Enviro Cous Tics

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In-Service Inspection and IntegrityAssessment of Above-Ground

Storage TanksDr. Athanasios Anastasopoulos

Presentation forTank Storage ConferenceISTANBUL 3 & 4 November 2010

www.envirocoustics.gr, [email protected], Tel.: (+30) 210-2846801, Fax: (+30) 210-2846805


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Copyright 2008 Proprietary information: No dissemination, use or duplication without prior written permission from MISTRAS Group, Inc..

OVERVIEW

FAILURE OF TIME-BASED MAINTENANCE & NEEDS FOR ONSTREAM INSPECTION

TANKPACTM : IN SERVICE CONDITION MONITORING FOR TANKFLOORS: Acoustic Emission Tank Floor Testing Overview

Case Studies

Validation and Verification

TALRUTTM: IN-SERVICE CRITICAL ZONE EXAMINATION

LSI TANK SHELL CORROSION AND WEAR MAPPING

PCMS: PLANT CONDITION MONITORING & RISK BASEDINSPECTION SOFTWARE

DISCUSSION AND CONCLUSIONS


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Failure of time-based maintenanceHot oil tank, 140C: Internally

inspected 12 months prior to

failure, including UT+MFL. This

collapse was due to a narrowband of annular ring corrosion.

When the ring split the very

rapid loss of hot liquid pulled a

vacuum collapsing the tankshell.

Naphtha Tank: Leaking 100 cubic meters

per day through a 1cm hole. Operations

noticed losses after a week, but no visible

product, which was disappearing intoground. When the plates were cut the

cavity under the floor was several cubic

metres in size.


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Copyright 2007Envirocoustics S.A.

Failures of time-based maintenance

Many more examples.

Tanks removed from service, cleaned,sludge dumped, tank inspected...and norepairs required..

Tanks inspected though leaks not alwaysprevented

If time based internal inspectionworked. this would not behappening....


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Tank Floors are the only structural part of a tank

with no access for inspection during operation Access to tank floors for inspection is difficult and costly.

Leakage is no longer environmentally acceptable.

Risk of catastrophic failure with severe annular ring damage. Cleaning costs can be >$200,000, + environmental waste

problem. If no repairs are required these costs are wasted.

Requirements:

To identify tanks which do NOT yet require internal inspectionand repair, this prevents the waste of maintenance resourcesand protects the environment.

To determine the relative condition of damaged floors so that acorrect priority for internal maintenance may be set.

To do the above with as little disruption to operations aspossible.


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TANKPAC: IN SERVICE CONDITION

MONITORING FOR TANK FLOORS


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AE sensor

Tank

AEInstrument

AE Van

Acoustic Emission Tank Floor Testing Overview

AE Sensors (in the Low Ultrasonic Range to

avoid Interference) mounted on tank wall 1-2m above knuckle

3-30 sensors per row used depending upon

size / 1 or 2 rows

Cables go to test instrumentation


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Acoustic Sources detectedCorrosion of steel causes

Acoustic Emission (Yuyama,

Condello etc).Sources detected by sensors on

the outside of the tank.

Spalling of corrosion products.

Leak noise: (flow interruption, orturbulence).

External Interference - noise to befiltered:

Roof movement noise, Structuralmovement, External and pipe-bornenoise, Condensation, Particleimpacts, Valve leakage.

Signal amplitude >>

^ Number of emissions

time

Shown above: one hour of emission from a

tank with very severe corrosion, characteristics

of emission change with scaling.


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Time (s)

mptu

e

Htrae

AE data analysis

Bottomplate

AE sensorLiquid bornwave

AEsource

Acoustic Emission Tank Floor Testing Overview

The tank is monitored in service, following conditioning (Valves closed, heaters

off, agitators off), for a pre-determined time (6-24 hours in advance of test)

The data is processed to eliminate unwanted sources of noise,

Location of 3+hit sources by triangulation.

