157880345-tankinspectiontechniques3

7/22/2019 157880345-TankInspectionTechniques3

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Tank Inspection

Techniques


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Ultrasonic Thickness of the

Shell


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Raw Shell Thickness Data

Averaged Thickness

Data over Lc


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Hammer Test


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Magnetic Flux Leakage

Coil Sensors

Hall Effect Sensors

Technology adapted from Smart Pig Technology


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Distribution of Flux in a Plate

With a Soil Side Defect


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Types of Sensors Coils

Passive Devices

Faradays Law

Measures Change in the Flux Field

Speed of Scanning is Important


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Types of Sensors Hall Effect Sensors

Solid State Device

Absolute Magnitude of Flux Density

More Sensitive

More Noise

Temperature Sensitive


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Calibration Manufacturers Recommendations

Simulate Tank Conditions Coating

Plate Thickness Temperature

Material Properties

API 653 Appendix G


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Why so criticalWhat an inspector cannot see cant be

effectively inspected.

Additionally, items such as vacuum box

inspections are severely compromised if tankbottom and weld seams arent properlycleaned.

Tank Surface Preparation


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Tank Surface Preparation

The visual portion of the API-653 inspection is

critical.


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Wish veryone WouldHere are some examples of good surfacepreparation using either brush blast or ultra-

high pressure water:


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Limitations of MFL Scanners

Bottom Plate Lap Welds

Weld Tacks


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Shell

Surface Condition


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Plate Curvature


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Change in Plate ThicknessA thinner plate causes more flux lines to appear above the plate


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Defect Orientation


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Defect Orientation


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Keys to a Good Inspection Well trained, experienced

inspectors/operators Proper cleanliness of tank floor

Understand limitations and plan your options Proper equipment


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Late 1994 1995 Industry Conducted a PERF Study

on MFL/MFE Floor Scanning Equipment

Results

1. Identified a few obviously inferior pieces of equipment,butthe key finding was the Major Factor in a QualityMFL/MFE Inspection was the Inspector/Operator by a widemargin.

2. A couple of key major oil companies began testing qualifyinginspector/operators.

3. API has now moved toward testing and will offer a certificationprogram based upon Appendix G.


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Training and Certification Continued

ASNT, Level II Ultrasonic Training and

Certification Know Your Vendors Training and Certification

Programs

a) Ask for internal documentation

b) Require in your purchasing process Appendix G.basic certification

c) Rely on specialists Just because someone canoperate a D-meter and has an API 653 certificationdoes not mean they know tanks


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Conclusion

MFL has physical limitations Successfully used for inspections every day

Scanner Operator should understand

limitations


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U.T. Prove-Up of Tank Bottom

Use Ultrasonic Thicknessto determine remainingthickness of bottomindications.

Flaw dectector to size

defects and otheranomalies.


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SLOFEC(Saturated LOw Frequency Eddy

Current)


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SLOFEC Corrosion testing of material thicknesses up

to 35 mm and more Much higher detectability than conventional

MFL techniques, especially on thicker walls

Testing through surface coatings of 8 mmand more

No physical coupling of the sensors


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Magnetic Particle Inspection

Consider

Inside Corner Weld

Outside CornerWeld

Sump to Bottom

Sump Welds

Nozzles

Reinforcement Pads


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Leak Testing Vacuum Box Test

Bottom Lap Welds Bottom Repairs

Pressure Test

Reinforcement Pads

False Bottom Sump

Tank Hydro Test


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Helium Leak Detector


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Helium Leak DetectorWand


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Alternative Internal Inspection In-Service Robotic Inspection


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In-Service Internal Inspections Sampling of tank bottom thickness

2 to 15 percent of the bottom inspected

Utilize Statistical Methods

Extreme Value Analysis

Not a substitute for an out-of-serviceinspection


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Risk Assessment


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Risk Assessment

Considers both the Likelihood andthe Consequences of Failure

Risk Assessment is not a new idea, but

has recently become more formalized


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RBI Background

1985 ASME was commissioned to create a

guidance document published 1991 1993 - API began development on RBI

2000 - API-581 - RBI(Base Resource Document)

