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MAGNETICPARTICLETESTINGMAGNETICPARTICLETESTING1IntroductionThismoduleisintendedtopresentinformationonthewidelyusedmethodofmagneticparticleinspection.Magneticparticleinspectioncandetectbothproductiondiscontinuities(seams,laps,grindingcracksandquenchingcracks)andin-servicedamage(fatigueandoverloadcracks).IntroductionThismoduleisint2OutlineMagnetismandFerromagneticMaterialsIntroductionofMagneticParticleInspectionBasicProcedureandImportantConsiderationsComponentpre-cleaningIntroductionofmagneticfieldApplicationofmagneticmediaInterpretationofmagneticparticleindicationsExamplesofMPIIndicationsOutlineMagnetismandFerromagn3MagneticlinesofforcearoundabarmagnetOppositepolesattractingSimilarpolesrepellingIntroductiontoMagnetismMagnetismistheabilityofmattertoattractothermattertoitself.Objectsthatpossessthepropertyofmagnetismaresaidtobemagneticormagnetizedandmagneticlinesofforcecanbefoundinandaroundtheobjects.Amagneticpoleisapointwheretheamagneticlineofforceexitsorentersamaterial.Magneticfieldlines:Formcompleteloops.Donotcross.Followthepathofleastresistance.Allhavethesamestrength.Haveadirectionsuchthattheycausepolestoattractorrepel.Magneticlinesofforcearound4FerromagneticMaterialsAmaterialisconsideredferromagneticifitcanbemagnetized.MaterialswithasignificantIron,nickelorcobaltcontentaregenerallyferromagnetic.Ferromagneticmaterialsaremadeupofmanyregionsinwhichthemagneticfieldsofatomsarealigned.Theseregionsarecallmagneticdomains.Magneticdomainspointrandomlyindemagnetizedmaterial,butcanbealignedusingelectricalcurrentoranexternalmagneticfieldtomagnetizethematerial.DemagnetizedMagnetizedSNFerromagneticMaterialsAmater5HowDoesMagneticParticle
InspectionWork?Aferromagnetictestspecimenismagnetizedwithastrongmagneticfieldcreatedbyamagnetorspecialequipment.
Ifthespecimenhasadiscontinuity,thediscontinuitywillinterruptthemagneticfieldflowingthroughthespecimenandaleakagefieldwilloccur.HowDoesMagneticParticle
In6HowDoesMagneticParticle
InspectionWork?(Cont.)Finelymilledironparticlescoatedwithadyepigmentareappliedtothetestspecimen.Theseparticlesareattractedtoleakagefieldsandwillclustertoformanindicationdirectlyoverthediscontinuity.Thisindicationcanbevisuallydetectedunderproperlightingconditions.
HowDoesMagneticParticle
In7BasicProcedure
Basicstepsinvolved:Componentpre-cleaningIntroductionofmagneticfieldApplicationofmagneticmedia
InterpretationofmagneticparticleindicationsBasicProcedureBasicste8Pre-cleaning
Wheninspectingatestpartwiththemagneticparticlemethoditisessentialfortheparticlestohaveanunimpededpathformigrationtobothstrongandweakleakagefieldsalike.Thepart’ssurfaceshouldbecleananddrybeforeinspection. Contaminantssuchasoil,
grease,orscalemaynot
onlypreventparticlesfrom
beingattractedtoleakage
fields,theymayalso
interferewithinterpretation
ofindications.Pre-cleaningWheninspecting9IntroductionoftheMagneticField
Therequiredmagneticfieldcanbeintroducedintoacomponentinanumberofdifferentways.UsingapermanentmagnetoranelectromagnetthatcontactsthetestpieceFlowinganelectricalcurrentthroughthespecimenFlowinganelectricalcurrentthroughacoilofwirearoundthepartorthroughacentralconductorrunningnearthepart.IntroductionoftheMagneticF10DirectionoftheMagneticField
Twogeneraltypesofmagneticfields(longitudinalandcircular)maybeestablishedwithinthespecimen.Thetypeofmagneticfieldestablishedisdeterminedbythemethodusedtomagnetizethespecimen.Alongitudinalmagneticfieldhasmagneticlinesofforcethatrunparalleltothelongaxisofthepart.Acircularmagneticfieldhasmagneticlinesofforcethatruncircumferentiallyaroundtheperimeterofapart.DirectionoftheMagneticFiel11ImportanceofMagneticFieldDirectionBeingabletomagnetizethepartintwodirectionsisimportantbecausethebestdetectionofdefectsoccurswhenthelinesofmagneticforceareestablishedatrightanglestothelongestdimensionofthedefect.Thisorientationcreatesthelargestdisruptionofthemagneticfieldwithinthepartandthegreatestfluxleakageatthesurfaceofthepart.Anorientationof45to90degreesbetweenthemagneticfieldandthedefectisnecessarytoformanindication.Sincedefectsmayoccurinvariousandunknowndirections,eachpartisnormallymagnetizedintwodirectionsatrightanglestoeachother.FluxLeakageNoFluxLeakageImportanceofMagneticFieldD12Question?
