SIGNIFICANCE AND CONTROL OF LAMELLAR TEARING OF STEEL ... · ssc-290 final report on project...

SIGNIFICANCE ANDCONTROL OF LAMELLAR

TEARING OF STEEL PLATEIN THE SHIPBUILDING

INDUSTRY

r.

.+

ThisdocumenthasbeanapprovedfOrpublicreleasaandsala;itsdistributionisunlimitad.

SHIP STRUCTURE COMMITTEE

1979

SSC-290

FINAL REPORT

on

Project SR-1Z50

“Lamel Tar Tearing”

SIGNIFICANCE AND CONTROL OF LAMELLAR

TEARING OF STEEL PLATE IN THE

SHIPBUILDING INDUSTRY

by

J. Sommella

Gibbs & Cox, Inc.

under

Department of TransportationU. S. Coast Guard

Contract No. DOT-CG-74355-A

TWS docwwnt has hen approved for publie w lease andsale; its distribution is unlimited.

U. S. Coast Guard Headquarters!Jashington, D.C..

1979

M&r Agenci~:Umtish&CcmtGuwd

Naval% S@emsCommandMilituryS9ditlConmlandAfm”hneA~ffm

unitedsfote3G13&imiSwvwyAmm”wnBurwuoftip~g

Ad&esCormpndenceto:S92retoiy,ShipstructureColmnittesU).CoxtGuadHmdqumtew(G-A4WW&@on,D.C.20599

AnInteragencyAdvisoryCommitkDedicataltoImprovingtheSbuctureofShips

SR-1250JULY1979

TheShipStructureCorrnnitteerecognizedtheneedofevaluatingavailableinformationonpreventinglarellartearinginm3rinestmctures.WhiletheincideneeoflamellartearinginshipstructureshasbeenlW,itismorecommoninmobileandfixedplatformsofthetypeusedintheoffshoremineralekplorationandproductionindustry.Itsoccumen=resultsin03stlyrepairs,and,insomeinstances,fabricationdelays.

Aprojectwasundertakento developaguidedescribingthefactorswhichcontributetoandinfluencelamellartearing,areviewoftheproceduresusedtodeterminesusceptibilitytolamellartearing,andmthodsforpost-weldingdetectionandrepairoflamellartears.Theresultsofthiseffo~tarecontainedinthisreport.AnycommentsOFrequestsforad-ditionalcopiesarewelmne.

~He&&[email protected]

Chairman,Ship?Lructure(hnnittee

.._- -—- .-.. . .—..—. —

I

TechnicalReportDocumentationPoge1.ReportNo.

TV’’””’”’ACCC’S’”’T’”

3. Rectp!ent’sCatalogNo.

SSC-290+--—

~ -– I4. Title apdSubt,tle

—I 5, RtportDo~o I

SIGNIFICANCEANDCONTROLOFLAMELLARTEARINGOFSTEELPLATEINTHESHIPBUILDINGINDUSTRY

k-- ———8. PerformingO,gonizationReportNo.

IJ. SOMMELLA 18521(1-146)———.—

9. PerlormIrBgOrganizottonNomeandAddress 10. werkun,t N6, (T RAIS)

GIBBS& COX,INC.SR-1250

11. ControctorGrantNo.I 40RectorStreet

k ‘“----- -

NewYork,N.Y.10006 13.Type01 ReportandPeriodCovered12. SponsoringAgent Name andAddress

ShipS{ructureCommitteeOfficeofMerchantMarineSafety

I U.S.CoastGuardHeadqua~ters

k

Washington,D.C.”2059015, SupplementaryNot,,

=I I16.Ah.?rac? Lamellartearingisa separationintheparentorbasemetalcausedby

through-thicknessstrains.Thesestrainsareusuallyinducedbywe”ldmetalshrinkageunderconditionsofhighrestraint.ThismanualprovidesspecificrecommendationsforcontrollinglamellartearinginthetypesofsteelsusedintheconstructionofshiFsandoffshoreplatforms.A briefdescriptionofthecharacteristics”andmechanismofIamellartearingshowsthatforIamellartearingtooccurtheremustbea criticalcombinationofmaterialsusceptibility,andweldingproceduresandjointdesignwhichpermitthedevelopmentofhighthrough-thicknessstrains.Tee(T)andcornerjoints,usedextensivelyinshipsandoffshorestructures,arethetwobasicjointconfigurationsmostsusceptibletolamellartearing.However,theincidenceoflamellartearinghasbeenextremelyrareinship-building.TheproblemoflamellartearingisconsiderablymoresignificantinnmbileandfixedoffshoredrillingplatformswhichusethickplatesinhighlyrestrainedT-andcruciformjoints.

Thefactorswhichcontributetoandinfluencelamellartearingaregroupedintothree.categories:jointdesignprocedures.

,materialselectionandfabricationForeachparameterrecommendationsarepresentedforreducing

theriskoflamellartearing.Inquiriesmadetothemajorshipclassifica-tionsocietiesindicatethatthemostsuccessfulandcost-effectivemethodofpreventinglamellartearingistheuseofsteelswithimprovedthrough-thickness(Z-direction)propertiesatsusceptibleconnections.Nethodsfortheposr-weldingdetectionandrepairoflamellartearsarereviewedasarethetestproceduresdevelopedtodatefordeterminingthesusceptibilityofsteelplatestola!wllartearing.

17, KeyWords 18. Dlstribu!ionStatement

LAMELLARTEARING SHIPBUILDING DocumentisavailabletothepublicliJELDING ULTRASONICTESTINGthroughtheNationalTechnicalSTEELS (UT) InformationService,Springfield,VA22161

.119. SecurityCIUSSII.(o(thisrepe,!)

.—20. SecurityClasSIl,(ofthispogc)

121.No.of~ages 22. Price

I UNCLASSIFIED UNCLASSIFIED 70FormDOTF 1700.7[8-72) Reproductionofcomplctcdpogeouthorized

-ii-

TheSHIPprogramtoimprovebyanextensionofconstruction.

RADMH.H.Bell

SHIPSTRUCTURECOMMITTEESTRUCTURECOMMITTEEisconstitutedtoprosecutearesearchthehullstructuresofshipsandothermarinestructuresknowledgepertainingtodesign,materialsandmethodsof

(Chairman) Mr.M.PitkinChief,OfficeofMerchantMarine “AssistantAdministratorforSafety CommercialDevelopment

U.S.CoastGuardHeadquarters MaritimeAdministration

14r.P.M.Palermo Mr.R.B.KzahlAssistantforStructures Chief,BranchofMarineOilandNavalShipEngineeringCenter GasOperationsNavalSeaSystemsCommand U.S.GeologicalSurvey

Mr.W.N.Hannan Mr.C.J.whitestoneVicePresident ChiefEngineerAmericanBureauofShipping MilitarySealiftCommand

LCDRT.H.Robinson,U.S.CoastGuard(Secretary)

SHIPSTRUCTURESUBCOMMITTEETheSHIPSTRUCTURESUBCOMMITTEEactsfortheShipStructure

Committeeontechnicalmattersbyprovidingtechnicalcoordinationforthedeterminationofgoalsandobjectivesoftheprogram,andbyevaluatingandinterpretingtheresultsintermsofstructuraldesign,constructionandoperation.

U.S.COASTGUARDCdr.J.C.CardLcdrS.H.DavisCaptC.B.GlassDr.W.C.Dietz

NAVALSEASYSTEMSCOMMANDMr.R.ChiuMr.R.JohnsonMr.G.SorkinMr.J:B.O’Brien(ContractsAdmin.)

MARITIMEADMINISTRATIONMr.F.J..DashnawMr.N.O.HammerMr.F.SeiboldMr.M.Touma

NATIONALACADEMYOFSCIENCESSHIPRESL4RCHCOMMITTEE

Mr.O.H.Oakley-LiaisonMr.R.W.Rumke-Liaison

SOCIETY0)?NAVALARCHITECTS&MARIKEENGINEERS

Mr.A.B.Stavovy-LiaisonWELDINGRESEARCHCOUNCILMr.K.H.Koopman-Liaison

MILITARYSEALIFTCOh!MANDMr.T.W.ChapmanMr.A.B.StavovyMr.D.SteinMr.J.Torresen

AMERICANBUREAUOFSHIPPINGDr.H.Y,JanMr.D.LiuMr.I.L.SternMr.S.G.Stiansen(Chairman)

U.S.GEOLOGICALSURVEYMr.R.GiangerelliMr.J.Gregory

INTERNATIONALSHIPSTRUCTURESCONGRESSProf.J.H.Evans-Liaison

AMliRICANIRON& STEELINSTITUTEMr.R.H.Sterne-LiaisonSTATEUNIV.OFNEWYORKMARTTTMECOLLEGE~r.W.R.Porter-LiaisonU.S.COASTGUARDACADEMYCaptW.C.Nolan-LiaisonU.S.NAVALACADEMYDr.R.Ba.ttacharyya-Liaison

U.S.NERCHANTMARINEACADEMYDr.Chin-Be.Kim-Liaison

-iii-

METR!CCONVERSIONFACTORS

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WhenYouKnow Multiolyby roFind symboSwlrhalsymbol Whenyouknow Mul!ipl~by ToFind symttol

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VOLUME

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TEMPERATURE[CXSCI)

Mull,t,1,!,sm,ll,tlh.,s,,,,11,1,0,(sI,wrsIImmk,WSIumrscub,cmewscubicnml=s

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Im,ll,liw,s U,031,1,,,s 7.11,1,,,s I.(WI,mr, 0.26C,dmc.*1.,5 35Cuticmeters 1.3

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t’; * ,1 1 I 1 1 1’ $ 1 1 1 1 4

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SECTION

1

2

3

4

5

6

TABLEOFCONTENTS

PAGENO.

GLOSSARY vii- ix

LISTOFABBREVIATIONS ix

THEWELDINGINSTITUTEOFGREATBRITAINLETTEROFRELEASE X

AUSTRALIANWELDINGRESEARCHASSOCIATION“ “ “ xiINTRODUCTION

DeSCriptiOnOFLAMELLARTEARING(LT)

2.1 WhatIsLamellarTearing?2.2 WhereDoesLamellarTearingOccur?2.3 WhatIsTheExtentofTearing?2.4 WhatDoesA LamellarTearLookLike?2.5 HowIsLamellarTearingNormallyObserved

OrDetected?

FACTORSCONTRIBUTINGTOLAMELLARTEARING

3.1 UnderWhatConditionsDoesLamellarTearingOccur?

3.2 ByWhatMeansDoesLamellarTearingOccur?3.3 DesignFactors3.4 MaterialFactors3.5 FabricationFactors

OCCURRENCEOFLAMELLARTEARING

4.1 WhatTypesofStructuresAreSusceptibleToLamellarTearing?

4.2 HowOftenDoesLamellarTearingOccur?4.3 WhenDoesLamellarTearingOccur?4.4 WhatTypesOfSteelAreSusceptibleto

LamellarTearing?4.5 WhatSteelThicknessesAreSusceptibleto

LamellarTearing?

SIGNIFICANCEOFLAMELLARTEARING

5.1 StaticLoadCondition5.2 DynamicLoadCondition5.3 Fatigue

CONTROLOFLAMELLARTEARING

6.1 JointDesign

6.1.1AvoidanceofExcessiveThrough-ThicknessStrains

6.1.2ReductionofJointRestraint6.1.3ReductionofComponentRestraint6.1.4SelectionofWeldMaterial

I-l&1-2

2-1- 2-3

2-12-12-22-2

2-3

3-1- 3-7

3-13-13-23’43-6

4-1- 4-lo

4-14-84-8

4-9

4-10

5-1&5-2

5-15-15-2

6-1- 6-16

6-1

6-16-36-56-6

-v-

SECTION

TABLEOFCONTENTS

TITLE

6.2 MaterialSelection

6.2.1GradeofSteel6.2.2ProductType

6.3 Fabrication

●

7

8

9

10

APPENDICES

A

B

6.3.1 LayoutandFormingComponents

6.3.2WeldingProcess6.3.3JointPreparation,6.3.4WeldingConditions

6.3.4.1Preheat

(Cent’d)

ofSusceptible

Fit-upandJigging

6.3.4.2DepositionRate6.3.4.3InterpassTemperature6.3.4.4WeldSizeandShape

6“.3.5WeldingTechniques

6.3.5.1RunSequence6.3.5.2Buttering6.3.5.3InSituButtering__ —-6.3.5.4Peenlng6.3.5.5WeldingandFabrication

Sequence6.3.5.6IntermediateStressRelief

DETECTIONANDREPAIROFLAMELLARTEARINGAFTERWELDING

7.1 When1s”Non-DestructiveTestingForLamellarTearingRequired?

7.2 WhichNon-DestructiveTestingMethodsAreApplicable?

7.3 UltrasonicTesting(UT)OfWeldedJoints7.4 RepairofLamellarTears

TESTSFORDETERMININGTHESUSCEPTIBILITYOFSTEELPLATESTOLAMELLARTEARING

REFERENCES

BIBLIOGRAPHY

MECHANISMOFLAMELLARTEARING

ORIGINSOFINCLUSIONS

PAGENO.

6-7

6-76-10

6-10

6-106-106-116-11

6-116-126-126-12

6-13

6-136-136-156-15

6-156-16

7-1- 7-5

7-1

7-17-17-3

8-1- 8-3

9-1&9-2

1o-1- 10-3

A-1-A77

B-1- B-10

-vi-

GLOSSARY

ANISOTROPIC- notisotropic,i.e.,havingdifferentmechanicalpropertiesindifferentdirections.

BASEMETAL- thebasicmill-rolledmaterialtobewelded.

COMPONENTRESTRAINT- restraintexistingduetorigidityofthevariousele-mentsofajointorconnection.

CONNECTION- completeassemblyconsistingof thevariousjointsmakingupthetotalunit.

CONSUMABLES- thefillermetaladdedinmak’theformofelectrodesorweldingrods.

DECOHESION- separationalongtheinterfaceaninclusion.

nga weldedjoint- usuallyin

betweenthematerialmatrixand

DISCONTINUITIES- lackofhomogeneouscharacteristicscausedbynonmetallicinclusions,cracks,tears,e~c.

DUCTILITY- abilityofamaterialsubjectedtostressto undergopermanentdeformationintheplasticrangepriortorupture.

ELECTRODESTRENGTH- usuallytheminimumtensilestrengthofdepositedweldmaterial.

ELECTRODEMATCHING- thepracticeofprovidingelectrodestrengthequaltothebasemetaltensilestrength.

ELONGATION- percentageelongationmeasuredina standardtensiontestandusedasa measureofductility.

