pilot operated pressure reliefvalves in compressible fluid service shallbe such that the static pressure devel-oped at the discharge flange of aconventional direct spring loaded valvewill not exceed 10% of the set pressurewhen flowing at stamp capacity. Othervalve types exhibit various degrees of

tolerance to back pressure and the manu-facturer’s recommendation should befollowed.

D. All discharge lines shall be run as di-rect as is practicable to the point offinal release for disposal. For thelonger lines, due consideration shall begiven to the advantage of long-radiuselbows, avoidance of closeup fittings,and the minimizing of excessive linestrains by expansion joints and well-known means of support to minimizeline-sway and vibration under operatingconditions.

E. Provisions should be made in all cases for adequate drainage of dis-charge lines.2

M-9Pressure Drop, NonreclosingPressure Relief DevicesPiping, valves and fittings, and vesselcomponents comprising part of a non-reclosing device pressure relieving sys-tem shall be sized to prevent the vesselpressure from rising above the allowableoverpressure.

M-10General Advisory Information onthe Characteristics of Safety ReliefValves Discharging into a CommonHeaderBecause of the wide variety of types andkinds of safety relief valves, it is not con-sidered advisable to attempt a descriptionin this Appendix of the effects producedby discharging them into a commonheader. Several different types of valvesmay conceivably be connected into thesame discharge header and the effect ofback pressure on each type may be radi-cally different. Data compiled by themanufacturers of each type of valve used should be consulted for information

relative to its performance under the con-ditions anticipated.

M-11Pressure Differentials for PressureRelief ValvesDue to the variety of service conditionsand the various designs of safety andsafety relief valves, only general guidancecan be given regarding the differential be-tween the set pressure of the valve (seeUG-134) and the operating pressure ofthe vessel. Operating difficulty will be min-imized by providing an adequatedifferential for the application. The follow-ing is general advisory information on thecharacteristics of the intended service andof the safety or safety relief valves thatmay bear on the proper pressure differen-tial selection for a given application.These considerations should be reviewedearly in the system design since they maydictate the MAWP of the system.

A. Consideration of the ProcessCharacteristics in the Establishment ofthe Operating Margin to Be Provided.To minimize operational problems, it isimperative that the user consider notonly normal operating conditions of flu-ids, pressures, and temperatures, butalso start-up and shutdown conditions,process upsets, anticipated ambientconditions, instrument response times,pressure surges due to quick closingvalves, etc. When such conditions arenot considered, the pressure relievingdevice may become, in effect, a pres-sure controller, a duty for which it is notdesigned. Additional considerationshould be given to hazard and pollutionassociated with the release of the fluid.Larger differentials may be appropriatefor fluids which are toxic, corrosive, orexceptionally valuable.

1. This construction has the further advantageof not transmitting discharge-pipe strains tothe valve. In these types of installation, theback pressure effect will be negligible, andno undue influence upon normal valve oper-ation can result.

2. It is recognized that no simple rule can beapplied generally to fit the many installationrequirements, which vary from simple shortlines that discharge directly to the atmos-phere to the extensive manifold dischargepiping systems where the quantity and rateof the product to be disposed of requirespiping to a distant safe place.


Notes



B. Consideration of Safety Relief ValveCharacteristics. The blowdown charac-teristic and capability is the firstconsideration in selecting a compatiblevalve and operating margin. After aself-actuated release of pressure, thevalve must be capable of reclosingabove the normal operating pressure.For example, if the valve is set at 100psig with a 7% blowdown, it will closeat 93 psig. The operating pressuremust be maintained below 93 psig inorder to prevent leakage or flow from apartially open valve. Users should exer-cise caution regarding the blowdownadjustment of large spring-loadedvalves. Test facilities, whether ownedby Manufacturers, repair houses, orusers, may not have sufficient capacityto accurately verify the blowdown set-ting. The settings cannot be consideredaccurate unless made in the field onthe actual installation.

Pilot-operated valves represent a spe-cial case from the standpoints of bothblowdown and tightness. The pilot por-tion of some pilot-operating valves canbe set at blowdowns as short as 2%.This characteristic is not, however, re-flected in the operation of the mainvalve in all cases. The main valve canvary considerably from the pilot de-pending on the location of the twocomponents in the system. If the pilot isinstalled remotely from the main valve,significant time and pressure lags canoccur, but reseating of the pilot assuresreseating of the main valve. The pres-sure drop in the connecting pipingbetween the pilot and the main valvemust not be excessive; otherwise, theoperation of the main valve will be ad-versely affected.

The tightness of the main valve portionof these combinations is considerablyimproved above that of conventionalvalves by pressure loading the maindisk or by the use of soft seats or both.

Despite the apparent advantages of pi-lot-operated valves, users should beaware that they should not be em-ployed in abrasive or dirty service, inapplications, where coking, polymeriza-tion, or corrosion of the wetted pilot

parts can occur, or where freezing orcondensation of the lading fluid at ambi-ent temperatures is possible. For allapplications, the valve Manufacturershould be consulted prior to selecting avalve of this type.

Tightness capability is another factor af-fecting valve selection, whether springloaded or pilot operated. It variessomewhat depending on whether metalor resilient seats are specified, andalso on such factors as corrosion ortemperature. The required tightnessand test method should be specified tocomply at a pressure no lower than thenormal operating pressure of theprocess. A recommended procedureand acceptance standard is given inANSI B146.1. It should also be remem-bered that any degree of tightnessobtained should not be considered per-manent. Service operation of a valvealmost invariably reduces the degree oftightness.

Application of special designs such as O-rings or resilient seats should be re-viewed with the valve Manufacturer.

The anticipated behavior of the valves includes allowance for a plus-or-minus tolerance on set pressure which varieswith the pressure level. Installation conditions, such as back pressure, variations, and vibrations, influence selection of special types and an in-crease in differential pressure.

C. General Recommendations. The following pressure differentials are rec-ommended unless the safety or safetyrelief valve has been designed or test-ed in a specific or similar service and asmaller differential has been recom-mended by the Manufacturer.

A minimum difference of 5 psi is recom-mended for set pressures to 70 psi. Inthis category, the set pressure toler-ance is ±2 psi [UG-134(D)(1)], and thedifferential to the leak test pressure is10% or 5 psi, whichever is greater.

A minimum differential of 10% is recom-mended for set pressures from 71 psi to 1000 psi. In this category, the setpressure tolerance is ±3% and the dif-

ferential to the leak test pressure is 10%.

A minimum differential of 7% is recom-mended for set pressures above 1000psi. In this category, the set pressure tolerance is ±3% and the differential tothe leak test pressure should be 5%.Valves having small seat sizes will re-quire additional maintenance when thepressure differential approaches theserecommendations.

M-12Installation of Safety and SafetyRelief ValvesSpring loaded safety and safety reliefvalves normally should be installed in theupright position with the spindle vertical.Where space or piping configuration pre-clude such an installation, the valve maybe installed in other than the vertical posi-tion provided that:

A. the valve design is satisfactory for suchposition;

B. the media is such that material will notaccumulate at the inlet of the valve; and

C. drainage of the discharge side of thevalve body and discharge piping is ad-equate.

M-13Reaction Forces and ExternallyApplied LoadsA. Reaction Thrust. The discharge of a

pressure relief valve imposes reactiveflow forces on the valve and associatedpiping. The design of the installationmay require computation of the bend-ing moments and stresses in the pipingand vessel nozzle. There are momen-tum effects and pressure effects atsteady state flow as well as transientdynamic loads caused by opening.

B. External Loads. Mechanical forces maybe applied to the valve by dischargepiping as a result of thermal expansion,movement away from anchors, andweight of any unsupported piping. Theresultant bending moments on a closedpressure relief valve may cause valveleakage and excessive stress in inletpiping. The design of the installationshould consider these possibilities.




M-14Sizing of Pressure Relief Devicesfor Fire ConditionsA. Excessive pressure may develop in

pressure vessels by vaporization of theliquid contents and/or expansion of va-por content due to heat influx from thesurroundings, particularly from a fire.Pressure relief systems for fire condi-tions are usually intended to releaseonly the quantity of product necessaryto lower the pressure to a predeter-mined safe level, without releasing anexcessive quantity. This control is espe-cially important in situations whererelease of the contents generates ahazard because of flammability or toxi-city. Under fire conditions,consideration must also be given to thepossibility that the safe pressure levelfor the vessel will be reduced due toheating of the vessel material, with acorresponding loss of strength.

B. Several formulas have evolved over theyears for calculating the pressure reliefcapacity required under fire conditions.The major differences involve heat fluxrates. There is no single formula yetdeveloped which takes into account allof the many factors which could beconsidered in making this determina-

tion. When fire conditions are a consid-eration in the design of a pressurevessel, the following references whichprovide recommendations for specificinstallations may be used:

API RP 520, Recommended Practicefor the Design and Installation ofPressure-Relieving Systems inRefineries, Part I– Design, 1976,American Petroleum Institute,Washington, DC

API Standard 2000, Venting Atmos-pheric and Low Pressure Storage Tanks(nonrefrigerated and refrigerated),1973, American Petroleum Institute,Washington, DC

AAR Standard M-1002, Specificationsfor Tank Cars, 1978, Association ofAmerican Railroads, Washington, DC

Safety Relief Device Standards: S-1.1,Cylinders for Compressed Gases; S-1.2,Cargo and Portable Tanks; and S-1.3,Compressed Gas Storage Containers.Compressed Gas Association, New York

NFPA Code Nos. 30, 59, and 59A, NationalFire Protection Association, Boston, MA

Pressure-Relieving Systems for MarineCargo Bulk Liquid Containers, 1973,

National Academy of Sciences,Washington, DC

Bulletin E-2, How to Size Safety ReliefDevices, Phillips Petroleum Company,Bartlesville, OK

A Study of Available Fire Test Data asRelated to Tank Car Safety DeviceRelieving Capacity Formulas, 1971,Phillips Petroleum Company, Bartlesville, OK

M-15Pressure Indicating DeviceIf a pressure indicating device is providedto determine the vessel pressure at ornear the set pressure of the relief device,one should be selected that spans the setpressure of the relief device and is gradu-ated with an upper limit that is neither lessthan 1.25 times the set pressure of the re-lief device nor more than twice themaximum allowable working pressure ofthe vessel. Additional devices may be in-stalled if desired.




Following is an Excerpt from API - RP 520



Section 2 – Pressure Relief Devices

2.1 GeneralThis section describes the basic princi-ples, operational characteristics,applications, and selection of pressure relief devices used independently or incombination. These devices includespring-loaded and pilot-operated pressurerelief valves, rupture disk devices, andother pressure relief devices. These de-vices are described in the text andillustrated in Figures 2-17.

2.2 Spring-Loaded Pressure ReliefValves

2.2.1 Safety ValvesSafety valves are spring-loaded pressurerelief devices designed to provide fullopening with minimum overpressure. Staticpressure retained in the huddling chamberand the kinetic energy of the gas or vaporare utilized to overcome the spring force onthe disc as it lifts, resulting in pop action.The closing pressure will be at a point be-low the set pressure and will be reachedafter the blowdown phase is completed.

2.2.2 Relief ValvesRelief valves are spring-loaded pressurerelief devices designed for use in liquidservice. At set pressure, the inlet pressureforce overcomes the spring force and thedisc begins to lift off the seat. As inletpressure increases, the disk lift increasesto allow an increase in the flow. The clos-ing pressure will be at a point below theset pressure and will be reached after theblowdown phase is completed. Reliefvalve capacities are usually rated at 10 or 25% overpressure, depending on theapplication.

2.2.3 Safety Relief ValvesSafety relief valves are spring-loaded pres-sure relief devices that provide thecharacteristics of a safety valve when usedin gas or vapor service and the character-istics of a relief valve when used in liquidservice. Safety relief valves are generallyprovided with bonnets that enclose thespring and provide a pressure-tight hous-ing for use in conventional or balancedtypes, depending on the effect of backpressure on their performance.

2.2.4 Pressure Relief Valves2.2.4.1 Conventional Pressure Relief ValvesConventional pressure relief valves areused when the discharge is through ashort tail pipe that vents to the atmosphereor through a low-pressure manifold systemthat carries the discharged fluid of one ormore valves to a remote location for dis-posal. Normally, the spring force is thedifferential between the set pressure andatmospheric pressure. The set pressurewill therefore be increased by superim-posed back pressure unless the springforce is adjusted accordingly. Built-up back pressure may also affect valve performance; therefore, the impact ofdownstream pressure when one or morevalves discharge into a common manifoldshould be determined by referring to theappropriate manufacturer’s catalog.

The interaction of the forces within thevalve and the effects of back pressure onthe opening are illustrated in Figure 18.Available conventional pressure reliefvalves have disks that have a greater diskarea, AD, than the nozzle seat area, AN. If the spring bonnet is vented to the at-mosphere, the back pressure acts withthe vessel pressure to overcome thespring force. This condition makes theopening pressure less than it is when thevalve is set with atmospheric pressure onits discharge; however, if the spring bon-net is vented to the valve dischargeinstead of to the atmosphere, the backpressure acts with the spring force to in-crease the opening pressure. Variation inthe superimposed back pressure will di-rectly affect the opening pressure andshould be evaluated in system design.

Conventional pressure relief valves, asnormally installed, show unsatisfactoryperformance when excessive built-upback pressure develops from the flowthrough valve and piping as a result of thesame unbalanced forces that affect theset pressure. Performance data observedduring the investigation of the built-upback pressure problem are shown inFigure 19. The information is plotted asthe ratio of the valve capacity at any givenbuilt-up back pressure to the valve capaci-ty without built-up back pressure versusthe ratio of the built-up back pressure to

the valve set pressure. The capacity curveis the result of the balance of forces actingon the disk. As long as the built-up backpressure is less than the overpressure af-ter the valve opens, the valve will remainopen and perform satisfactorily underflowing conditions, and it will have flowcharacteristics that are basically similar tothose in a theoretical nozzle performance.If, however, the built-up back pressure isincreased at a greater rate than the over-pressure, the balance of forces will tend toclose the valve, which can become unsta-ble and cause the flow to fall off rapidly.This instability is caused by a dynamicpressure imbalance or a harmonic reso-nance. The valve may start to flutter orchatter.

Flutter refers to the abnormally rapid reciprocating motion of the movable partsof a pressure relief valve in which the diskdoes not contact the seat. Chatter refersto the motion that causes the disk to con-tact the seat and damage the valve andassociated piping. The allowable built-upback pressure must therefore be consid-ered for each amount of overpressureused.

Conventional pressure relief valvesshould typically not be used when thebuilt-up back pressure is greater than10% of the set pressure at 10% overpres-sure. A higher maximum allowable built-upback pressure may be used for overpres-sure greater than 10%. The combinedeffect of the superimposed and built-upback pressures on the performance char-acteristics of the valves must beconsidered when more than one pressurerelief valve discharges into a commonmanifold at the same time.

The theoretical performance for a nozzleis plotted in Figure 20. The curve repre-sents the maximum theoretical flowattainable for any ideal gas that has thespecific heat ratio of K = 1.3. The theoreti-cal nozzle maintains flow capacity up tothe critical flow pressure and then gradu-ally diminishes to zero.

The theoretical rate of flow through thenozzle depends on the absolute upstreampressure and is independent of the down-stream pressure when the back pressureis less than the critical flow pressure;

API - RP 520 Part I (July 1991) - Sizing, SelectionExcerpts from API - 520 Part I Sizing, Selection, and Installation of Pressure Relieving Devices in Refineries



Figure 1 – Pressure-Level Relationships for Pressure Relief ValvesNotes

1. This figure conforms with the requirementsof Section VIII of the ASME Boiler andPressure Vessel Code.

2. The pressure conditions shown are forpressure relief valves installed on a pres-sure vessel.

3. Allowable set-pressure tolerances will bein accordance with the applicable codes.

4. The maximum allowable working pressureis equal to or greater than the design pres-sure for a coincident design temperature.

5. The operating pressure may be higher orlower than 90.

6. Section VIII, Division 1, Appendix M, of theASME Code should be referred to for guid-ance on blowdown and pressuredifferentials.

API - RP 520 Part I (July 1991) - Sizing, SelectionExcerpts from API - 520 Part I Sizing, Selection, and Installation ofPressure Relieving Devices in Refineries

Pressure Vessel Requirements VesselPressure

Typical Characteristics ofPressure Relief Valves

Maximum allowable accumulated

pressure (fire exposure only)

Maximum allowable accumulated pressure for multiple-valve installation (other than fire exposure)

Maximum allowable accumulated pressure for

single-valve installation (other than fire exposure)

Maximum allowableaccumulated pressure for

design pressure

Maximum expectedoperating pressure

(See Notes 5 and 6)

Leak test pressure (typical)

121

120

116

115

110

105

100

95

90

85

Perc

ent o

f max

imum

allo

wab

le w

orki

ng p

ress

ure

(gau

ge)

Closing pressurefor a single valve

Blowdown (typical)(see Note 6)

Start to open

Maximum allowable set pressure for single valveSimmer

(typical)

Maximum allowable set pressure for additional valves (process)

Overpressure (maximum)

Maximum allowable set pressurefor supplemental valves (fire exposure)

Single valve maximum relievingpressure for process sizing

Multiple valves maximum relieving pressure for process sizing

Maximum relievingpressure for fire sizing



Figure 2 – Conventional SafetyRelief Valve With a Single Adjust-ing Ring for Blowdown Control

Figure 3 – Balanced-Bellows SafetyRelief Valve1

Figure 4 – Balanced-BellowsSafety Relief Valve With anAuxiliary Balanced Piston

Figure 5 – Thermal Relief (Liquid Relief Valve)


Cap

Stem(spindle)

AdjustingScrew

Spring

Bonnet

SeatingSurface

Disk

AdjustingRingBody

Nozzle

Cap

Stem(spindle)

AdjustingScrew

Spring

Bonnet

Bellows

SeatingSurface

Disk

AdjustingRingBody

Nozzle

Vent

Cap

AdjustingScrew

Spring

Bonnet

SeatingSurface

Disk

Base,Body

Stem(spindle)

Cap

Stem(spindle)

AdjustingScrew

Spring

Bonnet

Bellows

SeatingSurface

Disk

AdjustingRing

Body

Nozzle

Vent

BalancedPiston

Note

1. For corrosion isolation, an unbalanced-bellows safety relief valve is available.



however, when the back pressure is in-creased beyond the critical flow pressure,the flow is reduced. (See 4.3 for informa-tion about the sizing of pressure reliefvalves for critical and subcritical flow.)

2.2.4.2 Balanced Pressure Relief ValvesThe design of balanced pressure reliefvalves incorporates means for reducingthe effect of back pressure on the setpressure and for minimizing the effect ofbuilt-up back pressure on performancecharacteristics such as opening and clos-ing pressure, lift, and relieving capacity(see Section 4). Balanced valves are oftwo basic types: the piston and the bel-lows (see Figure 21).

Several variations of the piston valve aremanufactured. The guide on the piston isvented so that the back pressure on opposing faces of the valve disk is can-celled. The top face of the piston has anarea, Ap, the same as the nozzle seatarea, AN, and is subjected to atmosphericpressure by venting the spring bonnet.The vented gas from the bonnets of bal-anced piston valves should be disposed ofsafely and with minimum restrictions.

The effective bellows area, AB, of bellowsvalves is the same as the nozzle seatarea, AN. The arrangement of the bellowsin the valve prevents the back pressurefrom acting on the top side of the diskwithin the effective bellows area, AB. Thedisk area, AD, extending beyond the bel-lows and the opposing nozzle seat areacancel the effect of the back pressure onthe valve disk so that there are no unbal-anced forces under any downstreampressure variations. The bellows addition-ally serves to isolate the disk guide,spring, and other top works parts from thelading fluid. This feature may be importantif the lading fluid is corrosive or may foulthe pressure relief valve. Because ofphysical size limitations, balanced bellowsare not available in certain valve designsand sizes. If balanced bellows are notavailable, unbalanced bellows valves maybe specified when corrosion isolationalone is intended.

The balanced pressure relief valve makespossible higher pressures in the relief dis-charge manifolds. Both balanced valvesshown in Figure 21 should have bonnetvents large enough to ensure that no

Figure 6 – Pop Action Pilot Operated Valve (Flowing Type)

Figure 7 – Pop Action Pilot Operated Valve (Nonflowing Type)


Set PressureAdjusting Screw

Outlet

PilotExhaust

SeatingSurface

MainValve

Spindle

Pilot SupplyLine

ExternalBlowdownAdjustment

OptionalPilot

Piston

Seat

Inlet

InternalPressurePickup

Spindle

Outlet

Remote PressurePickup (optional)

Optional PilotFilter

Main Valve

Relief Seat

Reseat Seat

Piston

Seat

Inlet

Pilot-to-Dome Connection

Backflow Preventor

Spacer Rod

Piston

PilotExhaust



appreciable back pressure exists duringflow conditions. If the valve is locatedwhere atmospheric venting (usually not alarge amount) would present a hazard,the vent should be piped to a safe locationthat is independent of the valve dischargesystem.

2.2.4.3 Valve CharacteristicsFigure 22 shows the disk travel from theset pressure, A, to the maximum relievingpressure, B, during the overpressure inci-dent and to the closing pressure, C,during the blowdown.

2.3 Pilot Operated Pressure ReliefValvesThe two basic types of pilot operatedpressure relief valves are the piston typeand the diaphragm type.

The piston type valve consists of the mainvalve, which encloses a floating piston,and an external pilot valve (see Figures 6-9). The piston is designed to have a largereffective area on the top than on the bot-tom. Up to the set pressure, the top andbottom areas are exposed to the same in-let operating pressure. Because of thelarger effective area on the top of the pis-ton, the net force holds the piston tightly tothe main valve seat. As the operating pres-sure increases, the net seating forceincreases and tends to make the valvetighter. At the set point, the pilot vents thepressure from the top of the piston; the re-sulting net force unseats the piston, andprocess flow is established through themain valve. After the overpressure inci-dent, the pilot will close the vent from thetop of the piston, thereby re-establishingpressure, and the net force will cause thepiston to reseat.

The diaphragm type pilot operated reliefvalve is similar to the piston type exceptthat the piston is replaced by a flexible diaphragm and disk. The diaphragm pro-vides the unbalance function of the piston.The disk, which normally closes the mainvalve inlet, is integral with a flexible di-aphragm (see Figure 10). The externalpilot valve serves the same function tosense process pressure, vent the top of

Figure 8 – Modulating Pilot Operated Valve (Flowing Type)

Figure 9 – Pilot Operated Relief Valve With A Non-flowing Modulating Pilot Valve


Spindle

Piston

Internal Pressure PickupMain Valve

Optional Pilot Filter

Sensitivity Adjustment

Outlet

Inlet

Sense Chamber

Sense Diaphragm

Pilot Supply Line

Seat

Seat

Vent Valve

Filter

Piston

Internal Pressure Pickup

Main Valve

SeatInlet Valve

Test Connection

Outlet

Inlet



the diaphragm at set pressure, and reloadthe diaphragm once the process pressure returns to normal. As with the piston valve,the seating force increases proportionallywith the operating pressure because ofthe differential exposed area of the diaphragm.

The pilot valve that operates the mainvalve can be either a pop action or modu-lating action pilot. Figure 23 shows theaction of the pop pilot; it shows that pilotoperation causes the main valve to lift ful-ly. Figure 24 shows the action of themodulating pilot; it shows that pilot opera-tion opens the main valve only enough tosatisfy the required relieving capacity.

The pilots may be either a flowing or non-flowing type. The flowing type allowsprocess fluid to flow through the pilotwhen the main valve is open; the nonflow-ing type does not. The user should consultthe manufacturer to determine the advan-tages and disadvantages of either type.

A backflow preventor is required when thepossibility exists of developing a pressureon the discharge side of the valve that ex-ceeds the inlet pressure of the valve. Thedifferential area will cause the piston to lift,and flow in the valve will be reversed (seeFigure 7).

Pilot-operated relief valves are availablefor use in liquid and vapor services. Sincethe main valve and pilot contain nonmetal-lic components, process temperature andfluid compatibility can limit their use. In ad-dition, fluid characteristics such assusceptibility to polymerization or fouling,viscosity, the presence of solids, and cor-rosiveness may affect pilot reliability. Themanufacturer should be consulted to en-sure that the proposed application iscompatible with available valves.

2.4 Rupture Disk DevicesThe remainder of Section 2 provides defi-nitions, descriptions, and operationalcharacteristics of rupture disk devices.Specific terms and uses are covered with-in the applicable sections of text andaccompanying illustrations (see Figures11-17).

Spring Bonnet Vented To Atmosphere Spring Bonnet Vented To ValveDischarge

Back Pressure Decreases Set Pressure Back Pressure Increases Set Pressure

PVAN = FS-PB (AD-AN)

AD>ANAD = disk area.AN = nozzle seat area.FS = spring force.PV = vessel pressure in pounds per square inch gauge.PB = superimposed back pressure, in pounds per square in gauge.

PVAN = FS+PBAN

Figure 10 – Low-Pressure Pilot Operated Valve (Diaphragm Type)

Figure 18 – Typical Effects of Superimposed Back Pressure on theOpening Pressure of Conventional Pressure Relief Valves


VentedSpring-Bonnet

Disk

Spr

ing

PB PB

PV

PB

Fs

Spring-Bonnet

Disk

PB PB

PB PB

PV

PB

Spr

ing

Fs

Piston Vent

Ap = AN

DiskGuide

Boost Diaphragm

Spindle Seat Diaphragm

Optional Pilot Filter

Variable Orifice

Main Valve Diaphragm

Main Valve Seat

Sense DiaphragmSet Spring

Adjustment Spring

Sense Cavity

Boost Cavity

Inlet

Outlet

Internal Pressure Pickup

Dome

Pilot Exhaust



Conventional pressure relief valve with spring bon-net vented to valve discharge

C1 = capacity with back pressureC2 = capacity with zero back pressureP´ = built-up back pressurePS = set pressure

Figure 19 – Typical Effects of Built-up Back Pressure on the Capacityof Conventional Pressure ReliefValves

Figure 21 – Typical Effects of Back Pressure on the Set Pressure ofBalanced Pressure Relief Valves

Balanced Disk and Vented Piston Type Balanced Disk and Vented Bellows Type

AB = effective bellows areaAD = disk areaAN = nozzle seat areaAP = piston area (top)FS = spring forcePV = vessel gauge pressure

PB = superimposed back pressure in poundsper square inch gauge

PS = set pressure, in pounds per square inchgauge

Note: In this figure, PV = PS; (PV)(AN) = FS (typical); and PS = FS/AN.

100

90

80

70

60

50

40

30

Valve(stable)

Valve(flutter chatter)

P´ less thanoverpressure

P´greater thanoverpressure

Per

cen

t (C

1/C

2) x

100

P´PS

C1 = capacity with backpressure

C2 = capacity with zeroback pressure

PB = back pressure, inpounds per squareinch absolute

PS = set pressure, inpounds per squareinch absolute

PO = overpressure, inpounds per squareinch

Figure 20 – Theoretical Performance for a Nozzle Discharging a Gas ThatHas a Specific Heat Ratio of 1.3


Spring-Bonnet Vent

Disk

Pis

ton

PB PB

PB PB

PV

PB

Fs

Piston Vent

Vent

Ap = AN

Disk

PV

PB

Fs

AB = AN

Spring-Bonnet Vent

Bellows Vent

VentedBellows

▲

0▲

10▲

20▲

30▲

40▲

50▲

60▲

70▲

80▲

90▲

100

100

90

80

70

60

50

40

30

20

10

0

Theoretical nozzle flow

Percent =PB

PS + PO

x 100

Per

cen

t (C

1/C2)

x 1

00



Figure 22 – Typical RelationshipBetween Lift of Disk in a PressureRelief Valve and Vessel Pressure

Figure 24 – Typical RelationshipBetween Lift of Disk in aModulating-Action Pilot OperatedRelief Valve and Vessel Pressure

Figure 23 – Typical RelationshipBetween Lift of Disk in a Pop-Action Pilot Operated Relief Valveand Vessel Pressure


100

0Blowdown Overpressure

Lift

of d

isk,

per

cent

B

Closing Setpressure

Maximumrelievingpressure

100

0Blowdown Overpressure

Lift

of d

isk,

per

cent

Closing


Setpressure

Closing

0

100

Blowdown Overpressure

Lift

of d

isk,

per

cent


Setpressure



4.1 Determination of ReliefRequirementsTo establish the size of a pressure reliefdevice for any application, the designermust first determine the conditions forwhich overpressure protection may be required. Reasonable care should be exercised in establishing the various contingencies that could result in over-pressure.

The contingencies that may cause over-pressure must be evaluated in terms ofthe pressures generated and the rates atwhich fluids must be relieved. Theprocess flow diagram, material balance,piping and instrument diagrams, equip-ment specification sheets, and designbasis for the facility are needed to calcu-late the individual relieving rates for eachpressure relieving device. Process equip-ment vendor data is also helpful ifavailable.

Appendix D provides relieving flow ratesfor fire conditions. Table 1 lists a numberof common operational conditions forwhich overpressure protection may be re-quired. This list is by no means complete;each plant may have unique features thatmust be considered in addition to thoselisted in Table 1. (See API RecommendedPractice 521 for a detailed discussion ofrelief requirements.)

Pressure relief valves may be sized usingthe equations presented in 4.3 through 4.5as appropriate for vapors, gases, or liq-uids. These equations are used to

calculate the effective nozzle area neces-sary to achieve a required flow ratethrough the valve. A valve is then chosenfor the application that has an effectivearea equal to or greater than the calculat-ed required effective area.

The effective areas and assumed dis-charge coefficient, Kd = 0.975, aregenerally different from actual orifice areas and discharge coefficients that areused to determine certified valve capaci-ties. However, effective areas calculatedusing the equations in 4.3 through 4.5 willresult in the selection of valves with certi-fied capacities that equal or exceed therequired capacities.

The effective-area concept allows for theselection of valve size independent of themanufacturer. Standard effective orificeareas and corresponding letter designa-tions may be found in API Standard 526.

