焊缝无损检测现状设计外文文献翻译中英文翻译外文翻译Word文档下载推荐.docx
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焊缝无损检测现状设计外文文献翻译中英文翻译外文翻译Word文档下载推荐.docx
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stateoftheart
R.J.Ditchburn,S.K.BurkeandC.M.Scala
Ultrasonics
UltrasonicswasintroducedasanNOTtechniqueforweldinspectioninthe1960’s.Sincethen,thetechniquehasundergoneextensivedevelopmentandgainedincreasingacceptance.Consequently,ultrasonicsisnowthemajortechniqueusedforvalidationofweldedstructuresinmanyin-serviceinspectionapplications,eginoff-shorestructures.Innuclearandpressurevesselindustriesandinarangeofnavalapplications.
TheemergenceofultrasonicsasapreferredtechniqueoverX-radiographyinthesein-serviceinspectionsisduebothtoinherentlimitationsinradiographyandtoactualbenefitsinapplyingultrasonics.Asdescribedabove,radiographyisexcellentforidentifyingvolumetricdefectsbutislimitedinitsabilitytodetectorsizeplanardefect,suchascracks,whicharelikelytobethemoreseriousdefectstype.Ultrasonicwavesarescatteredbyplanarandvolumetricdefects,makingtheultrasonictechniqueusefulfordetectingandsizingbothtypesofdefects.Evenclosedcracksaredetectablebyultrasonic.Providedthatappropriateproceduresareused.Ultrasonicsalsoreadilygivesdepthinformationconcerningadefect,whereasforX-rays,specializedandexpensivetechniquessuchascomputertomographyareneededtoobtainsuchinformation.Ultrasonicsalsooffersbenefitsoverradiographyintermsofcostsavingsthroughincreasedproductivity.Finally,inthe1990’stheincreasingconcernsaboutradiationsafelyareaseveredisincentivetothecontinueduseofX-radiography.
Inthelastfewdecades,ultrasonicshasdevelopedfromapurelymanualtechniquetoamanualtechniquewithcomputer-assistedprocessingtotheuseofautomaticscannersandmorerecentlytothedevelopmentoffullyautomatedsystemsincorporatingmultiplepiezoelectricstudiesontheuseofthisrangeofincreasinglysophisticatedsystemsfordefectdetectionhaveformedamajorfactorinestablishingthecredibilityofultrasonicsforweldinspection.StudiessuchastheProgrammeforInspectionofSteelComponents(PISC)ultrasonicinspectioninthenuclearandpressurevesselindustries.OutsidethePISCstudies,usefulworkhasbeencarriedouttodeterminereliableproceduresforinspectingspecificweldgeometriesincludingsingle-Vanddouble-Vweldsandalsocomparedthereliabilityofradiographyvs.ultrasonicinspectionOverall,theresultsofthereliabilitystudiesindicatethattheprobabilityofdetectingadefectwithultrasonicsincreaseswiththedegreeofsophisticationofthesystem.AccordingtoLebowitzandDeNaletheresultsalsoindicatethatmanualultrasonicprocedures,canbeexpectedtorejectanequalorgreaterpercentageofthediscontinuitiespresentthanwillradiography.
Ultrasonicvalidationofweldedstructuresrequiresnotonlyreliabledefectdetectionbutalsosufficientlyaccuratedefectlocationandsizingtoallowacceptance/rejectioncriteriatobecorrectlyimplementedManualultrasonicsystemsusuallyrelyontheuseofamplitudedependenttechniquesfordefectsizing.Techniquescommonlyusedarethe20dBdrop(showninFigurela),the6dBdrop,orcomparisonwiththeamplitudeformadrilledhole.Howeverthesetechniquesareknowntobeinaccurate.Theinaccuraciesarecausednotonlybytheeffectsofdefectshape,orientationandlocation,butalsobyattenuation,coupling,resolutionandequipmentcharacteristics.Theincorporationofcomputer-assistedprocessingintoultrasonicsystemshasallowedtheeasyimplementationofpotentiallybettermethodsfordefectdetectionandsizingsuchastime-of-flight-diffraction(TIFD)(seeFigure1b),eginPISCⅡtheadditionofTOFDtostandardproceduresgavenearlyperfectresultsintermsofrequiredrejectionratefor-defects.ImportantadvancesindefectsizinghavealsobeenmadepossiblebytheincorporationinautomatedultrasonicsystemsofultrasonicsimagingbasedonSyntheticaperturefocusing(SAFT)andvariantssuchasSUPERSAFT.