HEAT-AFFECTEDZONE(HAZ)- portionofthebasemetaladjacenttothefusionlineoftheweld,whichisnotmeltedbutisheatedduringweldingto atemperaturehighenoughtomodifythemechanicalpropertiesofmicro-structure.

INTERPASSTEMPERATURE- inmultiple-passwelds,thetemperatureof thedepositedweldmetalbeforethenextpassisstarted.

ISOTROPIC- havingthesamemechanicalpropertiesindifferentdirections.

JOINT- junctionoftwoormorestructuralmemberswhicharetobejoined;asingleelementofa connection.

LAMELLARTEARING- separationinthebasematerialcausedbyinducedstrainsinthethrough-thicknessdirectionduetoweldshrinkage.

LAMINATION- largediscontinuityinrolledsteelproductsresultingfromflatteningandelongatingof inclusionsor voidsduringtherollingprocess- usuallya layerofnonmetallicinclusions.

-vii---

MATRIXMATERIAL- themajorcontinuoussubstanceof a metalasopposedtoinclusionsorparticlesofmaterialshavingdissimilarcharacteris’:lcs.

MECHANICALPROPERTIES- tensilestrength,yieldstress,percentageelonga-tion,reductionofarea,etc.

MEMBERRESTRAINT- restraintinclosurememberwhereinherentrigidityrequiresweldshrinkagetobeabsorbedbythebasemetal.

MULTI-PASSWELDS- weldsrequiringmorethanonepasstocompletedepositionofrequiredweldmaterial.

NONMETALLICINCLUSIONS-microscopicparticlesofcompoundsinsteelmatrix;principallysulfides,silicatesandaluminumoxides.

PARENTMETAL- thebasicmill-rolledmaterialtobewelded.

PEENING- themechanicalworkingoftheweldbeadsbymeansoflightimpactblowstotheweldsurfacetoreduceresidualstress.

PLANARDISCONTINUITIES- discontinuitieshavingmajordimensionsof lengthandbreadthina plane,i.e.,likea flatplate.

PREHEATING- theapplicationofheattothebasemetalimmediatelybeforewelding.

PREPARATION- geometryof a jointdetailincludingtheedgebevelirootopening,andbackup.

REDUCTIONOFAREA(RA)- themaximumpercentagereductionincross-sectionalareameasuredina standardtensiontestatthepointofruptureandusedasameasureofductility.

RESTRAINT- resistanceofthejointorconnectiontomovementofanykind.

ROLLING(orX)DIRECTION- directionthathotrolledstructuralmaterialtravelsthroughtheformingrolls- ortheprincipalrollingdirectionforcrossrolledmaterial.

Rolling(X)Direction

/

,1 Through-Transverse Thictiess(Y)Direction

!(~)Direction

-viii-.-

STRAIN- deformationperunitoforiginallengthcausedby changesinap-pliedforces.

STRESS- forceperunitofcross-sectionalarea.

THROUGH-THICKNESS(orZ) DIRECTION- perpendicularto theplaneof therolledsurface.

TRANSVERSE(orY)DIRECTION- perpendiculartotherollingdirectionintheplaneofthematerial.

WELDINGPROCEDURE- thedetailedelementsofwelding(u’,iuallya writtenpro-cedure)whichdefinetheprocess,voltage,current,speed,electrodetypeandsize,position,edgepreparation,preheat,sequenceandanyotherrelatedfactorsrequiredforanacceptableweld.

WELDINGSEQUENCE- theorderinwhichweldsaremadein a particularweld-menttominimizedistortion,to compensateforshrinkageandto reduceinternalstresses.

ULTIMATESTRESS- maximumstressattainedbeforeruptureofthematerial.

UTMATERIAL-materialultrasonicallyinspectedin itsentiretypriortofabrication.

YIELDPOINT- thepointona stress-straincurvewhereelongationoccurswithverylittleincreaseinstress.

LISTOFABBREVIATIONS

HAZ - heat-affectedzone

LT - lamellartearing

RAz - percentagereductionofareaintheZ direction

UT - ultrasonictesting

-ix-

THE WELDING INSTITUTEPLEASEREPLYTO RESEARCHLABORATORY AEINGTON HALL ABINGTON CAMBRIDGE CB1 6AL

TelephoneCAMBRIDGE0223 891162 TelegramsWELDASERCHCAMBRIDGETelex81183

LONDONOFFICE 54 PRINCESGATE EXHIBITION ROAD LONDONSW72PGTelephone01-5848556 TelegramsWELDINSTLONDONS.W.7

Ourref: TGD/wH/50 9thJanuary,“1.979.

Mr.J.Sommella,GibbsandCoxInc.,40RectorStreet,NewYork10006,USA.

DearMr.SOmJElla,

Dr.Dolbyhasaskedmetoreplytoconcerningthereport“Significanceand

yourletterControlof

LamellarTearingofSteelPlatein theShipbuildingIndustry.”Wefeelyoushouldbecongratulatedonhavingdrawnthepublishedmaterialtogetherverywellandproduceda readabledocumentwhichclearsupanumberofcommonmisunderstandings(e.g.thedistinctionbetweena laminationanda lamell.artear),andgivessoundadviceonavoidanceandrepairsoflamellartearing.Wethushavenoobjectiontoyouruseofsomeofourmaterialinyourmanualinitspresentform.

Yourssincerely,

T.G.DAVEYMaterialsDepartment.

-x-

~

+.$lffll+’,

.. I!USTXALIM WELIMG HESEARCH”ANOCIATION-,—,.. . 118AL F~EO STREET, VI L50NSP0 INT, r ~,W.206i,? .,, TELEPHONE: 922-3711.,,-,,... . .,,

AV:pd397/62

8thDecember,1978

MrJ.SonunellaGibbsG CoxInc.40RectorStreetNEWYORKN.Y. 10006

DearMrSommella18521- SignificanceandControlofLamellarTearing

ofSteelPlatesintheShipbuildingIndustry-SSCProjectNo.SR-250

ThankyouforthecopyoftheabovedocumentwhichI perusedwithinterest.I amhappytogiveyouformalauthorisztionto includethematerialreproducedfromAWRATechnicalNote610nbe~alf?of theAssociation.

Yourssincerely,

/:- .L x“%+

DrA.VettersDIRECTOR

-xi-

i

zo4mWY

r-

1. INTRODUCTION

Lamellartearingisa separationintheparentorbasemetalcausedbythrough-thicknessstrains.Suchstrainsareinducedprimarilybyweldmetalshrinkageunderconditionsofhighrestraint.Whilethelamellartearingphenomenonhasbeenrecognizedbyweldingexpertsforoverthirtyyears,theincidenceoflamellartearinginshipbuildinghasbeenextremelyrareforshipsunderconstructionorinservice.Thelowrateof occurrenceshouldnotbeliethefactthatlamellartearingcanbe a potentiallysignificantproblemwhenitoccursincriticalconnections.Theincidenceof lamellartearingisconsiderablymoresignificantinmobileandfixedoffshoredrill-ingplatforms.ThesearecomplexstructureswhichusethickplatesinhighlyrestrainedT andcruciformjoints.

Wheredetected,lamellartearingcanresultinoftendifficultandcostlyrepairsandsubsequentconstructiondelays.Withtheproperselec-tionofjointdesigns,materials,andweldingprocedures,theoccurrenceoflamellartearingcanbeminimizedandcontrolled.Theintentofthismanualistoprovidetheengineerordesignerwithspecificrecommendationsforcontrollinglamellartearinginthetypesofsteelsusedintheconstructionofshipsandoffshoreplatforms.A briefdescriptionofthecharacteristicsandmechanismoflamellartearingisprovidedtogivea basicunderstandingofthecomplexitiesof theproblemandtherationaleforthesubsequentrecommendationsforitsprevention.Methodsof detectingandrepairinglamellartearsafterweldingarealsopresented.

Thefollowingorganizationshavegenerouslyprovideddataon theirexperiencewithlamellartearingandmethodsforitscontrol:

* AmericanBureauofShipping

o BureauVeritas

● DetNorskeVeritas

@ GermanisherLloyd

s Lloyd’sRegisterofShipping

@ NipponKajiKyokai

● AvondaleShipyards,Inc.

● ContinentalOilCompany

● LukensSteelCompany

1-1

Mostof thepublishedliteratureon lamellartearingaddressesindetailthefactorsandmechanismswhichcontributetolamellartearingwhilereviewingcontrolprocedures,particularlyweldingtechniques,ina morecursorymanner.Theprimaryexceptionstothisgeneralizationare“Techni-cal Note6 - ControlofLamellarTearing”publishedbytheAustralianWeld-ingResearchAssociationand“LamellarTearinginWeldedSteelFabrication”publishedbyTheWeldingInstitute.Withtheirpermissionportionsoftheirpreviouslypublishedmaterialhasbeenincorporatedinthismanualandtheexcellenceoftheirworkandtheirgenerosityinpermittingitsuseisac-knowledged.Specialthanksis alsoduetheAustralianWeldingResearchAssociationforpermittingthereproductioninthismanualofAppendicesAandB oftheirTechnicalNote6.

1-2

2. DESCRIPTIONOFLAMELLARTEARING(LT)

2.1 WhatIsLamellarTearing?

Lamellartearinginsteelfab-ricationsistheseparationofparentorbasemetal,primarilyinplanesparalleltotheroll-

Z ingplaneof theplate,duetohighthrough-thicknessstrains.Thehighstrainsinthethrough-thicknessdirectionareusuallyinducedbylocalizedweldmetalshrinkageathicihlyrestrained. .

TNOTE

Lamellartearing“laminations”wh”

shouldnotbeconfusedwithcharediscontinuitiesinro”led

steelproductsresultingfromflatteningandelongatingofinclusionsorvoidsduringtherollingprocess.

2.2 WhereDoesLamellarTearingOccur?

II

RemoteionLine

UnderbeLTNear

.HAZIIIIH-H--RootLT‘-w-

Thetearingalwayslieswithinthebasemetal,usuallyjustoutsidethe visibleheat-affectedzone (HAZ),and isgenerallyparallelto theweldfusionboundary.ThelocationmayvaryfromwithinthelowerHAZtowellintothebasemetalthickness.Thetearingmaybecompletelysubsurfaceanddif-ficultto detector readilyvisibleonexposedplateedgesor atthetoeandrootof theweld.

lNumbersinbracketsdesignateReferencesinSection9.

2-1

2.3 WhatIsTheExtentofTearing?

Lamellartearsmayvaryinlengthfromametersandhavea widthapproximatelyweld.Thethicknessofthefracturemayto approximately1 mm.

2.4 WhatDoesA LamellarTearLookLike?

fZ Direction

/1

//1/

i1

t

NOTE

Lamel

fewmillimeterstoseveralequalto thesizeof thevaryfroma hairlinecrack .

lartearsexhibituniqueappearancecharacteristicswhichenablethemtobedistinguishedfromotherformsof cracking,includingcracksin the HAZcausedbyhydrogen.Whena tearreaches a surface or issectioned,itgenerallyappearsasa straightlineinthebasemetalparalleltothedirectionofrollingoftheplate.

Thecross-sectionisstep-likewithlongitudinalterracesthataresubstantiallylongerthanthetransversedepth.

Thefracturesurfaceisfibrousor woodyin appearancewithlittleorno discolorationun-lesstheteariscorrodedorhasbeensubjectto hightempera-tures.Theflatfibrouster-raceslieparalleltotheplatesurface,withstepsor shearwallsbetweenterracesapproxi-matelynormalto the platesurface.

Thecharacteristicfibrousorwoodyappearanceofthefracturesurfacetogetherwiththeterracedprofileandlocationwithinthebasematerialdistinguishesa lamellartearfromotherformsofcracking.

2-2

2.5 HowIsLamellarTearingNormallyObservedOrDetected?

Lamellartearswhichpropagatetothesurfacecanbe detectedbyvisual,dyepenetrationandmagneticparticleinspectiontech-niques.However,sincemostlamellartearsarecompletelysub-surface,thesedetectionmethodsareoflimitedusefulness.Ultra-sonictestinghasbeenfoundto bethemosteffectivemethodofdetectingsub-surfacetears.A moredetaileddiscussionof thedetectionandrepairoflamellartearingispresentedinSection7.

2-3

3. FACTORSCONTRIBUTINGTOLAMELLARTEARING

3.1 UnderWhatConditionsDoesLamellarTearingOccur?

For.lamellartearingtooccurthefollowingthreeessentialcondi-tionsmustbesatisifed:

o Thematerialmustbe susceptibleto tearing.Thatis,thebasematerialIntheregionofthejointmusthavepoorduc-tilityintheZ-(through-thickness)direction.

● Theweldingproceduresmustproducestrainswhichactthroughthejointacrosstheplatethickness,thatis,through-thick-nessstrains.Sucha conditionexistswhentheweldfusionboundaryisroughlyparalleltothesurfaceofthebaseplate.

@ Thejointdesignmustpermitthedevelopmentofhighthrough-thicknessstrains.Thesestrainsusuallyresultfromweldmetalshrinkageinthejointbutcanbeincreasedby strainsdevelopedfromreactionwithotherjointsinrestrainedstruc-tures.

NOTE

Forlamellartearingtooccurtheremustbea criticalcombinationofmaterialsusceptibility,andweldingproceduresandjointdesignwhichpermitthedevelopmentofhighthrough-thicknessstrains.

3.2 ByWhatMeansDoesLamellarTearingOccur?

Lamellartearingisgenerallybelievedtooccurinthreedistinctphases.Duringthefirstphasevoidsareformedusuallyby deco-hesionorfractureofsingleelongatednonmetallicinclusionsorgroupsofinclusionslyingparallelto therollingplaneoftheplate.Althoughadditionalvoidinitiationmechanismshavebeenreported,thedecohesionofmicroscopicinclusionsisconsideredtheprimaryinitiationmechanism.Thefirstphaseprobablytakesplaceintheelasticrangewherethestressrequiredfor theinitialdecohesionwillbedependentonthetype,shapeanddistri-butionofinclusionsandthepropertiesofthematerialmatrix.

3-1

zi Terrace

“-”s

ShearWall

DecohesionatInclusions

Inthesecondphasetheinitiatedvoidsortearsonthesameplaneextendandjoinbymeansof neckingormicrovoiclcoalescencetoformterraces.Theelongationandlinkupof adjacentinclusionsiscausedbyincreasedstrainsduetocoolingofpreviouslydeposi-tedweldrunsand/orthedepositingofadditionalweldmetal,Asthestrainsincreasetheligamentsofmatrixmaterialbetweentheinclusionsbecomefullyplasticandthevoidsincreaseinsizebyductiletearing.

