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NondestructiveMaterialTestingwithUltrasonicsIntroductiontotheBasicPrinciplesUContentsYOURPARTNERFORQUALITYUContents3NondestructiveMaterialTestingwithUltrasonicsIntroductiontotheBasicPrinciplesMichaelBerkeContentsIntroduction.................................................41.Whyuseultrasonicsfornondestructivematerialtesting?.............52.Ultrasonictestingtasks.......................................53.Detectionofdiscontinuities....................................64.Methodoftestingandinstrumenttechnology.....................104.1Theultrasonicflawdetector...................................104.2Nearresolution.............................................154.3Theprobe.................................................164.4Refractionandmodeconversion...............................174.5Characteristicsofangle-beamprobes...........................194.6TheTRprobe..............................................205.Locatingdiscontinuities......................................225.1Calibrationoftheinstrument..................................225.1.1Calibrationwithastraight-beamprobe..........................225.1.2CalibrationwithaTRprobe...................................245.1.3Calibrationwithanangel-beamprobe...........................265.1.4Locatingreflectorswithanangle-beamprobe....................286.Evaluationofdiscontinuities...................................296.1Scanningmethod...........................................296.2Evaluationofsmalldiscontinuities:TheDGSmethod...............306.3Soundattenuation..........................................346.4Thereferenceblockmethod...................................346.4.1Comparisonofechoamplitudes...............................346.4.2Distanceamplitudecurve.....................................357.Documentation.............................................378.Diagnosisofindications(outlook)..............................40Referencelist..............................................414IntroductionNondestructivematerialtestingwithultrasonicsismorethan40yearsold.Fromtheveryfirstexaminations,usingultrasonicoscillationsfordetectionofflawsindifferentmaterials,ithasbecomeaclassicaltestmethodbasedonmeasu-rementswithdueregardtoalltheimpor-tantinfluencingfactors.Todayitisexpec-tedthatultrasonictesting,supportedbygreatadvancesininstrumenttechnology,givereproducibletestresultswithinnarrowtolerances.Thisassumesexactknow-ledgeoftheinfluencingfactorsandtheabilitytoapplytheseintestingtechnology.Notallinfluenceshavetobeseriouslyregardedbytheoperator.Inmanycasessomeoftheinfluencescanbeneglectedwithoutexceedingthepermittedmeasu-rementtolerances.Duetothis,thetestse-quenceissimplifiedandthetestingtimereduced.Despitethis,thefuturebelongstothequalifiedoperatorwhocarriesouthistaskresponsiblyandwhocontinuouslyendeavourstokeephisknowledgeatthelateststateoftheartUContents51.Whyuseultrasonicsfornondestructivematerialtesting?Atthebeginningofthefiftiesthetechnicianonlyknewradiography(x-rayorradioac-tiveisotopes)asamethodfordetectionofinternalflawsinadditiontothemethodsfornondestructivetestingofmaterialsur-faces,e.g.thedyepenetrantandma-gneticparticlemethod.AftertheSecondWorldWartheultrasonicmethod,asde-scribedbySokolovin1935andappliedbyFirestonein1940,wasfurtherdevelopedsothatverysooninstrumentswereavail-ableforultrasonictestingofmaterials.Theultrasonicprincipleisbasedonthefactthatsolidmaterialsaregoodconduc-torsofsoundwaves.Wherebythewavesarenotonlyreflectedattheinterfacesbutalsobyinternalflaws(materialsepara-tions,inclusionsetc.).Theinteractionef-fectofsoundwaveswiththematerialisstrongerthesmallerthewavelength,thismeansthehigherthefrequencyofthewave.c=Soundvelocity[km/s]f=Frequency[MHz]l=Wavelenght[mm]Thismeansthatultrasonicwavesmustbeusedinafrequencyrangebetweenabout0.5MHzand25MHzandthattheresultingwavelengthisinmm.Withlowerfrequen-cies,theinteractioneffectofthewaveswithinternalflawswouldbesosmallthatdetectionbecomesquestionable.Bothtestmethods,radiographyandultrasonictest-ing,arethemostfrequentlyusedmethodsoftestingdifferenttestpiecesforinternalflaws,partlycoveringtheapplicationrangeandpartlyextendingit.Thismeansthattodaymanyvolumetestsarepossiblewiththemoreeconomicalandnon-riskultrasonictestmethod,ontheotherhandspecialtestproblemsaresol-ved,thesameasbefore,usingradiogra-phy.Incaseswherethehighestsafetyre-quirementsaredemanded(e.g.nuclearpowerplants,aerospaceindustry)bothmethodsareused.2.UltrasonictestingtasksIsthereaprimaryclassificationoftasksassignedtotheultrasonicoperator?Ifwelimitourselvestotestingobjectsforpossiblematerialflawsthentheclassifica-tionisasfollows:1.Detectionofreflectors2.Locationofreflectors3.Evaluationofreflectors4.Diagnosisofreflectors(reflectortype,orientation,etc.)Insteadofusingthewordreflector,theultrasonicoperatorveryoftenusesthetermdiscontinuity.Thisisdefinedasbeinganirregularityinthetestobjectwhichissuspectedasbeingaflaw.Inreality,onlyafterlocation,evaluationanddiagnosishasbeenmade,canitbedeter-minedwhetherornotthereisaflawwhicheffectsthepurposeofthetestobject.Thetermdiscontinuityisthereforealwaysusedaslon