©2016ConcoServicesCorp.

TheScienceBehindEddyCurrentandRemoteFieldTes8ng:

forCondensersandHeatExchangers

ConcoServicesCorpora4on

2

Introduc4on

•  WhatIsEddyCurrentTes4ng(ECT)andRemoteFieldTes4ng(RFT)?

•  WhathasDriventheAdvancementofECTandRFTTechnology?

•  ProbeConstruc4on•  FillFactor•  Applica4ons•  Calibra4on•  Singlevs.Mul4-Frequency•  Conclusions

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WhatisECTandRFT?

•  Non-destruc4veinspec4ontechniques.

•  Basedoninducingelectricalcurrentsinmaterialsbeinginspectedandobservingtheinterac4onbetweenthosecurrentsandthematerials.

•  Usedtomonitorcondenserandheatexchangertubeintegrity.

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WhatisECTandRFT?

•  ECTandRFTtechnologycantraceitsrootsbacktoMichaelFaraday.

•  Modernelectromagne4ctechniquesrelyontheexperimentsperformedbyFaradayinthemid1800s.

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WhatisECTandRFT?

•  Eddycurrentsaregeneratedbyelectromagne4ccoilsinatestprobe.

•  Astheprobemovesthroughthetube,defectsinthetubewallwillinterruptoraltertheamplitudeandpaYernoftheeddycurrent,changingitsmagne4cfieldandcausingavarianceinthecoilselectricalimpedance.

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WhatisECTandRFT?

•  Bymeasuringtheprobeelectricalimpedance,atrainedtechniciancan“see”defectsinthetubewall,suchaspi]ng,cracking,erosion,corrosion,grooving,dentsandchangesinwallthickness.

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WhathasDrivenTheAdvancementofECTandRFTTechnology?

•  Worldwideincreaseinthedemandforpower.•  Increasedfocusonpowerplantequipmentreliabilityandefficiency.

•  Needtofindsmallerandsmallerdefectsthatcanleadtotubefailure,causingadropinMWoutputortriggeringaforcedoutage.

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ProbeConstruc4on

•  ECTandRFTProbesconsistofacoilorcoilswrappedaroundastructure.

•  Designwilldeterminehowtheeddycurrentsareinducedandhowflawsaredetected.

•  Builtonanonconduc4vebody(aircore)orusingferritecoresandconduc4veshieldingtohelpshapetheeddycurrentfieldforspecialapplica4ons.

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Probe(Pancake)Coils

•  Designedtotestthesurfaceofmaterials.

•  Canbeappliedeffec4velytoplatesandwelds.

•  WhenfixedtoaspinningdeviceitiscalledaMotorizedRota4ngPancakeCoil(MRPC)andisveryeffec4veontubes,butis4meconsumingandexpensivetooperate.

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BobbinCoils

•  Allowfortheinspec4onofinstalledtubesfromtheID.

•  Interrogatestheen4recircumferenceofatube.

•  Themostwidelyusedcoil.•  Consideredthe“workhorse”ofthetubetes4ngindustry.

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Encircling(Feedthrough)Coils

•  Allowfortheinspec4onofroundobjectssuchastubes,wiresandrodsfromtheOD.

•  Interrogatetheen4recircumferenceofthematerial.

•  Usedmostlyinproduc4onmonitoringac4vi4es.

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AbsoluteArrangement

•  Coilworksindependently,makingnoreferencetoanyothercoil,andisaffectedbyallchangesinthematerial.

•  Usuallylimitedtousebyconduc4vitytesters,coa4ngthicknessgaugesandsmallsurfaceridingpancakecoilsforsurfacescanning.

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Differen4alArrangement

•  Twoormorecoilselectricallyconnectedtoopposeeachotherandlookforanimbalanceor“difference”betweenthetwocoilimpedanceswhenaflawisencountered.

•  Subcategorizedintotwotypes:•  SelfComparison.•  ExternalReference.

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SelfComparisonDifferen4al

•  Twoormorecoilselectricallyconnected,placedincloseproximitytoeachotherandwoundinopposi4on.

•  Verysensi4vetosmallvolumeflaws.•  Minimizenoiseduetoprobemo4on(wobble),temperaturevaria4onsanddeposits.

•  Effec4veindetec4ngabruptchangesinwallthickness.•  Cannotdetectgradualwalllossassociatedwithsteamerosionortube-to-tubewear.

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ExternalReferenceDifferen4al

•  Twoormorecoilselectricallyconnected.•  Coilscanbeonthesametestpartseparatedbyadistance

toavoiddirectcouplingbetweenthetwocoils.•  Onecoilcanbeonthetestpartwhiletheothercoilsitsin

afixedloca4ononareferencesamplethatrepresentsnominalmaterialcondi4ons.

•  Sensi4vetoallmeasurablechangessimilartoabsolutecoils.•  Datacanbeerra4c–muchlikeabsolutecoils.•  Typicallyreservedfordefectconfirma4onagainsttheself

comparisondifferen4alchannelsandfordetec4onofspecificdamagelikeerosionandtube-to-tubewear.