Furtherstraininginthethirdandfinalphaseconnectstheter-racesondifferentlevelsbyductileshearingoftheverticalwallsbetweentheterraces.Theformationoftheshearwallscreatesthecharacteristicstep-likeappearanceofthecompletedlamellartear.Additionalinformationonthemechanismoflamellartearingispre-sentedinAppendixA. Thefactorswhichcontributeto andinflu-encelamellartearingmaybe groupedintothreecategories:design,materialandfabrication.

3.3 DesignFactors

Thesusceptibilityofa structuralcomponentorjointto lamellartearingisaffectedbythosedesignfactorswhichdeterminethein-ternalresistanceofthejointandtheresultingaccumulationofweldmetalshrinkagestraininthethrough-thicknessdirection.Theprincipaldesignfactorswhichinfluencetheriskoflamellartear-ingare:

3-2

A,........-;-.,..,...’ ‘“~-.. .,;,~:.,.,.,:,,,:.:

* WeldOrientation.Jointcon-figurationswhichorienttheweldfusionboundaryparalleltothedirectionof rollingofthebasemetalpromotethedevelopmentofthrough-thick-nessstrains.Tee (T)andcornerjoints,theprimaryexamplesofsuchjoints,areusedextensivelyinshipsandoffshorestructures,

o JointRestraint.Thelevelofjointrestraintisan importantfactorindeterminingtheamountandconcentrationof strainattheconnectionandis influencedby thesize,balance,anddistributionof theweld. Weldswhicharelargerthanthoserequiredtoaccommodatethedesignloadsunnecessarilyincreasetheweldshrinkagestrainsasdo theunwarranteduseof widegrooveanglesandfullpenetrationweldsinplaceof properlysizedfilletwelds.Inmultipasswelds,thesizeoftheweldbeaddeterminesthenumberofpassesrequiredtofillthejoint.Thesmallerthebeadsize,thegreaterthenumberofrequiredpassesandthehighertheweldshrinkagestrains.

Jointdesignswithlargesingle-sidedweldscauseunsymmetricstrainsto concentrateon thesideoftheweld. Double-sidedweldsreduceand balancetheshrinkagestrainswitha result-

I > ant decreasein the risk oflamellartearing.

FlangedGussetPlate7 @ ComponentRestraint.Struc-turalcomponentsfabricatedofthickand/orcurvedplates,and stiffenedwith heavybracketsor gussetshavein-herentlymorerestraintinthethrough-thicknessdirectionthancomponentsfabricatedofunstiffened,thin, flatplates.

3-3

—-

F1Examplesof.highcomponentre- ,straintusuallycanbefoundatthemulti-columnconnectionsornodejoints“ofmobileandfixed z.offshorestructures.

o WeldMetalStrength.Whentheyieldpointoftheweldmetalissignificantlyhigherthanthatof thebasemetal,allof theweldshrinkagestrainsmustbeaccommodatedbythebasemetalmatrix.Theconcentrationofthestraininthebasemetalin-creasestheriskoflamellartearing.Weldmetalisusually“matched”tothebasemetalonthebasisofequivalenttensilestrengths.However,weldmetalswhichmatchthe tensilestrengthof thebasematerialgenerallyhavesignificantlyhigheryieldpointsthanthebasematerial.

3.4 MaterialFactors

A detaileddiscussionofthemetallurgicalfactorswhichinfluencethesusceptibilityof rolledsteelplatesto lamellartearingwouldbetoovoluminoustoincludeina practicalguidancemanualfordesignersandengineers.However,anunderstandingofthefundamentalmetallurgicalconsiderationsisnecessarytoobtainanappreciationofthecomplexityoftheproblemandtheunderlyingrationaleforthecontrolmethodspresentedinSection6. Addi-tionalinformationonthematerialfactorsinfluencinglamellartearingmaybefoundinAppendixB andtheselectedworkslistedinthebibliography.

Lamellartearingisdirectionallysensitiveandatleastpartiallydependenton thethrough-thicknesspropertiesof the basematerial.Theanisotropyofhot-rolledsteelplatesusuallypro-ducesthegreateststrengthandductilityinthelongitudinalandtransversedirectionswithsignificantlylessductilityinthethrough-thicknessdirection.Thesusceptibilityof carbonandlow-alloysteelstolamellartearingisprimarilydependentontheselowthrough-thickness(Z-direction)ductilities.Thetype,number,shapeanddistributionofthenonmetallicinclusions,aswellasthematrixpropertiesoftheparticulargradeof steel,aregenerallyconsideredresponsibleforthereductioninductili-ty intheZ-direction.

3-4

Allnormalqualitystructuralsteelsforhullandmarineapplica-tionscontainquantities.ofexogenousandindigenousinclusions.Exogenousinclusionsusuallyconsistof ladlerefractory,ingotscum,orslagthatisoccasionallytrappedintheingotduringsolidification.Theyareusuallylargeincomparisonto indige-nousinclusionsandwhenlocatedclosetothesurfaceof a rolledplatesignificantlyincreasethesusceptibilityof theplatetolamellartearing.

Indigenousinclusionsareformedasa resultofthechemicalreac-tionof elementsinthesteelor elementsaddedto thesteelusuallyduringdeoxidation.Thenumberanddistributionofindig-enousinclusionsdependsonthe steelgradeanditschemicalcomposition,thedeoxiciationprocedure,themeltingtechnique,positionintheingot,andthehotworkingtemperature.Whentheingotisrolledtoforma plateorsectiontheinclusionsarepro-gressivelyelongatedandflattenedto varyingdegreesto formplatesorstringersparalleltotheplatesurface.Materialwhichhashighconcentrationsofelongatedorflattenedinclusionswillhavelowerthrough-thicknessductilityanda greatersusceptibili-tytolamellartearing.

Thedominantinclusionsaresulfidesandoxideswiththedeoxida-tionpracticedeterminingthetypeofeach,’inclusionpresent.Forcomparisonpurposesdeoxidationpracticesareusuallyclassifiedintwocategories:non-aluminumtreatedandaluminumtreated.Insemi-orfully-killednon-aluminumtreatedsteelssilicatesandTypeImanganesesulfidesaretheprimarytypesof inclusions.TypeIImanganesesulfidesandaluminaaretheprincipalinclu-sionsinfully-killedaluminumtreatedsteelswhileTypeIIImanganesesulfidesandaluminainclusionspredominateinfully-killedwithexcessaluminummaterials.Inthenon-aluminumtreatedsteelsthesilicatesbecomemoreelongatedthanthesul-fidesduringhotrollingandareprimarilyresponsibleforthereductioninZ-direction(ST)ductility.However,inaluminumdeoxidizedsteeltherodshapedmanganesesulfideinclusionsbecomehighlyelongatedduringrollingandaretheprimarycauseofthelowZ-directionductility.Highconcentrationsorelongat-edclustersofmanganesesulfidesandaluminacanalsoproducelocallypoorZ-directionductilityinnon-aluminumandaluminumtreatedsteels,respectively.

Manyoftheearlierworksonmetallurgicalaspectsof lamellartearingemphasizedtheimportanceofsulfurcontentandinclusionshapecontroltoimprovethrough-thicknessductilityasmeasuredbythepercentagereductionofareaintheshort-transversedirec-tion.Fora reductionofareahigherthan25percent(a levelatwhichtheriskoflamellartearingissignificantlyreduced),thesulfurcontentmustbe lowerthan0.010percent.Additionof .rare-earth(RE)metalreducestheresidualsulfurlevelswhilealsopreventingtheformationofmanganesesulfidesandsilicates,forminginsteadonlysmallglobularshapedRE-containinginclu-sions.However,fornon-alunlinumtreatedsteels,wheresilicatesareprimarilyresponsibleforreducingtheZ-directionductility,

3-5

thesulfurcontentalonecangiveaninadequateindicationof thesusceptibilityof thematerialto lamellartearing.Improvedmanufacturingprocessessuchaselectroslagremeltingandcalcium-argon-blowingmayalsobeusedtoreducethemaximumsulfurlevelsand/orremovemostofthenonmetallicinclusions.

Thepropertiesof thesteelmatrixarealsoimportantinallphasesoftearing.Forsteelswitha low-strength,highlyductilematrix~thematerialattheedgesof inclusionscandeformplas-ticallywithoutpropagatingthefracturesorvoidsformedby thedecohesionofthenonmetallicinclusionsandthematrixmaterials.Inhigherstrengthsteels,thethrough-thicknessductilityde-creaseswhilethehigheryieldstrengthof thematrixmaterialpermitsthedevelopmentofhigh-strainlevelsacrossaninclusionbeforethematrixyields.Thesehigherstrainlevelsinturnfacilitatetheextensionandjoiningof adjacentvoidsinthesecondphaseoftearing.

Ferrite-pearlitebandinginthesteelmatrixhasalsobeenre-portedtocausebothinitiationandpropagationoflamellartears,partiallybecausetheferritehasa lowercleavagefracturestressthanthepearlite.Strainaging,hydrogenembrittlementanddifferencesinthethermalexpansionbetweentheinclusionsandthesteelmatrixallcontributeinsomedegreeto thesuscepti-bilityofsteelplatestolamellartearing.Susceptiblesteelswithhighbrittlefracturetransitiontemperaturesshowimprovedresistancetotearingwhenpreheatedabovethebrittlefracturetransitiontemperaturebeforewelding[2].

3.5 FabricationFactors

Fabricationpractices,particularlyweldingvariables,helptode-terminethelevelofjointrestraintandtheresultingriskoflamellartearing.Factorswhichaffectlamellartearingsuscepti-bilityincludepreheattemperature,heatinputlevel,beadorrunsequence,andfabricationsequence.Increasingpreheatandheatinputlevelsarereportedtoincreasethepostweldductilityofthemetalwitha correspondi~yimprovementintearingresistance.Explanationsfortheapparentlylowerriskoftearingwithhigherpreheatandheatinputweldingprocessesarevariedandincludeincreasedweldpenetrationandweldmetaldepositionrate,reducedrateofpostweldcoclingandproductionof a wider,softerandtougherHAZ. Increasedpenetrationcaninterceptandbluntexist-inglaminationswhilehigherdepositionratesdecreasethere-quirednumberofweldrunsandthesubsequentnumberof straincycles.Thereductionincoolingratespermitsstressrelaxationandthedevelopmentofsmallerstraingradients.Theuseofhigh-erheatinputprocesseswillalsoproducelowerstrengthweldswhichwillaccommodatemoreoftheshrinkagestrain.In additionto improvingthepostweldductilityof thematerial,preheatingmayretardthepropagationof lamellartearingby raisingthetemperatureofthesusceptiblematerialaboveitsbrittlefracturetransitiontemperature.

3-6

Basedontheseresearchresultstheinfluenceof higherpreheatandheatinputweldingprocessesontheincidenceof lamellartearingappearssubstantial.However,reportsof fabricatorex-perienceindicatelittleornodiscerniblesuccesswithincreasingpreheatorheatinputwithina givenweldingprocess.Onthecon-trary,higherpreheatandheatinputlevelsmayincreasetheamountofsubcriticaltearingandcontractionstrains.

Thesequenceofdepositingtheweldbeadsorrunscansignificant-lyaffectthelevelandconcentrationof shrinkagestrainsneartheHA2andparallelto thedirectionof rollingof thebaseplate.Whenfabricatingdouble-sidedT jointsunsymmetricaldepositingoftheweldmetalcancausestrainsto concentrateonthesideoftheweld.Symmetricaldepositi[jnof therunswillreduceandsomewhatbalancetheweldshrinkagestrains.

In multi-jointcomponentsthefabricationorweldingsequencecanaffecttherestraintlevelofeachjointatthetimeof welding.Theriskoflamellartearingincreaseswhenthemoresusceptiblejointsaremadetowardstheendofthefabricationsequencewhenthemaximumrestraintofthestructureisbeingapproached.

3-7

4. OCCURRENCEOFLAMELLARTEARING

4.1 WhatTypesofStructuresAreSusceptibletoLamellarTearing?

Lamellartearingusuallyoccursathighlyrestrainedjointsinlargeweldedstructures,Therestraintmaybe imposedby a mas-sivecomponentorbya smalleronewhichhasbeenstiffened.Tee(T)andcornerjointsarethetwobasicjointconfigurationsmostsusceptibletolamellartearing. Thecruciformjointiscon-sidereda moresevereformoftheT jointsincetherestraintofthebaseplateinwayoftheweldishigher.Thesusceptibilityofthesejointsreflectsthefactthattheinternalrestraintofthejointinthethrouqh-thicknessdirectionissufficienttocausetheweldshrinkag;strainstoexceedtheductilitylimitsofthebasemetal.

Withtheexceptionofcruciformjoints,T jointswithsingleordouble-sidedfull-penetrationweldshavethegreatestinci-denceoftearing.T jointswithsimplefilletor partialpene-trationratherthanfull-pene-trationweldsappearto presentlessriskasdobalanceddouble-sidedweldscomparedto largesingle-sidedwelds.

In cornerjoints,tearingcanoccurin one or more planesthroughthebaseplatethick-ness.Thetearsoftenextendtotheexposedplateedgewherethey are eithervisible orreadilydetectedby standardnon-destructivetestingmethodssuchasdyepenetrationormag-neticparticleinspection.

4-1

...—

:FV=lE!!:$3~t<lgmm boundaryisata largeangle

tothe~latesurface.How- 1i ever,tearinghasbeenre-

tportedinbuttweldsofthickplates(ta 19mm)withanx-groove.

tt~19mm

In theheavyfabricationandconstructionindustriesjlamellartearingiscommonlyreportedtooccurinthefollowingtypesofstructures:

1 1

o Nozzleorinsertsetthrougha rlald~late.Tearingcanoccurin a rolled p-latenozzleor penetratorsetthrougha vesselshellplateorendwall,or in a fabri-catedinsertinthewebof alargegirder.Forexample,aVierendeelgirderfabricatedofheavyplatesectionswitha ringstiffenersetintothewebopeningissusceptibletolamellartearingintheringstiffener.Inallcases,anytearingwilloccuronlyinthenozzleorinsertplate.

%,e, :P1ate

4-2

s

ShellofVessel

●

Cylin’’&ical/

RigidEndPlate

Stiffenersor end closurePIatesIncylindricalstruc-tures.Shellplatesof cy-lindricalstructureswhichareinwayoftheendclosureplatesor heavyinternalstiffenersaresusceptibletolamellartearing.Instruc-turesofthistypethetearscanbecompletelysubsurfaceanddifficulttodetect.

Boxstructuresandstiffenedjointssuchas beam-to-column.Structuresinthiscategoryrangefromsimpleboxcolumnstolargestructuralconfigurationswithcomplexmulti-memberconnections.

