Developments of guided wave testing · Title: Microsoft PowerPoint - Developments of guided wave...

Copyright © TWI Ltd 2008World Centre for Materials Joining Technology

Application of guided wave Application of guided wave technology for long range inspection technology for long range inspection

of oil and gas pipelinesof oil and gas pipelines

Peter MudgePeter MudgePhil CattonPhil Catton

Malik KayousMalik KayousTatTat--Hean GanHean GanTWI Ltd, UKTWI Ltd, UK


Guided wave test equipment


Example result


Characteristics of guided wave tests• Survey of large areas from minimal test

locations,• Reduction of gaining access for inspection,

e.g. removal of insulation,• Ability to inspect inaccessible areas from

accessible locations,• The whole volume of material is tested; no

prior decisions required as to where degradation may have occurred.


Evidence for performance

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Flaw area, mm2

POD

, % PODPOD trend


but…• The guided wave phenomenon is a complex

combination of wave modes, many dispersive,• The sensitivity is limited; There is a trade-off

between volume examined and sensitivity & resolution,

• Energy can be lost into surrounding material; coatings, bonded insulation, back-fill, pipe contents,

• It is a new technology so there are few qualified test technicians available to implement it correctly.


BackgroundBackground•• Guided waves Guided waves -- an established screening tool for pipelinesan established screening tool for pipelines•• Amplitude of received signals broadly correlate to change Amplitude of received signals broadly correlate to change

in cross sectional area (CSA) :in cross sectional area (CSA) :–– Amplitude alone is a poor measure of size in UT.Amplitude alone is a poor measure of size in UT.–– Small defects cannot give large amplitude responses.Small defects cannot give large amplitude responses.–– Large defects do not necessarily give large responses, so other Large defects do not necessarily give large responses, so other

means are necessary to determine if a defect is large or not.means are necessary to determine if a defect is large or not.

•• These tests need to provide pipeline operators with the These tests need to provide pipeline operators with the information necessary to determine pipe integrity.information necessary to determine pipe integrity.

•• Combine amplitude data (from DAC) with the directionality Combine amplitude data (from DAC) with the directionality from focused tests:from focused tests:–– Focusing results can provide the necessary extra information. Focusing results can provide the necessary extra information.


Guided Wave CharacteristicsGuided Wave Characteristics• The ‘best’ wave modes are axi-symmetric.• To generate these a bracelet tool around the pipe is

used, which acts as a single transmitter.• If used as a phased array, the axi-symmetric

properties are lost as each segment around the circumference is energised at a different time, so that flexural modes will be generated.

• A simple implementation of a phased array, as in MHz frequency ultrasonics does not work here.

• The focusing method therefore has to take all possible modes into account.


Focal CharacteristicsFocal Characteristics

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Applying the appropriate correction factors allows a concentration of energy (focus) at a specific angle for a given distance from the transducer.


Benefits of focusingBenefits of focusing

Focusing allows the energy to beconcentrated where the defect is,increasing sensitivity and giving position and size information


Focal spot Focal spot –– Actual measured shapeActual measured shape

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Specified target shape function Numerically predicted shape Actual Measured Shape

Small sidelobespredicted

Similar sidelobes

Main lobes all at correct angle and shape


BenefitsBenefits•• Improved Sensitivity to smaller defectsImproved Sensitivity to smaller defects

•• Better call/no call informationBetter call/no call information

•• Improved prioritisation of callsImproved prioritisation of calls

•• Ability to find angular position of defectsAbility to find angular position of defects

•• Improved presentation possibilities for resultsImproved presentation possibilities for results


BenefitsBenefits

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sign

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Pipe endInitial pulse

•• Improved SensitivityImproved Sensitivity

•• UnUn--focusedfocused


BenefitsBenefits•• Improved SensitivityImproved Sensitivity

•• FocusedFocused

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Pipe end


Directionality data from focusingDirectionality data from focusingDefect

Windowed time domain of interest

Windowed time domain of interest

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Focused at z= 32.8 ft.