4.2 Relieving Pressure

4.2.1 GeneralRelieving pressure, shown in P1 in thevarious sizing equations, is the inlet pres-sure of the relief device at relievingconditions. The relieving pressure is thetotal of set pressure plus overpressureplus atmospheric pressure. The examplescited in this section for the determinationof relieving pressure refer to pressure re-lief valves; however, they are alsoapplicable to rupture disk devices. (SeeFigures 1 and 25 for pressure-level rela-tionships for these types of devices.)

The allowable overpressure is establishedfrom the accumulation permitted by theapplicable code. The allowable overpres-sure may vary for different applicationsdepending on the relationship of the setpressure to the maximum allowable work-ing pressure of the vessel or system thatis protected. Allowable overpressure is thesame as allowable accumulation onlywhen the set pressure is equal to themaximum allowable working pressure.1

Sections 4.2.2 through 4.2.4 discuss meth-ods of determining the relieving pressurefor pressure relief valves in gas and vaporservice. Standard atmospheric pressure(14.7 pounds per square inch absolute) isused for gauge/absolute pressure conver-sion in these sections. For design,barometric pressure corresponding to siteelevation should be used.

Relieving pressure for pressure reliefvalves in liquid service is determined in amanner similar to that used for vapor ser-vice except that the relieving pressure isexpressed in gauge rather than absoluteunits. In the case of ASME-application liquid service valves (that is, for the pro-tection of a liquid-full vessel), maximumaccumulated pressure is limited to 110%of the maximum allowable working pres-sure for operating contingencies – thesame constraint as for vapor service. Inthe case of non-ASME-application liquidservice valves (that is, for protection ofpiping without vessels included), 25%overpressure is generally specified.

Notes

1. The discussion in this section generallycites the ASME Code as the applicablecode. Unless stated otherwise, citations refer only to Section VIII of the ASMECode.The designer should be aware of revisions to the ASME Code. If pertinent revisions occur, the discussion in this sec-tion should be adjusted accordingly by the designer. Adjustments may also be re-quired by the designer if other (non-ASME)codes apply.




Table 2 summarizes the maximum accu-mulation and set pressure for pressurerelief valves specified in accordance withthe ASME Code.

4.2.2 Operating Contingencies4.2.2.1 Single-Valve InstallationIn accordance with the requirements ofthe ASME Code, accumulated pressureshall be limited to 110% of the maximumallowable working pressure in vessels thatare protected by a single pressure reliefvalve sized for operating (nonfire) contin-gencies. The set pressure of the valveshall not exceed the maximum allowableworking pressure.2

Table 3 shows an example determinationof relieving pressure for a single valvewhose set pressure is less than or equalto the vessel’s maximum allowable work-ing pressure.

4.2.2.2 Multiple-Valve InstallationA multiple-valve installation requires thecombined capacity of two or more pres-sure relief valves to alleviate a givenoverpressure contingency.

In accordance with the requirements ofthe ASME Code, accumulated pressureshall be limited to 116% of the maximumallowable working pressure in vessels thatare protected by multiple valves sized foroperating (nonfire) contingencies. The setpressure of the first valve shall not exceedthe maximum allowable working pressure.The set pressure of the additional valve orvalves shall not exceed 105% of the maxi-mum allowable working pressure.3

Table 4 shows an example determinationof relieving pressure for a multiple-valveinstallation in which the set pressure ofthe first valve is equal to the maximum al-lowable working pressure of the vessel,and the set pressure of the additionalvalve is 105% of the vessel’s maximum al-lowable working pressure.

4.2.3 Fire Contingencies4.2.3.1 GeneralIn accordance with the requirements of theASME Code, accumulated pressure shallbe limited to 121% of the maximum allow-able working pressure in vessels that areprotected by valves sized for fire contin-gencies. This applies to single-, multiple-,and supplemental-valve installations.

Single or multiple valves sized for fire mayalso be utilized for relieving requirementsattributed to secondary operating (nonfire)contingencies, if applicable, provided thatthe constraint of 110% (of the maximumallowable working pressure) accumulatedpressure for nonfire contingencies is ob-served.

4.2.3.2 Single-Valve InstallationWhere a vessel is protected by a singlevalve sized for fire, the set pressure shallnot exceed the maximum allowable work-ing pressure.

Table 5 shows an example determinationof relieving pressure for a single valvewhose set pressure is less than or equalto the vessel’s maximum allowable work-ing pressure.

4.2.3.3 Multiple-Valve InstallationA multiple-valve installation requires thecombined capacity of two or more valvesto alleviate overpressure from a fire. Theset pressure of the first valve to open shallnot exceed the maximum allowable work-ing pressure. The set pressure of the lastvalve to open shall not exceed 105% ofthe maximum allowable working pressure.

Table 6 shows an example determinationof relieving pressure for a multiple-valveinstallation in which the set pressure ofthe first valve is equal to the vessel’s maximum allowable working pressure,and the set pressure of the additionalvalve is 105% of the vessel’s maximum allowable working pressure.

4.2.3.4 Supplemental-Valve InstallationA supplemental-valve installation providesrelieving capacity for an additional hazardcreated by exposure to fire or other unex-pected sources of external heat. The setpressure of a supplemental valve for fireshall not exceed 110% of the maximum al-lowable working pressure.

Supplemental valves are used only in addition to valves sized for operating(nonfire) contingencies.

Table 7 shows an example determination ofrelieving pressure for a supplemental-valveinstallation in which the set pressure of thefirst (nonfire) valve does not exceed thevessel’s maximum allowable working pres-sure (see 4.2.1 for determination ofrelieving pressure), and the set pressure ofthe supplemental valve in 110% of the ves-sel’s maximum allowable working pressure.


Table 2

Set Pressure and Accumulation Limits for Pressure Relief Valves4

Contingency Single-Valve Installations Multiple-Valve Installations

Set Maximum Set MaximumPressure Accumulated Pressure Accumulated(percent) Pressure (percent) Pressure

(percent) (percent)

Nonfire only

First Valve 100 110 100 116

Additional Valve(s) – – 105 116

Fire only

First Valve 100 121 100 121

Additional valve(s) – – 105 121

Supplemental valve – – 110 121

Notes

2. Allowable accumulation is 3 pounds persquare inch when the maximum allowableworking pressure is between 15 and 30pounds per square inch gauge.

3. Allowable accumulation is 4 pounds persquare inch when the maximum allowableworking pressure is between 15 and 25pounds per square inch gauge.

4. All values are percentages of the maximum allowable working pressure.



Table 3

Example Determination ofRelieving Pressure for a SingleValve (Operating Contingencies)

Characteristic Value

Valve Set Pressure Less Than MAWP

Protected vessel MAWP, psig 100

Maximum accumulated pressure, psig 110

Valve set pressure, psig 90

Allowable overpressure, psig 20

Relieving pressure, P1, psia 124.7

Valve Set Equal to MAWP




Allowable overpressure, psi 10


Table 6

Example Determination ofRelieving Pressure for a Multiple-Valve Installation (FireContingencies)


First Valve (Set Pressure Equal to MAWP)






Additional Valve (Set Pressure Equal to 105% of MAWP)






Table 4

Example Determination ofRelieving Pressure for a Multiple-Valve Installation (OperatingContingencies)


First Valve (Set Pressure Equal to MAWP)






Additional Valve (Set Pressure Equal to 105% of MAWP)






Table 7

Example Determination ofRelieving Pressure for aSupplemental Valve (FireContingencies)


Supplemental Valve (Set Pressure Equal to110% of MAWP)






Table 5

Example Determination ofRelieving Pressure for a SingleValve (Fire Contingencies)


Valve Set Pressure Less Than MAWP






Valve Set Pressure Equal to MAWP









4.2.4 Steam ServiceValves for pressure vessels in steam ser-vice, excluding boilers designed inaccordance with Section I of the ASMECode, should be specified as discussedabove, depending on the contingency.

4.3 Sizing for Gas or Vapor Relief

4.3.1 Critical Flow BehaviorIf a compressible gas is expanded acrossa nozzle, an orifice, or the end of a pipe,its velocity and specific volume increasewith decreasing downstream pressure.For a given set of upstream conditions(using the example of a nozzle), the massrate of flow through the nozzle will in-crease until a limiting velocity is reachedin the throat. It can be shown that the lim-iting velocity is the velocity of sound in theflowing media at that location. The flowrate that corresponds to the limiting veloci-ty is known as the critical flow rate.

The absolute pressure ratio of the pres-sure in the throat at sonic velocity (Pcf) tothe inlet pressure (P1) is called the criticalpressure ratio. Pcf is known as the criticalflow pressure.

Under critical flow conditions, the actualpressure in the throat cannot fall belowthe critical flow pressure even if a muchlower pressure exists downstream. At criti-cal flow, the expansion from throatpressure to downstream pressure takesplace irreversibly with the energy dissipat-ed in turbulence into the surrounding fluid.

The critical flow pressure in absolute unitsmay be estimated using the ideal gas rela-tionship in Equation 1:

Pcf = 2

k

––– [–––– (k - 1) (1)P1 k + 1]

Where:

Pcf = critical flow throat pressure, in pounds per square inch absolute.

P1 = upstream relieving pressure, inpounds per square inch absolute.

k = ratio of specific heats for any idealgas.

The sizing equations for pressure reliefvalves in vapor or gas service fall into twogeneral categories depending on whetherthe flow is critical or subcritical. If the pres-sure downstream of the throat is less thanor equal to the critical flow pressure, Pcf,then critical flow will occur, and the proce-dures in 4.3.2 should be applied. If thedownstream pressure exceeds the criticalflow pressure, Pcf, then subcritical flow willoccur, and the procedures in 4.3.3 shouldbe applied. (See Table 8 for typical criticalflow pressure ratio values.)

4.3.2 Sizing for Critical Flow4.3.2.1 GeneralPressure relief valves in gas or vapor service that operate under critical flowconditions (see 4.3.1) may be sized usingEquations 2– 4. Each of the equationsmay be used to calculate the effective discharge area, A, required to achieve a required flow rate through a pressurerelief valve. A valve that has an effectivedischarge area equal to or greater thanthe calculated value of A is then chosenfor the application.

–––––– W TZ

A = –––––––– ––– (2)CKdP1Kb √ M

––––– V √TZM

A = –––––––––––– (3)6.32 CKdP1Kb

––––– V √TZG

A = ––––––––––––– (4)1.175 CKdP1Kb

Where:

A = required effective discharge area ofthe valve, in square inches (see1.2.2).

W = required flow through the valve, inpounds per hour.

C = coefficient determined from an ex-pression of the ratio of the specificheats of the gas or vapor at standardconditions. This can be obtained fromFigure 26 or Table 9.

Kd= effective coefficient of discharge =0.975 for use in Equations 2– 4.

P1= upstream relieving pressure, inpounds per square inch absolute.This is the set pressure plus the al-lowable overpressure (see 4.2) plusatmospheric pressure.

Kb= capacity correction factor due to backpressure. This can be obtained fromthe manufacturer’s literature or estimated from Figure 27. The back-pressure correction factor applies tobalanced-bellows valves only.5

T = relieving temperature of the inlet gasor vapor, in degrees Rankine (de-grees Fahrenheit + 460).

Z = compressibility factor for the deviationof the actual gas from a perfect gas, aratio evaluated at inlet conditions.

M = molecular weight of the gas or vapor.Various handbooks carry tables ofmolecular weights of materials, butthe composition of flowing gas or va-por is seldom the same as that listedin tables. This value should be ob-tained from the process data. Table 8lists values for some common fluids.

V = required flow through the valve, instandard cubic feet per minute at14.7 pounds per square inch ab-solute and 60°F.

G = specific gravity of gas referred to air= 1.00 for air at 14.7 pounds per

square inch absolute and 60°F.


Notes

5. See 4.3.3 for applications that involve su-perimposed back pressure of a magnitudethat will cause subcritical flow.



The value of the coefficient C can be eval-uated from the expression of the ratio ofthe specific heats of the gas or vapor asshown in Figure 26.

The ratio of specific heats of any ideal gasand possibly the ratio of specific heats ofa diatomic actual gas can be found in anyacceptable reference work.

Table 9 complements Figure 26 where k = Cp/Cv. When k cannot be determined,it is suggested that C = 315.

While ideal gas law behavior is generallyacceptable for the majority of refinery ap-plications, Appendix E should be referredto for unusual situations in which deviationfrom ideal behavior is significant.

4.3.2.2 ExampleIn this example, the following relief requirements are given:

a. Required hydrocarbon vapor flow, W,caused by an operational upset, of53,500 pounds per hour.

b. Molecular weight of hydrocarbon vapor [a mixture of butane (C4) andpentane (C5)], M, of 65.

c. Relief temperature, T, of 627°R(167°F).

d. Relief valve set at 75 pounds persquare inch gauge, the design pressureof the equipment.

e. Back pressure of 0 pounds per squareinch gauge.

In this example, the following data are derived:

a. Permitted accumulation of 10%.

b. Relieving pressure, P1, of 75 x 1.1 +14.7 = 97.2 pounds per square inch absolute.

c. Calculated compressibility, Z, of 0.84.(If a calculated compressibility is notavailable, Z = 1.0 should be used.)

d. Critical back pressure (from Table 8) of97.2 x 0.59 = 57.3 pounds per squareinch absolute (42.6 pounds per squareinch gauge).6

e. Cp/Cv = k (from Table 8) of 1.09. FromTable 9, C = 326.

f. Capacity correction due to back pres-sure, Kb, of 1.0.

The size of a single pressure relief valveis derived from Equation 2 as follows:

–––––––––– 53,500 627 x 0.84

A = ––––––––––––––– ––––––––– 326 x 0.975 x 97.2 √ 65

= 4.93 in2

See API Standard 526, which also pro-vides a purchase specification sheet forflanged steel safety relief valves (seeFigure 28).

Select a ‘P’ letter orifice size (6.38 in2).


Figure 26 - Curve for Evaluating Coefficient C in the Flow Equation Fromthe Specific Heat Ratio Assuming Ideal Gas Behavior

Notes

6. Since the back pressure (0 pounds persquare inch gauge) is less than the criticalback pressure (42.6 pounds per squareinch gauge), the relief valve setting is basedon the critical flow equation (see Equation 2and 4.3.1 and 4.3.2).

▲1.0

▲1.2

▲1.4

▲1.6

▲1.8

▲2.0

C = 520 k 2k + 1( (

k + 1k + 2

400

380

360

340

320

Specific heat ratio, k = CP/CV

Co

effi

cien

t, C



Table 8

Properties of Gases

Gas Molecular Specific Critical Flow Specific Critical Constants Condensation Flammability ReferencesWeight Heat Ratio Pressure Gravity at Pressure Temperature Temperature Limits

(k = Cp/Cv) Ratio at at 60°F (psia) (°F) 1 Atmosphere (volumeat 60°F at 60°F and 1 (°F) percentand 1 and 1 Atmosphere in air

Atmosphere Atmosphere mixture)

Methane 16.04 1.31 0.54 0.300 667 -117 -259 5.0-15.0 1

Ethane 30.07 1.19 0.57 0.356 708 90 -127 2.9-13.0 1

Ethylene 28.05 1.25 0.56 0.139 731 49 -155 2.7-36.0 1

Propane 44.10 1.13 0.58 0.507 615 206 -44 2.0-9.5 1

Proylene 42.08 1.15 0.57 0.518 672 198 -54 2.0-10.6 2, 3

Isobutane 58.12 1.10 0.59 0.563 528 274 11 1.8-8.5 1

n-Butane 58.12 1.09 0.59 0.584 549 306 31 1.5-9.0 1

1-Butane 56.11 1.11 0.58 0.600 586 296 21 1.6-9.3 2, 3

Isopentane 72.15 – – 0.625 490 369 82 1.3-8.0 1

n-Pentane 72.15 – – 0.631 488 386 97 1.4-8.3 1

1-Pentane 70.13 – – 0.646 510 377 86 1.5-8.7 1

n-Hexane 86.18 – – 0.664 437 454 156 1.1-7.7 1

Benzene 78.11 – – 0.882 710 552 176 1.4-7.1 2, 3

n-Heptane 100.20 – – 0.688 397 513 209 1.0-7.0 1

Toluene 92.14 – – 0.874 596 606 231 1.2-7.1 2, 3

n-Octane 114.23 – – 0.707 361 564 258 0.8-6.5 1

n-Nonane 128.26 – – 0.722 332 611 303 0.7-5.6 1

n-Decane 142.28 – – 0.734 305 653 345 0.7-5.4 1

Air 28.96 1.40 0.53 0.875 547 -221 -318 – 2, 3

Ammonia 17.03 1.31 0.54 0.616 1636 271 -28 16.0-25.0 2, 3

Carbon dioxide 44.01 1.29 0.55 0.818 1071 88 -109 – 2, 3

Hydrogen 2.02 1.41 0.53 – 190 -400 -423 4.0-75.0 2, 3

Hydrogen sulfide 34.08 1.32 0.54 0.801 1300 213 -77 4.3-45.5 2, 3

Sulfur dioxide 64.06 1.27 0.55 1.394 1143 316 14 – 2, 3

Steam 18.02 – – 1.000 3199 705 212 – 2, 3

Estimated


References

1. “Physical Constants of Hydrocarbons C1 toC10,” ASTM Special Technical PublicationNo. 109A, Philadelphia, Pa., 1963.

2. “International – Critical Tables,” McGraw-HillBook Co., Inc., New York.

3. “Engineering Data Book,” Gas ProcessorsSuppliers Association, 1977.

4. API Technical Data Book–PetroleumRefining, Fifth edition.



4.3.3 Sizing for Subcritical Flow:Gas or Vapor Other Than Steam4.3.3.1 GeneralWhen the ratio of back pressure to inletpressure exceeds the critical pressure ratio Pcf/P1, the flow through the pressurerelief valve is subcritical (see 4.3.1).Equations 5 –7 may be used to calculatethe required effective discharge area for aconventional relief valve that has its springsetting adjusted to compensate for super-imposed back pressure and for sizing apilot-operated relief valve.7

––––––––––––– W ZT

A = –––––––– –––––––––––– (5)735 F2Kd √MP1 (P1 - P2)

––––––––––– V ZTM

A = ––––––––––– –––––––––– (6)4645.2 F2Kd √P1 (P1 - P2)

––––––––––– V ZTG

A = ––––––––––– –––––––––– (7)863.63 F2Kd √P1 (P1 - P2)

Where:

A = required effective discharge area ofthe valve, in square inches (see 1.2.2).

W = required flow through the valve, inpounds per hour.

F2 = coefficient of subcritical flow (seeFigure 28 for values)

–––––––––––––––––––––––

= k 1 - r (k-1)k(––––) (r)2/k [–––––––]√ k - 1 1 - r

k = ratio of the specific heats.

r = ratio of back pressure to upstream relieving pressure, P2/P1.

Kd= effective coefficient of discharge = 0.975 for use in Equations 5–7.

Z = compressibility factor for the devia-tion of the actual gas from a perfectgas, a factor evaluated at relieving in-let conditions.

T = relieving temperature of the inlet gasor vapor, in degrees Rankine (de-grees Fahrenheit + 460).

M = molecular weight of the gas or vapor.Various handbooks carry tables ofmolecular weights of materials, butthe composition of the flowing gas orvapor is seldom the same as that list-ed in the tables. This value should beobtained from the process data. Table8 lists values for some common fluids.

P1 = upstream relieving pressure, inpounds per square inch absolute.This is the set pressure plus the al-lowable overpressure (see 4.2) plusatmospheric pressure, in pounds persquare inch absolute.

P2 = back pressure, in pounds per squareinch absolute.

V = required flow through the valve, instandard cubic feet per minute at14.7 pounds per square inch ab-solute and 60°F.

G = specific gravity of gas referred to air= 1.00 for air at 14.7 pounds persquare inch absolute and 60°F.


Note

7. Balanced-bellows relief valves that operatein the subcritical region should be sized us-ing Equations 2-4. The back pressurecorrection factor for this application shouldbe obtained from the valve manufacturer.

Table 9

Values of Coefficient C

k C k C k C k C

1.01 317a 1.31 348 1.61 373 1.91 395

1.02 318 1.32 349 1.62 374 1.92 395

1.03 319 1.33 350 1.63 375 1.93 396

1.04 320 1.34 351 1.64 376 1.94 397

1.05 321 1.35 352 1.65 376 1.95 397

1.06 322 1.36 353 1.66 377 1.96 398

1.07 323 1.37 353 1.67 378 1.97 398

1.08 325 1.38 354 1.68 379 1.98 399

1.09 326 1.39 355 1.69 379 1.99 400

1.10 327 1.40 356 1.70 380 2.00 400

1.11 328 1.41 357 1.71 381 – –

1.12 329 1.42 358 1.72 382 – –

1.13 330 1.43 359 1.73 382 – –

1.14 331 1.44 360 1.74 383 – –

1.15 332 1.45 360 1.75 384 – –

1.16 333 1.46 361 1.76 384 – –

1.17 334 1.47 362 1.77 385 – –

1.18 335 1.48 363 1.78 386 – –

1.19 336 1.49 364 1.79 386 – –

1.20 337 1.50 365 1.80 387 – –

1.21 338 1.51 365 1.81 388 – –

1.22 339 1.52 366 1.82 389 – –

1.24 341 1.54 368 1.84 390 – –

1.25 342 1.55 369 1.85 391 – –

1.26 343 1.56 369 1.86 391 – –

1.27 344 1.57 370 1.87 392 – –

1.28 345 1.58 371 1.88 393 – –

1.29 346 1.59 372 1.89 393 – –

130 347 1.60 373 1.90 394 – –

aInterpolated value, since C becomes indeterminate as k approaches 1.00.



The curves above represent a compromise of thevalues recommended by a number of relief valvemanufacturers and may be used when the makeof the valve or the actual critical flow pressurepoint for the vapor or gas is unknown. When the

make is known, the manufacturer should be con-sulted for the correction factor. These curves arefor set pressures of 50 pounds per square inchgauge and above. They are limited to back pres-sure below critical flow pressure for a given set

pressure. For subcritical flow back pressures below 50 pounds per square inch gauge, themanufacturer must be consulted for values of Kb.

Note

Figure 27 – Back Pressure Sizing Factor, Kb, for Balanced-Bellows Pressure Relief Valves (Vapors and Gases)


Figure 28 – Values of F2 for Subcritical Flow

C1 = capacity with backpressure.

C2 = rated capacity withzero back pressure.

PB = back pressure, inpounds per squareinch gauge.

PS = set pressure, inpounds per squareinch gauge.

▲0

▲5

▲10

▲15

▲20

▲25

▲30

▲35

▲40

▲45

▲50

1.00

0.90

0.80

0.70

0.60

0.50

20% overpressure

10% overpressure

Percent of gauge back pressure = PB/PS x 100

Kb =

C1/

C2

▲0.4

▲0.5

▲0.6

▲0.7

▲0.8

▲0.9

▲1.0

1.0

0.9

0.8

0.7

0.6

Critical flow linek =

1.8

k = 1.6

k = 1.4

k = 1.2

k = 1.0

r = P2/P1

F2



See API standard 526, which also pro-vides a purchase specification sheet forflanged steel safety relief valves.

Select a ‘P’ letter orifice size (6.38 in2).

4.3.4 Alternate Sizing Procedurefor Subcritical Flow4.3.4.1 GeneralCritical flow Equations may be used tocalculate the required discharge area of apressure relief valve used in subcriticalservice. The area obtained using this siz-ing procedure is identical to the areaobtained using the subcritical flow equa-tions. (The capacity correction factor dueto back pressure is derived by setting thesubcritical flow equation equal to the criti-cal flow equation and algebraically solvingfor Kb.) This alternate sizing procedure al-lows the designer to use the familiarcritical flow equation to calculate the samearea obtained with the subcritical flowequation. A graphical presentation of thecapacity correction factor, Kb, is given inFigure 30 on page 129. It should be notedthat this correction factor is used only forthe sizing of conventional (nonbalanced)relief valves that have their spring settingsadjusted to compensate for the superim-posed back pressure. The correction factorshould not be used to size balanced-typevalves.

4.3.4.2 ExampleIn this example, the following relief re-quirements are given:

a. Required hydrocarbon vapor flow, W,caused by an operational upset, of53,500 pounds per hour.

b. Molecular weight of hydrocarbon vapor[a mixture of butane (C4) and pentane(C5), M, of 65.

c. Relief temperature,T, of 627°R (167°F).

d. Relief valve set at 75 pounds persquare inch gauge, the design pressureof the equipment.

e. Constant back pressure of 55 poundsper square inch gauge. The spring set-ting of the valve should be adjustedaccording to the amount of constantback pressure obtained.


a. Permitted accumulation of 10 percent.

b. Relieving pressure, P1, of 75 x 1.1 + 14.7= 97.2 pounds per square inch absolute.

c. Calculated compressibility, Z, of 0.84. (Ifa calculated compressibility is not avail-able, Z = 1.0 should be used.)

d. Critical back pressure (from Table 8) of97.2 x 0.59 = 57.3 pounds per squareinch absolute (42.6 pounds per squareinch gauge).8

e. Built-up back pressure of 0.10 x 75 =7.5 pounds per square inch.

f. Total back pressure of 55 + 7.5 + 14.7 =77.2 pounds per square inch absolute.

g. Cp/Cv = k of 1.09.

h. P2/P1 = 77.2 / 97.2 = 0.794.

i. Back pressure correction factor, Kb, of0.88 (from Figure 30 on page 129).

j. Coefficient determined from an expres-sion of the ratio of the specific heats ofthe gas or vapor at standard conditions,C, of 326.

The size of the relief valve is derived fromEquation 2 as follows:9

––––––––– 53,500 627(0.84)

A = –––––––––––––––––– –––––––– 326(0.975)(97.2)(0.88)√ 65

= 5.60 in2

4.4 Sizing for Steam Relief

4.4.1 GeneralPressure relief valves in steam servicemay be sized using Equation 8.

WA = –––––––––––––– (8)

51.5 P1KdKNKSH

Where:

A = required effective discharge area, in square inches.

W = required flow rate, in pounds perhour.

P1 = upstream relieving pressure, inpounds per square inch absolute.This is the set pressure plus the allowable overpressure plus atmos-pheric pressure, in pounds persquare inch absolute.

Kd = effective coefficient of discharge= 0.975 for use in Equation 8.

KN = correction factor for Napier equation(see Reference 1)

= 1 where P1 ≤ 1515 pounds persquare inch absolute

= (0.1906P1 – 1000) /(0.2292P1 –1061)where P1 > 1515 pounds per squareinch absolute and ≤ 3215 poundsper square inch absolute.

KSH = superheat steam correction factor.This can be obtained from Table 10on page 127. For saturated steamat any pressure, KSH = 1.0.

4.4.2 ExampleIn this example, the following relief re-quirements are given:

W = saturated steam at 153,500 poundsper hour at 1600 pounds per squareinch gauge set pressure with 10% accumulation.


8. Since the back pressure (55 pounds persquare inch gauge) is greater than the criticalback pressure (42.6 pounds per square inchgauge), the sizing of the relief valve is basedon subcritical flow. The back pressure correc-tion factor, Kb, should be determined usingthe critical flow formulas (see Equations 2–4).

9. This area requirement is the same as that ob-tained using the subcritical flow equation (seeEquation 5).

Notes



Table 10

Superheat Correction Factors, KSH

Set Pressure Temperature (degrees Fahrenheit)(pounds perin2 gauge) 300 400 500 600 700 800 900 1000 1100 1200

15 1.00 0.98 0.93 0.88 0.84 0.80 0.77 0.74 0.72 0.70

20 1.00 0.98 0.93 0.88 0.84 0.80 0.77 0.74 0.72 0.70

40 1.00 0.99 0.93 0.88 0.84 0.81 0.77 0.74 0.72 0.70

60 1.00 0.99 0.93 0.88 0.84 0.81 0.77 0.75 0.72 0.70

80 1.00 0.99 0.93 0.88 0.84 0.81 0.77 0.75 0.72 0.70

100 1.00 0.99 0.94 0.89 0.84 0.81 0.77 0.75 0.72 0.70

120 1.00 0.99 0.94 0.89 0.84 0.81 0.78 0.75 0.72 0.70

140 1.00 0.99 0.94 0.89 0.85 0.81 0.78 0.75 0.72 0.70

160 1.00 0.99 0.94 0.89 0.85 0.81 0.78 0.75 0.72 0.70

180 1.00 0.99 0.94 0.89 0.85 0.81 0.78 0.75 0.72 0.70

200 1.00 0.99 0.95 0.89 0.85 0.81 0.78 0.75 0.72 0.70

220 1.00 0.99 0.95 0.89 0.85 0.81 0.78 0.75 0.72 0.70

240 – 1.00 0.95 0.90 0.85 0.81 0.78 0.75 0.72 0.70

260 – 1.00 0.95 0.90 0.85 0.81 0.78 0.75 0.72 0.70

280 – 1.00 0.96 0.90 0.85 0.81 0.78 0.75 0.72 0.70

300 – 1.00 0.96 0.90 0.85 0.81 0.78 0.75 0.72 0.70

350 – 1.00 0.96 0.90 0.86 0.82 0.78 0.75 0.72 0.70

400 – 1.00 0.96 0.91 0.86 0.82 0.78 0.75 0.72 0.70

500 – 1.00 0.96 0.92 0.86 0.82 0.78 0.75 0.73 0.70

600 – 1.00 0.97 0.92 0.87 0.82 0.79 0.75 0.73 0.70

800 – – 1.00 0.95 0.88 0.83 0.79 0.76 0.73 0.70

1000 – – 1.00 0.96 0.89 0.84 0.78 0.76 0.73 0.71

1250 – – 1.00 0.97 0.91 0.85 0.80 0.77 0.74 0.71

1500 – – – 1.00 0.93 0.86 0.81 0.77 0.74 0.71

1750 – – – 1.00 0.94 0.86 0.81 0.77 0.73 0.70

2000 – – – 1.00 0.95 0.86 0.80 0.76 0.72 0.69

2500 – – – 1.00 0.95 0.85 0.78 0.73 0.69 0.66

3000 – – – – 1.00 0.82 0.74 0.69 0.65 0.62




Figure 29 - Constant Back Pressure Sizing Factor, Kb, For ConventionalSafety Relief Valves (Vapors and Gases Only)


Set overpressure (MAWP)= 100 pounds per square inch gauge.

