Hook crack in ERW line pipe steel

UniversityofWollongongResearchOnlineAustralianInstituteforInnovativeMaterials-PapersAustralianInstituteforInnovativeMaterials2003HookcrackinelectricresistanceweldinglinepipesteelSimaAminorroaya-YaminiUniversityofWollongong,sima@uow.edu.auHosseinEdrisIsfahanUniversityofTechnologyMehrdadFatahiMobarakeSteelCompanyResearchOnlineistheopenaccessinstitutionalrepositoryfortheUniversityofWollongong.ForfurtherinformationcontacttheUOWLibrary:research-pubs@uow.edu.auPublicationDetailsAminorroaya-Yamini,S.,Edris,H.&Fatahi,M.(2003).Hookcrackinelectricresistanceweldinglinepipesteel.SouthEastAsiaIron&SteelInstituteConferenceandExhibition(pp.1-9).Malaysia:SouthEastAsiaIron&SteelInstitute.HookcrackinelectricresistanceweldinglinepipesteelAbstractOneoftheproductionmethodsforAPIlinepipesteeliselectricresistancewelding(ERW).ThiskindofpipesisencounteredwithhookcrackwhichisoneofthedefectsthatisobservedintheupsetzoneofERWpipes,detectingbyultrasonicinspection.Hookcrackisasmallcrackfollowingtheweldflowlinesandifsevereenough,openedupatthepipesurface.Thesedefectswerecommonlyassociatedwithsulphidestringersandnonmetallicoxideinclusions.Inthisresearch,weldscontaininghookcrackswereobtainedfromAhvazpipemakingfactory.Scanningelectronmicroscope(SEM)examinationshowedthatallhookcrackswereassociatedwithsmallnonmetallicinclusionsandX-raymicroprobeanalysis(EDX)wasperformedtodetectthemainelementsassociatedwiththeinclusion.HookcrackswerefoundtobeassociatedwithAl2O3,CaO,CaSandMgO.Thisworkrevealedthatthesedefectscanbeeliminatedusing;calciumtreatmentandArgonstirringimprovementinladlefurnace,alsousingtundishrefractorywithhigherqualityandcontrolofmeltflowinladlefurnaceandtundish.Keywordselectric,crack,hook,steel,line,pipe,welding,resistanceDisciplinesEngineering|PhysicalSciencesandMathematicsPublicationDetailsAminorroaya-Yamini,S.,Edris,H.&Fatahi,M.(2003).Hookcrackinelectricresistanceweldinglinepipesteel.SouthEastAsiaIron&SteelInstituteConferenceandExhibition(pp.1-9).Malaysia:SouthEastAsiaIron&SteelInstitute.ThisconferencepaperisavailableatResearchOnline:http://ro.uow.edu.au/aiimpapers/1409HOOKCRACKINELECTRICRESISTANCEWELDEDLINEPIPESTEELBYSIMAAMINORROAYA*,HOSSEINEDRIS**,MEHRDADFATAHI***SYNOPSIS:OneoftheproductionmethodsforAPIlinepipesteeliselectricresistancewelding(ERW).ThiskindofpipesisencounteredwithhookcrackwhichisoneofthedefectsthatisobservedintheupsetzoneofERWpipes,detectingbyultrasonicinspection.Hookcrackisasmallcrackfollowingtheweldflowlinesandifsevereenough,openedupatthepipesurface.Thesedefectswerecommonlyassociatedwithsulphidestringersandnonmetallicoxideinclusions.Inthisresearch,weldscontaininghookcrackswereobtainedfromAhvazpipemakingfactory.Scanningelectronmicroscope(SEM)examinationshowedthatallhookcrackswereassociatedwithsmallnonmetallicinclusionsandX-raymicroprobeanalysis(EDX)wasperformedtodetectthemainelementsassociatedwiththeinclusion.HookcrackswerefoundtobeassociatedwithAl2O3,CaO,CaSandMgO.Thisworkrevealedthatthesedefectscanbeeliminatedusing;calciumtreatmentandArgonstirringimprovementinladlefurnace,alsousingtundishrefractorywithhigherqualityandcontrolofmeltflowinladlefurnaceandtundish.Keywords:APIsteel,Hookcrack,Inclusion,ElectricResistanceWelding*MS.inMetallurgy,Director,Naghsh-e-JahanSteelResearchInstitute-IsfahanScienceandTechnologyTown,Isfahan,IRAN**PhDinMetallurgy,AssistantProffesor,MaterialsEngineeringDeparment-IsfahanUniversityofTechnology,Isfahan,IRAN***BS.inMetallurgy,MobarakeSteelCompany,Isfahan,IRANINTRODUCTION:Electricresistanceweldingprocess,locallyheatstheedgesoftheplatetoasuitableforgingtemperaturethentheedgesarepushedtogether,upsettingthewallthicknessandformingabond.Thesequenceofoperationsrequiredinthefabricationofelectricresistanceweldedtubingare[1]:I.Slitting:Manymanufactureroftubulargoodspurchasewide-widthcoilswhichcanbeslitintothedesiredwidths.Platesareslitbytoolsteeldiscsthenstripspasstothecoiler.Thebandedcoilsarereadyfortheformingprocess.II.Forming:ERWmillsnormallymakeuseofthreetypesofrollstoprogressivelyformtheflatsteelstationintotheroundformpriortowelding.Thesethreetypesofrollsare:1)Breakdownofformingrollswhichprovidetheinitialshapingofthestriptowardstheroundform,2)Idlerverticalclosingrollswhichfurthercloseandfluidthestripintothelastsection,3)finpassrollswhichprovideperfectguidanceintotheweldingsection.TheserollsareshownschematicallyinFig.1.Fig.1:SchematicofformingrollsIII.Welding:Afterforminghasoccurred,theopentubepassesdirectlyintotheweldingsectionofthemill.Theheatforweldingisprovidedeitherbylow-frequencypowerthroughelectrodeswheelsorradio-frequencypowerthroughslidingcontactsorcoilinduction,typicalradio-frequencypowerforweldingissuppliedat450KHZhigherorlowerfrequenciesmaybeused.IV.Heattreatment:Afterwelding,theweldedtubepassesunderacuttingtoolwhichremovestheflashresultingfromthepressureduringwelding.Afterremovingtheflash,thetubeissubjectedtoproperpost-weldtreatmentasmetallurgicalrequiredforinstancesuchtreatmentmayinvolvesub-Criticalannealingornormalizingoftheweldedseamornormalizingofthefullcrosssectionofthetube.V.Sizing:AfterCooling,thetubeissizedtoobtainaroundfinishedproductofdesireddiameter.Thesizingmillconsistsofseveraldrivenhorizontalrollsandseveralidleverticalrolls.Afterthetubeleavesthesizingmill,itiscutandistransferredtothefinishingfloorwheretheyarestraightened.Afterfinishingoperation,tubesareinspected.HookcrackisoneofthedefectswhichisobservedintheupsetzoneoftheERWpipe,afterdetectionbyultrasonicinspection.theyappearassmallcracksfollowingtheweldflowlinesandifsevereenough,openedupatthepipesurface.Ifinclusions(usuallymanganesesulfideinclusions)existinthewallthicknessbeforetheupsetting,theymaycrackduringtheupsettingprocess,creatingtheupturnedfiberdefect.Inthisweld,canalsobeobservedthattheupturnedfiberontheinsideoftheweld.Hookcrackareeliminatedbyusingcleanersteelandreducingtheheatinputtothestripedges(acoldweld)[2].Fig.2showsascanningelectronmicroscopemicrographofatypicalhookcrack,containaflowlinewhichhasbeendeformedupwardduringweldupset.Fig.2:TypicalhookcrackItshouldbementionedthatmetallurgistsregardnonmetallicinclusionsashookcrackdefectgeneratorsosteelmanufacturerlaunchedsomeresearchesonsteelcompositionandalsoinclusionremovalandtheirgenerationmechanismsonsteelmakingandcontinuouscastingprocesses[3,4].Eavesetal.research[4]hasshownthattheinclusioncompositionwhichobservedinthecrackswererelatedtoslab/coiledgesorslab/coilcentermaterial.EdgerelatedhookcrackswerefoundtobeassociatedwithCaO,Al2O3andCaS,whereascenteroneswereconsistentlylinkedtoMnSandAl2O3andalso76%oftheproblemwasassociatedwithslab/Coilcenters.ThemainreasonofhookcracksformationinAPIsteelpipesisnonmetallicinclusions.Generally,steelmakinginelectricarcfurnaces,secondarymetallurgyinladlefurnaces,slabcontinuouscastingandfinallyhotrollingareproductionprocessesforoilandgastransportationpipelinesteelplates.Table1summarizespossibleinclusionsourcesandtheirkeyelements[5].Table1:Possibleinclusionsourcesandkeyelements[5]SourceKeyelementsFurnaceFurnaceslagFurnacerefractoriesFerroalloysCaCaCr,Al,SiTappingLaunderrefractoriesOxidationMg,Ti,KFeOLadleDeoxidationLadleslagLadlerefractoriesCa,MgMg,Ti,KTeemingStopperandnozzlerefractoriesOxidationDeoxidationMg,Ti,KFeOIngotmoldRefractoriesDeoxidationMg,Ti,KHeattreatmentandrollingSurfaceoxidationSurfacesulfurizationInneroxidationHotshortnessFeoFeSSiO2FeSWeldingWeldingslagsElectrodecoatingsSteelinclusionsHottearingCa,TiTi,VSThistableshowsnon-metallicinclusiongeneratorsexistatthebeginningofEAFprocessandtheyareheadingtowardtheendofweldingprocesswhichproductionstagesarefinished.Electrodescoatingusuallywillbeaninclusionsourceentrance,whentheweldprocessuseselectrodes.However,inERWmethodwhichdoesnotuseelectrode,thispossibleinclusionsourceisomittedcompletely.Ontheotherhand,hookcracksareobservedintheplatethicknessthereforesurfaceoxidationthroughhotrollingandheattreatmentcannotberesponsibleforhookcrack.Itshouldbenotedthattherearestrongstirringinelectricarcfurnacesinordertoderivetheintensivemetallurgicalreactionsforthisreason.Asamatteroffact,inclusionremovalisimpossibleinthisstageofsteelmakingprocess.Hence,Inclusiongenerationprohibitionanditsremovalfromthesteelmeltbeginatthefurnacetappingprocessandwillbecontinueduntilsolidificationinthemold.EXPERIMENTAL:MobarakeSteelCompany(MSC)isabout50kmfarfromIsfahan,acentrallylocatedcityinIran.Steelmakingunitinthisfactoryincludeseight200metrictonselectricarcfurnaceswhichareequippedwitheccentricbottomtapping(EBT)andalsofourladlefurnaceswhichstirwithArgonblowingthroughporousplugs.Slabscastwithfourverticalbendingmachinesinthiscompany.ApartofMSCsteelproductsisincludedsteelforthemanufactureofelectricresistanceweldinglinepipestotheAPIspecifications.AhvazpipemakingfactoryusesMSCsteelplatestoproducepipeforsweetandsourgasapplications.HookCrackshadbeenthemostsignificantsteelrelateddefectreportedbythisfactory.WeldscontaininghookcrackswereobtainedfromAhvazpipemakingfactory.Table2showsthesamplenumbers,samplecodesinweldingfactoryandalsocoilandmeltnumbersforeachultrasonicinspectionandmetallographicexaminationsconfirmeddefectedsamples.ScanningElectronMicroscope(SEM)examinationhasshownthatallhookcrackswereassociatedwithnonmetalicinclusionsandX-raymicroprobe(EDX)wasperformedtodetectthemainelementsassociatedwiththeinclusions.Table2:SamplenumbersandtheircodesSamplenumberAhvazpipemakingcompanycodeMeltnumberCoilnumber1130-607069055261212126-60105657460213101-1603084856261414108-1201085755462715138-401085656260116145-8010856557611179-139118961646441813-89420471586501DISSCUSTION:Itisclearthatsomeofthecoilsarementionedintable2camefromthesamemelt.Becauseofthat,thesamplesarerearrangedintable3bythemeltnumbers.Energydispersivespectroscopyanalysiswhichwasperformedoninclusions,detectedCa,Al,Mg,SandOelements.Inthelastcolumnofthistable,theinclusionswhichmightbeassociatedwiththeseelementsareshownforeachsampleindividually.MajorcompondoftheseelementsareCaO.Al2O3,MgOandCaS.Table3:elementsandpossibleinclusionsincracksMeltNo.SampleNo.ElementsPossibleinclusionsCa,Al,S,OCaS,Al2O3,CaO0308483Ca,Al,OCaO,Al2O30108574Mg,OMgO2Mg,Ca,Al,OMgO,CaO,AL2O35Ca,Al,S,OCaO,Al2O3,CaS0108566Ca,Al,Mg,OCaO,Al2O3,MgO0706901Ca,Al,OCaO,Al2O3,9118967Al,OAl2O39420478Al,Mg,OAl2O3,MgOSimsandForgeng[5]classifiedtheinclusionsourcesintotwogroupsofendogenousandexogenous.Theendogenousinclusionsprecipitateduetoreactionfromsteelorduringfreezing.Thesekindofinclusionsaresmall,numerousandratheruniformlydistributedandalsoaretypicalofthesteelinwhichtheyoccur.Theexogenousinclusionsnotonlyareproducedfrommechanicalandchemicalerosionofrefractoriesandothermaterialsthatcomeincontactwithmoltensteel,butalsoariseoutofoxygenpickupbyteemingstreamandconsequentoxideformation.Thisgroupofinclusionsislarge,scarceandhaphazardinoccurrence.Recentstudyonhookcrackshasrevealedthattheinclusionsarenon-uniformindistributionandtheywereobservedinsomemeltsandalsosomecoilsofamelt.Thereforetheinclusionswhichweredetectedinhookcracksareintheexogenousinclusionclassification.Itisobviousthatthefirstcoilofthefirstmeltofthecontinuouscastingsequencehasthemostturbulenceintundish.Itseemsthatmechanicalerosionofrefractories,slag-metalmixingandreoxidationofkilledsteelsincreaseforthisspecialcoil.Hencetheproductionhistoryofthecoilswhichwereconsistedhookcrackswereinvestigatedinordertofindoutthatiftheyhavebeenproducedinmentionedaboveconditions.Table4summarizestheproductionhistoryofsupposedmelts.Itshouldbementionedthatnonofthecoilswasthefirstslabofthefirstmeltincontinuouscastingmachinesoitcanbeconcludedthattheslabpositionshouldbeomittedasasourceofobservedinclusions.Table4:productionhistoryofdefectiveplatesincontinuouscastingSampleNo.CoilNo.MeltNo.WhichmeltofsequenceWhichslabofmentionedmelt15526121070690Firstmeltofthirdseq.Fifth25746021010856Secondmeltofthirdseq.Sixth35626141030848Firstmeltoffirstseq.Fifth45546271010857Thirdmeltofthirdseq.Sixth55626011010856Secondmeltofthirdseq.Second65576111010856Secondmeltofthirdseq.Third71646441911896Firstmeltofsecondseq.Fifth81586501942047Firstmeltoffirstseq.TenthSteelmakingandcontinuouscastingprocessesofAPIsteelplateproductioninMobarakeSteelCompanywereinvestigatedandpossibleinclusionsourcesatdifferentstagesofproductionandalsotheirkeyelementssummarizedintable5.Theproductionhistoriesofsupposedmeltshowedthatallmeltshadtreatedbycalciumaluminateinladlefurnacebuttwolastones.Ascanbeseenintable4,theinclusionsareincludedCaO-Al2O3,CaO-Al2O3-MgO.Tostudythesecombinations,Fig.3showsapartoftheCaO-MgO-Al2O3phasediagram[6].Compositionofusedcalciumaluminatewas12CaO.7Al2O3.Thisfluxisfluidinsteelmakingtemperaturebutitisabletocreate3CaO.MgO.2Al2O3particles,whichissolidinthesteelmakingtemperaturerange,incompoundwithMgO.Ofcourse,thesolidinclusionshavelessopportunitytoremovethanliquidones[7].Table5:PossibleinclusionsourcesinMSCProductionstageSourcesKeyelementsElectricarcfurnacetappingFurnaceslagOxidationCa,Si,MgAl,Si,MnLadleLadleslagLadlerefractoriesCa,Al,MnMg,Al,TiLadletappingOxidationLadleslagSandfillerofnozzleAl,Si,MnCa,Al,MnSi,Cr,Mg,AlTundishTundishslagTundishrefractoriesNozzleandstopperrefractoriesSi,Ca,AlMg,TiMg,Al,TiMoldMoldpowderOxidationSi,Ca,Al,MgAl,Mn,SiSimsandForgeng[5]discussedsomeofthecommonformationmechanismsofexogenousinclusionsandconcludedthatmechanicalerosionisnotseriousreason.Themostseriousdamagetorefractoriesandthemostpotentsourceofexogenousinclusionsisacombinationofchemicalattackandmechanicalerosion.SincethepresenceofCaOininclusionsisacommonfindingandexogenousslagparticlesareresponsibleforit[5],theCapeakobservationinEDXpatternofmostexistenceinclusionsinhookcracksofthepresentstudyhaveshownthatslagparticleswereresponsibleforit.Therearevarietytypeofslagindifferentstagesofsteelmakingandcontinuouscastingprocessesandtheseinclusionscanbecomefromelectricarcfurnace,ladlefurnace,tundishormoldslag.Since,Sihasbeenobservedinnoneoftheinclusionsandontheotherhand,SiO2isthemajorcomponentinmoldpowder,itisobviousthatthesenonmetallicinclusionscannotbecausedbymoldpowderentrapment.Fig.3:TernaryphasediagramofCaO-Al2O3-MgO[6]Ascanbeseenintable3,thereareinclusionscontainSsuchasCaO-Al2O3-CaS.Thepresenceofsulfurinsamples3and5alongwithAl,CaandOhasshownthatcalciumAluminateisentrappedinthemeltafterdesulphurization.Thesummaryofthesampleswithinclusionsassociatedwiththemandtheirpossiblesourcesareshownintable6.Table7summarizesthemainsourcesbesidethesuggestedeliminationandreductionmethods.CONCLUSION:InvestigationonhookcracksinelectricresistanceweldedlinepipeswhichproducedfromMobarakeSteelCompanycoilshasdeclaredthatthisdefectwillbereducedbyrespecttobelowparametersinsteelmakingandcontinuouscastingprocessesofthiscompany:-controlandreductionofEAFslagcarryovertoladleandalsoladleslagcarryovertotundish-Meltflowcontrolinladlefurnaceandtundishtopromoteflotationofinclusions-Calciumtreatmentinladlefurnaceforlowsulfurcontentsteelgrades-Usingtundishrefractorywithhigherquality-UsingsuitabletundishpowderinsteadriceashTable6:PossiblenonmetallicinclusionsourceswhichwereobservedinHookcracksamplesSampleNo.ObservedinclusionsPossibleinclusionsources1CaO,Al2O3Entrappedcalciumaluminateparticles,LadleandTundishslag2CaO,Al2O3,MgOCalciumaluminateincompondwithMgO,LadleandTundishslag,Sandfillerofnozzle3CaO,Al2O3CaO,Al2O3,CaSEntrappedcalciumaluminateparticles,Calciumaluminateafterdesulphurization,LadleandTundishslag4MgOTundishrefractories5CaO,Al2O3,CaSCalciumaluminateafterdesulphurization6CaO,Al2O3,MgOCalciumaluminateincompondwithMgOLadleandTundishslag,Sandfillerofnozzle7Al2O3ReoxidationofAluminum8Al2O3,MgOLadle,nozzleandstopperrefractories,SandfillerofnozzleTable7:InclusionsourcesandtheirsuggestedeliminationmethodsInclusionsourcesInclusionreductionandeliminationmethodsRefractoriesSelectionoftundishrefractorywithhigherqualityMeltflowcontrolinladleMeltflowcontrolinTundishOxidationSelectionoftundishrefractorywithhigherqualityMeltflowcontrolinladleMeltflowcontrolinTundishSlagReductionofslagcarryoverMeltflowcontrolinTundishSuitableArgonstirringinladleSelectionofsuitabletundishpowderNozzlesandMeltflowcontrolinTundishSelectionofsuitabletundishpowderInclusionswhicharecausedbycalciumaluminateMeltflowcontrolinladleSuitableArgonstirringinladleACKNOWLEDGMENTS:TheauthorsaregratefultoMobarakeSteelCompanyandAhvasPipemakingFactoryforsupportingpartofthisresearch.TheauthorsalsowouldliketothankIsfahanScienceandTechnologyTownforpermissiontopublishthiswork.REFERENCE:1.W.T.Lankford,N.L.Samways,R.F.Craven,H.E.McGannon,“Themaking,shapingandtreatingofsteel”,10thEdition,USS,1985.2.ASMHandbook,Failuresofpipelines,pp.449.3.S.J.Oakman,I.D.Simpson,L.T.Hamilton,T.J.George,”ApplicationofCasterSteeltoERWlinepipe”,ContinuousCasting,FourinternationalironandSteelCongress,London,May1982,pp.D1/14.G.N.Eaves,S.R.Cameron,V.J.Casey,P.Nestico,W.Bernert,“HookCrackreductioninERWlinepipesteel”,SteelmakingConferenceproceedings,1992,pp.521-5285.A.Ghosh,“SecordarySteelmaking–principlesandapplications”,CRCPress,2000.6.V.D.Eisenhuttenleute,“slagatlas”,Dusscldorf,February1981.7.A.W.Cramb,“Highpurity,lowresidualandcleansteels”,Departmentofmaterialsscienceandengineering,CarnegieMellonuniversity,Pittsburgh,PA15217 UniversityofWollongong ResearchOnline 2003 Hookcrackinelectricresistanceweldinglinepipesteel SimaAminorroaya-Yamini HosseinEdris MehrdadFatahi PublicationDetails Hookcrackinelectricresistanceweldinglinepipesteel Abstract Keywords Disciplines PublicationDetails Ahvazpipemakingcompanycode Coilnumber 5526121 Possibleinclusions Mg,O 2 Mg,Ca,Al,O 5 6 1 7 8 Keyelements Possibleinclusionsources