I I ——/------[

.

For11.highlysusceptiblemateria.,

tearinghasbeenreportedinapparentlylowrestraint

y Heavy

l’c)

LiftingLug

situationssuchaspulloutofliftinglugsandinflange-to-webconnectionsinfabri-catedI-beams.Theriskoflamellartearinginappar-entlysimple,unrestrainedjointsmakesit essentialthatforcriticalcomponents,suchas liftinglugs,postweldinspectionfortearingbeperformedandoftenaccom-paniedbya reductioninthethrough-thicknessserviceloads;

4-3

.....— ..

Documentedcasesoflamellartearingareextremelyrareforshipsunderconstructionorinservice.However,isolatedinstancesoflamel”lartearinghavebeenreportedinthefollowingtypesofstructuralconnections:CVK/innerbottom,CVKriderplate/trans-versebulkheadgdeckstringerplate/sideshellsheerstrake,con-tainerbuttresssupportsandthick-walledboxgirdersof largecontainerships.

ngerInnerbottom-?1NoteUnusual

Configuration Il!!!rSheerStrake

DeckStringer/SheerStrake(\ \

CVK/Innerbottom

w

TransverseBulkhead

RiderPlate

.CVK

CVKRiderPlate/TransverseBulkhead

Bulkheadorinnerbottomheelconnections,heavysternframeweld-mentsandthickwebframeflangetolongitudinalbulkheadconnec-tionsinlargetankersarealsoconsideredsusceptibletoIamellartearing,althoughnoactualfailureshav@beenrePorted”

4-4

Shel1

BulkheadorCofferdam

Plating

\

TankTop

{ a

BulkheadorCofferdam

$

Plating

\

Itisimportanttonotethatallofthesesusceptibleshipdetailsareessentiallyvariationsofthebasiccorner,T andcruciformjointsdescribedinthebeginningof thissectionasbeingthemostsusceptibletolamellartearing.Theweldsmaybeeitherofthedoublecontinuousfilletor bevelgroovetypewithfullorpartialpenetration.

Todate,lamellartearinghasnotbeenresponsibleforeithernumerousorcriticalfailuresinshipbuilding.Whileitcannotbeconsidereda seriousproblembasedontherateofoccurrence,thedesignerorengineermustbeawarethatlamellartearingcanbe apotentiallysignificantproblemwhenitoccursincriticalconnec-tions,suchasbulkheadorcofferdamheels.Intheseareas)proced-uresforthecontrol,detectionand,Ifnecessary,therepairoflamellartearsshouldbeimplemented.Wheretheincreaseinthesizeofshipsresultsinstructuralassembliesfabricatedfromthickerplates,theriskoflamellartearinginjointswhichare

4-5

. . .

acceptablewhenfabricatedof thinnermaterialshouldbe re-evaluated.Whilethesignificanceoflamellartearingshouldnotbeunderestimated,theextentoftheproblemshouldnotbe exag-geratedtothepointthatexpensivematerials,andfabricationandinspectionproceduresareunnecessarilyspecified.

TheproblemsofIamellartearinginmarinestructuresareconsid-erablymoresignificantintheconstructionofmobileandfixed ..offshoredrillingplatforms.Theconfigurationof thesestruc-turesisverycomplexwiththeuseof thickplatesinhighlystressedweldedT andcruciformjoic:s.Thesejointsusuallytake ktheformofmulti-columnconnectionsornodejointsatwhichtubesof largediameterandthicksectionpassthroughor aresurfaceweldedtoanothertubewithfull-penetrationfilletwelds.

L’

L HeavyWallPipeAtIntersection

4-6

—

Samplestructuralconnectionsofcolumnstabilizedan’dself-eleva-tingmobileoffshoreunitsandfixedjackettypeplatformswhicharesusceptibletolamellartearinginclude:

ColumnStabilizedUnits

1. Intersectionofverticalcolumnsandupperandlowerhulls.

2. Majorintersectionsofhorizontalandverticalbraceswiththemselvesandwiththeverticalcolumn.

3. Portionsofdeckplating,heavyflanges,andbulkheadswith-intheupperhullorplatformwhichformi~oxorI typesup-portingstructure.

Self-ElevatingUnits

1. Jackhousesupportingstructureandbottomfootingstruc-ture.

2. Verticalcolumnsinwayof theintersectionwiththematstructure.

3. Combinationsof deck,side,bottomandbulkheadplatingwithintheupperhullwhichformboxor I typesupportingstructure.

4-7

JacketTypeFixedPlatforms

1. Decktolegcanintersections,

2. Majorintersectionsofhorizontalandverticalbraceswiththemselvesandwiththeverticalcancolumns.

4.2 HowOftenDoesLamellarTearingOccur?

Larnell”ar”tearinghasbeenestimatedtooccur“insignificantly-lessthanonepercentofallweldments.Thefrequencyof occurrenceincreasesslightlyforlargeweldedstructuresfabricatedofplatesorsectionsover25to30mm inthicknessunderconditionsofhighrestraintinthethrough-thicknessdirection.Forappli-cationswhichdonotsatisfytheessentialconditionsofmaterialsusceptibilityandthrough-thicknessstrainsdueto weldingpro-ceduresandjointconfiguration,theriskof lamellartearingisnegligible.

Thefrequencyoflamellartearingintheconstructionof ships,andmobileandfixedoffshorestructuresisdifficulttoestimate.Repliestoquestionnairessenttotheworld’smajorclassificationsocietiesindicatethattheincidenceoflamellartearinginship-buildingissmall.Isolatedcasesof lamellartearinginsuchconnectionsasthedeckstringerplate/sideshellsheerstrakehavebeenvirtuallyeliminatedby theuseof improvedweldandjointdetails.

Theproblemoflamellartearingisconsiderablymoreseriousintheconstructionofmobileandfixedoffshoredrillingplatforms.Thegreatersusceptibilitytotearingofthelargenumberofhigh-lyrestrainedT andcruciformjointsinthesestructuresincreasesthefrequencywithwhichlamellartearingoccurswhennormalstructuralqualitysteel(sulfurcontent> 0.020%by weight)isused.Thefrequencyof tearingisreducedsignificantlywhensteelswithimprovedthrough-thicknesspropertiesareusedincon-junctionwithrevisedweldingproceduresandjointdesigns.Oneoilcompanywhichfabricates15to20fixedoffshorestructuresayearestimatestheirfrequencyof lamellartearingat lessthanoneperyear.

4.3 WhenDoesLamellarTearingOccur?

Lamellartearingusuallyoccursduringfabricationjoftenatanad-vancedstagewherpthemaximumlevelofrestraintisapproached.Thereisconsiderabledisagreementintheliteratureconcerningthetimeandtemperatureattheonsetof tearing.Somereportsindicatethatlamellartearingisinitiatedshortlyafteraddi-tionalweldmetalisdepositedoverpreviousbeadswhichhavecooledtothepointofdevelopingweldshrinkagestrainssuffi-cienttocausedecohesionattheinterfacebetweenmicroscopicnonmetallicinclusionsandthesurroundingmatrix.Otherreportsconclude,however,thattearingisanambienttemperature,delayedcold-crackingphenomenon.

4-8

4.4 WhatTypesofSteelAreSusceptibleToLamellarTearing?

Lamellartearinghasbeenencounteredprimarilyinnormalqualitystructuralsteelplatesofthecarbon,carbon-manganeseandlow-alloytypes.Thesteelmaybeinthenormalized,as-rolled,con-trolled-rolledorquenchedandtemperedcondition,or be fineorcoarsegrain.Examplesoftypical.AmericanSocietyforTestingandMaterials(ASTM)andAmericanBureauofShippingsteelspeci-ficationswithreportedhistoriesoflamellartearinginclude[3]:

SpecificationTypeofProduct

ABSAH36 HigherStrengthHullStructuralSteelASTMA36 StructuralCarbonSteelASTMA283 StructuralCarbonSteel- LowandIntermediate

TensileStrengthASTMA285 PressueVesselCarbonSteel- LowandInter-

mediateTensileStrengthASTMA515 PressureVesselCarbonSteel- ForIntermediate

andHigherTemperaturesASTMA516 PressureVesselCarbonSteel- ForModerateand

LowerTemperatures

Nonmetallicinclusionshavebeenshowntobeprimarilyresponsibleforlowthrough-thicknessductilityandthevoidinitiationphaseof lamellartearing;andthedeoxidationmethodusedinthesteel-makingprocessdeterminesthetypesofinclusionspresentinthesteel.Theearlierliteratureindicatedthataluminumtreated-semikilledsteelscouldbeexpectedtohavebetterresistancetolamellartearingthansilicon-treatedsemiskilledsteels.However,recentstudiesreportthatthelamellartearingmechanismistoocomplextosimplyrelatesusceptibilitytosteelgradeor inclu-siontype.Hence,aluminumtreatedorsemiskilledsteelscannotbeconsideredmoreorlesssusceptibletotearingthannon-aluminumtreatedorfullykilledsteels.

Intheory,thereisanincreasedriskoflamellartearingwithin-creasingstrengthlevels.Forhigherstrengthsteel,thethrough-thicknessductilitydecreaseswhilethegreaterstrengthproper-tiesofthesteel’smatrixmaterialwillpermitthedevelopmentofhigherelasticstrainacrossaninclusionbeforethematrixitselfyields.Theincreasedsusceptibilityofhigherstrengthsteelsisoffsetinsomecasesbytheincreasedflexureduringweldingduetotheuseof thesmallerthicknessespermittedby thehigherstrength.Somehigherquality,high-strengthalloysteels,suchasHY-80,HY-1OO,HY-130andHY-180,haveshownminimumsuscepti-bilitytodecohesioncracking.However,thisresultisattributedtotheincreasedcleanliness(reducedinclusioncontent)of thesespecial-purposesteelsproducedby electricfurnacesteelmaking,coupledwithvacuumdegassing.

4-9

—.

Lamellartearingoccursprimarilyinrolledstructuralplates,toa lesserdegreeinrolledsectionsandrarelyinforgings.Steelcastingsarenotsusceptibletotearing.

4.5 WhatSteelThicknessesAreSusceptibleToLamellarTearing?

Lamellartearinghasoccurredinplatesranginginthicknessfrom10to200mm,withthemostcommonincidencebeinginplates25to ,.,60mmthick.Thinplatesusuallyhavelowerductilityinthethrough-thicknesssdirectionthanthickerplatesdue to thegreaterdeformationofinclusionsinthinplatesduringrolling. .:However,theydonotnecessarilyexhibita greaterincidenceoftearing,sinceflexureofthethinnerplatestendsto limitthestrainsinthethrough-thicknessdirection.Exceptionsto thisgeneralizationarerolledplatenozzles,cruciformjointsandhighlystiffenedstructuralconfigurationswhichlimittheflexurerfthethinnerplates.

4-10

5. SIGNIFICANCEOFLAMELLARTEARING

Wheredetected,lamellartearingcanresultincostlyrepairsandfab-ricationdelays.Thesignificanceofundetectedorunrepairedtearson theserviceperformanceofthestructurevarieswiththetypeof loading.Thefollowingsectionsevaluatetheeffectsoflamellartearingon thestatic,dynamicandfatiguemodesofloading.

5.1 Static LoadCondition

Theextremelyfewreportedincidenceoflamellartearingfailuresinserviceindicatesthatthestrainsdevelopedduringweldingaremorelikelytocausetearingthanthestaticdesignor serviceloads.Localizedstrainsashighas2%havebeenreportedduringweldingandtheimmediatepostweldingcool-downperiod.By com-parison,theoffsetstrainlevel,correspondingto theyieldpointofmoststructuralsteels,isonly0.2%.Sincedesignstressesarealwayssignificantlylowerthantheyieldstressofthematerial,thestrainsencounteredinserviceareatmostonly10%of thestrainsdevelopedduringwelding.PreliminaryresultsofresearchdoneintheUnitedKingdomatTheWeldingInstituteindicatethatevenincaseswhereextensivetearingis initiallypresentthrough-thicknessstaticstresslevelsgreaterthantheyieldstrengthofthebasemetalarerequiredto extendthetearstocompletefailure.Hgwever,astheextentoftheinitialtearingincreases,thestresslevelsnecessarytopromotefailuredecrease[3].

Lamellartearingisreportedtohavenoeffectontheserviceper-formanceof jointsstressedprimarilyincompressionin thethrough-thicknessdirection.Injointssubjecttoshear,theser-viceperformancewillnotbediminishedprovidedthereissuffic-ientareaintheremainingligamentsbetweenthetears.In areasofextensivetearing,themaximumshear-loadcapacityofthejointsmaybereduced.

5.2 DynamicLoadCondition

Verylittleinformationisfoundintheliteratureconcerningtheeffectoflamellartearingontheabilityofa structureto with-standdynamicloads.A fewstudiesreportreducedCharpyV-notchimpactenergiesanddynamictearingpropertiesinthethrough-thicknessdirection.ShocktestsperformedbytheBritishNavyonfull-penetrationweldedT-joints,fabricatedof HY 80 andtwogradesofC-Mnandlowalloysteels~showedthatlamellartearingcouldbeinitiatedbydynamicloads.Ofthethreesteelstested,onlytheHY80,withitsgreaterZ-directionductility,failedtodeveloplamellartears.Althoughnotconclusive,thesereportswouldseemto indicatethatmaterialswithlowerZ-directionpropertiesaremoresusceptibletolamellartearingwhenexposedtodynamicloads.Conversely,thepresenceof undetectedtearscanonlyincreasetheriskoffailureduringdynamicloading.

5-1

5.3 Fatigue

Forlowcyclefatigue,existinglamellartearswillgraduallyex-tendandmayultimatelyresultincompletefailureasthenumberofcyclesapproachesthedesignlimit[1].However,inpractice,catastrophicfailuremaybe avoidedby thetransferof loadtoothermembersofthestructure.StressconcentrationsattherootortoeoftheweldmaybemoredetrimentalthanexistingtearsorpoorZ-directionductilitywhenthe structureis exposedtohigh-cyclefatigue(greaterthan10 cycles)[3]. t

5-2

6. CONTROLOFLAMELLARTEARING

Sincedesign,materialandfabricationfactorscontributeto lam-ellartearing,controloftearingmustaddressthesesameparam-eters.ItisevidentfromSections2 and3 thatthecausesoflamellartearingareapplicableto generictypesofweldmentswhichareindependentof thespecificendproduct.Itmatterslittlewhetherthesusceptibleweldmentsarein a skyscraper,nuclearpowerplant,supertanker,or largeoffshorestructure.Accordingly,mostofthefollowingrecommendationsforthecontroloflamellartearinginthemarineindustryarepresentedintheirmostfundamentalform.Itisimperativethatthenavalarchitectordesignerusejudgementto arriveattheoptimumbalanceofjointdesign,materialselectionandcosteffectivefabricationproceduressuitablefortheapplication.