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HybridCoilsDriverPickup/Reflec4on

•  Havethewidestrangeofconfigura4ons.•  Basicconfigura4onu4lizesanexcita4oncoilandanindependentsensing(pick-up)coilorsetofsensingcoils.

•  Theexcita4onandsensingcoilscanbeincorporatedintoeachotherorseparatedbycertaindistance.

•  Hybridcoilshaveendlessconfigura4onstomeetspecialneedsoftheinspec4onindustry,butarenotnecessarilythemostaffordablebreeds.

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HybridCoilsArrayProbes

AdvancedArrayTechnology-DetailedDisplay

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ECTvsRFTProbes

•  MostECTProbesareBobbinProbesopera4nginthedifferen4almodes,selfcomparisonandexternalreference.

•  SomeECTProbesfallintotheHybridcategoryforspecializedconfigura4ons.However,assensi4vityisgainedforonespecificdamagemechanism,othermechanismsmaybemissed.

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ECTvsRFTProbes

•  RFTProbesareHybridProbes,(Driver/Pickup).

•  RFTProbesfeaturealargeexcita4oncoiltogeneratethemagne4cfieldandapickupcoillocatedtwotothreetubediametersfromtheexcitercoiltodetectthechangesinfieldstrength.

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FillFactor

•  FillFactor(FF)isthepercentagethetubeIDfilledbytheprobefortubinginspec4onsfromtheID.

•  Whencalcula4ngfillfactor,usetheformula:FF=d2/D2wheredistheoutsidediameterofthecoilandDistheinsidediameterofthetube.

•  ECTpreferredtohaveaFFof85%orbeYer.•  RFTpreferredtohaveaminimumFFof70%.•  SmallerFFvaluesmaybeacceptablebasedonsignal

responsefromacalibra4onstandard.•  SameformulaforODencirclingcoils,reversethevalues.

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ECTApplica4ons

•  Idealfornon-ferromagne4cmaterialssuchascopper,brass,copper-nickel,austeni4cstainlesssteelsandsimilaralloys.

•  Reliesondirectcouplingbetweentheinspec4oncoilandthetestmaterial.

•  CanbeusedonmildlypermeabletubeslikeMonelandferri4cstainlesssteelswiththeuseofmagne4cbiasprobes,to“zero”outthepermeabilityeffectsandlettheeddycurrentalterna4ngmagne4cfieldsrunfreetodotheirjob.

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RFTApplica4ons

•  Idealforpermeableandhighlypermeablematerialslikeferri4cstainlesssteel,carbonsteelandsimilaralloys.

•  Designedtoovercomethepermeabilityeffectsinferromagne4ctubing.

•  Couplingtakesplaceindirectlythroughthegenera4onofeddycurrentsandtheirresul4ngmagne4cfield.

•  RFTcanworkonnonpermeablematerialsbutitisnotasaccurateoreffec4veasconven4onalECT.

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Calibra4on

•  AllECTandRFTequipmentmustbecalibratedonaregularbasistoensurefunc4onalityandsensi4vityareadequatefortheintendedinspec4on.

•  TheASMEBoilerandPressureVesselCode,Sec4onV,ar4cle8andar4cle17specifytherequirementsforEddyCurrentTes4ngandRemoteFieldTes4ng.

•  ASMEsec4onValsodefinescer4fica4onrequirementsforinspec4onpersonnel.

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SingleFrequencyvsMul4FrequencyTes4ng

•  ForECT,themorefrequenciesthebeYer.•  Eachfrequencyhasitsstrengthfordetec4onandallowsforsignal

mixingtoeliminateunwantedinterferenceliketubesupportplatesignals.

•  Useofbothdifferen4alandabsolutemodesisalsorecommended.•  Thevarietyofanumberofeddycurrentchannelsandmode

combina4onsallowsanextensiveanalysisofdefect(flaw)depthandcharacteriza4on.

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SingleFrequencyvsMul4FrequencyTes4ng

Morechannelsofdataensuretheanalystismakingavaliddefectcall,notiden4fyingandpluggingfalseindica4ons.

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SingleFrequencyvsMul4FrequencyTes4ng

•  RFT,fewerfrequenciesthanECT.•  RFTdoesnoteasilylenditselftomul4frequencyinspec4onand

signalmixing.•  Duetothecharacteris4clowfrequencyopera4on,oneortwotest

frequenciesaretypicalforaRFTinspec4on.•  Addingtoomanylowfrequencieshasanimpactonproduc4onby

reducingthesamplerateandinturnforcesslowerscanningspeeds.

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Conclusions

•  ECTandRFTareeffec4vetoolsformeasuringtubeintegrity.•  ECTwithmul4plefrequenciesfornon-ferromagne4ctubes.•  RFTwithoneortwofrequenciesforferromagne4ctubes.•  Armedwithdetailedinforma4onaboutaHTX’stube

integrity,plantmanagerscantakeproac4vestepstoeitherrepair,replaceorplugdamagedtubesbeforetheyfail,preven4ngaforcedoutage.

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Ques4ons

JamesKocherEddyCurrentLevelIIIACONCOSERVICESCORP.1-800-345-3476jkocher@conco.net