Overpressure= 10 pounds per square inch.

Superimposed back pressure (constant)

= 70 pounds per square inch gauge.

Spring set= 30 pounds per square inch.

Built-up back pressure= 10 pounds per square inch

Percent absolute back pressure

=(70 + 10 + 14.7)

x 100 = 76(100 + 10 + 17.7)

Kb (follow dotted line)= 0.89 (from the curve).

Capacity with back pressure= 0.89 (rated capacity without back

pressure).

Note

This chart is typical and suitable for use onlywhen the make of the valve or the actual criticalflow pressure point for the vapor or gas is un-known; otherwise, the valve manufacturershould be consulted for specific data. This cor-rection factor should be used only in the sizingof conventional (nonbalanced) pressure reliefvalves that have their spring setting adjusted to compensate for the superimposed back pressure. It should not be used to size bal-anced-type valves.

Kb =

C1/

C2

=73

5 F2

l -

rC

▲70

▲0

▲10

▲20

▲30

▲40

▲50

▲60

▲80

▲90

▲100

Exch

ange

100

90

80

70

60

50

40

30

20

10

0

k = 1.1

k = 1.3

k = 1.5

k = 1.7

Percent of absolute back pressurePB

PS + PO

= x 100 = r x 100

C1 = capacity with back pressure.

C2 = rated capacity with zero back pressure.

P8 = back pressure, in pounds per square inchabsolute.

PS = set pressure, in pounds per square inchabsolute.

PO = overpressure, in pounds per square inch.




a. Relieving pressure, P1, of 1600 x 1.1 +14.7 = 1774.7 pounds per square inchabsolute.

b. Effective coefficient of discharge, Kd, of0.975.

c. Correction factor for Napier equation,KN, of [0.1906(1774.7) - 1000] /[0.2293(1774.7) - 1061] = 1.01.

d. Superheat steam correction factor, KSH,of 1.0.

The size of the relief valve is derived fromequation 8 as follows:

A = 153,500––––––––––––––––––––––––51.5(1774.7)(0.975)(1.01)(1)

= 1.705 in2

See API Standard 526, which also pro-vides a purchase specification sheet forflanged steel safety relief valves.

Select a ‘K’ orifice valve (1.838 in2), thatis, a 3K6 safety valve.

4.5 Sizing for Liquid Relief: ReliefValves Requiring Liquid CapacityCertification

4.5.1 GeneralSection VIII, Division I, of the ASME Coderequires that capacity certification be ob-tained for pressure relief valves designedfor liquid service. The procedure for ob-taining capacity certification includesdetermining the coefficient of discharge forthe design of liquid relief valves at 10%overpressure. Valves that require a capac-ity in accordance with the ASME Codemay be sized using Equation 9.

–––––––– Q G

A = ––––––––– ––––––– (9)38KdKwKv √P1 - P2

Where:

A = required effective discharge area, insquare inches.

Q = flow rate, in U.S. gallons per minute.

Kd = effective coefficient of discharge thatshould be obtained from the valvemanufacturer. For a preliminary sizing estimation, a discharge coefficient of 0.65 can be used.

Note

The curve above represents values recom-mended by various manufacturers. This curvemay be used when the manufacturer is notknown. Otherwise, the manufacturer should beconsulted for the applicable correction factor.

KW = correction factor due to back pressure.

PB = back pressure, in pounds per square inch gauge.

PS = set pressure, in pounds per square inch gauge.

Figure 30 – Capacity Correction Factor, Kw, Due to Back Pressure onBalanced-Bellows Pressure Relief Valves in Liquid Service

Figure 31 – Capacity Correction Factor, Kv, Due to Viscosity


▲0

▲10

▲20

▲30

▲40

▲50

1.00

0.90

0.80

0.70

0.60

0.50

Percent of gauge back pressure = (PB/PS) x 100

KW

▲

10▲

20▲

40▲

50▲

100▲

200▲

400▲

1000▲

2000▲

100,000▲

20,000▲▲

R = Reynolds number

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

KV =

vis

cosi

ty c

orr

ecti

on

fac

tor



Kw = correction factor due to back pressure. If the back pressure is atmospheric, Kw = 1. Balanced-bellows valves in back pressure ser-vice will require the correction factordetermined in Figure 31 on page129. Conventional valves require no special correction.

Kv = correction factor due to viscosity asdetermined from page 28.

G = specific gravity of the liquid at theflowing temperature referred to water = 1.0 at 70°F.

P1 = upstream relieving pressure, inpounds per square inch gauge. Thisis the set pressure plus allowableoverpressure.

P2 = total back pressure, in pounds persquare inch gauge.

When a relief valve is sized for viscous liq-uid service, it should first be sized as itwas for nonviscous-type application sothat a preliminary required discharge area,A, can be obtained. From manufacturers’standard orifice sizes, the next larger ori-fice size should be used in determiningthe Reynold’s number, R, from either ofthe following relationships:

R =Q(2800G)––––––––– (10)

µ ––√A

or

R =12,700Q–––––––– (11)10

––U √A

Where:

Q = flow rate at the flowing temperature,in U.S. gallons per minute.

G = specific gravity of the liquid at flowingtemperature referred to water

= 1.00 at 70°F.

µ = absolute viscosity at the flowing tem-perature, in centipoises.

A = effective discharge area, in squareinches (from manufacturers’ standardorifice areas).

U = viscosity at the flowing temperature, inSaybolt Universal seconds.

After the value of R is determined, the fac-tor Kv is obtained from page 28. Kv isapplied to correct the preliminary requireddischarge area. If the corrected area ex-ceeds the standard chosen orifice area,the above calculations should be repeatedusing the next larger standard orifice size.

4.5.2 ExampleIn this example, the following relief requirements are given:

a. Required crude-oil flow caused byblocked discharge, Q, of 1800 gallons perminute.

b. Specific gravity, G, of 0.90 (viscosity atthe flowing temperature is 2000 SayboltUniversal seconds.)

c. Relief valve set at 250 pounds persquare inch gauge, the design pressure ofthe equipment.

d. Back pressure variable from 0 to 50pounds per square inch gauge.


a. Overpressure of 10%.

b. Relieving pressure, P1, of 1.10 x 250 =275 pounds per square inch gauge.

c. Back pressure of (50/250) x 100 = 20%.

A balanced-bellows valve is indicated,since back pressure is variable. (FromFigure 31, Kw = 0.97.)

The manufacturer’s effective coefficient ofdischarge K = 0.75.

Sizing first for no viscosity correction, (Kv= 1.0), the size of the relief valve is de-rived from Equation 9 as follows:

–––––––– 1800 0.90

A = ––––––––––––––––––– ––––––– 38.0 x 0.75 x 0.97 x 1.0√ (275-50)

= 4.118 in2

See Equation 11. An area of 4.34 in2

(‘N’ orifice) should be used.

R =12,700 x 1800

= 5487––––––––––––––––2000 √4.34

From page 28, Kv = 0.965.

A = AR = 4.118–––– ––––––Kv 0.965

= 4.267 in2

Where:

AR = required area without viscosity correction.

See API Standard 526, which also pro-vides a purchase specification sheet forflanged steel safety relief valves.

Select an ‘N’ orifice pressure relief valve(4.34 square inches), that is, a 4N6 pres-sure relief valve.

4.6 Sizing for Liquid Relief: ReliefValves Not Requiring CapacityCertificationBefore the ASME Code made provisionsfor capacity certification, valves were generally sized for liquid service usingEquation 12. This method assumes a coefficient of discharge, Kd = 0.62, and 25 percent overpressure. An additional ca-pacity correction factor, KP, was obtainedfrom Figure 33 for relieving pressures oth-er than 25 percent overpressure. Thissizing method may be used where capaci-ty certification is not required.


Notes

10. Equation 11 is not recommended forviscosities less than 100 Saybolt Universalseconds.



–––––––––– Q G

A = –––––––––––– –––––––– (12)38 KdKwKvKp √ 125p - pb

Where:

A = required effective discharge area, insquare inches.

Q = flow rate, in U.S. gallons per minute.

Kd = effective coefficient of discharge thatshould be obtained from the valvemanufacturer. For a preliminary sizing estimation, a discharge coeffi-cient of 0.62 can be used.

Kw = correction factor due to back pressure. If back pressure is atmospheric, Kw = 1. Balanced-bellows valves in back-pressure service will require the correctionfactor determined from Figure 31.Conventional valves require no special correction.

Kv = correction factor due to viscosity asdetermined from page 28.

Kp = correction factor due to overpres-sure. At 25% overpressure, Kp = 1.0.For overpressures other than 25%,Kp is determined from Figure 32.

G = specific gravity of the liquid at theflowing temperature referred to water.

= 1.0 at 70°F.

p = set pressure, in pounds per squareinch gauge.

pb = total back pressure, in pounds persquare inch gauge.

4.7 Sizing for Two-PhaseLiquid/Vapor ReliefA pressure relief valve handling a liquid atvapor-liquid equilibrium or a homoge-neous mixed-phase fluid will produceflashing with vapor generation as the fluidmoves through the valve. The vapor gen-eration must be taken into account, sinceit may reduce the effective mass flow ca-pacity of the valve.

Calculations for determining propertiesand handling liquid/vapor phases areavailable; see Section 5 for emergingtechnical literature that can be used tosize relieving devices.

For information about saturated water, seespecifically Section VIII, Appendix 11, ofthe ASME Code.

A reasonable, conservative method of sizing for two-phase liquid/vapor relief isas follows:

a. Determine the amount of liquid thatflashes by an isenthalpic (adiabatic) expansion from the relieving conditioneither to the critical downstream pres-sure for the flashed vapor or to the backpressure, whichever is greater.

b. Calculate individually the orifice arearequired to pass the flashed vapor component, using Equations 2–7 asappropriate, according to service, typeof valve, and whether the back pres-sure is greater or less than the criticaldownstream pressure.

c. Calculate individually the orifice area required to pass the unflashed liquidcomponent using Equation 9. The pres-sure drop (P1 – P2) is the inlet relievingpressure minus the back pressure.

d. Add the individual areas calculated forthe vapor and liquid components to obtain the total orifice area, A, that isrequired.

e. Select a pressure relief valve that hasan effective discharge area equal to orgreater than the total calculated orificearea. The designer should recheck theback pressure that will exist for the specific relief valve selected, with itsparticular discharge installation, by examining the vapor generation down-stream of the pressure relief valvenozzle. Where appropriate, correctionscan be applied to the particular orificeareas previously calculated. Further-more, selecting a balanced pressurerelief valve is often desirable to mini-mize the effect of flashed vapor on thevalve capacity.

The designer should also investigate theeffect of any auto-refrigeration that mayarise from the flashing of liquid. Materialsof construction must be adequate for theoutlet temperatures involved; in addition,the installation must preclude the possibili-ty of flow blockage occurring from hydrateor possibly solid formation.

4.8 Sizing for Rupture Disk Devices

4.8.1 Rupture Disk Devices UsedIndependentlyRupture disk devices may be used aloneor in combination with a pressure reliefvalve in gas or vapor service or in liquidservice. The sizing of a rupture disk de-vice used alone is based on the equationsapplicable for pressure relief valves usingfor all fluids an effective coefficient of dis-charge Kd = 0.62.

The required discharge area, A in squareinches, is calculated using the appropriateequation for the flowing medium (seeEquations 2–7 for gas or vapor, Equation8 for steam, and Equation 9 for liquid).The rupture disk device selected shouldbe the nominal pipe size whose area isequal to or greater than the required dis-charge area calculated by the appropriateequation.

For rupture disk devices that have a struc-tural member (for example, a knife bladeor vacuum support) that reduces the ef-fective discharge area after bursting, theprojected area of the structural member isdeducted from the flow area of the pipe todetermine the net discharge area of theburst rupture disk.

Users should be aware of the followinglimitations in using Kd = 0.62 to determinethe capacity of a given size of rupturedisk, or conversely, the required area for a given flow quantity:

a. The rupture disk device is used in asize and pressure range that the manu-facturer has determined will give asatisfactory opening for the style of rup-ture disk in the particular fluid service.

b. The rupture disk device is installed in ashort piping system that does not addsignificantly to the flow resistance of theburst rupture disk device.

If a rupture disk device discharges into avent system or a closed relief system, itwill usually not contribute significantly tothe pressure loss obtained in the dis-charge piping. The sizing of the inlet anddischarge piping becomes a line sizingproblem that uses the relieving rate andthe maximum allowable inlet pressure de-fined by the code. In general, a pressure





Figure 32 – Capacity Correction Factors Due to Overpressure for Reliefand Safety-Relief Valves in Liquid Service

Notes

The curve in Fig. 32 shows that up to and in-cluding 25 percent overpressure, capacity isaffected by the change in lift, the change in ori-fice discharge coefficient, and the change inoverpressure. Above 25 percent, capacity is af-fected only by the change in overpressure.Valves operating at low overpressures tend tochatter; therefore, overpressures of less than 10percent should be avoided.

loss through the rupture disk device of ap-proximately 75 pipe diameters may beused. The manufacturer should be con-sulted if more accurate values arerequired. This problem is similar to the linesizing of a process line except that the ef-fect of volumetric expansion on thepressure loss must be considered. Thiswill include an acceleration effect (the vapor is exiting the discharge piping at ahigher velocity) as well as the effect ofchanging density. If the vent line subse-quently discharges into headers of varyingsizes, critical flow restrictions must beconsidered.

4.8.2 Rupture Disk Devices Used inCombination With Pressure ReliefValvesAn important application of a rupture diskdevice is at the inlet of a pressure reliefvalve. The sizing of the pressure reliefvalve/rupture disk device combination re-quires that the pressure relief valve firstbe sized to meet the required relieving ca-pacity. The certified and publishedcapacity of the pressure relief valve used

alone is then multiplied by the combina-tion capacity factor, Kc, to determine thecapacity of that combination. (See 2.6.2for further information on the combinationcapacity factor.)

The nominal size of the rupture disk de-vice installed at the inlet of the pressurerelief valve must be equal to or greaterthan the nominal size of the inlet connec-tion of the valve to permit sufficient flowcapacity and valve performance.

The design of the piping from the protect-ed vessel to the inlet of the pressure reliefvalve is crucial to the proper functioning ofthe valve. Users should consult applicableengineering codes for guidance on inletpiping design. Unless the pressure reliefdevice is installed directly on the vessel, agood practice is to analyze the frictionalpressure loss from the vessel to the valveinlet at the rated relieving capacity to com-ply with recommended limits. An inlet pipesized larger than necessary for the inlet tothe pressure relief valve is often required;this may dictate a rupture disk device tomatch the pipe size.

▲

10▲

20▲

30▲

40▲

50

Percent overpressure

1.10

0.90

0.70

0.50

0.30

0.10

Co

rrec

tio

n f

acto

r, K

p




References1. N.E. Sylvander and D.L. Katz,

“Investigation of Pressure RelievingSystems,” Engineering ResearchBulletin No. 31, University of Michigan,Ann Arbor, April 1948.

2. Recommended Practice for the Designand Construction of PressureRelieving Systems for ProcessEquipment and Pressure Storage inRefineries (tentative), AmericanPetroleum Institute, August 1954.

3. F.J. Heller, “Safety Relief Valve Sizing:API Versus CGA Requirements Plus aNew Concept for Tank Cars,” 1983Proceedings–Refining Department,Volume 62, American PetroleumInstitute, Washington, D.C., pp. 123-135.

4. H.R. Wharton, “Digest of Steels forHigh Temperature Service,” TimkenSteel, 1946.

5. J.J. Duggan, C.H. Gilmour, and P.F.Fisher, “Requirements for Relief ofOverpressure in Vessels Exposed toFire,” Transactions of the ASME, 1944,Volume 66, pp. 1-53.

6. I. Heitner, T. Trautmauis and M.Morrissey, “Relieving Requirements forGas Filled Vessels Exposed to Fire,”1983 Proceedings–RefiningDepartment, Volume 62, AmericanPetroleum Institute, Washington, D.C.,pp. 112-122.

7. J. O. Francis and W.E. Shackelton, “ACalculation of Relieving Requirementsof the Critical Region,” 1985Proceedings–Refining Department,Volume 64, American PetroleumInstitute, Washington D.C., pp. 179-182.

8. H.G. Fisher, “DIERS ResearchProgram on Emergency ReliefSystems,” Chemical EngineeringProgress, August 1985, pp. 33-36.

9. H.K. Fauske and J.C. Leung, “NewExperimental Technique forCharacterizing Runaway ChemicalReactions,” Chemical EngineeringProgress, August 1985, pp. 39-46.

10. M.A. Grolmes and J.C. Leung, “CodeMethod for Evaluating IntegratedRelief Phenomena,” ChemicalEngineering Progress, August 1985,pp. 47-52.

11. H.K. Fauske, “Emergency ReliefSystem Design,” ChemicalEngineering Progress, August 1985,pp. 53-56.

12. M.A. Grolmes, J.C. Leung, and H.K.Fauske, “Large-Scale Experiments ofEmergency Relief Systems,” ChemicalEngineering Progress, August 1985,pp. 57-62.

13. Publication 999 (English Edition),Technical Data Book–PetroleumRefining, American PetroleumInstitute, Washington, D.C.

14. O. Cox, Jr. and M.L. Weirick, “SizingSafety Valve Inlet Lines,” ChemicalEngineering Progress, November1980.

15. B.A. Van Boskirk, “Sensitivity of ReliefValves to Inlet and Outlet LineLengths,” Chemical Engineering,August 1982.

16. C.E. Lapple, “Isothermal and AdiabaticFlow of Compressible Fluids,”Transactions of the American Instituteof Chemical Engineers, 1943, Volume39, pp. 385-432.

17. H.Y. Mak, “New Method SpeedsPressure-Relief Manifold Design,” Oiland Gas Journal, November 20, 1978.

18. P. Kandell, “Program Sizes Pipe andFlare Manifolds for CompressibleFlow,” Chemical Engineering, June 29,1981.



D.1 BackgroundThe problem of estimating fire-relief requirements for storage tanks was firstrecognized in 1928 when the National FireProtection Association (NFPA) requestedAPI to recommend that a table of mini-mum emergency relief capacities for aseries of tank capacities be included in theNFPA Suggested Ordinance Regulatingthe Use, Handling, Storage and Sale ofFlammable Liquids and the ProductsThereof.

It was later recognized that tank capaci-ties did not provide the best basis forestimating the amount of vapor to be handled. Since the heat was absorbed almost entirely by radiation, the area exposed—not the volume of the tank con-tents—seemed to be the important factor.Many of the tanks were large and couldnever be expected to be entirely surround-ed by fire; the assumption was thereforemade that the larger the area of the con-tainer, the less the likelihood that the tankwould be fully exposed to radiation. In oth-er words, the larger the surface area ofthe tank shells, the lower the average unitheat absorption rate from a fire.

By 1948 several different equations [1]1

were in general use, prompting the APISubcommittee on Pressure-RelievingSystems to develop an equation for deter-mining the heat absorbed from open firesusing the test data available at the time.The resultant equation has remained ingeneral use since its publication in 1954[2], and its development is documented ina paper presented by F.J. Heller in 1983[3].

Table D-1 contains data from 16 fire testsand one actual fire. Data from these testswere considered in the development ofEquations D-1 and D-2.

These data result from tests in whichmeans were provided to measure the total heat absorbed by a vessel by (a)computing the heat required to bring theliquid contents to the boiling range and

(b) measuring the amount of liquid con-tents evaporated in a given time. The unitheat absorption rates in Table D-1 are average rates on the wetted surface.

Examinations of detailed reports on thesetests indicate that the setup for Tests 4, 5,and 8 was arranged to provide continuousand complete flame envelopment of thesmall vessels; under these conditions,maximum average heat input rates of 30,400-32, 500 British thermal units per hourper square foot were realized. The envi-ronmental conditions set up for tests 1, 3,6, 7, 9, and 10 allowed the flame to besubjected to air currents and wind. All oth-er factors were conducive to maintainingmaximum heat input, a condition thatshould not exist in a refinery. Under theseconditions, the maximum average heat in-put rates varied greatly. Test 2 differedfrom Test 1 in that drainage away from theequipment was provided. The maximumheat input rate is reduced by 60% whendrainage is provided; this fact was incor-porated in the development of EquationsD-1 and D-2. Test 11 gives an indication ofthe effect of a large area on average heatinput during an actual fire.

The test reports mentioned in some casesthat the tests were delayed until the arrivalof a calm day so that the wind would notblow the flames away from the vessel.Copious supplies of fuel were available. Inmost cases, the fuel was maintained bydikes in a pool beneath the vessel andwas not allowed to drain away as it nor-mally would. In the Rubber ReserveCorporation tests, a 2-inch gasoline line,running full, was required to keep the fuelsupplied during the test. Without thesespecial adverse conditions, the maximumheat absorption values obtained in thesetests are extremely unlikely to occur in anactual refinery fire.

D.2 Nature of an Open FireThe nature of an open fire of flammablefluid, as related to test data, is important.

This kind of fire differs from the fire in thefirebox of a boiler or still, where the fueland air are mixed by means other than theconvection currents caused by the heatedgases. The flame will accordingly have acore of flammable vapor, either unmixedwith air or insufficiently mixed to burn.Combustion occurs on the exterior enve-lope of this core. Because the actualcombustion zone is on the rich side, aconsiderable amount of black smoke isgenerated. This envelope of soot mayserve to mask a considerable portion ofthe flame.

Hot gases from the combustion rise, andthe air that supports the combustion flowsin at the bottom. The flame mass is quiteturbulent; as masses of the burning vaportumble and billow, the smoky mantle isdisplaced and the bright flame can beseen intermittently. This flame is not ablazing white, as it would be in a furnace;it is red or orange, indicating a lower tem-perature than that of a furnace flame.

Flames of this type tend to rise because oftheir temperature; however, they can alsobe blown aside by the wind and may beblown so far from a vessel that the heatingeffect on the vessel is small.

D.3 Effect of Fire on the UnwettedSurface of a Vessel

D.3.1 GeneralUnwetted wall vessels are those in whichthe internal walls are exposed to a singlefluid, vapor, or gas or are internally insu-lated regardless of the contained fluids.These include vessels that contain sepa-rate liquid and vapor phases under normalconditions but become single phase(above the critical) at relieving conditions.

Vessels may be designed to have internalinsulation. A vessel should be consideredinternally insulated when the internal wallcan become insulated by the deposition ofcoke or other materials as a result of thecontained fluids.

Note

1. Numbers in brackets correspond to refer-ences in Section 5.




1. H.C. Hottell, Private communication to APISubcommittee on Pressure-RelievingSystems, January 1948.

2. H.C. Hottell, Private communication to APISubcommittee on Pressure-RelievingSystems, December 1950.

3. F.L. Maker Private communication to APISubcommittee on Pressure-RelievingSystems regarding 1925 tests, December22,1950.

4. “Opacity of Water to Radiant Heat Energy,”Research Bulletin 3, UnderwritersLaboratory, Inc., 1938.

5. Safety Memorandum 89, Rubber ReserveCorporation, Washington, D.C., May 1944.

6. University of Michigan, Unpublished testsmade for API Subcommittee on Pressure-Relieving Systems, June 1947.

7. Anonymous report to API Subcommittee onPressure-Relieving Systems regarding a fire(not a test), June 1941.

8. J.J. Duggan, C.H. Gilmour, and P.F. Fisher,“Requirements for Relief of Overpressureon Vessels Exposed to Fire,” Transactionsof the ASME, 1944, Volume 66, pp. 1-53.

9. “Large Scale Fire Exposure Tests toEvaluate ‘Unox’ Foam for Fire ExposureProtection,” Fire Research LaboratoryReport No. FRL-62, Process SafetyDepartment, Carbide and CarbonChemicals Co., a Division of Union Carbideand Carbon Corporation, Dec. 8, 1954.

10. Lauderback.

11. National Fire Protection Association.


Table D-1

Comparison of Heat-Absorption Rates in Fire Tests

Test Source Type Fuel Vessel Total Wetted Total Temperature BTU/Hr/Ft2 Refer.of Exposure Capacity Area Area Heat Input of Wetted

(barrel) (ft2) (ft2) (BTU/Hr) Surface (°F)

1Hottell, average 6-inch thick

GasolineConning

296 123 3,760,000 30,500 1of 36 tests metal stack Tower

Hottell, average 6-inch thick Conning2

of 13 tests metal stackGasoline

Tower296 123 2,139,000 17,400 2

3Standard Oil Co. Heating water

Naphtha 2.6 26 416,000 16,000 3of California in drum

Standard Oil Co. Heating water4

of California in tankNaphtha 33 206 105 3,370,000 70-212 32,000 3

5Underwriters Water flowing

Gasoline 24 24 780,000 76 32,500 4Laboratories, Inc. over plate

Rubber Reserve Heating water6

Corp.Test No.17 in tankGasoline 119 568 400 9,280,000 300 23,200 5

7Rubber Reserve Generating

Gasoline 199 568 400 8,400,000 21,000 5Corp.Test No.17 steam in tank

Rubber Reserve Water flowing in8

Corp.Test No.17 3/4-inch standard pipeGasoline 9.0 9.0 274,000 30,400 5

9API Project Heating water

Kerosene 0.88 16.2 6.1 95,800 300 15,700 6Test No.1 in tank

API Project Heating water10

Test No. 2 in tankKerosene 0.88 16.2 6.1 102,500 320 16,800 6

11a Report to API on 38 ft.Plant fire Butane 5,000 4,363 4,363 23,560,000 5,400 7

butane sphere

12 Lauderback Chemical waste 100 100 3,210,000 32,100 8

13 NFPA (Tulsa) Cutback jet fuel 238 773 303 8,736,000 23,000 9

14 Union Carbide (1938) Propane 71.4 242 132 2,300,000 17,400 10

15 Union Carbide (1938) Propane 71.4 242 176 4,993,000 28,400 10

Liquefied petroleum Wood saturated16 Fetterly

gas container with kerosene7.7 83 57.8 1,350,000 23,300 11

aThis represents an actual fire

References



D.3.2 CharacteristicsA characteristic of a vessel with an unwet-ted internal wall is that heat flow from thewall to the contained fluid is low as a re-sult of the resistance of the contained fluidor any internal insulating material. Heat in-put from an open fire to the bare outsidesurface of an unwetted vessel may, intime, be sufficient to heat the vessel wallto a temperature high enough to rupturethe vessel. Figures D-1 and D-2 indicatehow quickly an unwetted vessel wall mightbe heated to rupture conditions. Figure D-1 illustrates the rise in temperature thatoccurs with time in the unwetted plates ofvarious thicknesses exposed to open fire;for example, an unwetted steel plate 1-inch thick would take about 12 minutesto reach approximately 1100°F and about17 minutes to reach 1300°F when theplate is exposed to an open fire.

Figure D-2 shows the effect of overheat-ing ASTM A 515, Grade 70 steel [4]. Thefigure indicates that at a stress of 15,000pounds per square inch, an unwettedsteel vessel would rupture in about 7hours at 1100°F and about 21/2 minutes at 1300°F.

D.4 Effect of Fire on the WettedSurface of a VesselThe surface area wetted by a vessel’s internal liquid contents is effective in gen-erating vapor when the area is exposed tofire. To determine vapor generation, onlythat portion of the vessel that is wetted byits internal liquid and is equal to or lessthan 25 feet above the source of flameneeds to be recognized. The term sourceof flame usually refers to ground grade butcould be at any level at which a substan-tial spill or pool fire could be sustained.Various classes of vessels are operatedonly partially full. Table D-2 gives recom-mended portions of liquid inventory foruse in calculations. Portions higher than25 feet are normally excluded.

D-5 Heat Absorption Equations

D.5.1 Heat Absorption Across theWetted Surface of a VesselThe amount of heat absorbed by a vesselexposed to open fire is markedly affectedby the type of fuel feeding the fire, the de-

gree to which the vessel is enveloped bythe flames (a function of vessel size andshape), and fireproofing measures. Thefollowing equivalent formulas are used toevaluate these conditions where there areprompt fire-fighting efforts and drainage offlammable materials away from the vessel:

q = 21,000FA-0.18 (D-1)

Q = 21,000FA0.82 (D-2)

Where adequate drainage and fire-fightingequipment do not exist, Equation D-2 be-comes the following [3]:

Q = 34,500FA0.82 (D-1)

Where:

q = average unit heat absorption, in Britishthermal units per hour per square footof wetted surface.

Q = total heat absorption (input) to thewetted surface, in British thermal unitsper hour.

F = environment factor. (Values for varioustypes of insulation are shown in TableD-3.)

A = total wetted surface, in square feet(see D.4). (The expression A-0.18, or1/A0.18, is the area exposure factor orratio. This ratio recognizes the factthat large vessels are less likely thansmall ones to be completely exposedto the flame of an open fire.)

D.5.2 Heat Absorption Across theUnwetted Surface of a VesselD.5.2.1 Simple EquationsSee D.3 for a discussion of the effect offire on the unwetted surface of a vessel.

The discharge areas for pressure reliefvalves on gas-containing vessels exposedto open fires can be determined using thefollowing formula:

A = F´A´

(D-3)––––– –––√P1

F´ can be determined from the followingrelationship. The recommended minimumvalue of F´ is 0.01; when the minimum value is unknown, F´ = 0.045 should beused.

F´ =0.1406 (Tω – T1)1.25

(D-4)–––––– –––––––––––CKD T1

0.6506

Where:

A = effective discharge area of the valve,in square inches.

A´ = exposed surface area of the vessel,in square feet.

P1 = upstream relieving pressure, inpounds per square inch absolute.This is the set pressure plus the allowable overpressure plus the atmospheric pressure.

C = coefficient determined by the ratio ofthe specific heats of the gas at stan-dard conditions. This can be obtainedfrom Figure 26 or Table 9.

KD = coefficient of discharge (obtainablefrom the valve manufacturer). Themaximum allowable KD establishedby ASME is 0.975.

Tω = vessel wall temperature, in degreesRankine.

T1 = gas temperature, absolute, in de-grees Rankine, at the upstreampressure, determined from the follow-ing relationship:

T1 =P1

Tη–––Pη

Where:

Pη = normal operating gas pressure, inpounds per square inch absolute.

