In-Service Inspection and Integrity Assessment of Above ... · PDF fileIn-Service Inspection and Integrity Assessment of Above-Ground ... Tank Storage Conference ISTANBUL 3 & 4 November

In-Service Inspection and Integrity Assessment of Above-Ground

Storage Tanks

Dr. Athanasios AnastasopoulosPresentation for

Tank Storage ConferenceISTANBUL 3 & 4 November 2010

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

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 ON STREAM INSPECTION

• TANKPACTM : IN SERVICE CONDITION MONITORING FOR TANK FLOORS:• 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 BASED

INSPECTION SOFTWARE• DISCUSSION AND CONCLUSIONS


Failure of time-based maintenanceHot oil tank, 140°C: Internally inspected 12 months prior to failure, including UT+MFL. This collapse was due to a narrow band of annular ring corrosion. When the ring split the very rapid loss of hot liquid pulled a vacuum collapsing the tank shell.

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 into ground. When the plates were cut the cavity under the floor was several cubic metres in size.


• Copyright © 2007 Envirocoustics S.A.

Failures of time-based maintenance• Many more examples…….• Tanks removed from service, cleaned,

sludge dumped, tank inspected…...and no repairs required…..

• Tanks inspected though leaks not always prevented …

• If time based internal inspection worked……. this would not be happening…....



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 inspection and repair, this prevents the waste of maintenance resources and protects the environment.

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

• To do the above with as little disruption to operations as possible.


TANKPAC: IN SERVICE CONDITION MONITORING FOR TANK FLOORS


•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


Acoustic Sources detected•Corrosion 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, or turbulence).•External Interference - noise to be filtered:

Roof movement noise, Structural movement, External and pipe-borne noise, Condensation, Particle impacts, 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.


•Time (s)

•Am

plitu

de

•AE

Hit

rate

•AE data analysis

•Bottom plate

•AE sensor•Liquid-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.)



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 RINGOverall 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 .


Recommendations Matrix

“Overall” Grade A B C D E

“PLD” Grade I I II (n/a) (n/a) (n/a-doesn’t 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.


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)


150’ Diameter, Gasoline

“ALL DATA”TANK -PAC

GRADE

A

B

C

D

E

North

Channel 1


TANKPAC: In-Service Floor Plate Corrosion Assessment


3-D view of an “E” grade crude tank and damage found


Leaking Tanks Cases

• Gasoline Tank• Very concentrated source:

scale usually 50!• Doesn’t show on tank plot, one

pixel. On product tanks small leaks are not easily identified, except by high concentration.

• ~1mm hole found when opened.

• Naphtha Tank• 100 cu.m/day loss• No visible indication of a leak• Faint smell only• TANKPACTM test at 2% sensitivity

due to noise - 2 minutes acquisition only:

• 1cm hole found at location shown


• Copyright © 2007 Envirocoustics S.A.•NEW TANK LEAKING

•DEFECTS IN THE WELDS.......LEAK

•TANKPACTM: / LEAK DETECTION


Limitations(see method statement)

• Detects and grades active corrosion only.• Not suitable for assessing the internal condition of tanks which are

cleaned 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 floor

condition.• Location may degrade on very active D/E tanks due to

simultaneous sources, (the tank needs opening anyway!).

• Not all tanks can be tested, due to noise/condensation etc.• Complex procedure requires extensive training + control.



TANKPACTM: VERIFIED RELIABILITY

1. TANPAC Tests All around the word (Europe, Middle East, Africa, South America, 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 Global Solutions (results presented in ECNDT 98)

5. 1999 EEMUA recommendations to members (1996 User group became part of EEMUA, ~30 Co’s -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 INDUSTRIES PETROLIERS (Γαλλικό API), Guide Pour L’inspection Et La Maintenance Des Reservoirs Mettaliques AeriensCylindriques Verticaux D’ Hydrocarbures Liquides En Raffinerie, ANNEXE: Recommandations pour l’utilization de l’emission acoustique a la verification de l’ etancheite et a l’evaluation de l’ activite des corrosion des reservoirs verticaux aeriens, Edition Aug. 2000, Paris


Comparison withSubsequent Inspection

• From correlation of TANKPACTM results with internal inspection and repairs carried out:» 100% of “A”-grade tanks - no repairs or

damage to floor» 56% of “C”-grade tanks - patch repairs» 52% of “E”-grade tanks - floor replaced


Reliability: TANKPACTM

“overall” grading vs. repairs required*

0

20

40

60

80

100

120

A B C D EFU 1/2 Minimal damage: no repairsFU 3 Damage: some repairsFU 4 Significant damage: major repair/new floor

Rel

ativ

e (%

)

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


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

TANKPACGRADE

sample size 598 tanks 6/96



TANKPAC™ is a maintenance planning tool

• Significant money savings: No money wasted for opening of good tanks.• Maintenance prioritisation: The most severely damaged tanks are programmed for internal inspection first.• Prevention of environmental losses:Early identification of potential leaks.•Very fast, low-cost inspection with minimal interruption of operations


TALRUT

In-Service Floor Plate (Critical Zone)

Assessment

• Inspects critical area, ~30cm in.

• Automated UT, Plan image.• 40 m/day.• Indicative, not

quantitative.• Detects first edge of

corrosion.• Detects at 30-50%.



TALRUT Annular Ring Test

Left - Example of Indications from a calibration plate (top of plate is the wall –tank shell), Right – area without indications and close up of the respective A-Scan at cursor position

•SHELL:

•PLAN VIEW IMAGE SHOWING

•SEVERE UNDERSIDE CORROSION:

Summary –Reporting Example

Shell Corrosion Survey’s Utilizing LSI


LSI Tank Shell CorrosionAnd 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 some data ( but still huge statistical sample )



C-SCAN of TANK SHELL & PROCESSING OF UT DATA

FFS throughout Composite C-Scan image reconstruction in Nominal-Caution-Reject coloring mode


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.


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 activitiesResources prioritized for greatest effectReduce costs

CONCLUSIONS


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In-Service Inspection and Integrity Assessment of Above ... · PDF fileIn-Service Inspection and Integrity Assessment of Above-Ground ... Tank Storage Conference ISTANBUL 3 & 4 November