2002 - API-581 Appendix O Tank RBI

Ad t f RBI


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Advantages of RBI (0.2.5.1)

Introduces a another scheduling option

Consistent approach for calculatingremaining life

Consistent approach for determiningConsequence of Failure

Focus inspection effort to reduce Risk

Improved record keeping

Ri k A t St t i


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Risk Assessment Strategies

Absolute RiskAbsolute Risk

Attempts to Quantify the ActualAttempts to Quantify the ActualProbability of a Failure TypeProbability of a Failure Type

Relative RiskRelative Risk

Calculates an Index Score Which IsCalculates an Index Score Which IsCompared to Scores of Other SegmentsCompared to Scores of Other Segments

Risk Assessment


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Relative Risk Is Equal to:

Relative ProbabilityTimes

Perceived Consequences

Risk Assessment


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Calculate relative probabilities of failure

Calculate perceived consequences

Calculate relative risk & rank segments


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Relative Risk Assessment


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Components:Components:

AlgorithmAlgorithm

DataData

SoftwareSoftware

Risk Assessment


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Identify Possible Failure Modes Service History, DOT Incident Data, Experience

Identify Possible Consequences

Public, Environment, Business

Risk Assessment Algorithms


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Risk Assessment Algorithms

Failures causes can typically be

classified

Failures often result from the interactionof several factors

Group the variables by failure mode andorganize into an algorithm

Develop Algorithms


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Data (Variables)

What data are available

What data are relevant

What data need to be collected



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Create variables that describe pipeline

attributes

Organize variables into an algorithmcorresponding to failure modes

Assign weighting factors

Perform sensitivity analysis


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Ranking by Relative Risk


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The risk is never zero

The more you do, the lower your

relative risk

Basic Tank RBI Methodology


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Basic Tank RBI Methodology

Three basic components:

Roof Shell

Bottom

Looking for INDIVIDUAL Risk andCOMBINED Risk

Example


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Example

Roof = High

Shell = Low Bottom = Low

Combined Risk = High What can be done to reduce RISK?

Quantitative Analysis (0 2 5 3)


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Quantitative Analysis (0.2.5.3)

Need to know future risk

Assume bottom corrosion rate and runcalculator for different years

Tabulated this data into a spreadsheet

From the data list tanks based on risk

Risk Matrix


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ProbabilityC

ategory

Consequence Category

Summary Tank Data Example

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

T-1 Btm 24 24 24 24 24 24 21 21 17 17 13 13

Sh ll 19 19 19 19 19 19 19 19 19 19 19 19


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11 7 4 2 1

16 13 8 6 3

20 17 14 9 5

23 21 18 15 10

25 24 22 19 12

Shell 19 19 19 19 19 19 19 19 19 19 19 19

Roof 14 14 14 8 8 8 8 4 4 4 4 4

T-2 Btm 24 24 24 24 24 24 21 21 17 17 13 13

Shell 22 22 22 22 22 22 22 22 22 22 22 22

Roof 19 19 15 15 15 9 9 6 6 2 2 2

T-3 Btm 24 24 24 24 24 24 21 21 17 17 13 13

Shell 19 19 19 19 19 19 19 19 19 19 19 19

Roof 25 25 25 25 25 23 23 23 20 20 20 16

T-4 Btm 25 25 25 25 25 25 23 23 23 23 23 23

Shell 22 22 22 22 22 22 22 22 22 22 22 22

Roof 12 12 12 12 12 10 10 10 5 5 5 3

T-5 Btm 22 18 18 14 14 8 8 8 4 4 4 4

Shell 19 19 19 19 19 19 19 19 19 19 19 19

Roof 22 22 22 22 22 22 18 18 18 18 18 18

Required Data


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Required Data

Design: Service, size, type, courses, year, new bottom,

roof, years in service, diked,

Required Data


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Required Data

Consequence: Fluid type, detection time, ignition source,

environmental risk, spill area, inventory (lbs), datein service, effective age per component, pressure,

potential release, bottom type

Required Data


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q

Probability: Shell Int / Ext corrosion type / rate Bottom Int / Ext corrosion type / rate

Bottom stock-side protection

Roof condition

Last internal inspection..