Tη = normal operating gas temperature, indegrees Rankine.

The recommended maximum vessel walltemperature for the usual carbon steelplate materials is 1100°F. Where vesselsare fabricated from alloy metals, the valuefor Tω should be changed to a more ap-propriate recommended maximum.

D.5.2.2 Rearrangement of SimpleEquationsThe relief load can be calculated directlyin pounds per hour by rearranging Equation2 and substituting Equations D-3 and D-4,which results in the following equation:

W = 0.1406 MP1 A´(Tω – T1)1.25

(D-5)√ ( ––––––––––)T11.1506

Where:

M = molecular weight of the gas.

Z and Kb in Equation 2 are assumed toequal 1.




▲0

▲4

▲8

▲12

▲16

▲20

▲24

Minutes after start of fire

1600

1400

1200

1000

800

600

400

200

0

Pla

te t

emp

erat

ure

, deg

rees

Fah

ren

hei

t (a

vera

ged

ove

r 24

sq

uar

e fe

et)

Plate 1/8-inch thick (as computed)

Plate 1/8-inch thick (as observed)




Figure D-1 – Average Rate of Heating Steel Plates Exposed to OpenGasoline Fire on One Side



D.5.2.3 Discussion of Simple EquationsThe derivation of Equations D-3 and D-5[5] is based on the physical properties ofair and the perfect gas laws. The deriva-tion assumes that the vessel is uninsulatedand has no mass, that the vessel walltemperature will not reach rupture stress,and that there is no change in fluid tem-perature. These assumptions should bereviewed to ensure that they are appropri-ate for any particular situation.

D.5.2.4 More Rigorous CalculationsWhen the assumptions in D.5.2.3 are notappropriate, more rigorous methods ofcalculation may be warranted. In suchcases, the necessary physical propertiesof the containing fluid may need to be ob-tained from the actual data or estimatedfrom equations of state. The effects ofvessel mass and insulation may need tobe considered. The pressure-relieving rateis based on an unsteady state. As the firecontinues, the vessel wall temperatureand the contained gas temperature andpressure increase with time. The pressure

relief valve will open at the set pressure,or if the pressure is set too high, the ves-sel will rupture. With the loss of fluid onrelief, the temperatures will further in-crease at the relief pressure. If the fire isof sufficient duration, the temperature willincrease until vessel rupture occurs.Procedures are available for estimatingthe changes in average vessel wall andcontained fluid temperatures that occurwith time and the maximum relieving rateat the set pressure [6, 7]. The proceduresrequire successive iteration.

D.5.2.5 Additional Protective MeasuresThe determination may be made that apressure relief valve will not provide suffi-cient protection for an unwetted wallvessel, and vessel rupture could occur be-fore or too soon after initial relief. Where apressure relief valve alone is not ade-quate, additional protective measuresshould be considered, including insulation(D.8.3.1), water sprays (D.8.3.3), and de-pressuring (D.8.2) to avoid vessel rupture.

Where calculations indicate that rupturewould not occur prior to relief, a rupturedisk device could also be considered.

The design should allow sufficient time foroperator action and initiation of fire-fight-ing procedures before possible vesselrupture. Operator action may include de-pressuring, using water sprays, andemploying firewater monitors.

D.6 Fluids To Be RelievedA vessel may contain liquids or vapors orfluids of both phases. The liquid phasemay be subcritical at operating tempera-ture and pressure and may pass into thecritical or supercritical range during theduration of a fire as the temperature andpressure in the vessel increase.

The quantity and composition of the fluidto be relieved during a fire depend on thetotal heat input rate to the vessel underthis contingency and on the duration ofthe fire.


Figure D-2 – Effect of Overheating Steel (ASTM A 515, Grade 70)

Time for rupture (hours at indicated temperature)

Ru

ptu

re s

tres

s (p

ou

nd

s p

er s

qu

are

inch

x 1

000)

▲ ▲

0.1▲

1.0▲

10▲

100▲

1000

100

10

1.0

0.1

900°F

1000°F

1100°F

1200°F1300°F

1400°F

Oxidation effect

0.01



The total heat input rate to the vessel maybe computed by means of one of the formulas in Section D.5 using the appro-priate values for wetted or exposedsurfaces and for the environment factor.

Once the total heat input rate to the vesselis known, the quantity and composition ofthe fluid to be relieved can be calculated,provided that enough information is avail-able on the composition of the fluidcontained in the vessel.

If the fluid contained in the vessel is notcompletely specified, assumptions mustbe made to obtain a realistic relief flowrate for the relief device. These assump-tions may include the following:

a. An estimation of the latent heat of boiling liquid and the appropriate mole-cular weight of the fraction vaporized.

b. An estimation of the thermal expansioncoefficient if the relieving fluid is a liquidbelow its boiling temperature, a gas, ora supercritical fluid.

D.6.1 VaporFor pressure and temperature conditionsbelow the critical point, the rate of vaporformation—a measure of the rate of vaporrelief required—is equal to the total rate of heat absorption divided by the latentheat of vaporization. The vapor to be re-lieved is the vapor that is in equilibriumwith the liquid under conditions that existwhen the valve is relieving at its accumu-lated pressure.

The latent-heat and molecular-weight values used in calculating the rate of va-porization should pertain to the conditionsthat are capable of generating the maxi-mum vapor rate.

The vapor and liquid composition maychange as vapors are released from thesystem. As a result, temperature and la-tent-heat values could change, thusaffecting the required size of the pressurerelief device. On occasion, a multicompo-nent liquid may be heated at a pressureand temperature that exceed the criticalsfor one or more of the individual compo-nents. For example, vapors that arephysically or chemically bound in solutionmay be liberated from the liquid upon heat-ing. This is not a standard latent-heatingeffect but is more properly termed de-gassing or dissolution. Vapor generation isdetermined by the rate of change in equi-librium caused by increasing temperature.

For these and other multicomponent mix-tures that have a wide boiling range, atime-dependent model may have to be de-veloped where the total heat input to thevessel not only causes vaporization butalso raises the temperature of the remain-ing liquid, keeping it at its boiling point.

Reference 7 gives an example of a time-dependent model used to calculate reliefrequirements for a vessel exposed to firethat contains fluids near the critical rangeor above.

The recommended practice of finding arelief vapor flow rate from the heat input to

the vessel and from the latent heat of liq-uid contained in the vessel becomesinvalid near the critical point of the fluid,where the latent heat approaches zeroand the sensible heat dominates.

When no accurate latent-heat value isavailable for these hydrocarbons near thecritical point, a minimum value of 50British thermal units per pound is some-times acceptable as an approximation.

When pressure-relieving conditions areabove the critical point, the rate of vapordischarge depends only on the rate atwhich the fluid will expand as a result ofthe heat input.

D.6.2 LiquidThe hydraulic expansion formula given inAppendix C may be used to compute theinitial liquid-relieving rate in a liquid-filledsystem when the liquid is still below itsboiling point. However, this rate is valid fora very limited time, after which vapor gen-eration will become the determiningcontributor in the sizing of the pressure relief device.

There is an interim time period betweenthe liquid expansion and the boiling vaporrelief in which mixtures of both phasesneed to be relieved simultaneously, eitheras flashing, bubble, slug, froth, or mistflow until sufficient vapor space is availableinside the vessel for phase separation.This mixed-phase condition is usually ne-glected, but for some vessels, particularlyoverfilled steam drums or polymerization

Table D-2

Wetted Surface Area of A Vessel Based on Fire Heat Absorbed

Class of Vessel Portion of Liquid Inventory Remarks

Liquid-full, such as treaters All up to the height of 25 feet —

Surge drums, knockout drums, process vessels Normal operating level up to the height of 25 feet —

Normal level in bottom plus liquid holdup from Level in reboiler is to beFractionating columns all trays; total wetted surface up to included if the reboiler is

the height of 25 feet an integral part of the column

Average inventory level up to For tanks of 15 psig operating pressureWorking storage

the height of 25 feet or less; see API Standard 2000

Up to the maximum horizontal diameterSpheres and spheroids or up to the height of 25 feet, —

whichever is greater




reactors, the limiting relieving contingencymay be the factor that would determinethe size of the relieving device. (See D.6.3for information about mixed-phase flow.)

Should a pressure relief device be locatedin the liquid zone of a vessel exposed tofire conditions, the pressure relief devicemust be able to pass a volume of liquidequivalent to the displacement caused byvapor generated by the fire.

D.6.3 Mixed PhaseAs stated in D.6.2, mixed-phase flow maysometimes be the limiting relieving contin-gency and thus will determine the size ofthe pressure relief device. This is particu-larly true for reactors during runawayreactions that may be caused by lack ofcooling or excess heat input (for example,under fire).

The Design Institute for Emergency ReliefSystems recently concluded an intensiveresearch program to develop methods forthe design of emergency relief systems tohandle runaway reactions. The interestedreader is advised to study some introduc-tory publications [8-12] on this subject inChemical Engineering Progress, August1985.

D.7 Data on Latent Heat ofVaporization of Hydrocarbons

Different hydrocarbon liquids have differ-ent latent heats of vaporization eventhough hydrocarbons as a group behavesimilarly to one another. The latent heat ofvaporization of a pure single-componentliquid decreases as the temperature at va-porization increases and the latent heatbecomes zero at the critical temperatureand pressure for that liquid.

Figure D-3 shows the vapor pressuresand latent heats of the pure single-compo-nent paraffin-hydrocarbon liquids. Thischart is directly applicable to such liquidsand applies as an approximation to paraf-fin-hydrocarbon mixtures composed oftwo components whose molecular weightsvary no more than propane to butane andbutane to pentane.

The chart may also be applicable to isomerhydrocarbons, aromatic or cyclic com-pounds, or paraffin-hydrocarbon mixturesof components that have slightly divergentmolecular weights. The equilibrium temper-ature should be calculated. Using therelationship for the calculated temperatureversus vapor pressure, the latent heat canthen be obtained from Figure D-3. The

molecular-weight relationship as shown bythe chart is not to be used in such cases;the molecular weight of the vapor shouldbe determined from the vapor-liquid equi-librium calculation.

For cases that involve mixtures of compo-nents that have a wide boiling range orwidely divergent molecular weights, a rig-orous series of equilibrium calculationsmay be required to estimate vapor gener-ation rates, as discussed in D.6.1.

Other recognized sources [13] of latent-heat data or methods of calculating latentheat of vaporization should be used whereFigure D-3 does not apply.

D.8 Protecting Vessels Against FireExposureThe measures described in D.8.1 throughD.8.3 for protecting vessels against fireexposure are contingent on properdrainage away from the vessel so thatpools of fuel cannot accumulate beneaththem.

Improper drainage under fire conditionswill limit the effectiveness of any of thesemeasures in reducing the intensity of heatabsorption by the vessels.

Table D-3

Environment Factor

Type of Equipment Factor F1

Bare vessel 1.0

Insulated vessel2 (These arbitrary insulation conductance values are shown as examples and are in British thermal units per hour per square foot per degree Fahrenheit):

4 0.3

2 0.15

1 0.075

0.67 0.05

0.5 0.0376

0.4 0.03

0.33 0.026

Water-application facilities, on bare vessel3 1.0

Depressurizing and emptying facilities4 1.0

Notes

1. These are suggested values for the condi-tions assumed in D.5.1. When these conditionsdo not exist, engineering judgment should beexercised either in selecting a higher factor or inproviding means of protecting vessels from fireexposure as suggested in D.8.

2. Insulation shall resist dislodgement by fire-hose streams. For the examples, a temperaturedifference of 1600°F was used. These conduc-tance values are based on insulation havingthermal conductivity of 4 BTU/hr-Ft2-°F per inchat 1600°F and correspond to various thickness-es of insulation between 1 and 12 inches.

3. See D.8.3.3.

4. See D.8.2.




D.8.1 Effectiveness of PressureRelief Devices as Related to FireExposureThe effect of fire exposure on the unwet-ted surface of vessels is described inD.3. A pressure relief device does notprevent weakening and failure of a ves-sel that becomes locally overheated andoverstressed at an unwetted surface. Itwill only prevent the internal pressurefrom rising beyond the allowable accu-mulation pressure. A vessel may beprotected against such failure by (a) de-pressurizing the vessel and (b) limitingthe heat input.

D.8.2 Depressuring SystemsControlled depressuring of the vessel re-duces internal pressure and stress in thevessel walls. It also guards against the po-tential addition of fuel to the fire should thevessel rupture. The design of depressur-ing systems should recognize thefollowing factors:

a. Manual controls near the vessel may beinaccessible during an emergency.

b. Unless anticipated, automatic controlscould fail in a direction that would pre-vent depressuring (for example, valvesthat fail closed).

c. Early initiation of depressuring is desir-able to limit vessel stress to acceptablelevels commensurate with the vesselwall temperature that results from a fire.

d. Safe disposal of vented streams mustbe provided.

e. No credit is recommended when safety valves are being sized for fire exposure.

Further information on depressuring is pro-vided in API Recommended Practice 521.

D.8.3 Methods of Limiting HeatInput From FireD.8.3.1 External InsulationLimiting the heat input from fires by exter-nal insulation reduces both the rise of thevessel wall temperature and the genera-tion of vapor inside the vessel. Insulationmay also reduce the problem of disposingof the vapors and the expense of providingan exceptionally large relieving system toconduct the effluent to a point of disposal.

The insulation must be fire resistant andprotected from dislodgement by fire-hosestreams (see API Recommended Practice521).

Where insulation or fireproofing is applied,the heat absorption can be computed byassuming that the outside temperature ofthe insulation jacket or other outer coveringhas reached an equilibrium temperature of1660°F. With this temperature and the op-erating temperature for the inside of thevessel, together with the thickness andconductivity of the fire-protection coating,the average heat transfer rate to the con-tents can be computed. It must be kept inmind that the thermal conductivity of theinsulation increases with the temperature,and a mean value should be used.

For insulated vessels, the environmentfactor for insulation becomes the following:

F =k (1660 – Tf)

––––––––––––21,000t

Where:

k = thermal conductivity of insulation, inBritish thermal units per hour persquare foot per degree Fahrenheit perinch at mean temperature.

Tf = temperature of vessel contents at relieving conditions, in degreesFahrenheit.

t = thickness of insulation, in inches.

D.8.3.2 Earth-Covered StorageCovering a pressure vessel with earth isanother effective method of limiting heatinput. The reduction of heat absorptiondue to the earth cover can be calculatedas suggested in D.8.3.1.

D.8.3.3 Cooling the Surface of a Vessel With WaterUnder ideal conditions, water films cover-ing the metal surface can absorb mostincident radiation. The reliability of waterapplication depends on many factors.Freezing weather, high winds, cloggedsystems, undependable water supply, andvessel surface conditions can prevent uni-form water coverage. Because of theseuncertainties, no reduction in environmentfactor (see Table D-3) is recommended;however, as stated previously, properlyapplied water can be very effective.

D.8.3.4 Limiting Fire Areas WithDiversion WallsDiversion walls can be provided to deflectvessel spills from other vessels.




Section 1 – General

1.1 ScopeThis recommended practice is intended tocover methods of installation for pressurerelief devices for equipment that has amaximum allowable working pressure(MAWP) of 15 pounds per square inchgauge (psig) (1.03 barg) or greater.Pressure relief valves or rupture disks maybe used independently or in combinationwith each other to provide the requiredprotection against excessive pressure ac-cumulation. As used in this recommendedpractice, the term pressure relief valve in-cludes safety relief valves used in eithercompressible or incompressible fluid ser-vice, and relief valves used inincompressible fluid service. This recom-mended practice covers gas, vapor,steam, and incompressible service; it doesnot cover special applications that requireunusual installation considerations.

1.2 Definition of TermsThe terminology for pressure relief de-vices that is used in this recommendedpractice is in general agreement with thedefinitions given in ASME PTC 25.

Section 2 – Inlet Piping

2.1 General RequirementsFor general requirements for inlet piping,see Figures 1 and 2.

2.1.1 Flow and Stress Considerations Inlet piping to the pressure relief deviceshould provide for proper system perfor-mance. This requires design considerationof the flow-induced pressure drop in theinlet piping. Excessive pressure losses inthe piping system between the protectedvessel and a pressure relief device will ad-versely affect the system-relievingcapacity and can cause valve instability. Inaddition, the effect of stresses derivedfrom both pressure relief device operationand externally applied loads must be con-sidered. For more complete piping designguidelines, see ASME B31.3.

2.1.2 Vibration ConsiderationsMost vibrations that occur in inlet pipingsystems are random and complex. Thesevibrations may cause leakage at the seatof a pressure relief valve, prematureopening, or premature fatigue failure ofcertain valve parts, inlet and outlet piping,

or both. Vibration in inlet piping to a rup-ture disk may adversely affect the burstpressure and life of the rupture disk.

Detrimental effects of vibrations on thepressure relief device can be reduced byminimizing the cause of vibrations, by ad-ditional piping support, by use of eitherpilot-operated relief valves or soft-seatedpressure relief valves, or by providinggreater pressure differentials between theoperating pressure and the set pressure.

2.2 Pressure-Drop Limitations andPiping ConfigurationsFor pressure-drop limitations and pipingconfigurations, see Figures 1-4.

2.2.1 Pressure Loss at the Valve InletExcessive pressure loss at the inlet of apressure relief valve can cause rapidopening and closing of the valve, or chat-tering. Chattering will result in loweredcapacity and damage to the seating sur-faces. The pressure loss that affects valveperformance is caused by non-recover-able entrance losses (turbulentdissipation) and by friction within the inletpiping to the pressure relief valve.

Chattering has sometimes occurred dueto acceleration of liquids in long inlet lines.

2.2.2 Size and Length of Inlet PipingWhen a pressure relief valve is installedon a line directly connected to a vessel,the total non-recoverable pressure lossbetween the protected equipment and thepressure relief valve should not exceed 3percent of the set pressure of the valveexcept as permitted in 2.2.3.1 for pilot-op-erated pressure relief valves. When apressure relief valve is installed on aprocess line, the 3 percent limit should beapplied to the sum of the loss in the nor-mally non-flowing pressure relief valveinlet pipe and the incremental pressureloss in the process line caused by the flowthrough the pressure relief valve. Thepressure loss should be calculated usingthe rated capacity of the pressure reliefvalve. Pressure losses can be reducedmaterially by rounding the entrance to theinlet piping, by reducing the inlet linelength, or by enlarging the inlet piping.Keeping the pressure loss below 3 per-cent becomes progressively more difficultas the orifice size of a pressure reliefvalve increases.

Figure 1 – Typical Pressure ReliefValve Installation: Atmospheric(Open) Discharge

Figure 2 – Typical Pressure ReliefValve Installation: Closed SystemDischarge

Note

1. See Section 5.

Notes

1. See Section 6.

2. Orient low-point drain – or weep hole –away from relief valve, structural steel, andoperating area.

API - RP 520 Part II (July 1991) - Valve InstallationExcerpts from API - 520 Part II Installation

Nonrecoverable losses not more than 3 percent of set pressure Vessel

Normal pipe diameter no less than valve inlet size

Long-radius elbow

Support to resist weight and reaction forces

Weather cap may be required

Pressurerelief valve

Body drain(See Note 1)

Low-point drain(See Note 2)

Bonnet vent piping for bellows type pressure relief valves, if required (See Note 1)

Vessel

Nominal pipe diameter no less than valve inlet size

Flanged spool piece, if required to elevate PRV

To closed system (self-draining)

Nonrecoverable pressure losses not more than 3 percent of set pressure



The nominal size of the inlet piping mustbe the same as or larger than the nominalsize of the pressure relief valve inletflange connection as shown in Figure 2.

An engineering analysis of the valve per-formance at higher inlet losses may permitincreasing the allowable pressure lossabove 3 percent.

When a rupture disk device is used incombination with a pressure relief valve,the pressure-drop calculation must includethe additional pressure drop developed bythe disk (see 2.6 for additional informationon rupture disk devices).

2.2.3 Remote Sensing for PilotOperated Pressure Relief ValvesRemote sensing for pilot-operated pres-sure relief valves can be utilized whenthere is excessive inlet pipe pressure lossor when the main valve must be located ata pressure source different from the pilotsensing point because of service limita-tions of the main valve (see Figure 5).

2.2.3.1 Inlet Pipe LossRemote sensing permits the pilot to sensethe true system pressure upstream of thepiping loss. Remote sensing may elimi-nate uncontrolled valve cycling orchattering for a pop action pressure reliefvalve and will permit a modulating actionpressure relief valve to achieve full lift atthe required overpressure. However, highinlet pressure losses may induce pressurepulsations in the inlet piping that cancause uncontrolled main valve cycling.Some valves incorporate design featuresto prevent uncontrolled cycling

Although remote sensing may eliminatevalve chatter or permit a modulating valveto achieve full lift at the required overpres-sure, the relieving capacity will be reducedby any pressure drop in the inlet pipe.

2.2.3.2 Installation GuidelinesRemote sensing lines should measurestatic pressure where the velocity is low.Otherwise, the pilot will sense an artificial-ly low pressure due to the effect ofvelocity.

Ensure that the pilot sensing point is with-in the system protected by the main valve.

For flowing pilots, remote sensing linesshall be sized to limit the pressure loss to3 percent of the set pressure based onthe maximum flow rate of the pilot at 110percent of set pressure. Consult the man-ufacturer for recommendations.

For non-flowing pilots, remote sensinglines with a flow area of 0.070 squareinches (45 square millimeters) is sufficientsince no system medium flows throughthis type of pilot when the main valve isopen and relieving.

Consider using pipe for remote sensinglines to ensure mechanical integrity.

If a block valve is installed in the remotesensing line, the guidelines in Section 4should be followed. A closed block valve ina remote sense line renders the pressurerelief valve inoperative.

2.2.4 Configuration of Inlet Piping forPressure Relief ValvesAvoid the installation of a pressure reliefvalve at the end of a long horizontal inletpipe through which there is normally noflow. Foreign matter may accumulate, orliquid may be trapped, creating interfer-ence with the valve’s operation or requiringmore frequent valve maintenance.

The inlet piping system to relief valvesshould be free-draining from the pressurerelief device to prevent accumulation ofliquid or foreign matter in the piping.

Figure 3 – Typical Pressure ReliefValve Mounted on Process Line

Figure 4 – Typical Pressure ReliefValve Mounted on Long Inlet Pipe


Pressure Relief ValveVessel

See 2.2.2 for pressure-loss limitation

Pressure Relief Valve

Vessel

Inlet piping sized so that pressure drop from vessel to pressure relief valve inlet flange does not exceed 3% of valve set pressure

Discharge Piping

Note

1. See 2.2.2 for pressure-loss limitation.

Note

1. Inlet piping sized so that nonrecoverablepressure losses form vessel to pressure relief valve inlet flange do not exceed 3 per-cent of valve set pressure.



2.3 Inlet Stresses That OriginateFrom Static Loads in the DischargePipingImproper design or construction of the dis-charge piping from a pressure reliefdevice can set up stresses that will betransferred to the pressure relief deviceand its inlet piping. These stresses maycause a pressure relief valve to leak ormalfunction or may change the burst pres-sure of a rupture disk. The pressure reliefdevice manufacturer should be consultedabout permissible loads and moments.

2.3.1 Thermal StressesFluid flowing from the discharge of a pres-sure-relieving device may cause a changein the temperature of the discharge piping.A change in temperature may also becaused by prolonged exposure to the sunor to heat radiated from nearby equip-ment. Any change in the temperature ofthe discharge piping will cause a changein the length of the piping and may causestresses that will be transmitted to thepressure relief device and its inlet piping.The pressure relief device should be iso-lated from piping stresses through propersupport, anchoring, or flexibility of the dis-charge piping.

2.3.2 Mechanical StressesDischarge piping should be independentlysupported and carefully aligned.Discharge piping that is supported by onlythe pressure relief device will inducestresses in the pressure relief device andthe inlet piping. Forced alignment of thedischarge piping will also induce suchstresses.

2.4 Inlet Stresses That OriginateFrom Discharge Reaction ForcesThe discharge of a pressure relief devicewill impose a reaction force as a result ofthe flowing fluid (see Figure 6). This forcewill be transmitted into the pressure reliefdevice and also into the mounting nozzleand adjacent supporting vessel shell un-less designed otherwise. The precisemagnitude of the loading and resultingstresses will depend on the reaction forceand the configuration of the piping system.The designer is responsible for analyzingthe discharge system to determine if thereaction forces and the associated bend-

ing moments will cause excessive stress-es on any of the components in thesystem.

The magnitude of the reaction force willdiffer substantially depending on whetherthe installation is open or closed dis-charge. When an elbow is installed in thedischarge system to direct the fluid up intoa vent pipe, the location of the elbow andany supports is an important considerationin the analysis of the bending moments.

2.4.1 Determining Reaction Forces inan Open Discharge SystemThe following formula is based on a condi-tion of critical steady-state flow of acompressible fluid that discharges to theatmosphere through an elbow and a verti-cal discharge pipe. The reaction force (F)includes the effects of both momentumand static pressure; thus, for any gas, va-por, or steam,

English Units--------------------

F =W kT

+ (AP)–––– √––––––– 366 (k + 1)M

[Metric Units] --------------------

F = 129 W√ kT+ 0.1 (AP)–––––––

(k + 1)M

Where:

F = reaction force at the point of dis-charge to the atmosphere, in pounds[newtons].

W = flow of any gas or vapor, in poundsper hour [kilograms per second].

k = ratio of specific heats (Cp/Cv).

Cp = specific heat at constant pressure.

Cv = specific heat at constant volume.

T = temperature at inlet, in degreesRankine [in degrees Kelvin].

M = molecular weight of the process fluid.

A = area of the outlet at the point of dis-charge, in square inches [squaremillimeters].

P = static pressure within the outlet atthe point of discharge, in pounds persquare inch gauge [bar gauge].

Figure 6 – Typical Pressure ReliefValve Installation With Vent Pipe

Notes

1. The support should be located as close aspossible to the centerline of the vent pipe.

2. F = reaction forceA = cross-sectional area.


Long-radiusElbow

Free supportto resist weightand reactionforces.

Vessel

PressureReliefValve

FAo(cross-sectionarea)

Vent Pipe

Figure 5 – Typical Pilot-OperatedPressure Relief Valve Installation

Pilot

Vessel

Integral pressure sensing

Optional remote pressure sensing

Main Valve

Note

1. See 2.2.3.



2.4.2 Determining Reaction Forces in aClosed-Discharge SystemPressure relief devices that relieve understeady-state flow conditions into a closedsystem usually do not create large forcesand bending moments on the exhaust sys-tem. Only at points of sudden expansionwill there be any significant reaction forcesto be calculated. Closed-discharge sys-tems, however, do not lend themselves tosimplified analytic techniques. A complextime-history analysis of the piping systemmay be required to obtain the true valuesof the reaction forces and associated mo-ments.

2.5 Isolation Valves in Inlet PipingIsolation valves located in the inlet pipingto pressure relief devices shall be in ac-cordance with the guidelines in Section 4.

2.6 Rupture Disk Devices inCombination with Pressure ReliefValvesA rupture disk device may be used as thesole pressure relief device, or it may be in-stalled between a pressure relief valveand the vessel or on the downstream sideof a pressure relief valve (see Figure 7).

For ASME Boiler and Pressure VesselCode applications, the capacity of a pres-sure relief valve used in combination witha rupture disk mounted as shown inFigure 7 must be derated by 10 percentunless that particular combination has acapacity factor derived from testing as list-ed in the National Board of Boiler andPressure Vessel Inspectors’ publication,Pressure Relief Device Certifications.

When a rupture disk device is used be-tween the pressure relief valve and theprotected vessel, a pressure indicator,bleed valve, free vent, or suitable telltaleindicator should be provided to permit de-tection of disk rupture or leakage. Theuser is cautioned that any pressurebuildup between the rupture disk and thepressure relief valve will increase the ves-sel pressure at which the rupture disk willburst.

Only non-fragmenting rupture disk devicesmay be used beneath a pressure reliefvalve.

Rupture disks are not available in all sizesat lower pressures; therefore, for theselow-pressure applications the availablerupture disk may have to be larger thanthe nominal size of the inlet piping andpressure relief valve.

Refer to API Recommended Practice 520,Part I, paragraphs 2.5 (Rupture Disks-General) and 2.6 (Rupture Disks inCombination with Pressure Relief Valves)for additional information.

2.7 Process Laterals Connected toInlet Piping of Pressure ReliefValvesProcess laterals should generally not beconnected to the inlet piping of pressurerelief valves. Exceptions should be ana-lyzed carefully to ensure that the allowablepressure drop at the inlet of the pressurerelief valve is not exceeded under simulta-neous conditions of rated flow through thepressure relief valve and maximum possi-ble flow through the process lateral (seeFigure 8).

2.8 Turbulence in Pressure ReliefDevice InletsSee 7.3 for information regarding the ef-fects of turbulence on pressure reliefvalves.

Section 3 – Discharge Piping FromPressure Relief Devices

3.1 General RequirementsFor general requirements for dischargepiping, see Figures 1, 2, 6, and 9.

The discharge piping installation must pro-vide for proper pressure relief deviceperformance and adequate drainage (free-draining systems are preferred - seeSection 6). Consideration should be givento the type of discharge system used, theback pressure on the pressure relief de-vice, and the set-pressure relationship ofthe pressure relief devices in the system.

Auto-refrigeration during discharge cancool the outlet of the pressure relief deviceand the discharge piping to the point thatbrittle fracture can occur. Materials mustbe selected which are compatible with theexpected temperature.

Figure 8 – Installation AvoidingProcess Laterals Connected toPressure Relief Valve Inlet Piping


Figure 7 – Typical Rupture DiskAssembly Installed in CombinationWith a Pressure Relief Valve

PressureGauge

Excess Flow Valve (optional)

Bleed ValveRupture disk(See Note 1)

Pressure Relief Valve

Aviod process laterals (See Note 1)

Vessel

Note

1. See 2.7.



3.2 Safe Disposal of RelievingFluidsFor a comprehensive source of informa-tion about the safe disposal of variousrelieving fluids, see API RecommendedPractice 521.