Fromthepreviousslideregardingtheoptimumtestsensitivity,whichkindsofdefectareeasilyfoundintheimagesbelow?Longitudinal(alongtheaxis)Transverse(perpendiculartheaxis)Question? Fromthepreviouss13ProducingaLongitudinalMagneticFieldUsingaCoilAlongitudinalmagneticfieldisusuallyestablishedbyplacingthepartneartheinsideoracoil’sannulus.Thisproducesmagneticlinesofforcethatareparalleltothelongaxisofthetestpart.CoilonWetHorizontalInspectionUnitPortableCoilProducingaLongitudinalMagne14ProducingaLongitudinalFieldUsingPermanentorElectromagneticMagnetsPermanentmagnetsandelectromagneticyokesarealsooftenusedtoproducealongitudinalmagneticfield.Themagneticlinesofforcerunfromonepoletotheother,andthepolesarepositionedsuchthatanyflawspresentrunnormaltotheselinesofforce.
ProducingaLongitudinalField15CircularMagneticFieldsCircularmagneticfieldsareproducedbypassingcurrentthroughthepartorbyplacingthepartinastrongcircularmagnetfield.
Aheadshotonawethorizontaltestunitandtheuseofprodsareseveralcommonmethodsofinjectingcurrentinaparttoproduceacircularmagneticfield.Placingpartsonacentralconductorscarryinghighcurrentisanotherwaytoproducethefield.MagneticFieldElectricCurrentCircularMagneticFieldsCircul16ApplicationofMagneticMedia(WetVersusDry)MPIcanbeperformedusingeitherdryparticles,orparticlessuspendedinaliquid.Withthedrymethod,theparticlesarelightlydustedontothesurface.Withthewetmethod,thepartisfloodedwithasolutioncarryingtheparticles.Thedrymethodismoreportable.Thewetmethodisgenerallymoresensitivesincetheliquidcarriergivesthemagneticparticlesadditionalmobility.