Conclusions from Quantitative

Analysis


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y

Had to create a judgment value for an

analytical task Adjusting the data will adjust the Risk 0.2.1

The bottom corrosion rate was the singlebiggest driver of Risk

Learned that the calculator is not a crystal

ball.

Next Two RBI Types


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yp

Qualitative too subjective and open to

interpretation Combo -

Use the same basic analytical data

Tank has a Secondary Containment

Lets Go Back In Time


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Early 80s A refinery realized they needed to

know if they had a tank leakage problem Tried every technique known to man plus a

few more to determine if a tank might be

leaking

Old Tank Bottoms


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60s applied Fiberglass

Up till 80s very few bottoms were replaced Their analysis showed that many of the FG

bottoms may be leaking even after a goodinspection


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Of 300 Tanks is One Leaking? Researched all forms of pipeline and tank

testing / inspection. Developed the secondary containment

bottom system.

How A Tank Leaks


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API-581 Appendix O

99.72% chance the tank will weep before leak.(Table 2)

1983-1993 0.9% bottom leak (Table 3)

After 20 years Heavy oil some corrosionbeneath coating Finished none

Combination Conclusions


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Weep before leak

Bottom condition may be determined basedon product type: Crude, Finished, and allothers

Beginning of learning curve

Conclusion


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Develop a methodology for Consequence

Develop a written process Develop a process to verify your

methodology

Some tanks are eligible for RBI!


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Similar Service

Similar Service Assessment:


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What is Similar Service Assessment?

The process by which corrosion rates and

inspection intervals are established for a

candidate tank using corrosion rates and otherrelevant service history from a control tank for

the purpose of establishing the next inspection

date.



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Why Have a Similar Service

Appendix?To provide industry with performance-

based guidance on conducting a similar

service assessment.

Currently, there is no definition of similar

service and no clear guidance onconducting a similar service assessment.



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If it looks like a duck, walks like a duck, and talks like a duck

then its probably a duck.



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How is a Similar Service AssessmentDone?

Collect data for control and candidate tanks.

Conduct assessment using Data Sheet from Appendix H.

Determine if Similar Service can be used for candidate tank.

Determine the corrosion rates to apply to the candidate tank. Establish the next internal inspection date for the candidate

tank.

Document internal inspection date for candidate tank.

As additional data becomes available, validate corrosion rateestablished for candidate tank.

Determine if additional inspection data changes theinspection date for the candidate tank.

Similar Service Assessment:Collect data for control and

candidate tanks


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candidate tanks

Conduct similar service

assessment using data sheet

Determine if similar service can

be applied to candidate tank

Determine the corrosion rate to

be applied to the candidate tank

Establish next internal inspection date

for the candidate tank

Document revised internal

inspection date for candidate tank

Validate revised inspection date for candidate

tank as additional information is available

Determine if additional inspection data

changes inspection date for candidate tank


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CANDIDATE TANK(S)


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900 Miles

CONTROL TANK

CANDIDATE TANK(S)



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Product Side

Side exposed tostored liquid or gasproduct

Soil Side Side exposed tosupporting soil,concrete, or othermaterial



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Similar Service Assessment Criteria

Year tank erected Bottom material

Shell material

Corrosion allowance, bottom and shell

Bottom lining type, thickness and age

Cathodic protection



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Similar Service Assessment Criteria (contd)

Double bottom?

