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CATHODIC PROTECTION DESIGN FOR BRACELET ANODE

This spreadsheet determines the anode requirements for the main line.

The output represents the anode requirements to satisfy the mean and final current demand of the pipelines.

Mthodology is in accordance with DNV-RP-B401 (2010).

1.0 INPUT DATA

Definition of Units for MATHCAD : C K years 8760 hr A amp

1.1 Pipeline Data

Pipeline Length Lp 16000 m:=

Outside Diameter D 273.1mm:=

Joint Length Lj 12.2m:=

Corrosion Coating thickness tc 3.5 mm:= (3LPE coating)

Design Life tf 15 years:=

Operating Temperature Top 55 C:= (Assume that the temperature for theanodes is the same as the

temperature of the pipeline)

Mean Current Density (Depth > 30-100 mand surface water temperature >20 oC)

icm 0.06 A m 2-

:= (Table 10-2, DNV-RP-B401, 2010)

Final Current Density (Depth > 30-100 m and

surface water temperature >20 oC)

icf 0.08 A m 2-

:= (Table 10-1, DNV-RP-B401, 2010)

Temperature correction (>25 deg C) Tc 0.001 A m 2-

C 1-

:= (Section 6.3.9 DNV-RP-B401, 2010)

Constant in Coating Breakdown Factor

(Coating Category III)a 0.02:= (Table 10-4 DNV-RP-B401, 2010)

Constant in Coating Breakdown Factor

(Coating Category III)b 0.008:= (Table 10-4 DNV-RP-B401, 2010)

Mean Coating Breakdown Factor fcm a btf

2 years

+:= fcm 0.08=

Final coating brakdown factor fcf a btf

years+:= fcf 0.14=

Design Protective Potential vs Ag/AgCl Ec 0.80- volt:= (Section 5.4.1 DNV-RP-B401, 2010)

Environmental Resistivity (Seawater, 21 deg C) 0.225 ohm m:= (Figure 10-1 DNV-RP-B401 2010,The salinity is assumed 35ppt as

average value)

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1.2 Half Shell Bracelet Anode Data (Al Based)

Clearance Between Anode ID & coating OD tg 0mm:=

Anode Inside Diameter IDa D 2 tc+ 2 tg+:= IDa 280.1 mm=

Anode Thickness ta 40mm:=

Anode Length La 450mm:=

Half Shell Gap ga 100mm:=

a 2700 kg m 3-

:=Anode Material Density

Anode Usage Factor u 0.8:= (Table 10-8, DNV-RP-B401, 2010)

Design Closed Circuit Anode Potential(Seawater)

Ea 1.05- volt:= (Table 10-6, DNV-RP-B401, 2005)

Electrochemical Capacity (Seawater) a 2000 A hr kg 1-

:= (Table 10-6, DNV-RP-B401, 2005)

2.0 CALCULATIONS

2.1 Net Mass per Anode

Surface Area of Anode SAa IDa 2 ta+( ) 2 ga- La:= SAa 0.419 m2

=

Cross-Sectional Area of Anode XAa IDa ta+( ) 2 ga- ta:= XAa 0.032 m2

=

Volume of Anode Va XAa La:= Va 0.015 m3

=

Net Mass per Anode as per calculation mac Va a:= mac 39.153 kg=

Net Mass per Anode as per availability from

Vendor Cataloguema 38kg:= ma 38kg=

2.2 Mean Current Requirement

Surface Area to be Protected Acm D Lp:= Acm 1.373 104

m2

=

Design Steel Current Density Demand

Correction for Steel Temperature (T)icmt if Top 25 C< icm, icm Top 25 C-( ) Tc+,:=

icmt 0.09A m 2-

=

Mean Coating Breakdown Factor fcmt if tf 30 years< fcm, fcm 0.002tf

years30-

+,

:=

fcmt 0.08=

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Current Demand for Specific Surface Area Icm Acm fcmt icmt:= Icm 98.838 A=

Electrochemical Efficiency a:= 2 10

3 A hr kg

1-=

Total Anode Mass M Icm tfu

:= M 8117.07 kg=

Anode Current Capacity ca ma u:= ca 6.08 104

A hr=

Minimum Number of Anodes Required nmM

ma:=

nm 213.607=

Maximum Required Anode Spacing (meter) LspmLp

nm:= Lspm 74.904 m=

Maximum Required Anode Spacing (numberof joints) Jointsm

Lspm

Lj:= Jointsm 6.14=

Mean Currrent Requirements Results:

RESULTmean if nm ca Icm tf "The Mean Current Requirements are met", "Not OK",( ):=

RESULTmean "The Mean Current Requirements are met"=

2.3 Final Current Requirement

End of Life Anode Mass mf ma 1 u-( ):= mf 7.6kg=

End of Life Anode Volume Vfmf

a

:= Vf 2.815 10 3-

m3

=

End of Life Anode CSA (Assume Anode

Length doesn't change)XAf

Vf

La:= XAf 6.255 10

3- m

2=

End of Life Anode Outer Diameter

Initial Aprroximation ODf IDa:=

Given XAf ODf 2 ga-( ) ODf IDa-( )=

ODf Find ODf( ):= ODf 0.289 m=

End of Life Anode Surface Area SAaf ODf 2 ga-( ) La:= SAaf 0.318 m2

=

End of Life Anode Resistance Raf0.315

SAaf

:= Raf 0.126 ohm=

End of Life Anode Current Output IafEc Ea-

Raf

:= Iaf 1.991A=

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The Design Final Current Density for Steel,