6..1 Joint Design

Theavoidanceandcontroloflamellartearingmustbeginatthedesignstage.Thedesignof susceptiblejointssuchasthoseshowninSection4.shouldbeoptimizedwherepracticableto:

● Avoidexcessivethrough-thicknessstrains

● Reducejointrestraint

o Reducecomponentrestraint

● Allowfortheuseoflow-strengthweldmetals

6.1,1AvoidanceofExcessiveThrough-ThicknessStrains

Methodsforavoidingthecreationofweldshrinkagestrainsinthethrough-thicknessdirectioninclude:

iiii?

● Weldingbetweentheends.,*:..... ofplatesratherthanon,...+....“,.4. thesurfaceofthesuscep-,,,.,..::..,:#,.-.:..-:..-..... tiblematerial. This

weldingtechniquedirectstheshrinkagestrainsinthe X or Y directionsratherthaninthecriti-calZ directionandmayrequiretheuseof elec-troslagwelding.

Susceptible Improved

6-1


A“*...‘~f.,*F?.:.,.-..


ElectroslagWeld

:

.7

ElectroslagWeld

● Orientingtheweldfusionboundaryat an angletothesurfaceofthesuscep-tibleplate.Largebevelanglesofferlessriskoftearing,buttheedgeprep-arationcostandthevol-umeofweldmetalrequiredis alsohigherthanforsmaller edge angles.Selectionofa cost-effec-tiveanglemustconsiderthesusceptibilityof theplate,theimportanceofthe connectionand therelativecostof fabrica-tion.

LeastImproved

6-2


I

Forgingor

Casting

6.1.2ReductionofJointRestraint

Methodsofreducing

Susceptible3

_l-13t T

ii

. Replacingofdouble-sided,full-penetrationweldswithsymmetricalfilletorpartial-penetrationweldstominimizethevolumeofweldmaterialandreducethestrainintheZ-direc-tion.Thetotalshrinkageofthefilletweldsoccursatanobliqueanqleto“theplatesurfaceth~rebvfur-therreducingthe~traincomponentintheZ-direc-tion.

. Usingcastingsorforgingsin somecriticalT andcruciformjointstoelimi-natethecriticalweldsandanyriskof lamellartearing.Thismethodisexpensive,involvescon-siderablymorewelding,andisgenerallyusedinhighlycriticalsituationsinpressurevessels.

jointrestraintinclude:

J

● Reducingthesizeof theweldby notusingweldslargerthannecessarytotransferthecalculateddesignloads.Forexam-ple,full-penetrationweldsatthedeckstringerplate/sheerstrakeconnec-tioncanoftenbere~laced

Improved bysmallerpartial‘~eri~-trationorf“illetwelds.

1

Improved

bs6-3

——


Susceptible!==3

Improved

0 Joiningplatesof differ-entthicknessesso thattheweldsizemaybere-ducedbyplacingitinthethinnerplate.

o Replacinglargesingle-sidedweldswithbalanceddouble-sidedwelds inordertoeliminatetheun-symmetricconcentrationofstrain.


6-4

.—

1


● Selectingweldconfigura-tionswhichdistributetheweldmetalovermoreofthesurfaceof thesusceptibleplate.Theuseof smallerweldsizesoflongerlengthordoublefilletsinplaceof fullpenetrationweldsreducesthevolumeof weldmetal and diffusestheshrinkagestrainsoveralargerareaofthesuscepti-bleplate.

o Othermethodsincludespeci-fyinglowyieldstrengthweldconsumablesandtheuseofbuttering.Thesemethodsare discussedin othersections.

6.1.3ReductionofComponentRestraint

Componentrestraintcansometimesbereducedbymodifyingthestructuralconfigurationorscantlings.Methodsofdecreasingthelevelofrestraintinclude:

● Avoidcomplex,multi-memberconnections.Thisprohibitionisnotalwayspracticalinstructuressuchasfixedandmobileoffshoredrillingunits.

o Minimizememberstiffnessby usingscantlingsofminimumthickness.

o Useflatplatesinsteadofcurvedmemberswhereverpossible.

o Donotusestiffeners,bracketsorgussetsnotspecificallyrequiredbythedesigncalculations.Scantlingsandweldingofallauxiliarystiffeningshouldbethesmallestrequiredtosuitthedesignloads.

6-5

-.

6.1.4SelectionofWeldMaterial

o In cruciformjointsstag-gerthememberson oppo-sitesidesofthesuscep-tibleplate.Thismethodisnotalwaysdesirableinhighlyloadedjoints.

s Ifpossible,use lowerstrengthmaterialforthemembercausingthestraininthethrough-ti.icknessdirection.

To accommodatemoreoftheweldshrinkagestrainintheweldmetselect,wherepossible,weldingconsumableswhichmatchtheylestrengthratherthanthetensilestrengthofthesusc@p\i~leb?plate.DetailcalculationsofthestressesacrosstheJointW1usuallyhavetobepreparedtojustifytheuseof lowertensistrengthconsumables.Low-hydrogenconsumablesarerecommendedordertoavoidembrittlementoftheheat-affectedzone.

alldse11lein

6-6

6.2 MaterialSelection

6.2.1GradeofSteel

Inquiriesmadetothemajorshipclassificationsocietiesindicatethatthemostsuccessfulandcost-effectivemethodof preventinglamellartearingistheuseofsteelswithimprovedthrough-thick-ness(Z-direction)propertiesatsusceptibleconnections.ImprovedZ-gradesteelshavebeenusedprimarilyintheconstructionoffixedandmobileoffshorestructures.Thelimiteduseto dateoftheZ-gradematerialsinshipbuildingreflectsthelimjtedoccur-renceoflamellartearingintheconstructionof conventionalshipsandthefactthatmanyofthesusceptibleconnections(suchasthegunwale)havebeeneasilycorrectedbymodifyingthejointconfigurationandweldingprocedures.However,BureauVeritashasreportedthattwoshipyardshaveputstrakesof specialZ-gradeplatesinthetanktopofLNGships[4].Theseplatesareusedatthecriticalintersectionsoftheheelsofcofferdamswhichformthesecondarycontainmentboundaryfortheliquefiedgas.

Specificationsforsteelsto be usedincriticalcomponentsofoffshorestructureshave,inthepast,specifiedmaximumsulfurcon-tent,minimumZ-directiontensilestrength,minimumZ-directionpercentageelongationandreductioninarea(RAz),andmaximumallowableinclusioncontent.However,highyieldandultimatetensile-strengthvaluesintheZ-directiondo notnecessarilyreducetheriskoflamellartearing.Thepercentageelongationmeasuredbyconventionaltensile-testproceduresalsodoesnotprovidea reliablemeasureoftearingsusceptibility,sinceitmayincludedeviationscausedby theformationof smallfissuresadjacenttononmetallicinclusions.Furthermore,thesmallgaugelengthofsamplestakenfromthinplatesmakesitverydifficultto measureelongationintheZ-directionwithanyacceptabledegreeofaccuracy.Whilesulfurcontentcangivean indicationofthesusceptibilityofaluminumdeoxidizedsteels,itisnotap-plicabletonon-aluminumtreatedsteelswheresilicatesarepri-marilyresponsibleforreducingtheZ-directionductility.Themeasureof inclusioncontentbytheprefabricationultrasonicinspectionofthesteelplateshasbyitselfbeeninadequateforassessingtheriskoflamellartearing.

Atpresent$thepercentagereductioninareaintheZ-direction(RAz)isthemostpracticalandaccuratemeasureofmaterialsus-ceptibility.ReportspublishedbytheWeldingInstituteshowgoodcorrelationbetweenmeasuredRAzandobservedincidenceoflamel-lartearing[5].RAzisbeingincreasinglyusedbythemajorshipclassificationsocietiestodefineandapproveZ-gradesteelsforuseinshipsandoffshorestructures.Theserequirementsdefine

6-7

uptothreeZ gradeplatecategorieswhichvaryaccordingtotheirminimumguaranteedmeanvalueandtheminimumindividualvalueofRAz. ThefollowingexamplefromBureauVeritas’rulesforoff-shoreplatformsistypical[6]:

MinimumGuaranteed MinimumIndividualGradeCategory RAz,MeanValue* RAzValue

Z15 15% 10%

Z25 25% 15%

Z35 35% 25%

* Meanobtainedfromthreetests.

Duetothecomplexinterrelationshipsbetweenthefactorswhichcancauseandcontrollamellartearing,theselectionofcandidatesitesandZ gradecategoryisusuallyleftto thediscretionofthedesignersubjectto theclassificationsociety’sapprovalduringdesignreview.

Whenselectingmaterialsforsusceptiblecomponentsinoffshorestructuresthefollowingrequirementsshouldbeobserved:

o Atjointsconnectingstructuralelementswhichareessentialtotheintegrityofthestructure,andwhicharesubjecttohighstressesinthethrough-thicknessdirection,specify .steelswithaminimumguaranteedmeanvalueRAzof25%andaminimumindividualRAzvalueof15%.ExamplesofsusceptibleconnectionsinmobileandfixedoffshorestructureswerenotedinSection4.1. It isnotedthatsomemarineclassifi-cationsocietiesandmajoroilcompaniesrequireminimummeanRAzvaluesof30%to35%forcriticalapplicationssuchasthenodeplatesinoffshoredrillingrigs.

s Foraluminumtreatedsteels}thesulfurcontentshouldnotexceed0.01%byweight.

● Prefabricationultrasonicinspectionofthesteelplatestobeusedinsusceptibleconnectionswillnotgivean adequateindicationofthematerialsresistanceor susceptibilitytolamellartearing.Whereultrasonicinspectionisto be usedto indicatethenumberandsizeoflaminationsorinclusions,theplateshouldbecontinuouslytestedalongthelinesof ameshgrid100mm square.Alledgesshouldbeinspectedforawidthequalto1-1/2timestheplatethicknessor 100mm,whicheverisgreater.

6-8

o Thefollowingfigure,publishedby theAustralianWeldingResearchAssociation[1],maybeusedas a generalguideinselectingminimumRAzvaluesformaterialto be usedinstructuralelementssusceptibleto lamellartearing.ThedesignermayvarytherequiredminimummeanRAzvaluewiththeimportanceofthecomponenttotheoverallintegrityofthestructureandthelevelofrestraintof theconnection.Forextiple,materialusedinthehighlyrestrainednodesconnectingcriticalmembersof anoffshoredrillingrigshouldhavea minimummeanRAzvalueof 25%. The riskcategoriesshownon thefigurearebasedon a qualitativeevaluationof therecommendationsof bothindustrialandmarinereferences(seeAppendixB)ratherthana statisticalforecastoftheprobabilityof a lamellartearoccurring.Similarly,thelevelsofjointrestraintcannotbe equatedwithan acceptedquantitativemeasureof restraint.Thefigureisa plicabletosteelswithaminimumyieldstressof

f40.8kg/mm (58,000PSI)or less.ThemeanRAz valuescorrespondto thoseobtainedusing6.4mm diametertestspecimens.AsnotedinAppendixBjthediameterof thetestspecimenissignificantwhenquotingRAzvalues.

MeanRAz(%)

30

25

20

15

10

5

0

NegligibleRisk

Low Medium High

JointRestraint

Withtheuseofelectroslagremeltingor calcium-argon-blowingsteelmanufacturingprocesses,essentiallyallgradesof hullsteelusedinshipsandoffshorestructurescanbepurchasedwithimprovedZ-directionproperties.Typicallytelectroslagremelting

6-9

— ---

willdoublethepriceperpoundofanABSAH32gradesteel.Thecostofmanufacturingthesamegradebythecalcium-argon-blowingprocessisconsiderablylessexpensive,addingonlyapproximately3 centstotheper.poundcostofthebasicqrade.However+cal-ciumprocessedsteelscanonlyobtaina min~mumRAzof25 percent,whilesteelsproducedbyESRcanobtainminimumRAzvaluesof30percentormore.SincetheimprovedZ-gradesteelsareonlyusedlocallyatsusceptiblejoints,thetotalextracostperstructurefortheimprovedmaterialsisoftenlessthanthecostofa singlerepairandtheassociatedconstructiondelays.

6.2.2ProductType

Wherepractical,replacingrolledsteelplateswithotherlesssusceptibletypesofsteelproducts,suchascastingsandfor9-ings,willdecreasetheriskoflamellartearing.

6.3 Fabrication

6.3.1LayoutandFormingofSusceptibleComponents

Whenfabricatingcomponentsoutofplatessusceptibleto lamellartearingthefollowingpracticescanbeusedtoreducetheriskoftearing:

.. PlatePosition- avoidmakingheavyattachmentweldsatthecenteroftheplatewidth,theextremeedgesof platewithas-rolledoruninspectedflamecutedges,andareasoftheplatewhereultrasonicinspectionindicatesheavyconcentra-tionsofinclusions.Cautionattheedgesofplatesiswar-rantedbythefactthatthematerialat an as-rollededgeusuallyhaslessthrough-thicknessductilitythantherestoftheplate.Theheateffectsofa cuttingtorchcanresultinthedecohesionofinclusionsinthesteelmatrix.

● DirectionofRolling- componentswithhighriskof lamellartearing,suchasheavyliftingeyesattachedtothickplates,shouldbeorientedwiththeweldaxisatrightanglesto theprimaryrollingdirectionofthesusceptibleplate.

● PlateForming- thickcold-formedplatesaremoresusceptibleto lamellartearingand,wherepractical,shouldnotbe usedincomponentsrequiringlargewelds.

6.3.2WeldingProcess

Withtheexceptionofelectroslagweldingmostconventionalweld-ingprocessesaresusceptibletolamellartearing.Thefrequencyofoccurrenceinprocesseswhichutilizehigherheatinputislessthanthosewhchhavea relativelylow-heatinput.Thisismostlikelyduetothedeeperpenetration,reducedhardnessintheHAZ,andthesmallerstraingradientsencounteredwithhigherheatin-put.Recommendedweldingprocessesinorderofdecreasingprefer-ence(orincreasingsusceptibilitytotearing)are:

6-10

-—

o Electroslag

● Submerged-arc

o Gasshieldedmetal-arc(MIGorC02)andflux-coredarcwelding

s Manualmetal-arc- lowhydrogenelectrodes

o Manualmetal-arc- non-lowhydrogenelectrodes

6,3.3JointPreparation,Fit-upandJigging

Otherthantherequirementsconformingto normalgoodpractice,jointpreparationstocontrollamellartearingshouldreflecttheimprovedjointdesignsdiscussedinSection6.1.Mainlythejointpreparationshouldprovidefora balancedweldwitha fusionboundarywhichisnotparalleltothesur~dceof thesusceptibleplate.Widegrooveangleswhichincreasedistortionandstrainshouldbeavoidedandthedepthoftheweldshouldbe limitedtothatnecessaryfortherequiredweldthroatthickness.Filletweldsorpartialpenetrationweldsshouldbegivenpreferenceoverfullpenetrationwelds.