Thedevelopmentofreliableproceduresfortheapplicationofultrasonicstoweldinspectionhadrequiredanunderstandingoftheinteractionwaveswiththevarioustypesofwelddefects,ofwavepropagationincomplicatedgeometries,ofparticularproblemscausedbyinspectingfordefectsclosetothesurfaceofastructureoftheeffectsofcladdingandothermicrostructuralinfluencesinfluencesonwavepropagation.Whilewavepropagationinferriticandlight-alloyweldsIsrelativelyuncomplicated,themicrostructuresofausteniticweldshavecausedspecialconcerns.Thesematerialsstronglyattenuateultrasonicwaves,causehighbackgroundnoiseduetoscatteringfromthelargegrainspresent,andresultinskewingoftheultrasonicbeamunlessthepropagationisalongprincipalcrystallographic
(a)20dBDropTechnique(b)TOFDTechnique
Figure1Ultrasonicdefectsizing(a)The20dBintensitydroptechnique.Wherethetransducerispositionedatpointsisusedalongwithprobecalibrationcharacteristicstoestimatethedefectlength.(b)Time-of-flight-diffraction(TOFD)technique.Atwoprobetechniqueusedtodeterminecracksizeandlocationutilizingthediffractedwavesfromthetipsofthedefect.
axes.Thus,muchrecentresearchhasbeendirectedtowardthedevelopmentofspecializedultrasonictechniquestodealwiththesecomplications.Considerableprogresshasalreadybeenmade,especiallyunderPISCⅡandⅢwheredetailedhasbeenundertaken.Inthefuture,thesemodelsshouldallowmoreaccurateestimationoflocationandsizingerrorsforspecificdefects,andprovidethebasisforimprovedcodesforinspectionofausteniticsteelsandweldsteels.
Intoday’sworld,thereisanincreasingneedtominimizethecostofweldinspection.Theadventofautomatedscanners,theuseofmultipleprobesandcomputer-assistedprocessinginmodernultrasonicsystemshavereducedcostsbyincreasingboththespeedandreliabilityofinspection.Onthenegativeside,equipment,andcalibrationcostsarehigherwithautomatedequipment.Also,thecostsinactuallyinterpretingultrasonicdatacouldriseduetotherecentadvancesinultrasonicsystems,sincealltypesofdefectsandevenverysmalldefectscanbedetected,whetherornotthedefectsarecritical.Thesolutiontothisproblemwouldbeimprovementsintheautomatedapplicationofacceptance/rejectioncriteriaondefectcriticality.Hence,considerableeffortisnowbeingdirectedtowardsthedevelopmentofneuralnetworkstobeusedinultrasonicsystemstoclassifydefecttype,sizeandlocation,andresultingconformancewithaparticularinspectioncode.Verypromisingresultshavealreadybeenobtainedinseverallaboratoriesinstudiesbothonsimulatedwelddefects,wherea100%correctclassificationratewasachievedindefecttype,andonrealwelddefectswheresuccessratesoftheorderof90%wereachievedusingavarietyodmethods.Preliminaryworkhasalsobeenmadeintheautomatedapplicationofacceptance/rejectioncodesvianeuralnetworks.
Clearlyneuralnetworkswillonlyprovesuccessfuliftheycanbetrialedonrepresentativedata.However,representativedatacanproveexpensivetoacquire.Forexample,thePISCprogrammeiscurrentlycostedat$200M,anditseemsunlikelythatthistypeofeffortwillbeduplicatedinotherindustriesinthenearfuture.Analternativeapproachwouldbetotrialthenetworksusingdatageneratedfromrobustmathematicalmodelsoftheinteractionofultrasonicwaveswithwelddefects.ThedevelopmentofsuchmodelsisacontinuingPISCobjectiveunderPISCⅢ。
Untilthesemathematicalmodelsaremorecomplete,anemphasisstaffseemsnecessaryandtechnicallyqualifiedstaffseemsnecessaryforultrasonicweldvalidation.
Forthefuture,manychallengesremaininoptimizingultrasonicinspectionofwelds.Substantialimprovementsarepossibleintheapplicationofneuralnetworkshasonlyjuststarted.Variousoptionsexistfortheimprovedgenerationanddetectionofultrasonicinweldingapplications,egbytheuseofphasedarrays,lasertechniques(asdescribedbelow)andotherspecialistprobes.Anumberofadditionalfactorsneedtobeconsideredintheultrasonicreliabilityarea,egresidualstress,theeffectofhigherfrequencies,moreextensiveconsiderationofrealratherthansimulatedefects.
Greaterconsiderationalsoneedstobegiventotheoverallcosteffectivenessofinspection.Oneoftheelementsinmaximizingcost-effectivenessistheselectionofthemostappropriatetechniquesforagiveninspection,includingthepossibleuseofmorethanonetechniquetovalidatedifferentpartsofaweldedstructure.Forexample,magneticparticletestingisalreadyusedinconjunctionwithultrasonicsforrapidandcost-effectivedetectionofsurfacecracksinwelds.Newelectromagneticmethodscouldalsohavearoletoplayhere(asdiscussedinthefollowingsection).Finally,thereareclearlychallengesinimplementingadvancesinultrasonicinspectiontechnologyintothecodesforweldvalidation.
In-productionweldinspection
On-linemonitoringandcontroloftheweldingprocesshasthepotentialtoimproveweldqualityandincreaseproductivityinautomatedwelding.Weldmonitoringandcontrolcanbeachievebytheintegrationofreal-timenondestructiveevaluationtechniqueswiththeweldingprocess.In-productionweldinspectioncanimproveweldqualityandmayprovideasignificantcostreduction.Theweldingparameterscanusuallybeadjustedtopreventdefectsdooccurtheflawscanbefoundandrepairedbeforetheyarecoveredbysubsequentweldingpasses,leadingtoadecreaseinthelevelofpost-weldinspectionandrepair.
Goodqualityweldsrelyinthecorrectweldpoolsizegeometryandposition
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