NonNon--directional response from a welddirectional response from a weld

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Practical ImplementationPractical Implementation


Energy focused inEnergy focused in--line with defectline with defect


Energy focused 180Energy focused 180°° from defectfrom defect


Plan view development from Plan view development from focused datafocused data

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8-106-84-62-40-2

WeldFlange/valve

3” Branch

•• AA--Scans can be plotted side by side in 3D Scans can be plotted side by side in 3D viewview

•• Gives plan view of pipe condition in a CGives plan view of pipe condition in a C--ScanScan--type plottype plot

•• Intuitive display of focused resultsIntuitive display of focused results


Test Method Incorporating FocusingTest Method Incorporating Focusing•• Circumferential information is obtained.Circumferential information is obtained.•• Data can be displayed in a more easily Data can be displayed in a more easily

interpreted manner.interpreted manner.•• The operator needs to distinguish between:The operator needs to distinguish between:

–– Areas of concern that need immediate attentionAreas of concern that need immediate attention–– Areas to earmark for inspection in the futureAreas to earmark for inspection in the future–– Areas of no significant problemsAreas of no significant problems

•• This method provides semiThis method provides semi--quantitative quantitative resultsresults

•• It is an efficient classifier of defectsIt is an efficient classifier of defects


Focused result from cased crossing with pittingFocused result from cased crossing with pitting

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ft from LH casing end circ. pos'

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Amplitude corrected for distance and normalised w.r.t. weld signals


Enhanced high resolution plots


Focal response Focal response –– Constant AreaConstant AreaDefect Defect

Shape with Shape with constant constant area lossarea loss

Axi Symmetric Axi Symmetric response response showing showing

amplitudeamplitude

Focus Focus response response showing showing angular angular

distributiondistribution

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Deep5% Area

Medium Depth5% Area

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Focal response Focal response –– Constant AngleConstant AngleDefect Defect

Shape with Shape with constant constant area lossarea loss

Axi Symmetric Axi Symmetric response response showing showing

amplitudeamplitude

Focus Focus response response showing showing angular angular

distributiondistribution

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Classification SchemeClassification SchemeCombine axisymmetric amplitude with distribution of the Combine axisymmetric amplitude with distribution of the angular response from focusingangular response from focusing, to get a follow, to get a follow--up priorityup priority

•• Defect Category C, whereDefect Category C, where–– Amplitude is less than Amplitude is less than --18dB from weld signal,18dB from weld signal, C = 1C = 1–– Amplitude is between Amplitude is between --18dB and18dB and --12dB from weld , 12dB from weld , C = 2C = 2–– Amplitude is greater than Amplitude is greater than --12dB from weld,12dB from weld, C = 3C = 3

•• Directionality Distribution D, whereDirectionality Distribution D, where–– Angular distribution is less than 45Angular distribution is less than 45°°, , D = 3D = 3–– Angular distribution is between 45Angular distribution is between 45°° and 90and 90°°,, D = 2D = 2–– Angular distribution is between 90Angular distribution is between 90°° and 315and 315°°,, D = 1D = 1–– Angular distribution is 360Angular distribution is 360°°,, D = 0D = 0


Classification of focus responsesClassification of focus responses

Category 3 response

Category 2 response

Category 1 response


Classification schemeClassification schemeProduct of C and D gives Follow up priorityProduct of C and D gives Follow up priority

If C x D = 0, the response is a weldIf C x D = 0, the response is a weld

Follow up Follow up prioritypriority

Defect Category, CDefect Category, C11 22 33

Directionality Directionality Distribution, Distribution,

DD

00 00 00 0011 11 22 3322 22 44 6633 33 66 99

Low priority Low priority Moderate priority Moderate priority High priorityHigh priority


ResultsResults

Response According to Defect Characterisation Scheme

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Weld Small defect Moderate defect Severe defect

Reflector type

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Weld Low Priority Medium Priority High Priority

No ‘small’defects in sample

No welds mis-

interpreted as defects


Ensuring that good data are collected• In response to industrial demands for consistency in this

area, TWI have established a training and certification scheme for guided wave technicians complying with EN 473 and ISO 9712,

• Independently assessed examinations at levels I and II under the CSWIP scheme,

• This is being expanded to a Europe-wide scheme through a number of national NDT societies – via the EC funded LRUCM project

• Provides the quality of data collection and interpretation required by oil and gas majors


Further developments - Monitoring using permanently mounted sensors

Long term test onTWI’s 100m loop


Result from ‘Permamount’ ™ Sensor


Acknowledgements• The focusing concept has been developed in

collaboration with Penn State University and FBS Inc.

• Development work has also been carried out under the EPSRC Engineering Doctorate Programme

Developments of guided wave testing · Title: Microsoft PowerPoint - Developments of guided wave...

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