J!lksoft0.8nun

InrJSteel

to1.6 Wire

Tightfit-upandheavyjigswhichinhibitlateralweldshrinkageshouldbe avoided.Theuseofanundressedflame-cutsurfaceor soft-steelwirespacerswillpermitcon-tractionof theweldmetalwithoutproducinghighcon-centrationsofstrain.Copperwire should not be usedbecauseitmaycontaminatetheweldmetal.Larqeqapswhichincreasethevolum~ofweldmetalshouldalsobeavoided.

6.3.4WeldingConditions

6.3.4.1Preheat

AsnotedinSection3.5,theuseofpreheatingtocontrollamellartearingcanbebothbeneficialandharmful.However,wheresus-ceptiblejointsarepreheatedeithertocontrollamellartearingortosatisfyotherweldingrequirements,suchasthepreventionofhydrogencracking,thefollowingconsiderationsshouldbe ob-served:

6-11

, Avoidthecreationofadditionalorconcentratedcontractionstrainsbyheatingallcomponentsaroundthejointforanequaldistanceandtoapproximatelythesametemperature.

● A preheattemperatureofapproximately100”Cor greaterisconsideredthemosteffective.

6.3.4.2DepositionRate

Weldingprocesseswithhighweld-metaldepositionratesarepre-ferred.Thehigherdepositionratesdecreasethenumberof weldrunsnecessarytocompletetheweldwitha correspondingdecreaseinthenumberofstraincycles.Sincedepositionratesarepri-marilya functionoftheheatinputof theweldingprocess,thelistandrankingofpreferredweldingprocessesarethesameaspresent~dinSection6.3.2.

6.3.4.3InterpassTemperature

Maintainingproperinterpasstemperatureisnecessaryto preventexcessivecoolingofpreviouslydepositedweldmetalbetweenruns.Repeatedheatingandcooli”ngcyclesmayunnecessarilyincreasethetotalshrinkagestrains.Recommendedpracticesinclude:

# Donotpermittheinterpasstemperaturetogobelowthepre-heattemperatureuntilallweldingonthejointiscompleted.

o ASinnormalweldingprocedures,avoidveryhighinterpasstemperatureswhichmayunfavorablyalterthepropertiesofthesteel.

● Allowcompletedjointstocoolslowlyandevenlyinordertopreventexcessivethermalstrains.

6.3.4.4WeldSizeandShape

Todecreasetheriskoflamellartearinginsusceptiblejointsthefollowingconsiderationsofweldsizeandshapeshouldhe imple-mented:

. Usetheminimumweldsizecompatiblewiththedesignloadsandstressdistributionsacrossthejoint.Oftenexcessiveweldsizesarechosenarbitrarilywhenthestrengthrequire-mentsacrossthejointareunknown.

● Weldswithdeeppenetrationandunevenshapepermitthedif-fusionofthecontractionstrainsintomoreofthesuscepti-blematerialandavoidconcentrations.

o Increasingthelengthofthelegonthebaseplatewillalsodistributethestrainsovermoreofthebasemetal.

6-12

6.3.5WeldingTechniques

6.3.5.1RunSequence

Propersequencingofweldrunswillhelptoreducethelevelandconcentrationoftheweldshrinkagestrains.Applicablemethodsinclude:

o Minimizethenumberof weldrunsinorderto reducethenumberofheatcycles.

● Deposita layerofweldmetalonthesurfaceofthesuscepti-bleplatepriortomakingconnectingrunsbetweenthecompon-ents.Theseinitialrunsshouldbedonein accordancewiththerecommendedproceduresforbutteringandinsitubutter-———.-inginSections6.3.5.2and6.3.5.3,respectively.

.—-——

0 StrainconcentrationsinsymmetricallyconfiguredTjointscanbe reducedbydepositingweldrunsinanalternating,balancedsequence.

6.3.5.2Buttering

Butteringconsistsofdepositingoneormorelayersof lowyieldstrengthweldmetaldirectlyonthesurfaceor in a gouged-outareaof thesusceptibleplate.Thepurposeof the butteredlayer(s)istoaccommodatetheweldshrinkagestrainsbyspreadingthemmoreuniformlythroughthelowerstrengthweldmetal.Butteringalsodisplacestheheat-affectedzoneawayfrom thesusceptibleparentmetal.In ge.neral~butteringhasbeenverysuccessfulinpreventinglamellartearinginnewweldmentsandintherepairofexistingtears.Pointstoconsiderwhenusingthebutteringtechniqueinclude:

6-13

9

0 The butteredlayer(s)shouldbe5 to10mmthickandextend15 to 25 mmbeyondeachweldtoe.

.——..—

0

Whenthebutteredlayeristobeappliedin a groove,thegrooveshouldbe ap-proximately5mm deepandextendunderthe fullwidthofthebuttering.

Wherebutteringisto beusedin placeof steelwithimprovedthrough-thicknessproperties,therelativecostsshouldbethoroughlyevaluatedpriortofabrication.

Theyieldstrengthof theweldmetalshouldbe lessthanthestrengthof thebaseplate.

Submergedarcweldingwithlow-hydrogenconsumablesshouldbe usedwheneverpossibleto obtaingoodpenetrationofthebutter-inglayer(s)andto avoidthebuildupofhydrogenintheweld. The levelofheatinputshouldalsobecarefullyregulated.

6-14

6.3.5.3InSituButtering

Thistechniqueisa modifica-tion to the run sequenceratherthanan additionalpreweldpreparationas isconventionalbuttering.Ininsitubutteringthefirst—. ..weldrunsaredepositedonthebaseplatepriorto com-pletingth,?connectingruns.Thismethcl.ihasprovensuc-cessfulindiffusingtheweldshrinkag~strainsata negli-gibleincreaseinfabricationcost.

6.3.5.4Peening

Peening,thecontrolledworkingof theweldbeadsbymeansoflightimpactblowstotheweldsurfacetoreduceresidualtensilestress,hasnotprovensuccessfulincontrollinglamellartearing.Excessivepeeningcancauselossoftoughnessandcrackingintheweldmetal.Althoughnota viablemethodofreducingtheriskoflamell,”tearing,peeningingeneraldoesnotincreasetheriskoftearinginsusceptiblematerial.Ifemployed,thefirstandclosingrunsshouldnotbe peened.Onereportindicatesthat~~~ningofthelastweldrunmaycontributeto IamellartearingLIJ.

6.3.5.5WeldingandFabricationSequence

Therestraintlevelofa weldedjointissequenceinwhichtheweldsinthejointricationseauenceofad.iacentcom~onents.

greatlyinfluencedbythearemadeandby thefab-The

shouldbeconsideredwhknpreparingfabricationules:

● In multi-jointcomponents,themoresuscept”bemadefirst.

‘Ollow’andwe”

blejo

ng factorsdingsched-

ntsshould

@ Completel!lweldsubassemblies~riorto finalassemblvtolimitthe-numberofcriticaljoints.

.

● Minimizestrainaccumulationbyweldingfromareaofmaximumrestrainttofreeedgesorotherareasofminimumrestraint.

● Forindividualjoints,sequencetheweldingsothatthelevelofrestraintwillbeminimizedforthelargestwelds.

o Minimizethesizeandnumberoftackweldsusedto holdcomponentstogetherduringwelding.

6-15

— —. .

● To reducerestraintatcriticalareas,suchascorners,leavea portionoftheconnectionbetweenlessrestrainedcomponentsunweldeduntilthecriti-calweldsarecompleted,asindicatedby ‘D’.

Dapprox.150mm

6.3.5.6IntermediateStressRelief

Theuseofintermediateheattreatmenttoreduce”residualstresseshasnotbeenparticularlysuccessfulincontrollinglamellartear-ing.Largememberswhichcannotbe placedin a furnacerequirelocalizedheatingwhichcanincreasethecontractionstrainsduringcooling.Heattreatmentmaycauseadditionaldecohesionofinclusionsinsusceptiblematerial,therebyincreasingtheindica-tionsoflamellartearsduringsubsequentultrasonicinspection.

6-16

7. DETECTIONANDREPAIROFLAMELLARTEARINGAFTERWELDING

7.1 WhenIsNon-DestructiveTestingforLamellarTearingRecommended?

Normalweldinspectionrequirementsandproceduresareadequatewheretheriskoflamel.lar..tearingissmall.However,wheretheriskof tearingissignificantbecauseof thecombinationofmaterialproperties,weldingproceduresandjointconfiguration,additionaltestmethodsforthedetectionoflamellartearsshouldbeemployed.Formembersandjointswhicharecriticalto theoverallintegrityofthestructure,suchasthenodejointsanddecktolegconnectionsofoffshorejackettypestructures,sup-plementaltestingisrecommended.

7.2 WhichNon-DestructiveTestingMethodsAreApplicable?

Standardnon-destructivetestingmethodssuchasvisualinspec-tion,dyepenetrationandmagneticparticleinspectionaresatis-factoryforsurfacecrackingbutnotforsub-surfacetears.Radi-ographyisgenerallynotpracticalforthedetectionof sub-sur-facetearssincetheinclusionsintheplatecanmaskdefectsanditisdifficult,ifnotimpossible,todirectradiationalongthetearaxis.Ofalltheconventionalnon-destructivetestingmeth-ods,ultrasonictestingisthemostpracticalandwidelyusedtech-niquefordetectinglamellartears.

7.3 UltrasonicTesting(UT)OfWeldedJoints

Thepulse-echoultrasonictestingtechniqueisbasedon thein-terpretationofreflectedultrasonicwavesfromthefracturesur-faceto detectlamellartears.Theinstrumentprobeisbothtransmitterandreceiver.Theultrasonicbeamisreflectedeitherbythefaceplateoppositetheoneonwhichtheprobeis applied(bottomecho),orpartlyatleastbyanareaof lamellartearingoranyotherdefectofthemetal(flawecho).WhileUTmethodsnormallylocateplateandwelddefectswhentheplatesurfacesareflatandreasonablyfreefromloosematerial,it isoftendiffi-culttodistinguishtruelamellartearsfrominclusionbandsandotherformsofcracking.Thematerialsthataremostsusceptibleto lamellartearing,suchasthickplateswithhighconcentrationsofnonmetallicinclusions,containthetypeof defectswhchcanattenuatethesignalsandmakeinterpretationdifficult.Misin-terpretedultrasonicindicatorscanoftenleadtounnecessaryandcostlyrepairs.

i-

CompreslionWave

Bothcompressionwave andshear(orangle)probeUTmethodsarecapableof accu-ratelylocatinglamellartearing.However,theuse-fulnessof compressionwavetechniquesislimitedtoT orcornerjoints.

7-1

—

ShearorAngleProbe

Probefrequenciesof 2 MHzareconsideredsuitablefortherapidlocationof truetears.Sufficientresolutiontoobtaingoodidentificationofthecharacteristicsteppedsurfaceof thetearcan beobtainedbytheuseof4 to5MHzprobes.Theuseofhigh-erprobefrequenciestogetherwithhighequipmentgainset-tingsarereportedto in-creasethe likelihoodoferroneousindicationsoflam-ellartears.

DetailsoftechniqueandequipmentfortheultrasonicdetectionoflamellartearingareessentiallythesameasforthenominalUTinspectionofwelds.Specificsmaybe obtainedintheAmericanBureauofShippingRulesforNon-destructiveInspectionof HullWeldsorASTME164-StandardforUltrasonicContactInspectionofWeldments.

POINTSTONOTE

● Ultrasonictestingshouldbespecifiedforhighlyrestrainedweldedconnections,criticaltotheintegrityof thestruc-ture,wheretheriskoflamellartearingissignificant.

s Thereliabilityoftheultrasonictestingmethoddependstoagreatextentontheabilityandexperienceof theoperator.Personnelresponsibleforconductingultrasonictestsshouldbefamiliarwiththeequipmentbeingusedandbe properlyqualifiedbytrainingandexperiencetoperformthenecessarycalibrations,andtointerpretandevaluateindicationsinaccordancewiththetermsofthespecification.InadditiontobeingqualifiedinaccordancewiththerequirementsoftheAmericanSocietyofNon-destructiveTestingPublicationTC-lA- SupplementC,UltrasonicTestingMethodsorotherrecog-nizedagencies,thepersonnelshouldpreferablyhaveexperi-encein,orbeabletodemonstrateabilitytoidentify,lam-ellartears.

● Ultrasonictestingshouldbeperformedwhenallweldingonthejointiscompletedandmaximumrestraintisreached.Sincelamellartearinghasbeenreportedto occurupto 36hoursafterthecompletionofallweldingandthecoolingofthecomponent,finalultrasonicinspectionofcriticaljointsshouldbeperformednosoonerthan36hoursafterweldingon .thejointiscompleted.

7-z

● Allcriticalweldedjoints,suchasthenodejointsanddeckto legconnectionsofoffshorestructures,shouldbe ultra-sonicallyinspected.

● Acceptancestandardsforlamellartearingshouldbe estab-lishedsothatclustersofinclusionsanddensemicrostruc-turalbandswhichappearasdefectindicationsdonotconsti-tuterejectabledefects.Sincetheremovalandrepairofminornon-criticaltearsmaydomoreharmthangood,theacceptancecriteriashouldconsiderthefunctionalrequire-mentsof thecomponentorjointaswellasthepracticallevelofworkmanshipwhichexperienceindicatescanbe ob-tainedinweldmentsofa giventype.Atpresent,theweldingacceptancecriteriaofmarineclassificationsocietiesandnationalcodesandspecificationsdo notcontainspecificacceptancestandardsforlamellartearing.

@ Inorderto distinguishlamellartearsfrompre-existingdefects(largeinclusions,laminations,etc.),the basematerialintheareaoftheweldshouldbe ultrasonicallyinspectedpriortofabrication.Theseinspectionsshouldbemethodicallyperformedandrecordedusinga gridsystemforlocatingcheckpoints.

s Ultrasonicindicationsoflamellartearingexhibita charac-teristicmultiplepeaksignalanda rapidchangeindepthastheprobeismoved.Thesecharacteristicshelptodifferen-tiatelamellartearsfromothercracks,laminationsor back-wallreflection.