The data is evaluated against TANKPAC Technology (database, special

algorithms for location, Correlations, etc.)


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TANKPACTM: CONDITION MONITORING FOR TANK FLOORS

Tank floor top view with

locations of corrosion and/or

leak sources

3D plots of located

corrosion and leak

sources

Separate analysis and

grading of the most

severe corrosion sites

100% FLOOR INSPECTION & ANNULAR RING

Overall Tank Grading, from A (no damage) to E (severe damage), indicate the general

condition of the Floor.Potential Leak Sites Identified & Graded indicating concentrated sources of severe

corrosion or leak.

Combination of Overall Grading with Potential Leak Result in Composite RBI compatible

Matrix .


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Recommendations Matrix

Overall Grade A B C D E

PLD Grade I I II (n/a) (n/a) (n/a-doesnt occur)

1 I I II (n/a) (n/a) I > ~4-5 years

2 I I II II (n/a) II > ~2 years

3 II II III III III III ~ 1 year*

4 II III III IV IV IV ~ 0.5 years*

5 III III IV IV IV *or schedule for internal inspection

Clearly leaking tanks often unable to grade, (should be opened anyway).

Active concentrated sources in all data will also increase severity of grading.


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Corrosion of Internal Zinc Anodes

Emission reaching three sensors

is located.

Internal sacrificial anodes corrode

in place of tank floor.

Zinc blocks can be large.

Oilfield production tanks use

sacrificial anodes-very active when

has coating failed, until zinc used,

then floor corrodes.

Special procedures used to

separate anode corrosion from

floor corrosion.

Emission from active anodes in a 55

metre tank, 2m x1m in size, (30 in

tank, 4/10/16)


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150 Diameter, Gasoline

ALL DATA

TANK -PAC

GRADE

A

B

C

D

E

North

Channel 1


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TANKPAC: In-Service Floor Plate

Corrosion Assessment


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3-D view of an E grade crude tank

and damage found


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Leaking Tanks Cases

Gasoline Tank

Very concentrated source:scale usually 50!

Doesnt show on tank plot, onepixel. On product tanks smallleaks are not easily identified,except by high concentration.

~1mm hole found whenopened.

Naphtha Tank

100 cu.m/day loss

No visible indication of a leak

Faint smell only

TANKPACTM test at 2% sensitivitydue to noise - 2 minutesacquisition only:

1cm hole found at location shown


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NEW TANK LEAKING

DEFECTS IN THE

WELDS.......LEAK

TANKPACTM:/ LEAK DETECTION


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Limitations(see method statement)

Detects and grades active corrosion only.

Not suitable for assessing the internal condition of tanks which arecleaned mechanically or chemically as this resets the condition,

(underside OK). Use history!!

Small leaks may be masked by active floor corrosion.

Large leaks will mask overall floor condition.

Activity from active corrosion under insulation may mask floorcondition.

Location may degrade on very active D/E tanks due tosimultaneous sources, (the tank needs opening anyway!).

Not all tanks can be tested, due to noise/condensation etc.

Complex procedure requires extensive training + control.


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TANKPACTM: VERIFIED RELIABILITY

1. TANPAC Tests All around the word (Europe, Middle East, Africa, SouthAmerica, Asia and Far East, North America)

2. PAC TANKPAC Procedure adopted by SAUDI

ARAMCO.3. PAC TANKPAC Procedure adopted by DOW

CHEMICALS

4. PAC TANKPAC Procedure verified by Shell GlobalSolutions (results presented in ECNDT 98)

5. 1999 EEMUA recommendations to members (1996 Usergroup became part of EEMUA, ~30 Cos -Engineering Equipment Material Users Association- experience now

>600 tank floor tests, feedback on internal inspection of >150 tanks, procedure at rev.4.)