3.3 Back Pressure Limitations andSizing of PipeWhen discharge piping for pressure reliefvalves is designed, consider the combinedeffect of superimposed and built-up backpressure on the operating characteristicsof the pressure relief valves. The dis-charge piping system should be designedso that the back pressure does not ex-ceed an acceptable value for anypressure relief valve in the system.

When rupture disks are used as the solerelieving device and discharge into aclosed system, the effect of the superim-posed back pressure on the burstingpressure for the disk must be considered.

The rated capacity of the pressure reliefvalve shall be used to size the dischargeline from the pressure relief valve to therelief header. Additional information onsizing of discharge piping systems for va-por or gas service is covered in APIRecommended Practice 521.

3.4 Considerations for Pilot-Operated Pressure Relief ValvesSuperimposed back pressure that ex-ceeds the inlet pressure of apilot-operated pressure relief valve cancause the main valve to open, allowingreverse flow through the main valve. Forexample, backflow can occur if severalpressure relief valves have their outletsmanifolded into a common dischargeheader, and one or more of these valvesis discharging while another is connectedto a system with a lower inlet pressure. Anaccessory should be specified that willprevent such backflow.

3.5 Stresses that Originate fromDischarge PipingThe effects of stresses that originate fromdischarge piping are discussed in 2.3.1and 2.3.2.

3.6 Isolation Valves in theDischarge PipingIsolation valves located in the dischargepiping system shall be in accordance withthe guidelines in Section 4.

Section 4 – Isolation (stop) Valvesin Pressure Relief Piping

4.1 GeneralBlock valves may be used to isolate apressure relief device from the equipmentit protects or from its downstream disposalsystem. Since improper use of block valvemay render a pressure relief device inop-erative, the design, installation, andmanagement of these isolation blockvalves should be carefully evaluated toensure that plant safety is not compro-mised.

4.2 ApplicationIf a pressure relief device has a servicehistory of leakage, plugging, or other severe problems which affect its perfor-mance, isolation and sparing of the reliefdevice may be provided. This design strat-egy permits the pressure relief device tobe inspected, maintained, or repairedwithout shutting down the process unit.However, there are potential hazards as-sociated with the use of isolation valves.The ASME Boiler and Pressure VesselCode, Section VIII, Appendix M, discussesproper application of these valves and theadministrative controls which must be inplace when isolation block valves areused. Local jurisdictions may have otherrequirements.

Additional examples of isolation valve in-stallations are given in 4.4.

4.3 Isolation Valve RequirementsIn addition to previously noted inlet andoutlet pressure drop restrictions, all isola-tion valves located in relief system pipingshall meet the following requirements:

a. Valves shall be full bore.

b. Valves shall be suitable for the line ser-vice classification.

c. Valves shall have the capability of beinglocked or carsealed open.

d. When gate valves are used, theyshould be installed with stems orientedhorizontally or, if this is not feasible, thestem could be oriented downward to amaximum of 45° from the horizontal tokeep the gate from falling off and block-ing the flow.

Consider painting the isolation valves aspecial color or providing other identifica-tion.

When isolation valves are installed inpressure relief valve discharge piping, ameans to prevent pressure buildup be-tween the pressure relief valve and theisolation valve should be provided (for ex-ample, a bleeder valve). Also, theinstallation of bleed valves should be con-sidered to enable the system to bedepressured prior to performing mainte-nance on the system as shown in Figures9 through 12.

Figure 9 – Typical Pressure ReliefValve Installation with an IsolationValve


Isolation valve with provision for car sealing or locking open

Bonnet vent piping for bellows type pressure relief valves, if required(See Note 2)

Vessel

Typical blinding points

Bleed valve

Nonrecoverable pressure

losses not mor than 3 percent of set pressure

Bleed valve installed on valve body (See Note 3)

Flanged spool piece, if required to elevate PRV

To closed system or atmoshperic piping

Isolation valve with provision for car sealing or locking open (not required for atmosheric discharge) (See Note 1)



Consider the installation of an additionalrelief device, so that 100 percent designrelieving capacity is available while anyrelief device is out of service. Examples ofthis type of installation are shown inFigures 10 and 11. Consider storing thespare valve until needed to preserve its in-tegrity and allow bench testing just prior toinstallation.

When spare relief devices are provided, amechanical interlock or interlocking proce-dure shall be provided which managesproper opening and closing sequences ofthe isolation valves to ensure that over-pressure protection of the vessel orequipment is not compromised. Typicallythe inlet isolation valves for spare reliefvalves are closed.

Three-way isolation valves are acceptableprovided the installation meets the sizeand inlet pressure drop requirements.

4.4 Examples of Isolation ValveInstallationsAn isolation valve downstream of a pres-sure relief device may be installed atbattery limits of process units. This is illus-trated in Figure 12. The purpose of batterylimit isolation valves is to allow processunits to be removed from service for main-tenance while other process unitsdischarging into the main plant flare head-er remain in service.

Similarly, relief system isolation valvesmay be used for equipment such as com-pressors, salt dryers, or coalescers, whichare spared and need to be shut down formaintenance while spare equipment re-mains online (see Figure 13).

4.5 Management ProceduresRelated to Isolation Valves Strict management procedures should bein place that will prohibit the inadvertentclosing of isolation valves in relief piping.These procedures should require that theopening and closing of the valves be doneby an authorized person.

An updated list should be kept of all isola-tion valve located in relief piping whichcould isolate relief valves. Documentationof the required position and reason for thelock or seal should be provided.

Periodic inspections of isolation valves lo-cated in relief piping should be madewhich verify the position of valves and thecondition of the locking or sealing device.

Section 5 – Bonnet or Pilot VentPiping

5.1 Conventional ValvesThe two types of conventional valves are:

a. Open spring, often used in steam ser-vice.

b. Closed spring, where the bonnet en-closing the spring is vented internally tothe pressure relief valve discharge. Thebonnet normally has a tapped vent thatis closed off with a threaded plug.

5.2 Balanced Bellows ValvesBalanced bellows valves are utilized in ap-plications where it is necessary tominimize the effect of back pressure onthe set pressure and relieving capacity.This is done by balancing the effect of theback pressure on the top and bottomsides of the disk. This requires the springto operate at atmospheric pressure.

The bonnets of bellows valves must al-ways be vented to ensure properfunctioning of the valve and to provide atell tale in the even of a bellows failure.The vent must designed to avoid pluggingcaused by ice, insects, or other obstruc-tions. When the fluid is flammable, toxic,or corrosive, the bonnet vent may need tobe piped to a safe location.

5.3 Balanced Piston ValvesBalanced piston valves are utilized in ap-plications to minimize the effect of backpressure, similar to the balanced bellowsvalve. Proper operation depends on can-cellation of the back pressure effect onopposing faces of the valve disk and bal-ance piston. Since the piston area is equalto the nozzle seat area, the spring mustoperate at atmospheric pressure.

Because of the flow of system media pastthe piston, the bonnets of balanced pistonvalves should always be vented to atmos-phere at a safe location. The amount offlow past the piston into the bonnet de-pends on the pressure differentialbetween the valve outlet and bonnet. Inan installation where superimposed backpressure of built-up back pressure is high,the flow past the piston could be substan-tial. This factor must be considered in thedesign of the bonnet venting.

5.4 Pilot-Operated ValvesThe pilot is often vented to the atmosphereunder operating conditions, since the dis-charge during operation is small. Whenvent discharge to the atmosphere is notpermissible, the pilot should be vented ei-ther to the discharge piping or through asupplementary piping system to a safe lo-cation. When vent piping is designed, avoidthe possibility of back pressure on the pilotunless the pilot is a balanced design.


Figure 10 – Typical Pressure ReliefValve Installation Arrangement for100 Percent Spare RelievingCapacity

To closed (isolation valving required) or atmosheric discharge system

Vessel

Nonrecoverable pressure losses not more than 3 percent of set pressure

Typical bleed valve



Section 6 – Drain Piping

6.1 Installation Conditions thatRequire Drain PipingDrain piping is normally not required onpressure relief valves at the valve bodyconnection provided for this purpose. Theoutlet piping to closed systems should beself-draining to a liquid disposal point,thereby eliminating the need for a drainfrom the valve. Drainage must be provid-ed when the discharge is not self-drainingand the valve is located where liquidscould accumulate at the valve outlet.

6.2 Safe Practice for Installation ofDrain PipingSince drain piping becomes part of the en-tire venting system, precautions that applyto the discharge system apply similarly tothe drain piping. The drain-piping installa-tion must not adversely affect the valveperformance, and flammable, toxic, or cor-rosive fluids must be piped to a safelocation.

Section 7 – Pressure Relief DeviceLocation and Position

7.1 Inspection and MaintenanceFor optimum performance, pressure reliefdevices must be serviced and maintainedregularly. Details for the care and servic-ing of specific pressure relief devices areprovided in the manufacturer's mainte-nance bulletins and in API RecommendedPractice 576. Pressure relief devicesshould be located for easy access, re-moval, and replacement so that servicingcan be properly handled. Sufficient work-ing space should be provided around thepressure relief device.

7.2 Proximity to Pressure SourceThe pressure relief device should normallybe placed close to the protected equip-ment so that the inlet pressure losses tothe device are within the allowable limits.For example, where protection of a pres-sure vessel is involved, mounting thepressure relief device directly on a nozzleon top of the vessel may be necessary.However, on installations that have pres-sure fluctuations at the pressure source(as with valves on a positive displacementcompressor discharge) that peak close to

the set pressure of the pressure reliefvalve or burst pressure of a rupture disk,the pressure relief device should be locat-ed farther from the source and in a morestable pressure region. (See Section 2 forinformation related to this subject.)

7.3 Proximity to Other EquipmentPressure relief devices should not be lo-cated where unstable flow patterns arepresent (see Figure 14). The branch en-trance where the relief device inlet pipingjoins the main piping run should have awell-rounded, smooth corner that mini-mizes turbulence and resistance to flow.

When pressure relief branch connectionsare mounted near equipment that cancause unstable flow patterns, the branchconnection should be mounted down-stream at a distance sufficient to avoid theunstable flow. Examples of devices thatcause unstable flow are discussed in 7.3.1through 7.3.3.

7.3.1 Reducing StationsPressure relief devices are often used toprotect piping downstream from pressurereducing valves, where unstable flow usu-ally occurs. Other valves andappurtenances in the system may alsodisturb the flow. This condition cannot beevaluated readily, but unstable flow atvalve inlets tends to generate instability.

7.3.2 Orifice Plates and Flow NozzlesProximity to orifice plates and flow nozzlesmay cause adverse operation of the pres-sure relief devices.

7.3.3 Other Valves and FittingsProximity to other fittings, such as elbows,may create turbulent areas that could re-sult in adverse performance of pressurerelief devices.

7.4 Mounting PositionPressure relief valves should be mountedin a vertical upright position. Installation ofa pressure relief valve in other than a ver-tical upright position may adversely affectits operation. The valve manufacturershould be consulted about any othermounting position, since mounting a pres-sure relief valve in other positions maycause a shift in the set pressure and a re-duction in the degree of seat tightness.

Additionally, another position may permitliquids to collect in the spring bonnet.Solidification of these liquids around thespring may interfere with the valve opera-tion.

7.5 Test or Lifting LeversTest or lifting levers should be provided onpressure relief valves as required by theapplicable code. Where simple levers areprovided, they should hang downward,and the lifting fork must not contact the lift-ing nuts on the valve spindle. Uploadscaused by the lifting-mechanism bearingon the spindle will cause the valve to openbelow the set pressure. The lifting mecha-nism should be checked to ensure that itdoes not bind on the valve spindle.

Where it is necessary to have the testlever in other than a vertical position, orwhere the test lever is arranged fro remote


Figure 12 – Typical Flare HeaderBlock Valves

Process unit flare header block valve (See Note 1)

Pressure relief valve installation (See Note 3)

Process unit relief header (self draining)

Pressure relief valve installation (See Note 4)

Pressurevessel A

Pressurevessel B

Isolation blind point (See Note 2)

Battery limit

To mainflare header

Notes

1. See 4.4.2. See Figure 8.3. See Figures 10 and 11.4. See Figures 2 and 9.



manual operation, the lever should becounterbalanced so that the lifting mecha-nism, unless actuated, does not exert anyforce on the valve spindle lifting nut.

In lieu of lifting levers for pilot-operatedpressure relief valves, means may bespecified for connecting and applying ade-quate pressure to the pilot to verify thatthe moving parts critical to proper opera-tion are free to move.

7.6 Heating Tracing and InsulationFor materials which are highly viscous,could result in corrosion upon cooling, or could potentially solidify in pressure relief valves, adequate heat tracing or in-sulation should be provided for both inletand outlet piping. Ensure that the valvenameplate and any discharge vent port arenot covered when the valve is insulated.

Section 8 – Bolting and Gasketing

8.1 Care in InstallationBefore a pressure relief device is installed,the flanges on the pressure relief valve orrupture disk holder and the mounting noz-

zle should be thoroughly cleaned to re-move any foreign material that may causeleakage. Where pressure relief devicesare too heavy to be readily lifted by hand,the use of proper handling devices willavoid damage to the flange gasket facing.Ring joint and tongue-and-groove facingsshould be handled with extreme care sothat the mating sections are not damaged.

8.2 Proper Gasketing and Boltingfor Service RequirementsThe gasket used must be dimensionallycorrect for the specific flanges; they mustfully clear the pressure relief device inletand outlet openings.

Gaskets, flange facings, and boltingshould meet the service requirements forthe pressure and temperature involved.This information can be obtained by refer-ring to other national standards and tomanufacturers’ technical catalogs.

When a rupture disk device is installed inthe pressure relief system, the flange gas-ket material and bolting loads may becritical. The disk manufacturer’s instruc-tions should be followed for properperformance.

Section 9 – Multiple PressureRelief Valves with StaggeredSettings

Normal practice is to size a single pres-sure relief valve to handle the maximumrelief from a piece of equipment. However,for some systems, only a fraction of thatamount must be relieved through thepressure relief valve during mild upsets. Ifthe fluid volume under a pressure reliefvalve is insufficient to sustain the flow, thevalve operation will be cyclic and will re-sult in poor performance. The valve'sability to reseat tightly may be affected.

When capacity variations are frequentlyencountered in normal operation, one al-ternate is the use of multiple, smallerpressure relief valves with staggered set-tings. With this arrangement, the pressurerelief valve with the lowest setting will becapable of handling minor upsets, and ad-ditional pressure relief valves will be put inoperation as the capacity requirement in-creases.

For inlet piping to multiple relief valves,the piping which is common to multiplevalves must have a flow area which is atleast equal to the combined inlet areas ofthe multiple pressure relief valves con-nected to it.

Refer to API Recommended Practice 520,Part I, to determine set pressure of thepressure relief valves based on maximumallowable pressure accumulation for multi-ple valve installations.

An alternate to the use of multiple pres-sure relief valves with staggered settingsis the use of a modulating pilot-operatedrelief valve.

Section 10 – PreinstallationHandling and Inspection

10.1 Storage and Handling ofPressure Relief DevicesBecause cleanliness is essential to thesatisfactory operation and tightness of apressure relief valve, take precautions tokeep out all foreign materials. Valvesshould be closed off properly at both inletand outlet flanges. Take particular care tokeep the valve inlet absolutely clean.

Figure 13 – Typical Isolation Block Valves for Spare Compressor

Isolation block valves (See Note 1)

Compressor relief headers Isolation blind points

Bleed valve

Process unit flare header

First stage Second stage Third stage

1 2 3

Pulsation dampners

From spare compressor

Note

1. See 4.4.





Rounded entry branch

connection

Inlet pipe

Inlet flanges

Run Pipe

D

Flow

Figure 14 – Typical InstallationAvoiding Unstable Flow Patterns atPressure Relief Valve Inlet

Note

1. D is typically not less than 10 pipe diametersfrom any device that causes unstable flow.

Pressure relief valves should, when possi-ble, be stored indoors on pallets awayfrom dirt and other forms of contamination.

Pressure relief devices should be handledcarefully and should not be subjected toshocks, which can result in considerableinternal damage or misalignment. Forvalves seat tightness may be adverselyaffected. Ruptured disks should be storedin the original shipping container.

10.2 Inspection and Testing ofPressure Relief ValvesThe condition of all pressure relief valvesshould be visually inspected before instal-lation. Consult the manufacturer’sinstruction manuals for details relating tothe specific valve. Ensure that all protec-tive material on the valve flanges and anyextraneous materials inside the valvebody and nozzle are completely removed.Bonnet shipping plugs must be removedfrom balanced pressure relief valves. Theinlet surface must be cleaned, since for-eign materials clinging to the inside of thenozzle will be blown across the seatswhen the valve is operated. Some ofthese materials may damage the seats orget trapped between the seats in such away that they cause leakage. Valvesshould be tested before installation to con-firm set pressure.

10.3 Inspection of Rupture DiskDevicesAll rupture disk devices should be thor-oughly inspected before installation,according to the manufacturer’s instruc-tion manuals. The seating surfaces of therupture disk holder must be clean,smooth, and undamaged.

Rupture disks should be checked forphysical damage to the seating surfacesor the prebulged disk area. Damaged ordented disk should not be used. Apply theproper installation and torquing procedureas recommended by the rupture disk de-vice manufacturer.

On reverse-buckling disk that have knife-blade assemblies, the knife blades mustbe checked for physical damage andsharpness. Nicked or dull blades must notbe used. Damaged rupture disk holdersmust be replaced.

10.4 Inspection and Cleaning ofSystems Before InstallationBecause foreign materials that pass intoand through pressure relief valves candamage the valve, the systems on whichthe valves are tested and finally installedmust also be inspected and cleaned. Newsystems in particular are prone to containwelding beads, pipe scale, and other for-eign objects that inadvertently get trappedduring construction and will destroy theseating surface when the valve opens.The system should be thoroughly cleanedbefore the pressure relief valve is in-stalled.

Pressure relief devices should be re-moved or isolated before hydrotesting orpneumatic pressure testing of the system,either by blanking or closing an isolationvalve. If an isolation valve is used, theflange at the pressure relief device shouldbe wedged open or a bleed valve provid-ed so that inadvertent leaking through theisolation valve does not damage the pres-sure relief device.



Following is an Excerpt from NACE MR0175-95, API - RP 521, and API - RP 527



Section 3: Ferrous MetalsFerrous metals shall meet the require-ments of this section if they are to beexposed to sour environments (defined inParagraph 1.3).

3.1 GeneralThe susceptibility to SSC of most ferrousmetals can be strongly affected by heattreatment, cold work, or both. The follow-ing paragraphs describe heat treatmentsfor specific materials that have been foundto provide acceptable resistance to SSC.

3.2 Carbon and Low-Alloy Steels3.2.1 All carbon and low-alloy steels areacceptable at 22 HRC maximum hardnessprovided they (1) contain less than 1%nickel, (2) meet the criteria of Paragraphs3.2.2, 3.3, and Section 5, and (3) are usedin one of the following heat-treat conditions:

(a) hot-rolled (carbon steels only);

(b) annealed;

(c) normalized;

(d) normalized and tempered;

(e) normalized, austenitized, quenched,and tempered; or

(f) austenitized, quenched, and tempered.

3.2.1.1 Forgings produced in accordancewith the requirements of ASTM A 105 areacceptable, provided the hardness doesnot exceed 187 HB maximum.

3.2.1.2 Acceptance criteria: Wrought car-bon and low-alloy steels with a hardnessgreater than HRC 22 that are not other-wise covered by this materials requirement standard must meet the fol-lowing minimum criteria for balloting priorto inclusion in this document. These crite-ria are necessary but may not be sufficientconditions for inclusion in all cases.

(1) The candidate steel must be tested inaccordance with the test procedures es-tablished in NACE Standard TM0177(latest revision). The tensile bar, O-ring,bent beam, and double cantilever beam

as described in NACE Standard TM0177are accepted test specimens. Any of thesespecimens may be used.

(2) A minimum of three specimens fromeach of three different commercially pre-pared heats must be tested in the(heat-treated) condition balloted forMR0175 inclusion. The composition ofeach heat and the heat treatment(s) usedshall be furnished as part of the ballot.The candidate material’s compositionrange and/or UNS number and its heat-treated condition requested for inclusion inMR0175 must be included with the ballot.

(3) The Rockwell hardness of each speci-men must be determined and reported aspart of the ballot. The average hardness ofeach specimen shall be the hardness ofthat specimen. The minimum specimenhardness obtained for a given heat/condi-tion shall be the hardness of that heat/condition for the purpose of balloting. Themaximum hardness requested for inclu-sion of the candidate material in MR0175must be specified in the ballot and shouldbe supported by the data provided.

(4) Further, in order for the material/ condi-tion to be considered for acceptance, it isrequired that, for each of the commercialheats tested, stress intensity values, etc.(as applicable to the test method used), ofall tests shall also be reported as part ofthe ballot item when submitted.

3.2.2 The metal must be thermally stressrelieved following any cold deforming byrolling, cold forging, or another manufactur-ing process that results in a permanent,outer fiber deformation greater than 5%.Thermal stress relief shall be performed inaccordance with the ASME Code, SectionVIII, Division I, except that the minimumstress relief temperature shall be 595°C(1100°F). The component shall have ahardness of 22 HRC maximum.

3.2.2.1 This requirement does not apply topipe grades listed in Table 3 or cold workimparted by pressure testing per the ap-plicable code. Cold-rotary straightened

pipe is acceptable only where permitted inAPI specifications. Cold-worked line pipefittings of ASTM A 53 Grade B, ASTM A106 Grade B, API 5L Grade X-42, or lower-strength grades with similar chemi-cal compositions are acceptable with coldstrain equivalent to 15% or less, providedthe hardness in the strained area does notexceed 190 HB.

3.2.3 Tubulars and tubular componentsmade of low-alloy steels in the Cr, Mo se-ries (AISI 41XX and its modifications) areacceptable at a 26 HRC maximum hard-ness, provided they are in the quenchedand tempered condition.

3.2.3.1 Careful attention to chemical com-position and heat treatment is required toensure SSC resistance of these alloys atgreater than 22 HRC. Accordingly, it iscommon practice, when using these alloysat above 22 HRC, for the user to conductSSC tests (in accordance with Paragraph1.6) to determine that the material isequivalent in SSC performance to similarmaterials that have given satisfactory ser-vice in sour environments.

3.2.3.2 If tubulars and tubular componentsare cold straightened at or below 510°C(950°F), they shall be stress relieved at aminimum of 480°C (900°F).

3.3 Free Machining Steels3.3.1. Free-machining steels shall not beused.

3.4 Cast Iron3.4.1 Gray, austenitic, and white cast ironsare not acceptable for use as a pressure-containing member. These materials maybe used in internal components related toAPI and other appropriate standards, pro-vided their use has been approved by thepurchaser.

3.4.2 Ferritic ductile iron ASTM A 395 is acceptable for equipment when API,ANSI, and/or other industry standards approve its use.

NACE MR0175-95 Excerpts on Valve Materials



1. These materials may be subject to chlorideSCC in certain environments.

2. Valve manufacturers generally do not usethese material for valve stems or other high-ly stressed components in sour service.

3. The hardness correlation tabulated in ASTME 140 does not apply to CA6NM or UNSS42400. When hardness is measured inBrinell units, the permissible BHN limit is255 maximum, which has been empiricallydetermined to be equivalent to HR 23 forthese alloys.

Notes

3.5 Austenitic Stainless Steels1

3.5.1 Austenitic stainless steels withchemical compositions as specified in accordance with the standards listed inTable 1, either cast or wrought, are ac-ceptable at a hardness of 22 HRCmaximum in the annealed condition pro-vided they are free of cold work designedto enhance their mechanical properties.

3.5.2 Austenitic stainless steel UNSS20910 is acceptable at 35 HRC maximumhardness in the annealed or hot-rolled(hot/cold-worked) condition, provided it isfree of subsequent cold work designed toenhance its mechanical properties.

3.5.3 Austenitic stainless steel alloy UNSN08020 is acceptable in the annealed orcold-worked condition at a hardness levelof 32 HRC maximum.

3.5.4 Cast CN7M meeting ASTM A 351, A743, or A 744 is acceptable for nondown-hole applications in the followingconditions (there are no industry stan-dards that address these melting andcasting requirements):

(1) solution-annealed at 1121°C (2050°F)minimum or solution-annealed at 1121°C(2050°F) minimum and welded with AWSE320LR or ER320LR;

(2) the castings must be produced fromargon-oxygen decarburization (AOD) re-fined heats or remelted AOD refinedheats. The use of scraps, such as turnings,chips, and returned materials is prohibitedunless melting is followed by AOD refining;

(3) the CN7M composition listed in ASTMA 351, A 743, or A 744 shall be further re-stricted to 0.03 percent maximum carbon,1.00% maximum silicon, 3.0 to 3.5% cop-per, 0.015% maximum sulfur, 0.030%maximum phosphorous, and 0.05 percentmaximum aluminum; and

(4) at a hardness level of 22 HRC maximum.

3.5.5 Wrought austenitic stainless steelUNS S31254 is acceptable in the an-nealed or cold-worked condition at ahardness level of 35 HRC maximum.

3.5.6 Austenitic stainless steel UNSN08367 is acceptable in the absence offree elemental sulfur at 22 HRC or less attemperatures below 150°C (302°F) whenthe salinity does not exceed 5,000 mg/Land the H2S partial pressure does not ex-ceed 0.31 MPa (45 psia).

3.6 Ferritic Stainless Steels3.6.1 Ferritic stainless steels are accept-able at a 22 HRC maximum hardness,provided they are in the annealed condi-tion and meet the criteria of Section 5.Acceptable ferritic stainless steels are list-ed in Table 1.

3.7 Martensitic Stainless Steels2

3.7.1 Martensitic stainless steels, as listedin Table 1, either cast or wrought, are ac-ceptable at 22 HRC maximum hardnessprovided they are heat treated perParagraph 3.7.1.1 and meet the criteria ofSection 5. Martensitic stainless steels thatare in accordance with this standard haveprovided satisfactory field service in somesour environments. These materials may,however, exhibit threshold stress levels inNACE Standard TM0177 that are lowerthan those for other materials included inthis standard.

3.7.1.1 Heat-Treat Procedure (Three-StepProcess)

(1) Normalize or austenitize and quench.

(2) Temper at 620°C (1150°F) minimum;then cool to ambient temperature.

(3) Temper at 620°C (1150°F) minimum,but lower than the first tempering temper-ature, then cool to ambient temperature.

3.7.1.2 Subsequent to cold deformation(see Paragraph 3.2.2) the material shallbe furnace stress relieved at 620°C(1150°F) minimum to 22 HRC maximumhardness.

3.7.2 Low-Carbon Martensitic StainlessSteels

3.7.2.1 Cast and wrought low-carbonmartensitic stainless steels meeting thechemistry requirements of ASTM A 487Grade CA6NM and UNS S42400 are ac-ceptable to HRC 23 maximum providedthey are heat treated per Paragraph3.7.2.1.1.3

3.7.2.1.1 Heat-Treat Procedure (Three-Step Process)

(1) Austenitize at 1010°C (1850°F) mini-mum and air or oil quench to ambienttemperature;

(2) Temper at 648° to 690°C (1200° to1275°F) and air cool to ambient tempera-ture;

(3) Temper at 593° to 620°C (1100° to1150°F) and air cool to ambient tempera-ture.

3.8 Precipitation-GardeningStainless Steels1

3.8.1 Wrought UNS S17400 martensiticprecipitation-hardening stainless steel isacceptable at 33 HRC maximum hardnessprovided it has been heat treated inaccordance with Paragraph 3.8.1.1 orParagraph 3.8.1.2. Precipitation-hardeningmartensitic stainless steels that are in ac-cordance with this standard have providedsatisfactory field service in some sour environments. These materials may, how-ever, exhibit threshold stress levels inNACE Standard TM0177 that are lowerthan those of other materials included inthis standard.




4. These materials may be subject to SCC fail-ure when highly stressed and exposed tosour environments or some well-stimulatingacids either with or without inhibitors.

5. Some of the materials in the wrought condi-tion may be susceptible to failure by

hydrogen embattlement when strengthenedby cold work and stressed in the transversedirection.

6. Plastic deformation in service may increasethe SSC susceptibility of these alloys.

3.8.1.1 Double Age at 620°C (1150°F).

(1) Solution anneal at 1040°C ± 14°C(1900°F ± 25°F) and air cool, or suitableliquid quench, to below 32°C (90°F).

(2) Harden at 620°C ± 14°C (1150°F ±25°F) for 4 hours minimum and cool in air.

(3) Cool material to below 32°C (90°F) be-fore the second precipitation-hardeningstep.

(4) Harden at 620°C ± 14°C (1150°F ±25°F) for 4 hours minimum at temperatureand cool in air.

3.8.1.2 Heat-Treat Procedure (Three-StepProcess)

(1) Solution anneal at 1040°C ± 14°C(1900°F ± 25°F) and air cool, or suitableliquid quench, to below 32°C (90°F).

(2) Harden at 760°C ± 14°C (1400°F ±25°F) for 2 hours minimum at temperatureand cool in air to below 32°C (90°F) be-fore second precipitation-hardening step.

(3) Precipitation harden at 620°C ± 14°C(1150°F ± 25°F) for 4 hours minimum attemperature and cool in air.

3.8.2 Austenitic precipitation-hardeningstainless steel with chemical compositionin accordance with UNS S66286 is ac-ceptable at 35 HRC maximum hardnessprovided it is in either the solution-an-nealed and aged or solution annealed anddouble-aged condition.

3.8.3 Wrought UNS S45000 martensiticprecipitation-hardening stainless steel isacceptable at 31 HRC maximum hardnessprovided it has been heat treated perParagraph 3.8.3.1

3.8.3.1 Heat-Treat Procedure (Two-StepProcess)

(1) Solution anneal;

(2) Precipitation harden at 620°C (1150°F)minimum for 4 hours.

3.9 Duplex Stainless Steels1

3.9.1 The wrought duplex (austenitic/ferrit-ic) stainless steels listed in Table 1 areacceptable 28 HRC maximum in the solu-tion-annealed condition.

3.9.2 The cast duplex (austenitic/ferritic)stainless steel Z6CNDU20.08M, NF A320-55 French National Standard is ac-ceptable at hardness levels of 17 HRCmaximum in the annealed and quenchedcondition provided the ferrite content is 25 to 40%. The annealing shall be at atemperature of 1150°C ± 10°C (2100°F ± 20°F) and shall be followed by a rapidquench to avoid the precipitation of sigmaphase.