7.4 RepairofLamellarTears

Therepairoflamellartearscanbedifficult,timeconsumingandcostly;and,inthecaseof highlyrestrainedconnectionstherepair,canbemoredetrimentalthantheoriginalweld. Thein-creasedriskoflamellartearingduringrepairispartiallyduetothegreateroverallrestraintof thecompletedstructure.Themechanicalandthermalstrainsinducedbytherepairweldingcancausetearingtooccurata greaterdepthbelowtheoriginalweldfusionline.Thebasicmethodsofrepairare:

● gougingoutofthetearandreplacementwithweldmetal

● cuttingoutthedefectivematerialandreplacingwithmaterialwithimprovedthrough-thicknessproperties.Thisprocedureisoftenaccompaniedbymodificationstotheweld-ingproceduresorjointdetailsinordertoavoidthecondi-tionswhichprecipitatedtheoriginaltear.

o providingadditionalstructuralmemberstocarrytheantici-patedserviceloadsacrossthejoint.

7-3

Priortoselectingrepairprocedure,itshouldbe verifiedthatthediscontinuityisa lamellartear. Thenumber,locationandextentofothertears,ifany,shouldalsobedetermined.If thecrackisinfacta lamellartearandexceedsthespecifiedaccept-ancestandards,allthefactorswhichcancontributetothedevel-opmentoflamellartears,namelymaterialsusceptibility,jointconfigurationandweldingprocedures,shouldbereviewed.Merelygougingoutthetearandreweldingusingtheoriginaljointgeome-tryandweldingproceduresunderconditionsofpossiblyevenhigh-errestraint,willprobablyresultinnewlamellartears.Forthisreason,itis.oftenmoreeconomicaltoreplacea componentorjointratherthantorepairit. Alternately,additionalsupportmemberscanbeprovidedto reducethejoint,thusreducingthecriticalityof

Wheregougingandreweldingisjudgedproceduresshouldbeused:

serviceloadsacross”thethejoint.

acceptable)thefollowing

● Removedamag~dmaterialusingflamegouging,arc-airgougingorgrinding.TheAustralianWeldingResearchAssociationreportsthatflamegougingisslightlypreferredto arc-airgougingduetothelessintensethermalgradientsandlowerthermalinducedstressesofflamegouging[1].On theotherhand,a fabricatorwithLTrepairexperiencereportsthatgasgougingdevelopstoomuchheatintheweldcausingthelamellarteartopropagate[7].Herecommendsusingonlyarc-airgougingwithnopreheat.Grindingisslowandimpracti-cal.

0 FlameGouging- thefirstpassofthegougingtorchshouldcutacrosstheendoftheplaneoftearingatsuchan attitudeas tominimizethetendencyofthe tearto openup aswellas “toreleaseanytensilestressacrossthetear. The baseof thegouge should be wellrounded.Subsequentpas-sesshouldremove2 to 3mmof thematerialbelow

theoriginaltearand3 to 4 mm beyondtheendsof thetear.Deeperandwidergougingwillincreasetheamountof reweldingwitha correspondingincreaseintheriskofnewtearing.In somecases,completereleaseordisassemblyoftheweldedjointmayberequired.

7-4

o Air-ArcGouging- thefirstarc-airgougeshouldbemadeadjacentto thetearandextend3 to4mm beyondtheendofthetear.Addi-tionalpassesshouldbemadeparallelto theini-tialgougeuntilmaterial2to3mm belowtheoriginaltearhasbeenremoved.

@

@

●

NOTE

Regardlessofthegougingmethod,allfinalsurfacesshouldbelightlygroundandinspectedusingmagneticparticleor dyepenetrationtestingmethodspriortowelding.

Butteringlayersof lowyieldstrengthweldmetalaregenerallyconsideredessentialpriortomakingconnectingwelds.TheweldingproceduresgiveninSection6.3shouldbeemployedinordertoreducestrainsinthethrough-thicknessdirection.It isrecommendedthatthe minimumpreheattemperaturebemaintainedfor8 hoursafterallweldingonthejointiscomplete.

Therepairedjointshouldbethoroughlyre-examinedinac-cordancewiththerequirementsforultrasonictestinggiveninSection7.3.

-

Duringtherepairprocess,theactuallocationofthelamellartearshouldbenotedandcomparedwiththatindicatedby theultrasonictestinordertovalidatethetestingprocedures.

7-5

~

i-

8. TESTSFORDETERMININGTHESUSCEPTIBILITYOFSTEELPLATESTOLAMELLARTEARING

Duringthelastfifteenyears,manytestshavebeendevelopedfordeter-miningthesusceptibilityofdifferentgradesof steelplateto lamellartearing.Withvaryingsuccess,thesetestsattempttoprovidereproducibleresultswhichcorrelatewellwithknowncasesof lamellartearing.Eachtestincorporatesdifferentcombinationsoftheactualjointdesign.,compon-entandjointrestraint,weldingprocedures,andmaterialproperties.Thedifficultyindevisinga single,universallyacceptabletestprocedurereflectsthefactthat,whileitispracticaltorepresenttosomedegreetheactualgeometryandfabricationprocedures,thetestmaterialmaynotberepresentativeofthematerialusedintheproductionjoint.Thethrough-thicknesspropertiesof individualplatesarevariablebecauseof theirregulardistributionofnonmetallicinclusionsintheplate.Themoreimportanttestsarelistedbelowbytype:

● NondestructiveTests(withoutwelding)

(i) Ultrasonicinspectionofsusceptiblesteelplatespriortofabrication[8] - oflimitedusefulnessindeterminingthesusceptibilityofsteelplatestolamellartearing;usefulfordistinguishinglamellartearsdetectedduringpost-weldingUTinspectionfrompre-existingdefects.

s DestructiveTestsWithoutWelding

(i)

(ii)

(iii)

(iv)

(v)

Through-thicknesstensiletest- practicaltest;RAzgivesgoodcorrelationwithknownincidenceoftearing.

Slice-bendtest[9]- groundsurfaceisexaminedforthesizeandlocationofcracksafterthespecimenissubjectedto increasingsurfacestrains;practicaltestwhichpro-ducesrealistictears.

Specialnotchedtensiletest[10]- comparestheshearfractureloadsonandacrossthelaminarplane;forprelim-inaryscreeningofsusceptiblematerial.

CharpyV-notchimpacttest[11]- limitedusefulness;canbeusedonlyforplates55mmthickorgreater.

Microscopiccountofnonmetallicinclusions- usesstandardmetallurgicalexaminationproceduresto determinenumber,size,shapeanddistributionofnonmetallicinclusions;im-practicalforproductiontest;moresuitableforresearch.

8-1

● DestructiveTestsWithWelding

(i)

(ii)

(iii)

(iv)

(v)

(vi)

WeldingInstitutewindowtest[12,13]- specimenof thesusceptiblebasematerialisinsertedthrougha rectangularholeorwindowina restrainingplateandweldedto formacruciformjoint;observedtearingcanoftenbe inducedbyrootcrackingnotlamellartearing;restraintlevelvarieswithjigandtestplatethickness;notpracticalforpro-ductionuse.

Cranfieldtest[14]- a stemplateisbeveledto45 or 60degreesandmultirunweldedto thesteelsampleto betested;severetestconditionsareonlycapableof identi-fyingmaterialswitha highresistanceto tearing;mixedcorrelationwithcasehistories.

Short-transversenotchedbendtest[15]- complexandex-pensivetestmoresuitabletoresearch.

Lehighrestrainttest[2]- suitableforquantitativelymeasuringlamellartearingsusceptibilityunderlaboratoryconditions.

H-typerestrainttest[16]- researchorientedtest.

Testsofprototypeweldedjoint- difficultto duplicatetheexactrestraintlevelsandweldingconditionpresentduringactualproduction;doesnottakeintoaccountthevariabilityofpropertiesinthethrough-thicknessdirec-tion;notpracticalforproductiontesting.

Wi”ththeincreasinguseofRAzbythemajorshipclassificationsocie-tiestodefineandapproveZ-gradesteelsforthe.useinshipsandoffshorestructures)RAz,asmeasuredbythrough-thicknesstensiletest,isquicklybecomingthestandardtestfordeterminingthesusceptibilityof steelplatesusedinthemarineindustry.Todate,astandardRAztestprocedurehasnotbeenadoptedbythedifferentclassificationsocieties.Whilesimi-larintheory,allofthecurrentlypublishedRAztestproceduresdifferslightlyintherequireddimensionsandconfigurationoftensile-testspeci-mens.ofthelowing

Fabricatorsandsteelmakershouldfollowthespecificrequirementscognizantclassificationsocietyruleswhilekeepinginmindthefol-additionalconsiderations:

@ TheRAzacceptancelimitsshowninSection6.2areappropriateformaterialswithyieldstrengthslessthan40.8kg/mm2(58,000psi).

● Becauseof thesmallcross-sectionalareaofmaterialbeingtested,theuseofsixspecimenswillgivea statisticallybettersamplingthanthethreesamplesrequiredbysomerules.

o Theresultscanbegreatlyinfluencedbysinglelargeinclusionsorclusters.

8-2

o RAzvaluesarestronglyinfluencedby thediam.qterof thetest ,specimen.Smallerdiameterspecimensareinfluencedby thesizeandpositionoflargeinclusionswhichdecreaseminimumvalueswhileincreasingmaximumvalues.Largerdiameterspecimenshavemorelateralrestraintwhichlowersthemeanvaluesandreducesscatter.Accordingly,caremustbeexercisedincomparingRAzvaluesobtainedfromdifferentsourcesortestprocedures.

.

8-3

9. REFERENCES

1. AustralianWeldingResearchAssociation,“Controlof LamellarTearing”,AWRATechnlcalNote6,April1976.

2. Oates,R.P.,andStout,R.D.,“AQuantitativeWeldabilityTestforSusceptibilitytoLamellarTearing”,SupplementtoWeldingJournal,November1973.

3. McEnerney,J.W., “AssessmentofLamellarTearing”,Oak RidgeNationalLaboratoryReportORNL/NUREG/TM-171,OakRidge,Tennesse@,March1978.

4. BureauVeritas,“LamellarTearing(Non-confidentialTechnicalNoteofGeneralInformation)”,August1974.

5. Farrar,J.C.M.,“TheProblemofLamellarTearing.TheRelationshipBetweenShortTransverse% RAValuesandtheIncidenceof LamellarTearing”,inPhaseIVof“InvestigationsintoLamellarTearing- ACompendiumofReportsfroma SponsoredResearchProgrammed”,TheWeldingInstitute,Cambridge,England,March1975.

6. BureauVeritas,“RulesandRegulationsfortheConstructionandClassificationofOffshorePlatforms”,1975.

7. Smith,R.K.,“FabricationTechniquestoControlLamellarTearing”,AustralianWeldingResearchAssociation,“Symposiumon ControlofLamellarTearing”,April8,1976.

8. AmericanSocietyforTestingandMaterials,“StandardSpecificationforStraight-BeamUltrasonicExaminationofPlainandCladSteelPlatesforSpecialApplications”,ASTMA578.

9. Drury,M.L.,andJubb,J.E.M.,“LamellarTearingandtheSliceBendTest”,WeldingJournal,WeldingResearchSupplement,February1973.

10. Kanazawa,S.,Yamato,K.,Takeshi,Y.,etal,“OntheAssessmentofLamellarTearingSusceptibilityofSteelPlate”,IIWDocIX-840-73.

11. AmericanSocietyforTestingandMaterials,“StandardMethodsforNotchedBarImpactTestingofMetallicMaterials”,ASTME23.

12. NipponSteelCorporation,EngineeringDataBrochureNo.QT21248.9,“NSC’sSteelPlatesforMarineStructures”,Section5, LamellarTearResistantSteels,1974.

13. Farrar,J.C.M.,andDolby,R.E.,“AnInvestigationintoLamellarTearing”,MetalConstructionandBritishWeldingJournal,February1969.

9-1

14. Elliott,D.N.,“LamellarTearinginMulti-PassFilletJoints”,WeldingJournal,September1969.

15. Farrar,J.C.M.,“InclusionsandSusceptibilitytoLamellarTearingofWeldedStructuralSteels”,SupplementtoWeldingJournal,August1974.

16. Nishio,Y.,Yamamota,Y.,“Kajimota,K.,andHirozane,T.,“OnLamellarTearinginMultirunFilletWelds”,MitsubishiHeavyIndus-tries,Ltd.TechnicalReview,Vol.9,No.3,October1972.

9-2

10. BIBLIOGRAPHY

AmericanInstituteofSteelConstruction,“CommentaryonHighlyRestrainedWeldedConnections”,AISCEngineeringJournal,ThirdQuater,1973.

Araki,M.,Nagao,T.,andNarasaua,H.,“CrackinginMultirunFilletWelds”,Nippon-KokanTechnicalReport- Overseas,June1974.

Arita,Yukio,Kajimoto,Katsuya(MitsubishiHeavyIndustries,Ltd.),andOhba,Kenui(NipponSteelCo.,Ltd.),“TheStudyof LamellarTearinginOffshoreStructures”,OffshoreTechnologyConference,Houston,Texas,May2,1972.

Baker,T.J., Gove,K.B.,andCharles,J.A., “InclusionDeformationandToughnessAnisotropyinHotRolledSteels”,PreprintsofaMetalsSocietyMeetinq:DirectionalityofPro~ertiesinWrouahtProducts.27-28thNov.1974,vol. 1.

Banks,E.E.,“AssessmentofSteelSusceptibilitytoLamellarTearing”,ItralianWeldingResearchAssociation,“Symposiumon Controlof Lame”Tearing”,April8,1976.

Bernard,G.,Grumbach,M.,andMoliexe,F.,“InclusionsinSteelPlatesMechanicalAnisotropy”,PreprintsofaMetalsSocietyMeeting:Direct’alityofPropertiesInWroughtProducts,27-28thNov.1974,vol.2.

us-1ar

andon-

Chapman,J.A., Clark,A.,andKirkwood,P.R.,“SteelsforNorthSeaStruc-tures”,presentedatWeldinginOffshoreStructures,Newcastle,UK,1974.

Charleux,J.,“Metallurgical,WeldingandInspectionProblemsRaisedby theConstructionofSteelOff-ShorePlatforms”,TechnicalBulletinof theBureauVeritas,February,1976.

Croll,J.E., “MaterialFactorsAffectingLamellarTearing”,AustralianWeld-ingResearchAssociation,“Symposiumon Controlof LamellarTearing”,April8,1976.

Dolby,R.E.,“TheWeldabilityof LowCarbonStructuralSteels”,WeldingInstituteResourceBulletin,18(8):pp.209-16,August,1977.