ApplicationofMagneticMedia17DryMagneticParticles
Magneticparticlescomeinavarietyofcolors.Acolorthatproducesahighlevelofcontrastagainstthebackgroundshouldbeused.DryMagneticParticlesMagn18WetMagneticParticlesWetparticlesaretypicallysuppliedasvisibleorfluorescent.Visibleparticlesareviewedundernormalwhitelightandfluorescentparticlesareviewedunderblacklight.WetMagneticParticlesWetpart19InterpretationofIndications
Afterapplyingthemagneticfield,indicationsthatformmustinterpreted.Thisprocessrequiresthattheinspectordistinguishbetweenrelevantandnon-relevantindications.Thefollowingseriesofimagesdepictrelevantindicationsproducedfromavarietyofcomponentsinspectedwiththemagneticparticlemethod.InterpretationofIndications20CraneHookwith
ServiceInducedCrack
Fluorescent,WetParticleMethod
CraneHookwith
ServiceInduc21Gearwith
ServiceInducedCrack
Fluorescent,WetParticleMethodGearwith
ServiceInducedCra22DriveShaftwith
HeatTreatmentInducedCracks
Fluorescent,WetParticleMethodDriveShaftwith
HeatTreatme23
SplinedShaftwith
ServiceInducedCracksFluorescent,WetParticleMethodSplinedShaftwith
Servi24
ThreadedShaftwith
ServiceInducedCrackFluorescent,WetParticleMethod
ThreadedShaftwith
Servic25LargeBoltwith
ServiceInducedCrackFluorescent,WetParticleMethod
LargeBoltwith
ServiceInduc26CrankShaftwith
ServiceInducedCrackNearLubeHoleFluorescent,WetParticleMethod
CrankShaftwith
ServiceIndu27LackofFusioninSMAWWeldVisible,DryPowderMethodIndicationLackofFusioninSMAWWeldVis28ToeCrackinSMAWWeldVisible,DryPowderMethodToeCrackinSMAWWeldVisible,29ThroatandToeCracksin
PartiallyGroundWeldVisible,DryPowderMethodThroatandToeCracksin
Part30DemagnetizationPartsinspectedbythemagneticparticlemethodmaysometimeshaveanobjectionableresidualmagneticfieldthatmayinterferewithsubsequentmanufacturingoperationsorserviceofthecomponent.Possiblereasonsfordemagnetizationinclude:Mayinterferewithweldingand/ormachiningoperationsCaneffectgaugesthataresensitivetomagneticfieldsifplacedincloseproximity.Abrasiveparticlesmayadheretocomponentssurfaceandcauseandincreaseinweartoenginescomponents,gears,bearingsetc.DemagnetizationPartsinspected31Demagnetization(Cont.)Demagnetizationrequiresthattheresidualmagneticfieldisreversedandreducedbytheinspector.Thisprocesswillscramblethemagneticdomainsandreducethestrengthoftheresidualfieldtoanacceptablelevel.DemagnetizedMagnetizedDemagnetization(Cont.)Demagne32Advantagesof
MagneticParticleInspection
Candetectbothsurfaceandnearsub-surfacedefects.Caninspectpartswithirregularshapeseasily.Precleaningofcomponentsisnotascriticalasitisforsomeotherinspectionmethods.Mostcontaminantswithinaflawwillnothinderflawdetectability.Fastmethodofinspectionandindicationsarevisibledirectlyonthespecimensurface.ConsideredlowcostcomparedtomanyotherNDTmethods.Isaveryportableinspectionmethodespeciallywhenusedwithbatterypoweredequipment.Advantagesof
MagneticPartic33Limitationsof
MagneticParticleInspectionCannotinspectnon-ferrousmaterialssuchasaluminum,magnesiumormoststainlesssteels.Inspectionoflargepartsmayrequireuseofequipmentwithspecialpowerrequirements.Somepartsmayrequireremovalofcoatingorplatingtoachievedesiredinspectionsensitivity.Limitedsubsurfacediscontinuitydetectioncapabilities.Maximumdepthsensitivityisapproximately0.6”(underidealconditions).Postcleaning,andpostdemagnetizationisoftennecessary.AlignmentbetweenmagneticfluxanddefectisimportantLimitationsof