Soil material in contact with bottom plate Soil or material type

pH, Alkalinity

Moisture Salinity

Resistivity

Oil type (If oiled sand foundation)

Soil /material cleanliness

Soil gradation

Chlorides

Sulfates



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Similar Service Assessment Criteria (contd) Ambient conditions

Current service conditions Product classification

Specific gravity of liquid

Reid vapor pressure at 60F Normal operating temperature Inert gas blanket, if used

Water bottom, if used

Sulfur content

Length of t ime in service Product corrosivity

Previous service conditions



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Similar Service Assessment Criteria (contd)

Product classification

Additional considerations

MFL or MFE data for tank bottom

Ultrasonic thickness measurement data

Fiber optic monitoring system data

Cathodic protection monitoring tube data

Tank bottom integrity testing data

Maintenance procedures, including frequency andmethod of tank cleaning


TABLE 1.0


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Classification Description Example

A Low Sulfur Light Oils (< 1% sulfur) No. 2 fuel oil, diesel, kerosene, jet fuel,gasoline

B High Sulfur Light Oils (>1% sulfur) Unfinished heating oil, distillate

C Sweet Sulfur Heavy Oils (< 1% sulfur) Heavy gas oil & sweet residual

D Sweet Sulfur Heavy Oils (>1% sulfur) Sour residual

E Slops & Process Waters See description

F Finished Lube Oils Automotive, diesel and aviation oil

G Sludges Acidic, non-acidic

H Crude Oils Light volatile oil (Class 1),Non-sticky oil (Class 2),Heavy sticky oil (Class 3),

Non-fluid (heavy crude, high paraffin)(Class 4)

I Additives Gasoline performance additives

J Solvents Ketones, alcohol, toluene, xylene, glycols,glycol ethers

K Chemicals Phosphoric, sulfuric, hydrochloric, formic,and nitric acids



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What is the Objective of the Assessment?

Establish corrosion rates and inspectionintervals for a candidate tank using corrosion

rates and other relevant service history from a

control tank for the purpose of establishing thenext inspection date.

The concept is shown graphically on the next

slide.


Tank was new in 1970


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Tank was new in 1970

Original bottom thickness = 1/4

At 20 years, thickness = 0.05

Metal loss = .25 - .05 = 0.20

Corrosion rate = .2*1000/20 =

10mpy

New 1/4 bottom installed in 1990

In same service*, the new bottom

can be expected to corrode at thesame rate, from which a

retirement date can be

calculated.

* All other factors being equal


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Section 1.0 - Tank Bottom Product Side Assessment


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Tank Characteristic Control

Tank

Candidate

Tank

Match

?

Year Tank Erected 1984 1986 No

Bottom Material A36 A36 Yes

Corrosion Allowance None 1/16 No

Bottom Lining Type None None Yes

Bottom Lining

Thickness

N/A N/A Yes

Bottom Lining Age N/A N/A Yes


Current Service Control Tank Candidate Match?


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Current Service

Conditions

Control Tank Candidate

Tank

Match?

Current Product Name No. 2 Fuel Oil No. 2 Fuel Oil Yes

Product Classification 1 1 Yes

Specific Gravity of

Product

0.87 0.87 Yes

Normal Operating

Temperature

60F 60F Yes

Water Bottom? No No Yes

Sulfur Content < 1% < 1% Yes

Time in This Service 10 Years 15 Years No

Product Corrosivity Mild Mild Yes


P i S i C l T k C did M h?


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Previous Service

Conditions


Tank

Match?

Previous Product Name Gasoline Diesel Fuel No

Product Classification 1 1 Yes

Specific Gravity of

Product

0.80 0.85 No

Normal Operating

Temperature

50F 60F No

Water Bottom? No No Yes

Sulfur Content < 1% < 1% Yes

Time in This Service 11 Years 6 Years No

Product Corrosivity Mild Mild Yes


Section 2 0 - Tank Bottom Soil Side Assessment


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Tank Characteristic Control Tank Candidate

Tank

Match?

Year Tank Erected 1984 1986 No

Bottom Material A36 A36 Yes

Corrosion Allowance None 1/16 No

Double Bottom? None None Yes

Section 2.0 Tank Bottom Soil Side Assessment


Soil / Material Control Tank Candidate Match?


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Soil / Material

Characteristics


Tank

Match?