6. French Petroleum Institute: UNION FRANCAISE DES INDUSTRIESPETROLIERS (API), Guide Pour Linspection Et La Maintenance Des Reservoirs Mettaliques Aeriens

Cylindriques Verticaux D Hydrocarbures Liquides En Raffinerie, ANNEXE: Recommandations pour lutilization de

lemission acoustique a la verification de l etancheite et a levaluation de l activite des corrosion des reservoirs

verticaux aeriens, Edition Aug. 2000, Paris


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Comparison with

Subsequent Inspection

From correlation of TANKPACTM results withinternal inspection and repairs carried out:

100% of A-grade tanks - no repairs ordamage to floor

56% of C-grade tanks - patch repairs

52% of E-grade tanks - floor replaced


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Reliability: TANKPACTM

overall grading vs. repairs required*

0

20

40

60

80

100

120

A B C D E

FU 1/2 Minimal damage: no repairsFU 3 Damage: some repairs

FU 4 Significant damage: major repair/new floor

R

elative(%)

AE-grade

Follow-up results versus AE-grades, normalised per AE-grade

population of 157 tanks (Shell, Dow-Stade, DSM, PKE, Total and PAL database)

* P.van de Loo/Shell, B.Hermann/Dow, ECNDT 1998


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Overall AE Grade vs. % of Tanks for crude

and product tanks from Major Sites

0

10

20

30

40

50

A B C D E

%CRUDE

%PROD.

%ALL

ALL SITES IN SURVEY% of tanks

TANKPAC

GRADE

sample size 598 tanks 6/96


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TANKPAC is a maintenance planning tool

Significant money savings: No moneywasted for opening of good tanks.

Maintenance prioritisation: The mostseverely damaged tanks are programmed

for internal inspection first. Prevention of environmental losses:Earlyidentification of potential leaks.

Very fast, low-cost inspection withminimal interruption of operations


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TALRUT

In-Service Floor Plate

(Critical Zone)Assessment

Inspects critical area,~30cm in.

Automated UT, Plan image.

40 m/day.

Indicative, notquantitative.

Detects first edge ofcorrosion.

Detects at 30-50%.


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TALRUT Annular Ring Test

Left - Example of Indications from a calibration plate (topof plate is the wall tank shell), Right area withoutindications and close up of the respective A-Scan at

cursor position

SHELL:

PLAN VIEW IMAGE SHOWING

SEVERE UNDERSIDE CORROSION:

Summary ReportingExample


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Shell Corrosion

Surveys Utilizing LSI


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LSI Tank Shell Corrosion

And Wear Mapping 18 meter x 500 mm strip:

10 x2 mm resolution 45 minutes

scan time (5 min/2m). 450,000 readings.

Typically: North, South, East, West(drive around above rings).

Larger tanks add NE, SE, SW, NW Preferential HAZ corrosion and

local thinning by wear

Limitations:

Poor surfaces may loose somedata ( but still hugestatistical sample )


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C-SCAN of TANK SHELL & PROCESSING OF UT DATA

FFS throughout Composite C-Scan imagereconstruction in Nominal-Caution-Reject coloring

mode


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PCMS & RBI TANKREPORTER S/W

Mistras TANKREPORTER and PCMS S/W is usedto enhance reporting and assist assetintegrity management. Capabilities includes3D model of the tank with detail weld seamlocations, nozzle locations, TML locations,repair locations, hyperlinks torecommendations and photos of the defectareas, corrosion rate calculations and RBI.


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In-Service Inspection, using Modern State of the art techniques,

Integrated within Plant Condition Monitoring Software (PCMS) and

Risk Based Inspection lead to reliable Integrity Assessment

offering:

Determine the condition of damaged floors so that a correct

priority for internal maintenance may be set, thus:

Increased Safety, Availability, Reliability

Reduce rate and impact of unexpected failures

Identify tanks which do not require internal inspection and

repair, thus:

Reduce the number and duration of tank shutdownReduce scope of routine activities

Resources prioritized for greatest effect

Reduce costs

CONCLUSIONS

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Thank you for your attention,

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