MagneticPartic34GlossaryofTermsBlackLight:ultravioletlightwhichisfilteredtoproduceawavelengthofapproximately365nanometers.Blacklightwillcausecertainmaterialstofluoresce.Centralconductor:anelectricallyconductivebarusuallymadeofcopperusedtointroduceacircularmagneticfieldintoatestspecimen.Coil:anelectricalconductorsuchacopperwireorcablethatiswrappedinseveralormanyloopsthatarebroughtclosetooneanothertoformastronglongitudinalmagneticfield.GlossaryofTermsBlackLight:35GlossaryofTermsDiscontinuity:aninterruptioninthestructureofthematerialsuchasacrack.Ferromagnetic:amaterialsuchasiron,nickelandcobaltoroneofit’salloysthatisstronglyattractedtoamagneticfield.Heads:electricalcontactpadsonawethorizontalmagneticparticleinspectionmachine.Theparttobeinspectedisclampedandheldinplacebetweentheheadsandshotofcurrentissentthroughthepartfromtheheadstocreateacircularmagneticfieldinthepart.Leakagefield:adisruptioninthemagneticfield.Thisdisruptionmustextendtothesurfaceofthepartforparticlestobeattracted.GlossaryofTermsDiscontinuity36GlossaryofTermsNon-relevantindications:indicationsproducedduetosomeintendeddesignfeatureofaspecimensuchakeyways,splinesorpressfits.Prods:twoelectrodesusuallymadeofcopperoraluminumthatareusedtointroducecurrentintoatestpart.Thiscurrentinturncreatesacircularmagneticfieldwhereeachprodtouchesthepart.(Similarinprincipaltoaweldingelectrodeandgroundclamp).Relevantindications:indicationsproducedfromsomethingotherthanadesignfeatureofatestspecimen.Cracks,stringers,orlapsareexamplesofrelevantindications.GlossaryofTermsNon-relevant37GlossaryofTermsSuspension:abathcreatedbymixingparticleswitheitheroilorwater.Yoke:ahorseshoemagnetusedtocreatealongitudinalmagneticfield.Yokesmaybemadefrompermanentmagnetsorelectromagnets.GlossaryofTermsSuspension:38MAGNETICPARTICLETESTINGMAGNETICPARTICLETESTING39IntroductionThismoduleisintendedtopresentinformationonthewidelyusedmethodofmagneticparticleinspection.Magneticparticleinspectioncandetectbothproductiondiscontinuities(seams,laps,grindingcracksandquenchingcracks)andin-servicedamage(fatigueandoverloadcracks).IntroductionThismoduleisint40OutlineMagnetismandFerromagneticMaterialsIntroductionofMagneticParticleInspectionBasicProcedureandImportantConsiderationsComponentpre-cleaningIntroductionofmagneticfieldApplicationofmagneticmediaInterpretationofmagneticparticleindicationsExamplesofMPIIndicationsOutlineMagnetismandFerromagn41MagneticlinesofforcearoundabarmagnetOppositepolesattractingSimilarpolesrepellingIntroductiontoMagnetismMagnetismistheabilityofmattertoattractothermattertoitself.Objectsthatpossessthepropertyofmagnetismaresaidtobemagneticormagnetizedandmagneticlinesofforcecanbefoundinandaroundtheobjects.Amagneticpoleisapointwheretheamagneticlineofforceexitsorentersamaterial.Magneticfieldlines:Formcompleteloops.Donotcross.Followthepathofleastresistance.Allhavethesamestrength.Haveadirectionsuchthattheycausepolestoattractorrepel.Magneticlinesofforcearound42FerromagneticMaterialsAmaterialisconsideredferromagneticifitcanbemagnetized.MaterialswithasignificantIron,nickelorcobaltcontentaregenerallyferromagnetic.Ferromagneticmaterialsaremadeupofmanyregionsinwhichthemagneticfieldsofatomsarealigned.Theseregionsarecallmagneticdomains.Magneticdomainspointrandomlyindemagnetizedmaterial,butcanbealignedusingelectricalcurrentoranexternalmagneticfieldtomagnetizethematerial.DemagnetizedMagnetizedSNFerromagneticMaterialsAmater43HowDoesMagneticParticle
InspectionWork?Aferromagnetictestspecimenismagnetizedwithastrongmagneticfieldcreatedbyamagnetorspecialequipment.
Ifthespecimenhasadiscontinuity,thediscontinuitywillinterruptthemagneticfieldflowingthroughthespecimenandaleakagefieldwilloccur.HowDoesMagneticParticle
In44HowDoesMagneticParticle
InspectionWork?(Cont.)Finelymilledironparticlescoatedwithadyepigmentareappliedtothetestspecimen.Theseparticlesareattractedtoleakagefieldsandwillclustertoformanindicationdirectlyoverthediscontinuity.Thisindicationcanbevisuallydetectedunderproperlightingconditions.