Corrected for Temperatureicft if Top 25 C< icf, icf Top 25 C-( ) Tc+,:=

icft 0.11A m 2-

=

Steel Surface Area to be Protected Acf D Lp:= Acf 1.373 104

m2

=

Final Coating Breakdown Factor fcft if tf 20 years< fcf, fcf 0.004tf

years20-

+,

:=

fcft 0.14=

End of Life Current Demand for Surface Area

to be Protected Icf Acf fcft icft:= Icf 211.404 A=

Minimum Number of Anodes Required nf

Icf

Iaf:= nf 106.2=

Maximum Required Anode Spacing (meter) LspfLp

nf:= Lspf 150.659 m=

Maximum Required Anode Spacing (number

of Joints) Jointsf

Lspf

Lj:= Jointsf 12.349=

Final Current Requirements Results

RESULTfinal if nf Iaf Icf "The Final Current Requirements are met", "Not OK",( ):=

RESULTfinal "The Final Current Requirements are met"=

2.4 Required Anode Spacing and Number of Anodes

Required Anode Spacing (number of Joints) Jointsrequired min Jointsm Jointsf,( ):= Jointsrequired 6.14=

Jointsrounded floor Jointsrequired( ):= Jointsrounded 6=

Required Number of Anodes NrequiredLp

Jointsrounded Lj:= Nrequired 218.579=

Nrounded ceil Nrequired( ):= Nrounded 219=

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2.5 Check Final Anode Thickness

Steel Surface Area Protectable per Anode Acmc D Jointsrounded Lj( ):= Acmc 62.803 m2

=

Current Demand for Surface Area to be

Protected per Anode Icmc Acmc fcmt icmt:= Icmc 0.452A=

Mass of Anode Used to Protect the Surface

Area mused

Icmc tf

:= mused 29.708 kg=

Remaining Mass per Anode (Final Anode

Mass)mfinal ma mused-:= mfinal 8.292 kg=

Final Anode Volume Volfinalmfinal

a

:= Volfinal 3.071 10 3-

m3

=

Final Anode Thickness tafVolfinal

SAaf:= taf 9.643 mm=

taf_req

ODf D- 2 tc-( )2

:= taf_req 4.419 mm=Final Anode Thickness requirement

Check Final Anode Thickness Check_taf if taf taf_req "OK", "Not OK",( ):=

Check_taf "OK"=

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23 - 41 Willowdale Place, Aberdeen, AB24 5AQ

Aluminium and Zinc Castings Aluminium Offshore Anodes Zinc & Al Marine Hull Anodes

Tank Anodes Pipeline Anodes Down-hole Centralisers and Clamps Ballast Weights

AFA Bracelet Anodes Sheet B 1 Rigid Pipes taper NEW sept 09 to Ab internet (2).doc

AF Defender Rigid Pipe Aluminium Bracelet Anodes B1

Examples

Anode

Code

(A =AlBracelet

Wt x 10 )

Design

ExamplesRigid pipes

Anode ID

(mm)

(NB pipe)D double, S-

Single band

Anode

OD

(mm)

O/all

Length

(mm)

Anode

Weight

(Nett kg/Gross kg)

AFA B 200

.Fully Bolt on gussetedbands

(Single, S or Double, D)Tapered ends

Continuity straps;

Epoxy coat inside

neoprene liner optional

(4) 118 D 198 416 20/25

AFA B 126 (6) 170 S 250 235 12.6/16

AFA B 186 (6) 170 S 250 368 18.6/16

AFA B 235 (8) 225 D 315 410 23.5 / 28.4

AFA B 333 (8) 223.5 303.5 475 33.3/37.7

AFA B 280 (10) 280 S 360 325 28 /35

AFA B 380 (10) 280 D 360 450 38/35

AFA B 292 (12) 328 S 408 290 29.2 / 34

AFA B 400 (12) 328 S 408 425 42 / 46

AFA B1200 (16) 410 D 492 800 120/ 135

AFA B350 (16) 435 D 515 280 35/47.5

AFA B610 (20) 512 D 592 450 61/85

AFA B520 (20) 520 D 610 315 55/69

AFA B550 (20) 550 D 640 300 55 / 70

AFA B570 (22) 570 D 660 295 55/71

AFA B790 Example: High temp pipe anode

heavy rubber lined to order

(10) 286

Rubber lined,40mm to363 D

Hinged

453 680 75/90

* All weights and dimensions are nominal

Material Specification:AF Defender G3 AF Al-Zn-In-Si anode alloy

Fe Si Cu Zn In Others Al

0.12 max. 0.08-0.21 0.006 max. 2.8 6.5 0.01 0.02 0.02 max remainder

Potential 1.09* Volts Ag/AgCl Capacity (Amp Hrs) 2540* per Kg min Density 2750Kg/m3

* AFDefender G3 alloy performance Data for long term test by DNV Certificate No S-5615 to DNV RP B401 Appendix B

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