Soil Type Crushed

stone & sand

Crushed

stone & sand

Yes

Soil pH 6.7 7.1 No

Soil Alkalinity No No Yes

Soil Moisture 15% 20% No

Soil Salinity Insignificant Insignificant Yes

Soil Resistivity 3500 ohm-cm 3000 ohm-cm No

Oil Type If Oiled Sand

Cushion

Diesel Oil None No

Soil Cleanliness Some sulfate

contaminants

No known

contaminants

No


Current Operating Control Tank Candidate Match


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Current Operating

Conditions


Tank

Match

?

Normal Operating

Temperature

Ambient Ambient Yes

Cathodic Protection Yes Yes Yes

Ponding/Water Yes No No

Previous Operating

Conditions


Tank

Match

?

Normal Operating

Temperature

Ambient Ambient Yes

Cathodic Protection No No Yes

Ponding/Water Yes No No


Si il S i A t C l i


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Similar Service Assessment Conclusions:

Does this assessment include additional

assessment documentation? Based on the criteria reviewed in this Similar

Service Evaluation Is Or Is Not

recommended for this tank. The corrosion rate to be applied to the

product side of this tank is ______ mpy.

Comments


Si il S i A t D t ti


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Similar Service Assessment Documentation:

THE DATA SHEET SHALL BE MAINTAINED IN THE RECORD

FILE AS PER 6.8.

ASSESSED BY:___________________ DATE:___________

APPROVED BY:__________________ DATE:___________

(tank owner/operator)

TANKPAC - Condition

Monitoring for Storage


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Monitoring for Storage

Tank Bottoms

Acoustic Emissions

Information provided by:

Tank bottoms are the only structural part

of a tank with no access for inspection

during operation
http://www.conaminsp.com/main.htmhttp://www.conaminsp.com/main.htm


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TANKPAC - In-Service Condition Assessment of TankBottoms Case Study for MHG Sales Growth.A $2-7K Traditional NDT test that just became a $40-45K complete inspection

package with zero competition


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Traditional NDT (Visual and MFL after opening

Acoust ic Emission TANKPAC

Complete API-653

Automated Ultrasonics (LSI)

Risk Based Inspection (RBI)

Failure of time-basedmaintenance


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Hot oil tank, 140 deg.C

Internally inspected 12months prior to failure,including UT+MFL. Thiscollapse was due to anarrow band of annularring corrosion. When thering split the very rapidloss of hot liquid pulled avacuum collapsing thetank shell.


50m CRUDE OIL TANK


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One of 40+ holes in thetank floor, although the tankwas not leaking duringservice, only the sludge and

debris were sealing thefloor. Attempts to re-suspend the sludge have

resulted in major leakageon many occasions.


Naptha Tank


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Naptha Tank

Leaking 100 cubic metres perday through a 1cm hole.Operations noticed lossesafter a week, but no visible

product, which wasdisappearing into ground.When the plates were cut the

cavity under the floor wasseveral cubic meters in size.

Failures of time-basedmaintenance

1mm diameter pinhole leak in a 25m diesel tank where


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1mm diameter pinhole leak in a 25m diesel tank, whereepoxy coating failed.

Collapse of a 25m sulphur tank due to annular-to-shellcorrosion.

200 cubic meters per day leakage in a 75m crude tank, 100cu.m/hour in a 97m crude tank...

Many more examples. Tanks removed from service, cleaned, sludge dumped, tank

inspected...and no repairs required..

If time based internal inspection worked. this would not

be happening....

Summary and Requirements

Summary:


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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


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1989 PAL approached by customers, discussion on requirements fortank floor condition assessment.

1990 First AE trials on tank floors, Esso, BP, .

1992 User group formed, grew from 5 to 20+ Cos.

1996 User group became part of EEMUA, ~30 Cos (EngineeringEquipment Material Users Association) experience now >600 tank

floor tests, feedback on internal inspection of >150 tanks, procedureat rev.4.

1997 Procedure accepted by Saudi Aramco.

1998 Results of TANKPAC correlation study presented at ECNDT

by Shell/Dow etc. >1000 tests now completed. 1999 EEMUA recommendations to members.


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Corrosion of InternalZinc Anodes

I t l ifi i l d


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Internal sacrificial anodescorrode in place of tank floor.

Zinc blocks can be 1m in size.