HowDoesMagneticParticle
In45BasicProcedure
Basicstepsinvolved:Componentpre-cleaningIntroductionofmagneticfieldApplicationofmagneticmedia
InterpretationofmagneticparticleindicationsBasicProcedureBasicste46Pre-cleaning
Wheninspectingatestpartwiththemagneticparticlemethoditisessentialfortheparticlestohaveanunimpededpathformigrationtobothstrongandweakleakagefieldsalike.Thepart’ssurfaceshouldbecleananddrybeforeinspection. Contaminantssuchasoil,
grease,orscalemaynot
onlypreventparticlesfrom
beingattractedtoleakage
fields,theymayalso
interferewithinterpretation
ofindications.Pre-cleaningWheninspecting47IntroductionoftheMagneticField
Therequiredmagneticfieldcanbeintroducedintoacomponentinanumberofdifferentways.UsingapermanentmagnetoranelectromagnetthatcontactsthetestpieceFlowinganelectricalcurrentthroughthespecimenFlowinganelectricalcurrentthroughacoilofwirearoundthepartorthroughacentralconductorrunningnearthepart.IntroductionoftheMagneticF48DirectionoftheMagneticField
Twogeneraltypesofmagneticfields(longitudinalandcircular)maybeestablishedwithinthespecimen.Thetypeofmagneticfieldestablishedisdeterminedbythemethodusedtomagnetizethespecimen.Alongitudinalmagneticfieldhasmagneticlinesofforcethatrunparalleltothelongaxisofthepart.Acircularmagneticfieldhasmagneticlinesofforcethatruncircumferentiallyaroundtheperimeterofapart.DirectionoftheMagneticFiel49ImportanceofMagneticFieldDirectionBeingabletomagnetizethepartintwodirectionsisimportantbecausethebestdetectionofdefectsoccurswhenthelinesofmagneticforceareestablishedatrightanglestothelongestdimensionofthedefect.Thisorientationcreatesthelargestdisruptionofthemagneticfieldwithinthepartandthegreatestfluxleakageatthesurfaceofthepart.Anorientationof45to90degreesbetweenthemagneticfieldandthedefectisnecessarytoformanindication.Sincedefectsmayoccurinvariousandunknowndirections,eachpartisnormallymagnetizedintwodirectionsatrightanglestoeachother.FluxLeakageNoFluxLeakageImportanceofMagneticFieldD50Question?
Fromthepreviousslideregardingtheoptimumtestsensitivity,whichkindsofdefectareeasilyfoundintheimagesbelow?Longitudinal(alongtheaxis)Transverse(perpendiculartheaxis)Question? Fromthepreviouss51ProducingaLongitudinalMagneticFieldUsingaCoilAlongitudinalmagneticfieldisusuallyestablishedbyplacingthepartneartheinsideoracoil’sannulus.Thisproducesmagneticlinesofforcethatareparalleltothelongaxisofthetestpart.CoilonWetHorizontalInspectionUnitPortableCoilProducingaLongitudinalMagne52ProducingaLongitudinalFieldUsingPermanentorElectromagneticMagnetsPermanentmagnetsandelectromagneticyokesarealsooftenusedtoproducealongitudinalmagneticfield.Themagneticlinesofforcerunfromonepoletotheother,andthepolesarepositionedsuchthatanyflawspresentrunnormaltotheselinesofforce.
ProducingaLongitudinalField53CircularMagneticFieldsCircularmagneticfieldsareproducedbypassingcurrentthroughthepartorbyplacingthepartinastrongcircularmagnetfield.
Aheadshotonawethorizontaltestunitandtheuseofprodsareseveralcommonmethodsofinjectingcurrentinaparttoproduceacircularmagneticfield.Placingpartsonacentralconductorscarryinghighcurrentisanotherwaytoproducethefield.MagneticFieldElectricCurrentCircularMagneticFieldsCircul54ApplicationofMagneticMedia(WetVersusDry)MPIcanbeperformedusingeitherdryparticles,orparticlessuspendedinaliquid.Withthedrymethod,theparticlesarelightlydustedontothesurface.Withthewetmethod,thepartisfloodedwithasolutioncarryingtheparticles.Thedrymethodismoreportable.Thewetmethodisgenerallymoresensitivesincetheliquidcarriergivesthemagneticparticlesadditionalmobility.