3.9.3 Wrought duplex stainless steel UNSS32404 (0.1% to 0.2% nitrogen) is accept-able at 20 HRC maximum in thesolution-annealed condition.

3.9.4 Solution-annealed and cold-workedUNS S31803 is acceptable for use at anytemperature up to 232°C (450°F) in sourenvironments if the partial pressure of hy-drogen sulfide does not exceed 0.002MPa (0.3 psia), the yield strength of the materials is not greater than 1100MPa (160 ksi) and its hardness is notgreater than 36 HRC.

3.9.5 Wrought duplex stainless steel UNSS32750 is acceptable at 32 maximum inthe solution-annealed condition in sourenvironments up to 232°C (450°F) if theH2S partial pressure does not exceed0.010 MPa (1.5 psia).

Section 4: Nonferrous Metal4–6

4.1 General.Nonferrous metal referenced in this sec-tion and meeting the stated requirementsfor both condition and hardness are accept-able for use in sour environments (definedin Paragraph 1.3). See also Table 2.

4.1.1 Nickel-Copper Alloys

4.1.1.1 UNS N04400, ASTM A 494 GradesM-35-1 and M-35-2, and UNS N04405 areacceptable to 35 HRC maximum.

4.1.1.2 UNS N05500 is acceptable to 35HRC maximum in each of the three follow-ing conditions: (1) hot-worked andage-hardened; (2) solution-annealed; and(3) solution-annealed and age-hardened.

4.1.2 Nickel-lron Chromium Alloys

4.1.2.1 UNS N08800 is acceptable to 35HRC maximum.

4.1.3 Nickel-lron-Chromium-MolybdenumAlloys

4.1.3.1 UNS N08825, UNS N06007, andwrought UNS N06975 are acceptable to35 HRC maximum; UNS N06950 is ac-ceptable to 38 HRC maximum; and UNSN06985 is acceptable to HRC 39 maximum.

4.1.3.2 UNS N09925 is acceptable ineach of the five following conditions: (1)cold-worked to 35 HRC maximum; (2) so-lution-annealed to 35 HRC maximum; (3)solution-annealed and aged to 38 HRCmaximum; (4) cold-worked and aged to 40HRC maximum; and (5) hot-finished andaged to 40 HRC maximum.

4.1.3.3 UNS N08024 to 32 HRC maximum.


Notes



4.1.3.4 UNS N08028 in the solution-an-nealed and cold-worked condition to 33HRC maximum.

4.1.3.5 Nickel-iron-chromium-molybde-num-tungsten alloy UNS N06030 isacceptable in the solution-annealed or solution-annealed plus cold-worked condi-tion to a maximum hardness of HRC 41.

4.1.3.6 UNS N07048 is acceptable in thesolution annealed, solution-annealed andaged, or direct-aged condition to HRC 4Omaximum.

4.1.3.7 UNS N08535 is acceptable in thesolution-annealed and cold-worked condi-tion to 35 HRC maximum.

4.1.3.8 Wrought UNS N08042 is accept-able in the solution-annealed orsolution-annealed plus cold-worked condi-tions to HRC 31 maximum when theservice environment does not contain ele-mental sulfur.

4.1.3.9 UNS N06952 is acceptable in thesolution-annealed or solution-annealedplus cold-worked conditions to 35 HRCmaximum when the service environmentdoes not contain elemental sulfur.

4.1.4 Nickel-Chromium Alloys

4.1.4.1 UNS N06600 is acceptable to 35HRC maximum.

4.1.4.2 UNS NO7750 is acceptable to 35HRC maximum in each of the four follow-ing conditions: (1) solution-annealed andaged; (2) solution-annealed; (3) hot-worked; and (4) hot-worked and aged.

4.1.5 Nickel-Chromium-MolybdenumAlloys

4.1.5.1 UNS N06002 and UNS N06625are acceptable to 35 HRC maximum.

4.1.5.2 UNS N10002, UNS N10276, andASTM A494 Grade CW-12 MW are ac-ceptable in the solution-annealed or solution-annealed plus cold-worked condi-tions to 35 HRC maximum (except asnoted in Paragraph 4.1.5.2.1). Alloy UNS

N06022 is acceptable in the solution-annealed or solution-annealed plus cold-worked conditions to 40 HRC maximum.

4.1.5.2.1 Alloy UNS N10276 is also ac-ceptable in the cold-worked and unagedcondition at 45 HRC maximum when usedat a minimum temperature of 121°C(250°F).

4.1.5.3 Wrought UNS N07718 is accept-able in each of the five followingconditions: (1 ) solution-annealed to 35HRC maximum; (2) hot-worked to 35 HRCmaximum; (3) hot-worked and aged to 35HRC maximum; (4) solution-annealed andaged to 40 HRC maximum; and (5) cast,solution-annealed, and aged condition to40 HRC maximum.

4.1.5.4 UNS N07031 is acceptable ineach of the two following conditions: (1)solution-annealed condition to 35 HRCmaximum; and (2) solution-annealed andaged at 760° to 870°C (1400° to 1600°F)for a maximum of 4 hours to 40 HRCmaximum.

4.1.5.5 UNS N06110 and wrought UNSN06060 are acceptable in the annealed orcold-worked conditions to 40 HRC maxi-mum.

4.1.5.6 UNS N07716 and wrought UNSN07725 are acceptable to 40 HRC maxi-mum in the solution annealed and agedcondition.

4.1.5.7 UNS N07626, totally dense hotcompacted by a powder metallurgyprocess, is acceptable in the solution-an-nealed (925°C [11700°F] minimum) plusaged condition (525°C to 825°C [1000°Fto 1500°F]) or the direct-aged (525°C to825°C [1000°F to 1500°F]) condition to amaximum hardness of HRC 40 and amaximum tensile strength of 1380 MPa(200 ksi).

4.1.5.8 Cast CW2M meeting ASTM A 494is acceptable for nondownhole applica-tions in the following conditions (there areno industry standards that currently ad-

dress these melting and casting require-ments):

(1) solution-annealed at 1232 ± 14°C(2250°F ± 25°F) or solution-annealed at1232°C ± 14 °C (2250°F ± 25°F) andwelded with AWS ENiCrMo-7, ERNiCrMo-7, ENiCrMo-10, or ERNiCrMo-10;

(2) the castings must be produced by ar-gon-oxygen decarburization (AOD)refined heats, remelted AOD refinedheats, or virgin remelt stock. The use ofscrap, such as turnings, chips, and re-turned material is prohibited unlessfollowed by AOD refining;

(3) the CW2M composition listed in ASTMA 494 shall be further restricted to 0.015%maximum sulfur and 0.05% maximum alu-minum; and

(4) at a hardness level of 22 HRC maxi-mum.

4.1.6 Cobalt-Nickel-Chromium-Molybdenum Alloys

4.1.6.1 Alloys UNS R30003, UNSR30004, UNS R30035, and BritishStandard, Aerospace Series HR3 are acceptable at 35 HRC maximum exceptwhen otherwise noted.

4.1.6.2 In addition, UNS R30035 is ac-ceptable at 51 HRC maximum in thecold-reduced and high-temperature agedheat-treated condition in accordance withone of the following aging treatments:

Minimum Time (hours) Temperature

4 704°C (1300°F)

4 732°C (1350°F)

6 774°C (1425°F)

4 788°C (1450°F)

2 802°C (1475°F)

1 816°C (1500°F)




4.1.6.3 Wrought UNS R31233 is acceptable in the solution-annealed condi-tion to 22 HRC maximum.

4.1.7 Cobalt- Nickel-Chromium-TungstenAlloy

4.1.7.1 UNS R30605 to 35 HRC maximum.

4 .2 Other Alloys4.2.1 Materials described in this sectionand listed in Table 2 are acceptable.

4.2.1.1 Aluminum-base alloys

4.2.1.2 Copper alloys7

4.2.1.3 Commercially pure tantalum. UNSR05200 is acceptable in the annealed andgas tungsten arc-welded annealed condi-tions to 55 HRB maximum.

4.2.1.4 Titanium alloys. Specific guide-lines must be followed for successfulapplications of each titanium alloy speci-fied in this standard. For example,hydrogen embrittlement of titanium alloysmay occur if galvanically coupled to cer-tain active metals (i.e., carbon steel) inH2S-containing aqueous media at temper-atures greater than 80°C (176°F). Sometitanium alloys may be susceptible tocrevice corrosion and/or SCC in chlorideenvironments. Hardness has not beenshown to correlate with susceptibility toSSC. However, hardness has been in-cluded for alloys with high strength toindicate the maximum testing levelswhere failure has not occurred.

4.2.1.4.1 UNS R53400 is acceptable in theannealed condition. Heat treatment shallbe annealing at 774°C ± 14°C (1425°F ±25°F) for 2 hours followed by air cool.Maximum hardness to be 92 HRB.

4.2.1.4.2 UNS R58640 is acceptable to 42HRC maximum.

4.2.1.4.3 UNS R50400 is acceptable to100 HRB maximum.

4.2.1.4.4 UNS R56260 is acceptable to 45HRC maximum in each of the three followingconditions: (1) annealed; (2) solution-an-nealed; and (3) solution-annealed and aged.

4.2.1.4.5 Wrought UNS L56403 is accept-able in the annealed condition to 36 HRCmaximum.

Section 5: Fabrication

5.1 GeneralMaterials and fabrication processes shallmeet the requirements of this section ifthe material is to be exposed to sour envi-ronments (defined in Paragraph 1.3).

5.2 Overlays5.2.1 Overlays applied to carbon and low-alloy steel or to martensitic stainlesssteels by thermal processes such as weld-ing, silver brazing, or spray metallizingsystems are satisfactory for use in sour en-vironments, provided the substrate does notexceed the lower critical temperature duringapplication. In those cases in which the lower critical temperatures are exceeded,the component must be heat treated orthermally stress relieved according to pro-cedures that have been shown to return thebase metal to 22 HRC maximum.

5.2.2 Tungsten-carbide alloys and ceram-ics are satisfactory, subject to theconditions of Paragraph 5.2.1.8

5.2.3 Joining of dissimilar materials, suchas cemented to alloy steels by silver braz-ing, is acceptable. The base metal afterbrazing shall meet the requirements ofParagraph 5.2.1.

5.2.4 The materials listed in Sections 3and 4 are acceptable as weld overlays,provided they meet the provisions ofParagraph 5.2.1.

5.2.5 Overlays of cobalt-chromium-tung-sten alloys or nickel-chromium-boronhardfacing alloys are acceptable, subjectto the conditions of Paragraph 5.2.1.8

5.3 Welding5.3.1 Welding procedures shall be used toproduce weldments that comply with thehardness requirements specified for thebase metal in Sections 3 and 4. Weldingprocedures shall be qualified per AWS,API, ASME, or other appropriate industry

codes. Welders using this procedure shallbe familiar with the procedure and shallbe capable of making welds that complywith the procedure.

5.3.1.1 Tubular products listed in Table 3with specified minimum yield strength of360 MPa (52 ksi) or less and pressurevessel steels classified as P-No 1, Group1 or 2, in Section 9 of the ASME Codeand listed in Table 3 meet the require-ments of Paragraph 5.3.1 in theas-welded condition. Welding procedurequalifications, per AWS, API, ASME, orother appropriate specifications shall beperformed on any welding procedure thatis used.

5.3.1.2 Welding procedure qualificationson carbon steels that use controls otherthan thermal stress relieving to control thehardness of the weldment shall also in-clude a hardness traverse across theweld, HAZ and base metal to ensure thatthe procedure is capable of producing ahardness of 22 HRC maximum in the con-dition in which it is used.

5.3.1.3 Low-alloy steel and martensiticstainless steel weldments shall be stressrelieved at a minimum temperature of620°C (1150°F) to produce a hardness of22 HRC maximum.

5.3.2 Welding rods, electrodes, fluxes,filler metals, and carbon and low-alloysteel welding consumables with morethan 1% nickel are not allowed for weldingcarbon and low-alloy steels as indicated inParagraph 3.2.1.

5.4 Identification Stamping5.4.1 Identification stamping using low-stress (dot, vibratory, and round V)stamps is acceptable.

5.5.2 Conventional sharp V stamping isacceptable in low-stress areas, such asthe outside diameter of flanges. Sharp Vstamping is not permitted in high-stressareas unless subsequently stress relievedat 595°C (1100°F) minimum.

7. Copper-base alloys may undergo weightloss corrosion in sour oilfield environments,particularly if oxygen is present.

8. Denotes editorial revision.

Notes




5.5 Threading5.5.1 Machine-Cut Threads

5.5.1.1 Machine-cut threading processesare acceptable.

5.5.2 Cold-Formed (Rolled) Threads

5.5.2.1 Subsequent to cold formingthreads, the threaded component shallmeet the heat-treat conditions and hard-ness requirements given in either Section3 or 4 for the parent alloy from which thethreaded component was fabricated.

5.6 Cold-Deformation Processes5.6.1 Cold-deformation processes such asburnishing that do not impart cold workexceeding that incidental to normal ma-chining operations, such as turning orboring, rolling, threading, drilling, etc., areacceptable.

5.6.2 Cold deformation by controlled shotpeening is permitted when applied to basematerials that meet the requirements ofthis document and when limited to the useof a maximum shot size of 230 (0.584 mmnominal diameter) and a maximum of0.356 mm A Almen intensity. The processshall be controlled in accordance withMilitary Specification MIL-S-13165-B, latest revision.

Section 6: Bolting

6.1. General.Materials shall meet the requirements ofthis section if they are to be exposed tosour environments (defined in Paragraph1.3).

6.2 Exposed Bolting6.2.1 Bolting that will be exposed directlyto sour environment or that will be buried,insulated, equipped with flange protectors,or otherwise denied direct atmosphericexposure must be of either a Class I orClass II material (see Paragraph 6.2.1.1).9

6.2.1.1 Class I and Class II Nuts and Bolts

6.2.1.1.1 Acceptable nuts and bolting ma-terials shall meet the requirements ofSections 3 and 4.

6.2.1.1.2 Bolting materials that meet thespecifications of ASTM A 193 Grade B7M,550 MPa (80,000 psi) minimum yieldstrength, and 22 HRC maximum are ac-ceptable.

6.2.1.1.3 Nuts shall meet the specifica-tions of ASTM A 194 Grade 2HM (22 HRCmaximum) or Paragraph 6.2.1.1.1.

6.3 Nonexposed Bolting6.3.1 Class III Bolting

6.3.1.1 Bolting that is not directly exposedto sour environments and is not to beburied, insulated, equipped with flangeprotectors, or otherwise denied direct at-mospheric exposure may be furnished toapplicable standards such as ASTM A 193Grade B7.

Section 7: Platings and Coatings

7.1 General7.1.1. Materials shall meet the require-ments of this section if they are to beexposed to sour environments (defined inParagraph 1.3).

7.1.2 Metallic coatings (electroplated orelectroless), conversion coatings, andplastic coatings or linings are not accept-able for preventing SSC of base metals.The use of such coatings for other purpos-es is outside the scope of this standard.

7.2 Nitriding7.2.1 Nitriding with a maximum casedepth of 0.15 mm (0.006 inch) is an acceptable surface treatment when con-ducted at a temperature below the lowercritical temperature of the alloy system being treated. Its use as a means of pre-venting SSC is not acceptable.

Section 8: Special Components

8.1 General.Materials for special components includ-ing instrumentation, control devices,seals, bearings, and springs shall meetthe requirements of this section if they aredirectly exposed to sour environmentsduring normal operation of the device.Paragraph 1.3 provides guidelines to de-termine the applicability of this standard tospecific applications.

8.2 Bearings8.2.1 Bearings directly exposed to sourenvironments shall be made from materi-als in Sections 3 and 4.

8.2.2 Nickel-chromium-molybdenum-tung-sten alloy UNS N10276 bearing pins, i.e.core roll pins, are acceptable in the cold-worked condition to 45 HRC maximum.

8.2.3 Bearings made from other materialsmust be isolated from the sour environ-ment in order to function properly, exceptas noted in Paragraph 8.2.2.

8.3 Springs8.3.1 Springs directly exposed to the sourenvironment shall be made from materialsdescribed in Sections 3 and 4.

8.3.2 Cobalt-nickel-chromium-molybde-num alloy UNS R30003 may be used forsprings in the cold-worked and age-hard-ened condition to 60 HRC maximum. UNSR30035 may be used for springs in thecold-worked and age-hardened conditionof 55 HRC maximum when aged for aminimum of 4 hours at a temperature nolower than 648°C (1200°F).

8.3.3 Nickel-chromium alloy UNS N07750springs are acceptable in the cold-workedand age-hardened condition to 50 HRCmaximum.

8.3.4 UNS N07090 may be used for springsfor compressor valves in the cold-workedand age-hardened condition to 50 HRCmaximum.


Notes

9. Designers and users should be aware thatit may be necessary to derate the pressurerating in some cases when using low-strength bolts. For API 6A flanges usingClass II bolting, see API Standard 6A.



8.4 Instrumentation and ControlDevices8.4.1 Instrumentation and control devicecomponents directly exposed to sour envi-ronments shall be made from materials inSections 3 through 8.

8.4.1.1 Paragraph 3.5.1 is not intended topreclude the use of AISI Type 316 stain-less steel compression fittings andinstrument tubing even though they won’tsatisfy the requirements stated inParagraph 3.5.1.1

8.4.2 Diaphragms, Pressure-MeasuringDevices, and Pressure Seals.4–6

8.4.2.1 Diaphragms, pressure-measuringdevices, and pressure seals directly ex-posed to a sour environment shall bemade from materials in Sections 3 and 4.

8.4.2.2 Cobalt-nickel-chromium-molybde-num alloys UNS R30003 and UNSR30004 for diaphragms, pressure-mea-suring devices, and pressure seals areacceptable to 60 HRC maximum.

8.4.2.3 Cobalt-nickel-chromium-molybde-num-tungsten alloy UNS R30260diaphragms, pressure-measuring devices,and pressure seals are acceptable to 52HRC maximum.

8.4.2.4 Pressure seals shall comply withthe requirements of Sections 3 and 4 andTables 1 and 2 or may be manufactured ofwrought cobalt-chromium-nickel-molybde-num alloy UNS R30159 to 53 HRCmaximum with the primary load-bearing orpressure-containing direction parallel tothe longitudinal or rolling direction ofwrought products.

8.5 Seal Rings8.5.1 Seal rings directly exposed to a sourenvironment shall be made from materialsin Sections 3 and 4.

8.5.2 Austenitic stainless steel API com-pression seal rings made of centrifugallycast ASTM A 351 Grade CF8 or CF8Mchemical compositions are acceptable in

the as-cast or solution-annealed conditionto 160 HB (83 HRB) maximum.

8.6 Snap Rings8.6.1 Snap rings directly exposed to asour environment shall be made from ap-plicable materials in Sections 3 and 4,except as noted in Paragraph 8.6.2.

8.6.2 Precipitation-hardening stainlesssteel alloy UNS S15700 snap rings origi-nally in the RH950 solution-annealed andaged condition are acceptable when fur-ther heat treated to a hardness of 30 to 32HRC as follows:

8.6.2.1 Heat-Treatment Procedure (3-StepProcess)

(1) Temper at 620°C (1150°F) for 4 hours,15 minutes. Cool to room temperature instill air.

(2) Retemper at 620°C (1150°F) for 4hours, 15 minutes. Cool to room tempera-ture in still air.

(3) Temper at 560°C (1050°F) for 4 hours,15 minutes. Cool to room temperature instill air.

8.7 Bearing Pins8.7.1 Bearing pins, e.g., core roll pins,made from UNS N10276 in the cold-worked condition with a maximumhardness of 45 HRC, may be used.

8.8 Duplex Stainless Steel forWellhead Components10

8.8.1 Cast duplex (austenitic/ferritic) stain-less steel UNS J93345 is acceptable inthe solution-treated condition providedthat the hardness does not exceeded 223HB. The material must be restricted to thefollowing products: valve components,compressor components, casting and tub-ing heads (excluding mandrel hangers),spools, side entry caps, tail pieces, ham-mer caps, and spider caps. Laboratorytests have shown that duplex stainlesssteels’ susceptibility to SSC is a functionof the percentage of ferrite. The user maydetermine the acceptability of a duplex

stainless steel with a given ferrite contentfor each application.

8.9 Special Process Parts11

8.9.1 Cobalt-chromium-tungsten alloys,whether cast, powder-metallurgyprocessed, or thermomechanicallyprocessed, are acceptable.

8.9.2 Tungsten carbide alloys, whethercast or cemented, are acceptable.

Section 9: Valves and Chokes

9.1 General9.1.1 Materials shall meet the require-ments of this section if they are to beexposed to sour environments (defined inParagraph 1.3).

9.1.2 Valves and chokes shall be manu-factured from materials in accordance withSections 3 through 8.

9.2 Shafts, Stems, and Pins9.2.1 Shafts, stems, and pins shall bemanufactured from materials in accor-dance with Sections 3 through 8.

9.2.2 Austenitic stainless steel UNSS20910 is acceptable for valve shafts,stems, and pins at a maximum hardnesslevel of 35 HRC in the cold-worked condi-tion, provided this cold working ispreceded by an anneal.

9.3 Internal Valve and PressureRegulator Components9.3.1 Cast CB7Cu-1 in the H1150 DBLcondition per ASTM A 747 is acceptablefor non-pressure-containing, internalvalve, and pressure regulator componentsat 310 HB maximum (30 HRC maximum)providing it complies with Paragraph 1.2.Precipitation-hardening martensitic stain-less steels that are in accordance with thisstandard have provided satisfactory fieldservice in some sour environments. Thesematerials may, however, exhibit thresholdstress levels in NACE Standard TM0177that are lower than other materials includ-ed in this standard.


10. Aging over 260°C (500°F) may reduce tem-perature toughness and reduce resistanceto environmental cracking.

11. Some of these materials may be used inwear-resistant applications and can be brittle. Environmental cracking may occur if these materials are subject to tension.

Notes



Table 1

Stainless Steels Acceptable for Direct Exposure to Sour Environments (see Paragraph 1.3)

Ferritic Martensitic Precipitation- Austenitic DuplexHardening (Austenitic /Ferritic)3

(Wrought Condition Only)

AISI AISI ASTM AISI UNS S31803

405 410 A 453 Gr. 6601 302 UNS S32550

430 501 A 638 Gr. 6601 304 UNS S32404

304L

305

308

309

310

316

316L

317

321

347

ASTM ASTM UNS S17400 ASTM Cast Duplex

A 268 A 217 Gr. CA 15 UNS S45000 A 182 (Austenitic/Ferritic)

TP 405, TP 430, A 268 Gr. TP 410 UNS S66286 A 1932 Stainless steel

TP XM 27, TP XM 33 A 743 Gr. CA 15M Gr. B8R, B8RA, B8, Z6CNDU20.08M, NF A

A 487 CI CA 15M B8M, B8MA 320-55 French National

A 487 CI CA 6NM A 1942 Standard

UNS S42400 Gr. 8R, 8RA, 8A, 8MA

A 3202

Gr. B8, B8M

A 351

Gr. CF3, CF8, CF3M,

CF8M

B463

B473

UNS S20910

UNS N08020

UNS S31254

Materials listed in this table should be used only under conditions noted in the text of this standard.

Notes

1. See Paragraph 3.8.2.

2. Carbide solution-treated.

3. Aging over 260°C (500°F) may reduce low-temperature toughness and reduce resistance to environmental cracking.




Materials listed in this table should be used only under conditions noted in the text of this standard.Mechanical properties described in the specifications noted below are not necessarily in accordance with MR0175.

Table 2

Nonferrous Materials Acceptable for Direct Exposure to Sour Environments (see Paragraph 1.3)

Nickel-Copper Alloys Nickel-Iron- Nickel-Iron-Chromium- Nickel-Chromium Alloys Coatings, Overlays, andChromium Alloys Molybdenum Alloys Special Process Parts

UNS1 UNS UNS UNS UNS UNS UNSN05500 N04400 N08800 N06007 N08825 N06600 N07750

SAE/AMS ASTM SAE/AMS ASTM SAE/AMS ASTM ASTM ASTM SAE/ ASTM SAE/AMS Co-Cr-W Alloys as in AWS

4676 B 127 4544 B 163 5766 B 366 B 163 B 163 AMS B 637 5542 A5.13-80

B 163 4574 B 366 5871 B 581 B 366 B 166 5540 5582 Ni-Cr-B Alloys as in AWS

B 164 4575 B 407 B 582 B 423 B 167 5580 5598 A5.13-80

B 366 4730 B 408 B 619 B 424 B 366 5665 5667 Tungsten Carbide Alloys

B 564 4731 B 409 B 622 B 425 B 516 7232 5668 Ni-B Alloys as in AMS 4779

7233 B 514 B 626 B 704 B 517 5669 Ceramics

B 515 B 705 B 564 5670

B 564 5671

5698

5699

A 494 UNS N09925

Gr. M-35-1 UNS N08024

Gr. M-35-2 UNS N08028

UNS N07048

UNS N08535

UNS N08042

UNS N06952

UNS N04405


Note

1. Unified Numbering System for Metals and alloys: ASTM E527 or SAE J1086.




Table 2 – continued…Nickel-Chromium-Molybdenum

UNS N006625 UNS 10002 UNS N10276 UNS N07718 UNS N06002

ASTM SAE/ ASTM SAE/ ASTM ASTM SAE/ ASTM SAE/ UNS N06030

B 336 AMS A 597 Gr. 4 AMS B 366 B 637 AMS A 567 AMS UNS N06975

B 443 5581 5388 B 574 B 670 5383 Gr. 5 5390 UNS N07725

B 444 5599 A 494 5389 B 575 5589 B 366 5536 UNS N06985

B 446 5666 Gr. Cw-12MW 5530 B 619 5590 B 435 5587 UNS N06110

B 564 5837 5750 B 622 5596 B 572 5788 UNS N07031

B 704 B 626 5597 B 619 5754 UNS N07716

B 705 5662 B 622 5798 UNS N06022

5663 B 626 5799 UNS N06060

5664 7237

5832

Table 2 – continued…

Cobalt-Nickel-Chromium- Cobalt-Nickel-Chromium- Cobalt-Nickel-Chromium- Other AlloysMolybdenum Alloys Tungsten Alloys Tungsten Alloys

UNS R30035 UNS R30003 UNS R30605 UNS R30260 Aluminum Tantalum Titanium

Base UNS R05200 Alloys

Alloys

UNS R03004 UNS R30159 UNS R50400

Copper UNS R53400

UNS R31233 Alloys UNS R58640

UNS R56260

UNS L56403



5.4.4.3 NoiseThe noise level at 100 feet (30 meters) fromthe point of discharge to the atmosphere canbe approximated by equation (9):

L100 (30) = L (from Fig. 12) + 10 log10 (1/2MC 2) (9)

Figure 12 illustrates the noise intensity mea-sured as the sound pressure level at 100feet (30 meters) from the stack tip versus thepressure ratio across the safety valve.

The following symbols are used in theprocedure for calculating the noise level:

M = mass flow through the valve, in slugsper second (kilograms per second).

C = speed of sound in the gas at the valve,in feet per second (meters per second).

Note: In feet per second,

C = 223kT 0.5( –––––––––––––– )Molecular weight

In meters per second,

C = 9.12 kT 0.5( –––––––––––––– )Molecular weight

Where:

k = ratio of the specific heats in the gas.

r = gas temperature, in degreesRankine (Kelvin).

PR = ratio of the upstream to the down-stream pressure across the safetyvalve (absolute).

An example of calculating, in Englishunits, the noise level at 100 feet from thepoint of discharge to the atmosphere ispresented below:

1. Calculate 1/2MC 2 in watts. Divide theweight flow (pounds per second) by 32 toobtain M. Multiply 1/2MC2 (foot-pounds persecond) by 1.36 to obtain 1/2MC2 in watts.

2. Calculate 10 log10(1/2MC2)

3. In Figure 12, enter PR as the abscissaand read the ordinate.

4. Add Items 2 and 3 to obtain the aver-age sound pressure level at 100 feet,L100, in decibels. Assume the following:

M = 1 slug per second= 32 pounds per second

k = 1.4

Molecular weight =29

T = 560 degrees Rankine

PR = 48/16 = 3

(1.4) (560) C = 223 [––––––––––––– ]0.5

29

= 1159 feet per second

1. 1/2MC2 = (1/2)(1)(1159)2(1.36) = (9.1)(105).

2. 10 log10(1/2MC2) = 60

3. From Figure 12, at PR = 3, the ordinate= 54.

4. L100 at 100 feet = 54 + 60 = 114 decibels

An example of calculating, in metric units,the noise level at 30 meters from the pointof discharge to the atmosphere is present-ed below:

1. Calculate 1/2MC2 in watts.

2. Calculate 10 log10(1/2MC2).

3. In Figure 12, enter PR as the abscissaand read the ordinate.

4. Add Items 2 and 3 to obtain the aver-age sound pressure level at 30 meters,L30, in decibels. Assume the following:

M = 14.6 kilograms per second

k = 1.4

Molecular weight= 29

T = 311 kelvins

PR = 48/16 = 3

(1.4) (311)C = 91.2 [–––––––––––––]0.5

29

= 353 meters per second

1. 1/2MC2 = (1/2)(14.6)(353)2 = (9.1)(105).

API - RP 521 NoiseExcerpts from API - RP 521 Guide for Pressure-Relieving and Depressuring Systems

2. 10 log10(1/2MC 2) = 60

3. From Figure 12, at PR = 3, the ordinate= 54.

4. L30 at 30 meters = 54 + 60 = 114 decibels.

Note: These calculations are based onspherical spreading of the sound. If dis-tances much larger than the height of thevent above ground are of concern, add 3decibels to the calculated result to correctfor hemispherical diffusion.

By applying equation (10), the noise levelcan be adjusted for distances that differfrom the 100-foot (30-meter) referenceboundary:

rLp = L100 - 20 log10(––––––-) (10)100

In metric units, this translates to:

rLp = L30 - 20 log10 (–– ––– ) (10A)30

Where:

Lp = sound pressure level at distance r, in decibels.