Oilfield production tanks use

sacrificial anodes-very activeuntil used.

Special procedures used to

separate anode corrosion fromfloor corrosion.

Location of remaining activeanodes

TANKPAC: outline procedure

Tank is isolated and allowed to settle.


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Sensors are attached to the tank wall around the entirecircumference, ~1m above annular. One row, or two rows

where condensation or high noise is possible.

The tank is monitored, duration is ~1-2 hours.

The data is processed to eliminate unwanted noise.

Note: effect of noise is conservative >increases grade. The result is graded per procedure for the overall grade on

an A (good) to E (bad) scale.

Location of 3+hit sources by triangulation. Location and grading of 3+hit potential leak sources*.

Discussion and recommendations.*Shell EWGAE paper


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Acoustic Sources detected

Sources of interest:


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Spalling of corrosion products.

Leak noise: flow interruption,or turbulence.

Extraneous noise to be removed:

Roof movement noise.

Structural movement.

External and pipe-borne noise. Condensation.

Particle impacts.

Valve leakage.

Inputs to Grade and

Recommendations

Overall activity level, A-good condition, E-bad condition,


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O e a act ty e e , good co d t o , bad co d t o ,B, C, D, intermediate conditions:

Diameter, product, sludge height. Normalise using: number of sensors, data filtered, threshold.

Special procedures for sacrificial anodes, soft rubber lining.

Locate overall data: The ~5-30% which hits >3 sensors, any concentrated

sources?

Separate, locate, and grade potential leak data:

More severe local damage, A to E scale.

Retest recommendation based on above factors.

Recommendations Matrix

Overall GradeA B C D E


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PLD Grade 4 4 2 (2) (1) (n/a)

A 4 4 2 (2) (1)

B 4 4 2 2 (1)

C 2 2 1 1 1

D 2 1 1 1 1

E 1 1 1 1 1Clearly leaking tanks often unable to grade, (should be opened anyway).

Limitations

Detects and grades active corrosion only.

N t it bl f i th i t l diti f t k hi h


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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 floor condition. Location may be unreliable 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.

Quality Control and Training Documentary quality control system under ISO 9002:

Trained and certified engineers


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Trained and certified engineers.

Controlled TANKPAC procedures.

Controlled TANKPAC Field worksheets . Quality plan for each test.

Digital storage of data and full traceability.

Engineer training and certification: ASNT II general AE

TANKPAC procedure class and field training.

TANKPAC written and practical examination.

TANKPAC minimum experience requirement (~50 tanks). PAC level III review of and approval of report.

Overall AE Grade vs. % of tanks for

crude and product tanks from major

sites% of tanks


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0

5

10

1520

25

30

3540

45

A B C D E

%CRUDE

%PROD.

%ALL

ALL SITES IN SURVEY% of tanks

TANKPACGRADE

sample size 598 tanks 6/96

Reliability: TANKPAC overall grading versus repairs

required*

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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0

20

40

60

80

100

120

A B C D E

FU 1/2 Minimal damage: no repairs

FU 3 Damage: some repairs

FU 4 Significant damage: major repair/new floor

R

elative(%)

AE-grade

Naptha Tank-Before: E grade,

and after repair: A grade


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3-D view of E grade crude tank

and damage found


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110m GRP lined Crude Oil Tank:

TANKPAC and MFL


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Hot Fuel Oil Tank 50m

E grade overall.

Annular ring very active


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Annular ring very active.

Dug underneath annular ring inmost active areas:

Up to 8mm loss of metal on15mm annular plates

Tank shut down immediately,avoiding failure (see next

slide).

Leaking Naptha Tank

100 cu.m/day loss

No visible indication of a


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No visible indication of a

leak Faint smell only

TANKPAC test at 2%sensitivity due to noise-2mins. only:

1cm hole found at locationshown

Strategy for Using TANKPAC


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TANKPAC is a maintenance planning tool.

Use TANKPAC to help identify the tanks which requireinspection and repair, and leave others in-service until theircondition indicates action is required.

Use TANKPAC results to set the maintenance priority.

157880345-tankinspectiontechniques3

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