ApplicationofMagneticMedia55DryMagneticParticles
Magneticparticlescomeinavarietyofcolors.Acolorthatproducesahighlevelofcontrastagainstthebackgroundshouldbeused.DryMagneticParticlesMagn56WetMagneticParticlesWetparticlesaretypicallysuppliedasvisibleorfluorescent.Visibleparticlesareviewedundernormalwhitelightandfluorescentparticlesareviewedunderblacklight.WetMagneticParticlesWetpart57InterpretationofIndications
Afterapplyingthemagneticfield,indicationsthatformmustinterpreted.Thisprocessrequiresthattheinspectordistinguishbetweenrelevantandnon-relevantindications.Thefollowingseriesofimagesdepictrelevantindicationsproducedfromavarietyofcomponentsinspectedwiththemagneticparticlemethod.InterpretationofIndications58CraneHookwith
ServiceInducedCrack
Fluorescent,WetParticleMethod
CraneHookwith
ServiceInduc59Gearwith
ServiceInducedCrack
Fluorescent,WetParticleMethodGearwith
ServiceInducedCra60DriveShaftwith
HeatTreatmentInducedCracks
Fluorescent,WetParticleMethodDriveShaftwith
HeatTreatme61
SplinedShaftwith
ServiceInducedCracksFluorescent,WetParticleMethodSplinedShaftwith
Servi62
ThreadedShaftwith
ServiceInducedCrackFluorescent,WetParticleMethod
ThreadedShaftwith
Servic63LargeBoltwith
ServiceInducedCrackFluorescent,WetParticleMethod
LargeBoltwith
ServiceInduc64CrankShaftwith
ServiceInducedCrackNearLubeHoleFluorescent,WetParticleMethod
CrankShaftwith
ServiceIndu65LackofFusioninSMAWWeldVisible,DryPowderMethodIndicationLackofFusioninSMAWWeldVis66ToeCrackinSMAWWeldVisible,DryPowderMethodToeCrackinSMAWWeldVisible,67ThroatandToeCracksin
PartiallyGroundWeldVisible,DryPowderMethodThroatandToeCracksin
Part68DemagnetizationPartsinspectedbythemagneticparticlemethodmaysometimeshaveanobjectionableresidualmagneticfieldthatmayinterferewithsubsequentmanufacturingoperationsorserviceofthecomponent.Possiblereasonsfordemagnetizationinclude:Mayinterferewithweldingand/ormachiningoperationsCaneffectgaugesthataresensitivetomagneticfieldsifplacedincloseproximity.Abrasiveparticlesmayadheretocomponentssurfaceandcauseandincreaseinweartoenginescomponents,gears,bearingsetc.DemagnetizationPartsinspected69Demagnetization(Cont.)Demagnetizationrequiresthattheresidualmagneticfieldisreversedandreducedbytheinspector.Thisprocesswillscramblethemagneticdomainsandreducethestrengthoftheresidualfieldtoanacceptablelevel.DemagnetizedMagnetizedDemagnetization(Cont.)Demagne70Advantagesof
MagneticParticleInspection
Candetectbothsurfaceandnearsub-surfacedefects.Caninspectpartswithirregularshapeseasily.Precleaningofcomponentsisnotascriticalasitisforsomeotherinspectionmethods.Mostcontaminantswithinaflawwillnothinderflawdetectability.Fastmethodofinspectionandindicationsarevisibledirectlyonthespecimensurface.ConsideredlowcostcomparedtomanyotherNDTmethods.Isaveryportableinspectionmethodespeciallywhenusedwithbatterypoweredequipment.Advantagesof
MagneticPartic71Limitationsof
MagneticParticleInspectionCannotinspectnon-ferrousmaterialssuchasaluminum,magnesiumormoststain
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