L100(30) = sound pressure level at 100 feet(30 meters), in decibels.

r = distance from the sound source(stack tip), in feet (meters).

For distances greater than 1000 feet (305meters), some credit may be taken formolecular noise absorption. When safetyvalves prove to be excessively noisy dur-ing operation, the sound can be deadenedby the application of insulation around thevalve body and the downstream pipe up toapproximately five pipe diameters from thevalve.

Figure 12 – Noise Intensity at 100 Feet (30 Meters) From the Stack Tip

▲1.5

▲2

▲3

▲4

▲5

▲6

▲7

▲8

▲9

▲10

70

60

50

40

30

20

Pressure Ratio (PR)

Sound Pressure Level at 100 feet [30 meters] from stack tip minus

10 log [1/2 MC2]



1.0 ScopeThis standard describes methods of deter-mining seat tightness of metal and softseated pressure relief valves, includingthose of conventional, bellows and pilotoperated designs.

The maximum acceptable leakage ratesare defined for pressure relief valves withset pressures from 15 psig (103 kPag) to6,000 psig (41,379 kPag). If greater seattightness is required, the purchaser shallspecify it in the purchase order.

The test medium for determining the seattightness – air, steam or water – shall bethe same as that used for determining theset pressure of the valve.

For dual-service valves, the test medium –air, steam, or water – shall be the same asthe primary relieving medium.

To ensure safety, the procedures outlinedin this standard shall be performed by per-sons experienced in the use and functionsof pressure relief valves.

2.0 Testing with Air

2.1 Test ApparatusA test arrangement for determining seattightness with air is shown in Figure 1.Leakage shall be measured using a tubewith an outside diameter of 5/16 inch (7.9millimeters) and a wall thickness of 0.035inch (0.89 millimeter). The tube end shallbe cut square and smooth. The tube open-ing shall be 1/2 inch (12.7 millimeters)below the surface of the water. The tubeshall be perpendicular to the surface ofthe water.

Arrangement shall be made to safely re-lieve or contain body pressure in case thevalve accidentally pops (see Figure 2).

2.2 Procedure2.2.1 Test MediumThe test medium shall be air (or nitrogen)near ambient temperature.

2.2.2 Test ConfigurationThe valve shall be vertically mounted onthe test stand, and the test apparatus shallbe attached to the valve outlet, as shownin Figure 1. All openings–including but notlimited to caps, drain holes, vents, andoutlets–shall be closed.

2.2.3 Test PressureFor a valve whose set pressure is greaterthan 50 pounds per square inch gauge(345 kilopascals gauge), the leakage ratein bubbles per minute shall be determinedwith the test pressure at the valve inletheld at 90 percent of the set pressure. Fora valve set at 50 pounds per square inchgauge (345 kilopascals gauge) or less, thetest pressure shall be held at 5 poundsper square inch (34.5 kilopascals) lessthan the set pressure.

2.2.4 Leakage TestBefore the leakage test, the set pressureshall be demonstrated, and all valve bodyjoints and fittings should be checked witha suitable solution to ensure that all jointsare tight.

Before the bubble count, the test pressureshall be applied for at least 1 minute for avalve whose nominal pipe size is 2 inches(50 millimeters) or smaller; 2 minutes for avalve whose nominal pipe size is 21/2, 3,or 4 inches (65, 80, or 100 millimeters);and 5 minutes for a valve whose nominalpipe size is 6 inches (150 millimeters) orlarger. The valve shall then be observedfor leakage for a least 1 minute.

2.3 Acceptance CriteriaFor a valve with a metal seat, the leakagerate in bubbles per minute shall not ex-ceed the appropriate value in Table 1. Fora soft-seated valve, there shall be no leak-age for 1 minute (0 bubbles per minute).

3.0 Testing with Steam

3.1 Procedure3.1.1 Test MediumThe test medium shall be saturated steam.

3.1.2 Test ConfigurationThe valve shall be vertically mounted onthe steam test stand.

3.1.3 Test PressureFor a valve whose set pressure is greaterthan 50 pounds per square inch gauge(345 kilopascals gauge), the seat tightnessshall be determined with the test pressureat the valve inlet held at 90 percent of theset pressure. For a valve set at 50 poundsper square inch gauge (345 kilopascalsgauge) or less, the test pressure shall beheld at 5 pounds per square inch (34.5kilopascals) less than the set pressure.

API - RP 527 Seat TightnessExcerpts from API - RP 527 (July 1991) Seat Tightness of Pressure Relief Valves

Figure 2 - Devise to Relieve BodyPressure Caused by AccidentalPopping of the Valve

Soft Rubber Gasket Attached To Face Of Detector To Prevent Leakage

Cup-weld to detector

C Clamp

Air Pressure

Outlet tube - cut end smooth and square

Water level control hole maintain 1/2 inch [12.7mm] from bottom of tube to bottom of hole

Membrane - seals during test and bursts if valve accidentally opens

1/2 inch

Safety Valve

Figure 1 – Apparatus to Test SeatTightness With Air

Flanged or threaded outlet adapter for pressure relief valve

1/2 inch [12.7mm]

Water

Tube with outside diameter of 5/16 inch [7.9mm] and wall thickness of 0.035 inch [0.89mm]

Note

1. See Figure 2 for an example of a device torelieve body pressure in case the valve ac-cidentally pops.



Table 1

Maximum Seat Leakage Rate for Metal Seated Pressure Relief Valves in Bubbles Per Minute

Set Pressure Effective Orifice Sizes Effective Orifice Sizes(psig) 0.307 inch and Smaller Larger than 0.307 inch

at(60°F) [15.6°C]

Bubbles

Approximate

Bubbles

Approximate

Per

Leakage Rate

Per

Leakage Rate

Minute

per 24 Hours

Minute

per 24 Hours

Standard Standard Standard StandardCubic Cubic Cubic CubicFeet Meters Feet Meters

15-1000 [.103-6.896 MPA] 40 0.60 0.017 20 0.30 0.0085

1500 [10.5 MPA] 60 0.90 0.026 30 0.45 0.013

2000 [13.0 MPA] 80 1.20 0.034 40 0.60 0.017

2500 [17.2 MPA] 100 1.50 0.043 50 0.75 0.021

3000 [20.7 MPA] 100 1.50 0.043 60 0.90 0.026

4000 [27.6 MPA] 100 1.50 0.043 80 1.20 0.034

5000 [38.5 MPA] 100 1.50 0.043 100 1.50 0.043

6000 [41.4 MPA] 100 1.50 0.043 100 1.50 0.043

3.1.4 Leakage TestBefore starting the seat tightness test, theset pressure shall be demonstrated, andthe test pressure shall be held for leastthree minutes. Any condensate in thebody bowl shall be removed before theseat tightness test. Air (or nitrogen) maybe used to dry condensate.

After any condensate has been removed,the inlet pressure shall be increased to thetest pressure. Tightness shall then bechecked visually using a black back-ground. The valve shall then be observedfor leakage for at least one minute.

3.2 Acceptance CriteriaFor both metal- and soft-seated valves,there shall be no audible or visible leak-age for one minute.

4.0 Testing with Water

4.1 Procedure4.1.1 Test MediumThe test medium shall be water near am-bient temperature.

4.1.2 Test ConfigurationThe valve shall be vertically mounted onthe water test stand.

4.1.3 Test PressureFor a valve whose set pressure is greaterthan 50 pounds per square inch gauge (345kilopascals gauge) the seat tightness shallbe determined with the test pressure at thevalve inlet held at 90% of the set pressure.For a valve set at 50 pounds per squareinch gauge (345 kilopascals gauge) or less,the test pressure shall be held at 5 poundsper square inch (34.5 kilopascals) less thanthe set pressure.

4.1.4 Leakage TestBefore starting the seat tightness test, theset pressure shall be demonstrated andthe outlet body bowl shall be filled withwater, which shall be allowed to stabilizewith no visible flow from the valve outlet.The inlet pressure shall then be increasedto the test pressure. The valve shall thenbe observed for 1 minute at the test pres-sure.

4.2 Acceptance CriteriaFor a metal-seated valve whose inlet hasa nominal pipe size of 1 inch or larger, theleakage rate shall not exceed 10 cubiccentimeters per hour per inch of nominalinlet size. For a metal-seated valve whoseinlet has a nominal pipe size of less than 1inch, the leakage rate shall not exceed 10cubic centimeters per hour. For soft-seat-ed valves, there shall be no leakage for 1minute.

API - RP 527 Seat TightnessExcerpts from API - RP 527 (July 1991) Seat Tightness of Pressure Relief Valves



5.0 Testing with Air—AlternateMethod

5.1 Type of Valve to be TestedValves with open bonnets–bonnets whichcannot be readily sealed, as specified in2.2.2–may be tested in accordance withthis section instead of Section 2.

This alternative method shall not be usedto test valves in which air bubbles cantravel to the open bonnet through anypassageway inside the valve guide with-out being observed at the valve outlet.

5.2 Procedure5.2.1 Test MediumThe test medium shall be air (or nitrogen)near ambient temperature.

5.2.2 Test ConfigurationThe valve shall be vertically mounted onthe air test stand. The valve outlet shall be partially sealed with water to about 1/2-inch [12.7 mm] above the nozzle’sseating surface.

5.2.3 Test ProcedureFor a valve whose set pressure is greaterthan 50 pounds per square inch gauge[345 kPag], the leakage rate in bubblesper minute shall be determined with thetest pressure at the valve inlet held at90% of the set pressure. For a valve set at 50 pounds per square inch gauge [345kilopascals gauge] or less, the test pres-sure shall be held at 5 pounds per squareinch gauge [34.5 kilopascals] less than theset pressure.

5.2.4 Leakage TestBefore starting the seat tightness test, theset pressure shall be demonstrated, andthe outlet body bowl shall be filled withwater to the level of the partial seal. Theinlet pressure shall then be increased tothe test pressure and held at this pressurefor one minute before the bubble count.The valve shall then be observed for leak-age for at least one minute.

Caution: When looking for leakage, theobserver shall use a mirror or some otherindirect means of observations so that theobserver’s face is not in line with the outletof the valve, in case the valve accidentallypops.

5.3 Acceptance CriteriaFor a valve with a metal seat, the leakagerate in bubbles per minute shall not ex-ceed 50 percent of the appropriate valuein Table 1. For a soft-seated valve, thereshall be no leakage for 1 minute (0 bub-bles per minute).

API - RP 527 Seat TightnessExcerpts from API - RP 527 (July 1991) Seat Tightness of Pressure Relief



The following table should be used onlyas a guide for selecting materials for vari-ous applications. This table does not implya guarantee of corrosion resistance due tothe fact the complicating factors, (ie; agita-tion, impurities, aeration and velocity ofcorrosives encountered in commercial op-

erations) cannot be realistically duplicatedin a controlled laboratory environment.

Symbol Guide:A = Excellent Resistance

B = Good Resistance

C = Fair Resistance

N = Not Recommended

Blank spaces indicate insufficient data

Chemical Resistance Guide For Metals

Corrosive Media Material UsedConditions Gray Iron CS 304 316 416 17-4 PH Stellite Inconel® Brass Bronze Copper Monel® Hastelloy® C

Ductile Iron SS SS SS

Acetaldehyde C B B A N B A N N N A A

Acetate Solvents (Crude) N N A A B A A C B B A A

Acetate Solvents (Pure) N C A A A A A A B A A

Acetic Acid (Crude) N N B N B B N N N A B

Acetic Acid (Pure) N N A A N A B A N N N A A

Acetic Acid (30%) N A N B N N N A A

Acetic Acid (Vapors) N B N B N N B B N N N A A

Acetic Anhydride C N B A N B A N N A B A

Acetone A B A A A A A N N A A A

Acetylene A A A A A A C N N A B

Air A A A A A A A A A A A A

Alcohols C B A A B A A B B B A A

Amines B A A C A A B A A

Ammonia (Anhydrous) B B A A B A A N A A B B

Ammonia Solution A B A A B A N N N B C

Ammonium Oxalate N C B A B B C C B

Ammonium Persulphate N N A A B A A N N N N B

Ammonium Phosphate (Mono) N N A A B A A N N N

Ammonium Phosphate (Di) B B A A B A C C C B B

Ammonium Phosphate (Tri) A A B A B B C C C B B

Ammonium Sulphate N C N B B N B N N N B

Ammonium Sulfite C N C B C C N N N N C A

Amyl Acetate C C A A B A C N N A B

Amyl Alcohol C B B A B B N N N

Aniline C C B A B B B N N N B B

Aniline Dyes C C A A B A N N N A

Aniline Hydrochloride N N N C N B N N N B N

Animal Oil (Lard) A A A A A B B B

Arsenic Acid N N B A B B N N N C B

Asphalt A B A A A A A B B B A

Barium Carbonate B B A A A B B B B B

Barium Chloride C C C B C C C C A A

Section 16 – Chemical Resistance Guide for Metals






Barium Cyanide B A C C C

Barium Hydroxide C C A A A A A C C C A B

Barium Nitrate C C A A A B N N N C B

Barium Sulphate C C B A B N N N A

Barium Sulphide C C B A A B N N N

Battery Acid A A

Beer (Food) N N A A N A A A B B B A

Beet Sugar Liquor B B A A A A A A C C C A C

Black Sulphate Liquor A A A A B A N N N A

Blast Furnace Gas A A A A A A A A A

Borax (Sodium Borate) B B A A A A A C C C A

Bordeaux Mixture A A A A A A A A B

Boric Acid N N B B C B A C C C A

Bromine (Dry) N N N N N N B B B B A A

Bromine (Wet) N N N N N N B N N N C B

Butane B B A A A A N N N A B

Butanol A A A A B A A A A A A

Buttermilk C N A A A A N N N A B

Butyl Acetate C C B A A B A A A A A

Calcium Bisulphite N N C B N C N N B B N B

Calcium Carbonate N N A A A B B B B B

Calcium Chlorate C C C C B C N N N B A

Calcium Chloride C C C B B C A B B B A A

Calcium Hydroxide C C A A A A A C C C A A

Calcium Hypochlorite N N N N N N C C C C C A

Calcium Sulphate B B B A A B B B B A B

Cane Sugar Liquors A A A A A A B A A

Carbolic Acid N N A A A A C C C B A

Carbon Dioxide (Dry) B B A A A A A A A A A A

Carbon Dioxide (Wet) C C A A A A A C C C C B

Carbon Disulphide B B A A B A A C N N B B

Carbon Monoxide A B A A A B B B

Carbon Tetrachloride N C C C B C A A A B

Carbonated Beverages N N A A A N N N

Carbonic Acid N N A A B A A C C C A

Casein B B B

Castor Oil A A A A B A A A A

Caustic Soda B C A B N N N







Caustic Solutions B A B A N N N

Caustic Potash B C

Cellulose Acetate C B B B A A A B

Cellulose Nitrate B B B B B B B B B

China Wood Oil C C A A A B B B

Chloracetic Acid N N N C N N N N A

Chlorbenzol B B C C C A A A A

Chloramine

Chlorex A A N N A A A

Chloric Acid N N N C N N N N C

Chlorinated Solvents C C A A A C N N N

Chlorinated Water N N N C N C N N N

Chlorine (Dry) C B B B B B A B B B A B

Chlorine (Wet) N N N C N N N N N N C A

Chlorosulfonic Acid N N B N B N N N B A

Citric Acid N N B A C B C B B B A

Coconut Oil A A A A N A N N N

Cod Liver Oil A A

Coffee A A N A N N N A

Coke Oven Gas A A A A A A C C C B

Corn Oil B B A A A N N N A

Cottonseed Oil B B A A A A N N N A

Creisike B B A A A A A C B B A

Cresylic Acid N C A A B A N N N A

Crude Oil A A A A B A A C C C A

Diethylamine A A A A A A A A A

Dowtherm A or E N N A A A A B B B

Ethylene Dichloride N C C C C B B B A B

Ethylene Glycol B A A A A A A B A A A A

Ethylene Oxide B C A A B A C C C A A

Fatty Acids N N B A B A N N N A A

Ferric Chloride N N N N N N N N N N N C

Ferric Nitrate N N B A B C N N N N C

Ferric Sulphate N N B A A B N C C C B

Ferrous Chloride N N N N N B N N C B

Ferrous Sulphate N N B A B B C C C B

Fish Oils B B A A A A

Flourine Gas N A C B C C C C C A A







Foamite (Acid) N N C C N N N

Foamite (Alkaline) A A A A A N N N

Formaldehyde N C A A B A A A A A A B

Formic Acid N N C A N C N B N N N B A

Freon N C C C A C B B B B A B

Fruit Juices N N A A C A N N N A B

Fuel Oil B A A A A A A B B B A B

Gallic Acid N N A A A B B B A B

Gasoline (Natural) A A A A A A N N N A A

Gasoline (Refined) A A A A A A A A A A A

Gelatin N N A A N A N N N A

Glucose B B A A A A A A A A

Glycerine or Glycerol A A A A A A A B A A A B

Hydraulic Oil (Petro.) B B A A B A A A A

Hydraulic Oil (Synthetic) A A A A B A A A A

Hydrazine A

Hydrobromic Acid N N N N N N N C A

Hydrochloric Acid N N N N N N N N N N N A

Hydrocyanic Acid N C A A A N N N B B

Hydroflouric Acid N N N N N N N N N B B

Hydrofluosilic Acid N N N C B N B N N N A B

Hydrogen (Gas) A A A A B A A A A A A

Hydrogen Chloride (Dry) B N C A C A C C C A A

Hydrogen Chloride (Wet) N N N N N N N N C A

Hydrogen Fluoride (Dry) C N C C N A C B B A B

Hydrogen Peroxide N N B B A B B N C C B A

Hydrogen Sulphide (Dry) B C B A B B A C N N A B

Hydrogen Sulphide (Wet) B C B A C B A C N N B A

Kerosene B A A A A A A A A A A B

Ketchup N N A A A C

Ketones A A A A A A A

Lacquers and Solvents C C A A A A B A A A A

Lactic Acid N N B B C B A C C C C B

Lactose A

Lard A A A A A N A

Lead Acetate N N B B B A N N C B B

Lime-Sulfur A A A A B A N C C

Linseed Oil A A A A A A C C C B







Lubricating Oil (Petro.) A A A A A A A A A B

Lubricating Oil (Synth.) A A A A A A A A A B

Magnesium Chloride N C C B C C A B A A A A

Magnesium Hydroxide N B A A A A B A A A A

Magnesium Nitrate N N A N N N B

Magnesium Sulphate N C A A A A B B A A A B

Magnesium Sulphite N N A C C C

Maleic Acid N C C A C B B B A B

Mercaptans A A A A A N N N

Mercuric Chloride N N N N N N N N N N N B

Mercuric Cyanide N N B B B B N N N N B

Methane B A A A A A A A B A

Methanol B B B B B B B B B A A

Methyl Chloride C C B B B B A B B B B B

Naphtha B A A A A A A A A A A B

Naphthalene B A A A A A B B B B B

Nickel Chloride N N N C N N B N C C B A

Nickel Nitrate N N B B B C C C B B

Nickel Sulphate N N B A C B C B B A B

Nitrating Acid N N C C N N N

Nitric Acid (Crude) N N C B B C N N N N N B

Nitric Acid (Pure) N N N A B A N N N N N C

Nitrobenzene B A A A A B B B B B

Oxalic Acid N N B A C B C B B A B

Oxygen A A A A A A A A A A

Palmitic Acid C C B A B B C B B B B

Paraffin Oils B B A A A B B B A B

Petroleum (Sour Crude) B B A A B A A C N N A A

Petroleum (Sweet Crude) A A A A A C N N A A

Petroleum Oils (Refined) A A A A A A A A A A A

Phenol N N B B B A A A A B

Phosphoric Acid N N B A C B N B N N N B B

Potassium Bromide N N C A C A C C C B A

Potassium Carbonate B C A A A A C C C A B

Potassium Chlorate B B A A A A B B B B B

Potassium Chloride C N B B C B A N N N A B

Potassium Cyanide N B B B B B B C B B B B







Potassium Dichromate C C A A A B N N N B B

Potassium Hydroxide C C C C B C N N N A B

Potassium Hypochlorite N N C B C N N N N B

Potassium Nitrate B A B B B B A A A B B

Potassium Sulphate N N B A B B B A A A A

Producer Gas A A A A A C C C

Propane A B A A A A A A A A A B

Rosin B B B B A B A B B B A

Salicylic Acid N N B A B B B B B B A

Sea (Salt) Water N N A A C A A B C B B A B

Sewage C A B B B B A B

Shellac N N A A A A B A A A

Silver Bromide N N C B C C N B

Silver Chloride N N N N N C N N N B B

Silver Nitrate N N A A A A N N N N A

Sludge, Acid C C C N N N

Soap Solutions (Liquid) B A A A C A C C C A

Sodium Acetate N N A A C A A B B B B B

Sodium Aluminate A A A A A A B B B B B

Sodium Bicarbonate B A B B A B A A A A A

Sodium Bisulphate N N B A A B B N N N A A

Sodium Bisulphite N N B A B N N N B B

Sodium Carbonate A A B B A B B B B A A B

Sodium Chlorate B A B B B C C C B B

Sodium Chloride C C C B C C N C B B A A

Sodium Cyanide C C C B A C B N N N A A

Sodium Fluoride N N C A C C C C A B

Sodium Hydroxide C C C C A C N N C C B B

Sodium Hypochlorite N N C B N C C N C C C A

Sodium Nitrate C B B A A B A C B B B B

Sodium Nitrite B A B B B B B B B B

Sodium Perborate C C A A A A A C B B B B

Sodium Peroxide C C A A A A A C B B B B

Sodium Phosphate (Mono) N N A A B A C C C A B

Sodium Phosphate (Di) N N A A B A A A A B B

Sodium Phosphate (Tri) C C A A B A A C C C B B

Sodium Silicate B B A A B A A C B B B







Sodium Sulphate B B B A B B B B A A A B

Sodium Sulphide B B C A B C A N N N A B

Sodium Sulphite N C A A A C B B B B B

Sodium Thiosulphate N N A B A B B B B B B

Stannic Chloride N N N N N N N N N C B

Stannous Chloride N N N A N B N N N B B

Steam, 212°F A A A A B A A A B B B A A

Steam, 600° F C C A A B A B A N N N A A

Sulfur C C A A A A A C C C C A

Sulfur Chloride N N N C N N B N N N B B

Sulfur Dioxide (Dry) B B A A A A B C A A B

Sulfur Dioxide (Wet) N N B A N B N N B B C

Sulfur Trioxide B B B B B B B B B B B

Sulfuric Acid, 2% and Less N N C B N C N B N N N B A

Sulfuric Acid, 2-40% N N N N N N N B N N N B B

Sulfuric Acid, 40% N N N N N N N B N N N B B

Sulfuric Acid, 93-100% B B B B B B N B N N N N B

Sulfurous Acid N N B B N B C N N N N A

Tannic Acid C B A A C A B B B B

Tar A B A A B A A B A A A A

Tartaric Acid N N B A C B A C B B

Tung Oil C C A A N A C C C A

Turpentine B B A A B A A C B B C B

Varnish C C A A A A A B B B A

Vegetable Oil B A A A A B B B B B

Water (Acid Mine) N N B B A B B A N N N A

Water (Boiler Feed) B B A A A A A A C C C A

Water (Distilled) N N A A A A A A N N N A B

Water (Fresh) A A A A A A A A C B B A A

Water (Salt) N N N C N N A B C B B A

Wine and Whiskey N N A A N A A A B B B C A

Xylene (Xylol) B B A A A A A A A A A A

Zinc Chloride N N N C N N B N B B B B

Zinc Sulphate N N A A B A B C B B A B




Acetaldehyde X X X X X X X X

Acetamide X X X X X X X X X X

Acetic Acid X X X X X

Acetic Anhydride X X X X X

Acetone X X X X X X X

Acetophenone X X X X X X X

Acetyl Acetone X X X X X X X

Acetyl Chloride X X X X X X X

Acetylene X X X X X X X X X X

Acetylene Tetrabromide X X X X X X X X

Acrylonitrile X X X X

Adipic Acid X X X X X

Air X X X X X X X X X X X

Alkazene X X X X X X X

Alkyl Alcohol X X X X X X

Alkyl Amine X X X X X X

Alum Solution X X X X X X

Aluminum Acetate X X X X X X X X

Aluminum Chloride X X X X X X X X X X

Aluminum Fluoride X X X X X X X X X X

Aluminum Hydroxide X X X X X X

Aluminum Nitrate X X X X X X X X

Aluminum Phosphate X X X X X X X X X X

Aluminum Potassium 10% X X X X X X X X

Aluminum Sulfate X X X X X X X X X X

Alum-NH3-Cr-K X X X X X X X X X

Amines - Mixed X X X X X X X

Ammonia Anhydrous X X X X X X X X

Ammonia Aqueous Liquid X X X X X X X X X

Ammonia Gas X X X X X X X X X

Ammonium Bifluoride X X X X X X

Ammonium Carbonate X X X X X X X

Ammonium Chloride X X X X X X X X

Ammonium Hydroxide X X X X X X X X X

Section 17 – Chemical Resistance Guide for Elastomers and Thermoplastics

Chemical Resistance Guide For Elastomers and Thermoplastics

Fluid BUNA-N EPR Viton® Silicone Kalrez® Chemraz® Teflon® PEEK Kel-F® Vespel Urethane

Note

X = General acceptability

Blank = Not acceptable or no available data



Ammonium Nitrate X X X X X X X X X

Ammonium Nitrite X X X X X X X X

Ammonium Persulphate X X X X X X X

Ammonium Phosphate Dibasic X X X X X X X X

Ammonium Phosphate Tribasic X X X X X X X X

Ammonium Sulfate X X X X X X X X

Ammonium Sulfite X X X X X X X

Amyl Acetate X X X X X X X

Amyl Alcohol X X X X X X X X X

Amyl Borate X X X X X X X X

Amyl Chloride X X X X X X X

Amyl Chloro Naphthalene X X X X X X X

Amyl Naphthalene X X X X X X X

Aniline X X X X X X X

Aniline Dyes X X X X X X X X

Aniline Hydrochloride X X X X X X X X X

Animal Fats X X X X X X X X X X X

Ansul Ether X X X X X X X

Antimony Trichloride X X X X

Apple Juice X X X X X X X X

Aqua Regia X X X X X X X

Argon X X X X X X X X X X X

Arochlor(s) X X X X X X X X

Aromatic Fuels X X X X X X

Arsenic Acid X X X X X X X X X

Arsenic Trichloride X X X X X X X

Arsenous Acid X X X

Askarel X X X X X X X X X

Asphalt X X X X X X X X

Astm Oil X X X X X X X X

Automatic Transmission Fluid X X X X X X X X

Barium Carbonate X X X X X X X X

Barium Chloride X X X X X X X X X X X

Barium Hydroxide X X X X X X X X X X X




Note





Barium Nitrate X X X X X X

Barium Sulfate X X X X X X X X X X X

Barium Sulfide X X X X X X X X X X X

Beer X X X X X X X X X X

Beet Juice X X X X X

Beet Pulp X X X X X

Beet Sugar Liquors X X X X X X X X X

Bentonite X X X X X

Benzaldehyde X X X X X X X

Benzene X X X X X X X

Benzochloride X X X X X X X X

Benzoic Acid X X X X X X X

Benzophenone X X X X X X X X

Benzyl Alcohol X X X X X X X X X

Benzyl Benzoate X X X X X X X

Benzyl Chloride X X X X X X X

Beryllium Sulfate X X X X

Bichloride of Mercury X X X X X X

Bittern X X X X X X

Black Liquor X X X X X X

Blast Furnace Gas X X X X X X X X

Bleach Liquor X X X X X X X X X

Bleach Solutions X X X X X X

Blood X X X X X X

Boiler Feed Water X X X X X X

Borax X X X X X X X X X X

Bordeaux Mixture X X X X X X X X X

Boric Acid X X X X X X X X X X

Brake Fluid (Non Petroleum) X X X X X X X

Brine X X X X X X X X

Brine, Calcium X X X X X X

Brine, Cal. and Sodium Chloride X X X X X X

Brine, Cal. and Mag. Chloride X X X X X X

Brine, Seawater X X X X X X




Note





Bromine X X X X X X X

Bromine Anhydrous X X X X X X X

Bromine Trifluoride X X X X X X X

Bromine Water X X X X X X X

Bromobenzene X X X X X X X

Bromochloro Trifluoroethan X X X X X X X

Bunker Oil X X X X X X X X X

Butadiene Monomer X X X X X X X X X

Butane X X X X X X X X

Butane, 2,2-Dimethyl X X X X X X X X

Butane, 2,3-Dimethyl X X X X X X X X

Butanol (Butyl Alcohol) X X X X X X X X X X X

Butene, 2-Ethyl X X X X X X X X

Butter X X X X X X X X

Buttermilk X X X X X X X X

Butyl Acetate X X X

Butyl Acetyl Ricinoleate X X X X X X X X

Butyl Acid X X X X X X

Butyl Acrylate X X X X

Butyl Alcohol X X X X X X X X X X X

Butyl Amine or N-Butyl Amine X X X X X X

Butyl Carbitol X X X X X X X X X

Butyl Cellosolve X X X X X X X

Butyl Chloride X X X X

Butyl Oleate X X X X X X X X

Butyl Stearate X X X X X X X X X

Butylene X X X X X X X X

Butyraldehyde X X X X X X X

Butyric Acid X X X X X X X

Calcium Acetate X X X X X X X X

Calcium Bisulfide X X X X X X

Calcium Bisulfite X X X X X X X X X

Calcium Carbonate X X X X X X X X X X

Calcium Chlorate X X X X X X




Note





Calcium Chloride X X X X X X X X X X X

Calcium Cyanide X X X X X X X X X X

Calcium Hydroxide X X X X X X X X X X

Calcium Hypochloride X X X X X

Calcium Hypochlorite X X X X X X X X X X

Calcium Nitrate X X X X X X X X X X X

Calcium Phosphate X X X X X X X X X X X

Calcium Silicate X X X X X

Calcium Sulfate X X X X X X X X

Calcium Sulfide X X X X X X X X X X

Calgon X X X X

Caliche Liquor X X X X

Camphor X X X X X

Cane Juice X X X X X

Cane Sugar Liquors X X X X X X X X X X

Carbamate X X X X X X X X

Carbitol X X X X X X X X X X

Carbolic Acid Phenol X X X X X X X X

Carbon Bisulfide X X X X X X X

Carbon Dioxide Dry X X X X X X X X X X X

Carbon Dioxide Wet X X X X X X X X X X

Carbon Disulfide X X X X X X X

Carbon Monoxide X X X X X X X X X X X

Carbon Tetrachloride Dry X X X X X X X

Carbon Tetrachloride Wet X X X X X X

Carbonate of Soda X X X X X X

Carbonic Acid X X X X X X X X X X

Casein X X X X X

Castor Oil X X X X X X X X X X X

Catsup X X X X X

Caustic Manganese X X X X X X

Caustic Potash (Aqueous) X X X X X X

Caustic Soda (Aqueous) X X X X X X

Caustic Sulphide X X X X X X




Note





Caustic (Chloride of Sodium) X X X X X X

Cellosolve X X X X X X X

Cellosolve Acetate X X X X X X X

Cellulube X X X X X X X

Cetene (Hexadecane) X X X X X X X X

Chloric Acid X X X X X

Chloride of Lime X X X X X

Chloride of Zinc (Aqueous) X X X X X

Chlorinated Salt Brine X X X X X X

Chlorine, Dry X X X X X X X

Chlorine, Wet X X X X X X X

Chlorine Dioxide X X X X X X X

Chlorine Trifluoride X X X X X X X

Chloro 1-Nitro Ethane X X X X X X

Chloroacetic Acid X X X X X X

Chloroacetone X X X X X X X

Chlorobenzene X X X X X X X

Chorobromo Methane X X X X X X X X

Chlorobutadiene X X X X X X X

Chlorododecane X X X X X X X

Chloroform X X X X X X X

Chlorosulfonic Acid X X X X X

Chlorosulfuric Acid X X X

Chlorotoluene X X X X X X X

Chlorox X X X X X X X X X X

Chrome Alum X X X X X X

Chrome Plating Solutions X X X X X X X X X

Chromic Acid X X X X X X

Chromic Oxide (Aqueous) X X X X X X

Citric Acid X X X X X X X X X X

Cobalt Chloride X X X X X X X X

Coca Cola Syrup X X X X X

Cocoa Butter X X X X

Coconut Oil X X X X X X X X X




Note





Cod Liver Oil X X X X X X X X X X

Coffee Extracts Hot X X X X

Coke Oven Gas X X X X X X X X

Cooking Oil X X X X X X

Copper Acetate X X X X X X X X

Copper Chloride X X X X X X X X X X X

Copper Cyanide X X X X X X X X X X X

Copper Nitrate X X X X X X

Copper Sulfate X X X X X X X X X X X

Corn Oil X X X X X X X X

Cottonseed Oil X X X X X X X X X X X

Creosote X X X X X X X X X

Cresol X X X X X X X

Cresylic Acid X X X X X X

Crude Oil Sour X X X X X X

Crude Oil Sweet X X X X X X X

Cumene X X X X X X X

Cupric Chloride X X X X X X

Cutting Oil X X X X X X

Cyclohexane X X X X X X X X

Cyclohexanol X X X X X X X X

Cyclohexanone X X X X X X X

Decalin X X X X X X X

Decane X X X X X X X X X

Denatured Alcohol X X X X X X X X X X X

Detergent, Watered Solution X X X X X X X X X X

Developing Solutions X X X X X X X X X X

Dexron X X X X X X X X

Dextrin X X X X X

Diacetone X X X X X X X

Diacetone Alcohol X X X X X X X

Dibenzyl Ether X X X X X X X

Dibenzyl Sebacate X X X X X X X X

Dibromoethyl Benzene X X X X X X X




Note





Dibutyl Amine X X X X X X

Dibutyl Ether X X X X X X X

Dibutyl Phthalate X X X X X X X

Dibutyl Sebacate X X X X X X X X

Dichloroethane X X X

Dichloro-Butane X X X X X X X X

Dichloro-Difluromethane X X X

Dichloro-Ethyl Ether X X X

Dichloro-Isopropyl Ether X X X X X X X

Dichloro-Pentane X X X

Dicylohexylamine X X X X X X

Diesel Oil X X X X X X X X

Diester Synthetic Lubricants X X X X X X X X

Diethanol-Amine X X X X X

Diethyl Amine (DEA) X X X X X X X

Diethyl Benzene X X X X X X X

Diethyl Carbonate X X X X X X

Diethyl Ether X X X X X X X

Diethyl Sebacate X X X X X X X X X X X

Diethylene Glycol X X X X X X X X X X X

Diethylene Triamine X X X X X X

Diisobutylene X X X X X X X X

Diisopropyl Benzene X X X X X X X

Diisopropyl Ketone X X X X X X X

Dimethyl Aniline X X X X X X X

Dimethyl Formomide (DMF) X X X X X X X X X

Dimethyl Phthalate X X X X X X X X

Dimethyl Terephthalate X X X X X X

Dinitrotoluene X X X X X X

Dioctyl Amine X X X X X X

Dioctyl Phthalate X X X X X X X X

Dioctyl Sebacate X X X X X X X X

Dioxane X X X X X X X

Dioxolane X X X X X X X




Note





Dipentane X X X X

Dipentene X X X X X X X X

Diphenyl X X X X X X X

Diphenyl Oxides X X X X X X X X X X X

Dish Water X X X X X X

Disodium Phosphate X X X X X

Dowtherm A X X X X X X X

Dowtherm E X X X X X X X

Dry Cleaning Fluids X X X X X X X

Drying Oil X X X X

Dye Wood Liquor X X X X X X

Enamel X X X X X X

Epichlorohydrin X X X X X X X

Epsom Salt X X X X X X

Essential Oils X X X X X

Ethan (Methylmethane) X X X X X X

Ethane (Ethylene) X X X X X X X X

Ethanol X X X X X X X X

Ethanol Amine X X X X X X X X

Ethone X X X X X

Ethyl Acetate-Organic Ester X X X X X X X X

Ethyl Acetoacetate X X X X X X X X

Ethyl Acrylate X X X X X X X X

Ethyl Alcohol X X X X X X X X X X

Ethyl Benzene X X X X X X

Ethyl Benzoate X X X X X X X

Ethyl Bromide X X X X X X X X

Ethyl Cellosolve X X X X X X X

Ethyl Cellulose X X X X X X X X X

Ethyl Chloride X X X X X X X X

Ethyl Chlorocarbonate X X X X X X X X

Ethyl Chroroformate X X X X X X X

Ethyl Cyclopentane X X X X X X X X

Ethyl Ether X X X X X X X




Note





Ethyl Formate X X X X X X X X

Ethyl Hexanol X X X X X X X X X X X

Ethyl Mercaptan X X X X X X X

Ethyl Oxalate X X X X X X X X

Ethyl Pentachlorobenzene X X X X X X X

Ethyl Silicate X X X X X X X X X

Ethyl Sulfate X X X X X X X X

Ethylene Chloride X X X X X X X

Ethylene Chlorohydrin X X X X X X X X

Ethylene Diamine X X X X X X X X

Ethylene Dibromide X X X X X X X

Ethylene Dichloride X X X X X X X

Ethylene Glycol X X X X X X X X X X X

Ethylene Oxide X X X X X X

Ethylene Trichloride X X X X X X X

Fatty Acids X X X X X X X

Ferric Chloride X X X X X X X X X X X

Ferric Chloride Boiling X X X X X X

Ferric Nitrate X X X X X X X X X X X

Ferric Sulfate X X X X X X X X X X X

Ferrous Chloride X X X X

Ferrous Sulfate X X X X

Fish Oil X X X X X X X X X

Florine Gas X X X X X X

Flue Gases X X X X X

Fluorinated Cyclic Ethers X X X X X X X

Fluorine Gas Dry X X

Fluorine (Liquid) X X X X X

Fluorobenzene X X X X X X X

Fluoroboric Acid X X X X X X X

Fluorocarbon Oils X X X X X X X

Fluorolube X X X X X X X X X

Fluorosilic Acid X X X X X X

Formaldehyde X X X X X X X




Note





Formic Acid X X X X X X X X

Freon 11 X X X X X X X X



Freon 114 X X X X X X X X X

Freon 114B2 X X X X X X

Freon 115 X X X X X X X


Freon 121 X X X X


Freon 13B1 X X X X X X X X X


Freon 142b X X X X X X

Freon 152a X X X X X X

Freon 21 X X X X X X





Freon 502 X X X X X X

Freon BF X X X X X X

Freon C316 X X X X X X

Freon C318 X X X X X X X

Freon MF X X X X X X

Freon TA X X X X X X X

Freon TC X X X X X X X

Freon TF X X X X X X

Freon TMC X X X X X X X

Freon T-P35 X X X X X X X X

Freon T-WD602 X X X X X X X

Fruit Juices X X X X

Fuel Oil X X X X X X X X

Fuel Oil Acidic X X X X X X X X

Fuel Oil #6 X X X X X X X X X




Note





Fumaric Acid X X X X X X X X X X

Furan X X X X X X

Furfural X X X X X X X

Furfuraldehyde X X X X X X X

Furfuran X X X X X X

Furfuryl Alcohol X X X X X X X

Furyl Carbinol X X X X X X X

Gallic Acid X X X X X X X X

Gas, Natural X X X X X X X X

Gas, Sour X X X X X X X

Gas Odorizers X X X X X

Gas Oil X X X X X X

Gasoline Aviation X X X X X X

Gasoline Leaded X X X X X X

Gasoline Refined X X X X X

Gasoline Sour X X X X X

Gasoline Unleaded X X X X X

Gelatin X X X X X X X X X X

Glauber’s Salt X X X X X X X X

Glucose X X X X X X X X X X X

Glue X X X X X X X X X X X

Glue Sizing X X X X X X

Glycerine-Glycerol X X X X X X X X X X X

Glycol Amine X X X

Glycols X X X X X X X X X X X

Glyoxal X X X

Grape Juice X X X X X

Graphite X X X X X

Grease X X X X X X

Green Sulfate Liquor X X X X X X X X X X X

Halothane X X X X X X X

Halowax Oil X X X X X X X

Helium X X X X X X X X X X X

Heptane X X X X X X X




Note





Hexamine X X X X

Hexanol Tertiary X X X X X

Hexyl Alcohol X X X X X X X X

Hops X X X X X

Hydraulic Oil, Petroleum Base X X X X X X X X X

Hydraulic Oil, Synthetic Base X X X

Hydrazine X X X X X X X X

Hydrazine Anhydrous X X X X X X

Hydrobromic Acid X X X X X X X

Hydrocarbons X X X X X X X X

Hydrochloric Acid over 158°F X X X X

Hydrochloric Acid to 158°F X X X X X X X

Hydrocyanic Acid X X X X X X X X

Hydrofluoric Acid Cold X X X X X X X

Hydrofluoric Acid Hot X X X X X X

Hydrofluoric Acid-Anhydrous X X X X X X

Hydrofluosilicic Acid X X X X X X X X

Hydrogen Gas X X X X X X X X X

Hydrogen Peroxide X X X X X X X

Hydrogen Sulfide Dry X X X X X

Hydrogen Sulfide (Wet) Cold X X X X X X X X

Hydrogen Sulfide (Wet) Hot X X X X X X X

Hydroquinone X X X X X X

Hydyne X X X X X X X X

Hypochlorous Acid X X X X X X X

Illuminating Gas X X X X X

Ink, Newspaper X X X X X X

Iodine X X X X X X X X X

Iodine Pentafluoride X X X X X X

Iodoform X X X X X X X X

Isobutane X X X X X X

Isobutyl Alcohol X X X X X X X X X X X

Isobutyl N-Butyrate X X X X X X X X

Isododecane X X X X X X X X




Note





Isooctane X X X X X X X X

Isophorone (Ketone) X X X X X X X

Isopropanol X X X X X X X X X X X

Isopropyl Acetate X X X X X X X

Isopropyl Alcohol X X X X X X X X X X X

Isopropyl Chloride X X X X X X X

Isopropyl Ether X X X X X X X

JP-3 to JP-10 X X X X X X X

Kerosene X X X X X X X X

Ketchup X X X X X X

Ketones X X X X X X

Lacquer solvents X X X X X X

Lacquers X X X X X X

Lactic Acid X X X X X X

Lactones X X X X X X X

Lard X X X X X X X X X

Latex X X X X X X

Lavender Oil X X X X X X X X

Lead Acetate X X X X X X X X

Lead Nitrate X X X X X X X X X

Lead Sulfamate X X X X X X X X X X

Lime Bleach X X X X X X X X X X

Lime Liquor X X X X X X

Lime Sulfur X X X X X X X X X

Lime Water X X X X X X

Lindol X X X X X X X X

Linoleic Acid X X X X X X X X

Linseed Oil X X X X X X X X X

Liquid Petroleum Gas (LPG) X X X X X X X X X

Lithium Bromide X X X X X X

Lithium Chloride X X X X X X

Lubricating Oils X X X X X X X X

Ludox X X X X X

Lye Solutions X X X X X X X X X X X

Magnesium Bisulfate X X X X X

Magnesium Bisulfide X X X X X




Note





Magnesium Carbonate X X X X X

Magnesium Chloride X X X X X X X X X X X

Magnesium Hydroxide X X X X X X X X X

Magnesium Nitrate X X X X X X

Magnesium Sulfate X X X X X X X X X X

Majamie Resins X X X X

Malathion X X X X X X X X

Maleic Acid X X X X X X

Maleic Anhydride X X X X X X

Malic Acid X X X X X X X X X X

Manganese Carbonate X X X X X

Manganese Chloride X X X X X X

Manganese Sulfate X X X X X X

Mayonnaise X X X X X X

Mea with Copper Sulfate X X X X X

Mea (Mono Ethanol Amine) X X X X X X X

Meat Juices X X X X

Menthol X X X X X

Mercuric Chloride X X X X X X X X X

Mercuric Cyanide X X X X X X

Mercurous Nitrate X X X X

Mercury X X X X X X X X X X X

Mercury Salts X X X X X X

Mercury Vapors X X X X X X

Mesityl Oxide (Ketone) X X X X X X X

Methane X X X X X X X X X

Methanol X X X X X X X X

Methyl Acetate X X X X X X X

Methyl Acetoacetate X X X X X X X X

Methyl Acetone X X X

Methyl Acrylate X X X X X X X

Methyl Alcohol X X X X X X X X X

Methyl Amine X X X

Methyl Benzoate X X X X X X X

Methyl Bromide X X X X X X X X

Methyl Butyl Ketone X X X X X X X




Note





Methyl Carbonate X X X X X X X

Methyl Cellosolve X X X X X X X

Methyl Cellulose X X X

Methyl Chloride X X X X X X X

Methyl Chloroformate X X X X X X X

Methyl Chlorosilanes X X X X X X

Methyl Cyclopentane X X X X X X X

Methyl Ether X X X X X X X X X

Methyl Ethyl Ketone (MEK) X X X X X X X

Methyl Formate X X X X X X X

Methyl Isobutyl Ketone X X X X X X

Methyl Isopropyl Ketone X X X X X X X

Methyl Mercaptan X X X X X X X

Methyl Methacrylate X X X X X X

Methyl Oleate X X X X X X X

Methyl Salicylate X X X X X X X

Methylacrylic Acid X X X X X X

Methylene Chloride X X X X X X X

Milk X X X X X X X X X X

Milk of Lime X X X X X X

Mine Water X X X X X X

Mineral Oils X X X X X X X X X X

Molasses X X X X X

Molybdic Acid X X X

Mono Bromobenzene X X X X X X X

Mono Chlorobenzene X X X X X X X

Mono Ethyl Ether X X X X X X X X

Mono Methyl Aniline X X X X X X X X

Mono Methyl Hydrazine (Hypergol) X X X X X X X

Mono Vinyl Acetylene X X X X X X X X X X X

Mopholine X X X X

Muriatic Acid X X X X X

Mustard X X X X X

Mustard Gas X X X X X X X X

Naphtha X X X X X X X X

Naphtha Crude X X X X X X




Note





Naphthalene X X X X X X X

Naphthenic Acid X X X X X X X

Natural Gas X X X X X X X X

Neatsfoot Oil X X X X X X X X X X

Neon X X X X X X X X X X X

Neville Acid X X X X X X X

Nickel Acetate X X X X X X X X X

Nickel Ammonium Sulfate X X X X X X

Nickel Chloride X X X X X X X X X X X

Nickel Cobalt Sulfate X X X X X X X X X X

Nickel Nitrate X X X X X

Nickel Salts X X X X X X X X X X X

Nickel Sulfate X X X X X X X X X X X

Nicotine Sulfate X X X X X X

Nicotinic Acid X X X X

Niter Cake X X X X X X X X X X

Nitric Acid-Concentrated X X X X X

Nitric Acid-Dilute X X X X X X

Nitric Acid-Red Fuming X X X

Nitrobenzene X X X X X X X X

Nitrobenzine X X X X X X X

Nitroethane X X X X X X X

Nitrogen X X X X X X X X X X X

Nitrogen Tetroxide X

Nitromethane X X X X X X X

Nitropropane X X X X X X X

Nitrous Acid X X X X X

Nitrous Gases X X X X

Nitrous Oxide X X X X X X

N-Butyl Acetate X X X X X X X

N-Butyl Benzoate X X X X X X X X

N-Butyl Butyrate X X X X X X X X

N-Heptane X X X X X X X X

N-Hexaldehyde X X X X X X X X

N-Hexane X X X X X X X X

N-Hexane-1 X X X X X X X X




Note





N-Methyl-2-Pyprolldone X X X X X X X

N-Octane X X X X X X X

N-Pentane X X X X X X X X

N-Propyl Acetone X X X X X X X

Octadecane X X X X X X X X X

Octadene X X X X X X X

Octochloro Toluene X X X X X X X

Octyl Alcohol X X X X X X X X

Olefin, Crude X X X X X X

Oleic Acid X X X X X

Oleum X X X

Oleum Spirits X X X X X X X X

Olive Oil X X X X X X X X

Orthochloro Ethylbenzene X X X X X X

Ortho-Dichlorobenzene X X X X

Oxalic Acid X X X X X X X X X X

Oxygen Cold X X X X X X X X X X X

Oxygen (-200°F to +400°F) X X X X X X X X

Ozone X X X X X X X X X X

O-Chloronaphthalene X X X X X X X

O-Chlorphenol X X X X X X X

O-Dlchlorobenzene X X X X X X X

Paint Thinner, Duco X X X X X X X

Palm Oil X X X X X

Palmitic Acid X X X X X X X X

Paraffin Liquid X X X X X X

Paraformaldehyde X X X X

Para-dichlorobenzene X X X X X X

Peanut Oil X X X X X X X X X

Pectin Liquor X X X X X X

Pentachloro Phenol X X X X X X

Pentane X X X X X X X X

Perchloric Acid X X X X X X X

Perchloroethylene X X X X X X X X

Petrolatum X X X X X X X X

Petroleum Oil above 250° F X X X X X X X




Note





Petroleum Oil below 250° F X X X X X X X X X X

Phenol X X X X X X X

Phenyl Benzene X X X X X X X

Phenyl Ethyl Ether X X X X X X

Phenyl Hydrazine X X X X X X X

Phorone X X X X X X

Phosphate Esters X X X X X X

Phosphoric Acid to 158°F X X X X X X X X

Phosphoric Anhydride X X X X

Phosphorous Trichloride X X X X X X X X

Phosphorus Pentoxide X X X

Phosphorus Trichloride X X X

Photographic Solutions X X X X

Phthalic Acid X X X X

Phthalic Anhydride X X X X

Pickling Solution X X X X X X X

Picric Acid X X X X X X X X X

Pine Oil X X X X X X X X

Pineapple Juice X X X X X X

Pinene X X X X X X X X

Piperidine X X X X X X

Plating Solutions - Chrome X X X X X X X X

Plating Solutions - Other X X X X X X X X X

Poly Glycols X X X X X X

Polysulfide Liquor X X X X X X

Potash X X X X X X

Potash Alum X X X X X X

Potash Sulfide X X X X X X

Potassium Acetate X X X X X X X X

Potassium Bicarbonate X X X X X X

Potassium Bichromate X X X X X X

Potassium Bisulfite X X X X X X

Potassium Bromide X X X X X X

Potassium Carbonate X X X X X X

Potassium Chlorate X X X X X X

Potassium Chloride X X X X X X X X X




Note





Potassium Cupro Cyanide X X X X X X X X X X

Potassium Cyanide X X X X X X X X X X

Potassium Dichromate X X X X X X X X X X

Potassium Diphosphate X X X X X X X X

Potassium Ferricyanide X X X X X X X

Potassium Ferrocyanide X X X X X X X

Potassium Hydroxide X X X X X X X X X X

Potassium Hypochlorite X X X X X X

Potassium Iodide X X X X X

Potassium Nitrate X X X X X X X X X

Potassium Oxalate X X X

Potassium Permanganate X X X X X

Potassium Phosphate X X X X X

Potassium Salts X X X X X X X X X X

Potassium Sulphate X X X X X X X X X

Potassium Sulphite X X X X X X X X X

Potassium (Molten) X X X

Prestone X X X X X

Producer Gas X X X X X X X X X X

Propane X X X X X X X X

Propane Propionitrile X X X X X X X X

Propyl Acetate X X X X X X X

Propyl Alcohol X X X X X X X X X X

Propyl Bromide X X X X X

Propyl Nitrate X X X X X X X

Propylene X X X X X X X

Propylene Glycol X X X X X X

Propylene Oxide X X X X X X X

Pulp Stock X X X X X X

Pydrauls X X X X X X X X X

Pyranol X X X X X X X X X X

Pyridine X X X X X X X

Pyrogallic Acid X X X X X X X X

Pyroligneous Acid X X X X X

Pyrrole X X X X X X X

P-Cymene X X X X X X X




Note






P-Dichlorobenzene X X X X X X X

P-Tertiary Butyl Catechol X X X X X X X X

Quench Oil X X X X X X

Radiation X X X X X X

Rapeseed Oil X X X X X X X X

Red Oil X X X X X X X X X

Rosin X X X X X X

RP-1 Fuel X X X X X X

Rubber Solvents X X X X

Sal Ammoniac X X X X X X X X X X X

Salad Oil X X X X X

Salicylic Acid X X X X X X X X X

Salt Cake X X X X X

Seawater, Saltwater X X X X X X X X X

Sewage X X X X X X X X X X

Shellac X X X X X

Silicate Ethers X X X X X X X X X

Silicic Acid X X X X X X X X

Silicone Greases X X X X X X X X X X

Silicone Oils X X X X X X X X X

Silver Bromide X X X X X X

Silver Chloride X X X X X X X

Silver Cyanide X X X X X

Silver Nitrate X X X X X X X X X X

Skydrol 500 X X X X X X X

Skydrol 7000 X X X X X X X X X

Soap Liquors X X X X X X

Soap Solutions X X X X X X X X X X

Soda Ash X X X X X X X X X X

Sodium X X X

Sodium Acetate X X X X X X X X

Sodium Aluminate X X X X X X

Sodium Bicarbonate X X X X X X X X X X

Sodium Bichromate X X X

Sodium Bisulfate X X X X X X X X X X

Sodium Bisulfite X X X X X X X X X X



Note





Sodium Borate X X X X X X X X X X

Sodium Bromide X X X X X X X

Sodium Carbonate (Caustic) X X X X X X X X X X

Sodium Chlorate X X X X X X

Sodium Chloride X X X X X X X X X X

Sodium Chromate X X X X X X X X

Sodium Citrate X X X

Sodium Cyanamide X X X X X X

Sodium Cyanide X X X X X X X X X

Sodium Fluoride X X X X X X X

Sodium Hydrosulfite X X X X X X

Sodium Hydroxide X X X X X X X X

Sodium Hypochlorate X X X X X X X X X X

Sodium Hypochlorite X X X X X X X X X X

Sodium Hyposulfite X X X X X X X

Sodium Lactate X X X

Sodium Metaphosphate X X X X X X X X X

Sodium Metasilicate X X X X X

Sodium Nitrate X X X X X X X X

Sodium Perborate X X X X X X X X X X

Sodium Peroxide X X X X X X X X X

Sodium Phosphate X X X X X X X X X

Sodium Plumbite X X X X X X

Sodium Silicate X X X X X X X X X

Sodium Sulfate X X X X X X X X X X

Sodium Sulfide X X X X X X X X X X

Sodium Sulfite X X X X X X X

Sodium Sulfite X X X X X X X X X X

Sodium Tetraborate X X X X X X

Sodium Thiosulfate X X X X X X X X X X

Sodium Trisulfate X X X X X X X X X X

Sorbitol X X X X X X

Soybean Oil X X X X X X X X X

Stannic Chloride X X X X X X X X X X

Stannous Chloride X X X X X X

Starch X X X X X X




Note





Steam over 300°F X X X X X X

Steam under 300°F X X X X X X

Stearic Acid X X X X X X X X X

Stoddard Solvent X X X X X X X

Styrene X X X X X X X

Sucrose Solutions X X X X X X X X X X

Sulfate Liquors X X X X X X

Sulfate of Hydrogen X X X X X X

Sulfate of Lime X X X X X X

Sulfate of Sodium X X X X X X

Sulfite Liquors X X X X X X X X X

Sulfite Pulp X X X X X X

Sulfur X X X X X X X

Sulfur Chloride X X X X X X X

Sulfur Dioxide X X X X X X X X

Sulfur Hexafluoride X X X X X X X X X X

Sulfur Trioxide X X X X X X X X X

Sulfur Trioxide, Dry X X X X X X X X X

Sulfuric Acid (20% Oleum) X X X X

Sulfuric Acid (Concentrated) X X X X X

Sulfuric Acid (Dilute) X X X X X X

Sulfurous Acid X X X X X X X X

Sulphonated Fatty Alcohol X X X X X X

Sulphonated Vegetable Oils X X X X X X

Syrup X X X X X

Tall Oil X X X X X X

Tallow X X X X X X

Tannic Acid X X X X X X X X X X

Tar, Bituminous X X X X X X X X X X

Tar, Pine X X X X X X

Tartaric Acid X X X X X X X X X

Terpineol X X X X X X X X

Tertahydrofuran X X X X X X X

Tertiary Butyl Alcohol X X X X X X X X X X

Tertiary Butyl Mercaptan X X X X X X X

Tetrabromoethane X X X X X X X




Note





Tetrabromomethane X X X X X X X

Tetrabutyl Titanate X X X X X X X X X

Tetrachloroethane X X X X X X X

Tetrachloroethylene X X X X X X X

Tetraethyl Lead X X X X X X X X

Tetralin X X X X X X

Tetraphenyl X X X X X X

Therminol VP-1,44,55,60,66 X X X X X X X

Thionyl Chloride X X X X X X

Titanium Tetrachloride X X X X X X

Toluene X X X X X X X

Toluene Diisocyanate X X X X X X X

Tomato Pulp X X X X X

Transformer Oil X X X X X X X X X

Transmission Fluid Type A X X X X X X X X X

Triacetin X X X X X X X X

Triaryl Phosphate X X X X X X X X

Triaryl Phosphate X X X X X X X X X

Tributoxyl Ethyl Phosphate X X X X X X X X

Tributyl Mercaptan X X X X X X X

Tributyl Phosphate X X X X X X X

Trichloroacetic Acid X X X X X X X

Trichloroethane X X X X X X

Trichloroethylene X X X X X X X

Tricresyl Phosphate X X X X X X X

Triethanol Amine X X X X X X

Triethyl Aluminum X X X X

Triethyl Borane X X X X

Trifluoroethane X X X X X X X

Trinitrotoluene (TNT) X X X X

Trioctyl Phosphate X X X X X X X

Tripoly Phosphate X X X X X X X

Trisodium Phosphate X X X X X

Tung Oil (Chine Wood Oil) X X X X X X X X

Turbine Oil X X X X X X X X X

Turpentine X X X X X X X X




Note





Unsym. Dimethyl Hydrazine X X X X X X X X

Urea and Phenolic Resins X X X X X X

Uric Acid X X X

Varnish X X X X X X X X

Vegetable Oil X X X X X X X

Versilube X X X X X X X X X

Vinegar X X X X X X X

Vinyl Chloride X X X X X X X X

Vinyl Chloride Monomer (VCM) X X X X X X X

Vinylidine Chloride X X X X X X

Wagner 21B Fluid X X X X X X X

Water X X X X X X X X X

Waxes X X X X X X

Whiskey and Wines X X X X X X X X X

White Liquor X X X X X X

White Oil X X X X X X X X

White Pine Oil X X X X X X X X

White Water, Paper Mill X X X X X X

Wood Oil X X X X X X X X

Wood Pulp X X X X X X

Wood Vinegar X X X X X X

Xenon X X X X X X X X X X

Xylene X X X X X X X

Xylidenes X X X

Xylol X X X X X X X

Yeast X X X X X

Zeolites X X X X X X X X X

Zinc Acetate X X X X X X X X

Zinc Bromide X X X X X

Zinc Chloride X X X X X X X X X

Zinc Hydrosulfite X X X X X

Zinc Nitrate X X X X X X

Zinc Phosphate X X X X X X

Zinc Salts X X X X X X X X X X

Zinc Sulfate X X X X X X X X X X




Note



Pressure Relief ValveTechnical ManualRevised May 1998Catalog: PRVTM-US.97

Anderson GreenwoodP.O. Box 944Stafford, Texas 77497, USATel: (281) 274-4400 Fax: (281) 240-1800International Tel: +1 281 274-4400International Fax: +1 281 240-1800

Anderson GreenwoodCorrie Way, Bredbury Industrial Estate,Stockport, Cheshire SK6 2ST, UKTel: 0161 494 5363 Fax: 0161 494 5672 Telex: 668379International Tel: +44 161 494 5363International Fax: +44 161 494 5672

© 1997 Anderson Greenwood Printed in USA

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Pressure Relief Valves - 한국에너지공단kemco.or.kr/up_load/iecenter/club00000204_energyqa/PRVtechman.pdf · Valve Sizing Nomenclatures ... complete line of pressure relief