Farrar,J.C.M.,andDolby,R.E.,“LamellarTearinginWeldedSteelFabrica-tion”,TheWeldingInstitute,PublicationNo.SBN85300068,1972.

Farrar,J.C.M.,Dolby,R.E.,andBaker,R.G.,“LamellarTearinginWeldedStructuralSteels”,WeldingJournal,July1969,pp274s-282s.

Frost-Drury,M.L.,“QualityAssuranceandSpecificationsforLamellarTear-ing”,AustralianWeldingResearchAssociation,“Symposiumon ControlofLamellarTearing”,April8,1976.

1o-1

Ganesh,S.,andStout,R.D.,“EffectofWeldingVariablesonLamellarTear-ingSusceptibilityinLehighTest”,WeldingJournal,March1977,pp.39:78s-87s.

Hancock,J.,Cowling,M.J.andMackenzie,H.C.,“TheEffectsofDirectional-ityontheMechanismsofHoleGrowthandDuctileFailureinThreeHighStrengthSteels”,Preprintsofa MetalsSocietyMeeting:DirectionalityofPropertiesinWroughtProducts,27-28thNov.1974,Vol.1.

Jubb,J.E.M.,“LamellarTearing”,WeldingResearchCouncil,BulletinNo.168,December1971.

Lay,M.G.,“TheStructuralSignificanceofLamellarTearing”,AustralianWeldingResearchAssociation,“SymposiumonControlofLamellarTearing”,April8,1976.

Little,H.H.,McCombe,A.A.F.andRatnapuli,R.C.,“TheEffectof SlabtoPlateDeformationRatioonPropertyDirectionalityof E.S.R.andContin-uouslyCastSteels”,Preprintsofa MetalsSocietyMeeting:DirectionalityofPropertiesinWroughtProducts,27-28thNov.1974,Vol.1.

Morrison,W.B.,“TheInfluenceofTestingDirectionontheMechanicalProp-ertiesofWroughtSteel”,Preprintsofa MetalsSocietyMeeting:Direc-tionalityofPropertiesinWroughtProducts,27-28thNov.1974,Vol.2.

Nakao,N.,andOhsuzu,H.,“PropertiesofSteelPlatesinThicknessDirec-tion”,NipponKokanTechnicalReport-Overseas,Decembei’1972.

Peterson,MarvinL. (ContinentalOilCompany),“SteelSelectionforOffshoreStructures”,JournalofPetroleumTechnology,March1975,pp.274-282.

Pope,C.W.,andCard,K.J., “Detectionof LamellarTearingby UltrasonicTesting”,AustralianWeldingResearchAssociation,“Symposiumon ControlofLamellarTearing”,April8,1976.

Porter,L.F.,“LamellarTearinginPlateSteels(ALiteratureSurvey)”,TechnicalReport1O-F-OO2(O18-5),ResearchLaboratory,UnitedStatesSteelAugust1975.

Rodgerson,P.,Rowntree,G.,andSchofield,R.,“Aspectspf [email protected]”,Preprintsofa MetalsSocietyMeeting:DlrectlonalltyofPropertiesinWroughtProducts,27-28thNOV.1974,VO1.2.

Santini,W.,Repetto,G.,andPosini,G., “ColdCrackingandLamellarTear-inginWeldedCarbon-ManganeseStructuralSteels.DiscussionoftheProb-lemsandPossibleWaysforPreventionwithParticularRegardto ShipBuildingApplications”,TransactionsJapanWeldingSociety,Vol.2,No.2,April1951(WeldingResearchAbroad,October1972).

.,

.

Scott,R.,“DirectionalityofMechanicalPropertiesinHotRolledSteelPlates”,Preprintsofa MetalsSocietyMeeting:DirectionalityofProper-tiesinWroughtProducts,27-28thNov. 1974,Vol.2.

10-2

.—

Takeshi,Y.(NipponSteelCorporation),“LamellarTearingandMarineStruc-tures”,WeldingandMetalFabrication,December1975,pp740-746.

Thomson,A.D.E.,Christopher,P.R.,andBird,J.,“ShortTransverseProper-tiesofCertainHighStrengthSteels”,J.Eng.Ind.,TransactionsASME,90.627-735(Nov.1968).

Wilson,A.D.,“TheEffectofAdvancedSteelmakingTechniquesontheInclu-sionsandMechanicalPropertiesofPlateSteel”,presentedatSymposiumonToughnessCharacterizationandSpecificationsforHSLAandStructuralSteels,AIMEAnnualMeeting,March6-10,1977.

Wilson,A.D.,“TheInfluenceofThicknessandRollingRatioontheInclusionBehaviorinPlateSteels”,presentedattheASM1977rflaterialsConference,Chicago,Illinois,October25-27,1977.

Wilson,W.G.,“MinimizingLamellarTearingbyImprovingZ-DirectionDuci~i-ty”,WeldingJournal,Vol.12,No.1, 1975,pp.274-282.

Weld,-GunnarandKristoffersen,Thorbjorn(DetNorskeVeritas),“DevelopmentofMethodforMeasuringSusceptibilityofSteelPlateto LamellarTear-ing”,OffshoreTechnologyConference,Houston,Texas,April29-May2,1973

-.

Note:WeldingResearchCouncilBulletinNo.232“ThroughThicknessProper-tiesandLamellarTearing(ABibliography)”,by D.H.SkinnerandM.Toyamalistsover400papersrelatingto through-thicknessor Z-directionpropertiesandlamellartearingpublishedpriortoApril1977.

10-3

APPENDIXA

MECHANISMOFLAMELLARTEARING

ReprintedwiththepermissionoftheAustralianWeldingResearchAssociationfromAppendixA ofAWRATechnicalNote6,

ReferencesforAppendixA arelistedattheendoftheAppendix.

A-1 BASIS

Lamellartearingoccurswhentensilestressesandstrainsappliedtothematerialinthethrouqh-thickness(Z)directionofthesteelexceedtheabilityofthesteel‘towithstandthes~stressesandstrains,andtherearesufficientinclusionspresenttoresultinthetypicalLTfracture.

Alternativelystated,lamellartearingoccurswhenthesteelpropertiesareinadequatetowithstandthestressesandstrainsintheZ-direction.

A-2 STEELPROPERTIES

.1 Anisotropy.““Aninherentfeatureofwroughtsteelproductsisthedif-ferenceswhichcanoccurinpropertiesindifferentdirections,i.e.thesteelisanisotropic;althoughformostapplicationsitcanbe treatedas iso-tropic.Thisanisotropyisbroughtaboutbytherollingor forgingopera-tionswhichmainlyflatteninclusionsandmaymodifythemetallurgicalstructureofthesteel.

.2 MechanicalProperties.MechanicalpropertiesintheZ-directionusuallyarereducedtoa varyingdegree.Thetensilestrengthandductility(asmeasuredbyreductionofareaor% elongation)aremostaffected.Inexceptionalcasestensilestrengthmaybereducedby30%andductilitytovirtuallyzero.Yieldorproofstressishardlyaffectedexceptwhenin-clusionsaregross.

.3 Cause.TheZ-directionpropertiesarereducedasa resultof:

(a) increaseinmaximumandaveragelengthandwidthofinclusions.

(b) increasednumberofinclusionsandcloserspacing.

(c) increasedalignmentofinclusionsonplanes.

Thiseffecthasbeenestablishedby theoreticalworkusingfracturemechanicsandprovenbytesting.

Thesepropertiesmayalsobereducedby:

(d) hydrogenfromweldingoperationsorparentmetal;

andasmorerecentlyreported(RefAl)by:

(e) thetemperatureandstresscyclesleadingto strainageingorsimilareffects;and

(f) priorcoldworkleadingtoexhaustionof ductilityandpossiblestrainageingeffectsinthematrixbetweeninclusions.

A-2

.’,

.

A-3 THROUGH-THICKNESSTENSILESTRESSESANDSTRAINS

.1 Cause.Thesestressesandstrainsresultfrom:

(a) weldandparentmetalcontractiononcoolingafterweld”

(b) restraintofthejointcomponents,ieexternalrescontraction,

ng,

stanceto

(c) otherthermalorloadinfluences,eg.unevenpreheat;andfrom

(d) thePoissoneffectdueto highlongitudinalstressesalongtheweldresultinginhightriaxialstressing.

.2 LocationofMechanicalStrains.TensilestressesandstrainsvaryacrossandalongtheweldedJoint,andmaximumvaluesmaybelocated:

(a) atextremeweldrunssuchasundertherootortoe(lastrun)asinFig.A-la.Loaddiffusionandstrainacrosstheplatewillbeconcentratedintheseareasbecauseof thenotchor stresscon-centration,particularlyif anybendingmomentis involved,aswithsinglesidedorunbalancedwelding.

(b) inthecentralplateareaasinFigA-lb,oftenwhenthisismoresusceptiblethannearthesurface.

(c) atweldormaterialdefectsor poorweldor penetrationshape.Thesecanactasseverestressandstrainconcentrators- seeFigsA-lc-e.

* ~~

1~~~IB Z-strainisgreaterat:

- “1’1

A – whencomponent(2) isfreeto rotateB– whencomponent(2) isprevemedfromrotating

..-—- InpracticemostLToccursnearfinalweldrun(Ref.K3)-: “’~11I .=(3-- ,,,:!,l,1-===,

‘1”‘iAa) “~1~

eHAZS.highhardness,n

IeterootpenetrationslopeofHAZratesstrain

d)

anglentratesstrain

Smallunderbeadcoldinhightration

Fi9 A-l LocationofmaximumstraininZ-direction.

A-3

— —

(d) justoutsidethevisibleHAZ,particularlywheretheHAZboundaryisparalleltotheplatesurface.ThispartoftheparentmetalalmostalwayshasloweryieldstressthantheHAZorweldmetalatthetemperatureswhereLToccurs.

Weldandparentmetalcontractionincreasesastheweldwidth,volumeandnumberofrunsincrease.

A-4 FRACTURE

It is believedthatfractureor tearingoccursinthestagesshowndiagrammaticallyinFig10(fromAWRATechnicalNote6 datedApril1976),ie:,

“Elasticstressconcentrationattips,.

J-W:,*;.fCohesionbetweensteelandinclusion

oPrincipal

L plasticzoneatinclusionrips

ShearWalltensilestrength(inZ direction)

/(locatedatterracesatdifferentlevels)

iecompletefracturethrouahinclusionsI I

~ dandli~aments

Decohesionat inclusion ,,~&, ... /,&+v+&E7///~ ~

/

Ductilefractureof

Heavyplastic ligamenttfeavvt31astic shearingbetween betweenstrairiirigof terracesligament

inclusions

Fig10 MechanismofLT.

.1 Onfirstencounteringsignificantstress- almostcertainlywithintheelasticrange,decohesionoccursattheinclusion/matrixinterface.Thestressrequiredwillbedependentonthetypeandshapeofinclusionandthemicrostresssystemdeveloped.

.2 Atthesametimeatthetipsorendsofinclusionsandotheradjacentdefects,plasticdeformationoccursfirstatthelargerinclusionsor thosesocloselyspacedthatthereisinteractionbetweenthetwo,i.e.wherethespacingislessthanaboutthesizeofthelargerinclusion.

.3 Onfurtherstrainingdueto furthercoolingormostlikelyduetofurtherweldingruns,theligamentbetweentheinclusionsbecomesfullyplasticandthevoidsatinclusionsincreaseinsizegenerallyby ductiletearing.

.4 Withadditionalstraining,theextendedvoidslinkup inplanesofgeneralweakness,iewheretheinclusionsarealigned;andthe“terrace”isformed- see-FigA-2. FigA-3showsthenatureoftheterracesurface.

—

A-4

— —

I

FigA-2 Linkingupofvoidstoformterracesx50.

FigA-3 Fracturesurfaceofterraceshowingduct~lefractureandinclusionsXIOO.

A-5

.5 Slightlyfurtherstrainingconnectstheterracesondifferentlevelsbyductileshearingofthe“walls”,virtuallytogivecompleteseparation.SeeFigsA-4andA-5. Shearwallsin lamellartearingaresmaller‘~haninmechanicaltests.

.6 Ifthematerialformingtheligamentbetweeninclusionshasexception-allypoorproperties,~e.lowplane-strainfracturetoughness(Klc)or lowcriticalcrackopeningdisplacement(&c ),theseareasmayshowareasofbrittlefracture.

.7 Theroleof hydrogenisnotclear,butprobablyaccentuateslocalstressatvoidtips,iea positionto whichhydrogenpreferentiallydif-fuses.Hydrogenhasbeenshownexperimentallytohavea greatereffectonLTinsteelswithhighercarbonequivalent.Thisismostlikelydueto theincreasedriskofunderbead(orcold)cracking,whichevenifon a micro-scalemaytriggeroffLT.

.8 ForLTtooccur,theconnectionsystemmusthaveconsiderablestrainenergyandbeabletotransferthistotheareaoftearing.

FigA-d Smallsheaxwalllinkingcloselyal,igr[edterracesX150.

A-6

FigA-5 Electronscanningmicrographgiving3--dimensionalviewofshearwallx200.

LISTOFREFERENCESFORAPPENDIXA

Al Takeski,Y.,“LamellarTearingandMarineStructures”,WeldingandMetalFabrication,December,1975.

A-T

,—

APPENDIXB

ORIGINSOFINCLUSIONS

ReprintedwiththepermissionoftheAustralianWeldingResearchAssociationfromAppendixB ofAWRATechnicalNote6,

ReferencesforAppendixB arelistedattheendoftheAppendix,

B-1 GENERAL

LToccursinparentmaterialandhenceisgreatlyinfluencedby thematerialproperties.LTisalsohighlydirectionalsensitiveanddependentonthrough-thicknessdirectionproperties.

ThesepropertiesandtheriskofLTdepend:

(a) primarilyoninclusionsinsteel;butalsoon

(b) thesteelmatrixitself.

Theeffectofinclusionsonpropertieshasbeennotedin2.3of Appen-dixA. Thevarioustypesof inclusion,theirorigininsteelmakingandmodificationinrollingarediscussedbelow,togetherwiththeuseofvariousmaterialpropertiesinassessingthesusceptibilityofsteeltoLT.

B-2 INCLUSIONS

Inconstructionalsteelplatesandsections,typicalnonmetallicin-cisionsare:

.1 Sulphides,mainlymanganesesulphide(MnS)whichmaybe:

(a) TypeI,i.e.ellipsoidalorsphericalinshape.TheseareusuallysmallinsizeandareseldomresponsibleforLT.

(b) TypeII,i.e.flattenedlamellarshapeas inFigB-1a. Theseareoftena majorfactorinLT,particularlywhenelongatedinstringers.Theyarepredominantinaluminumtreatedsiliconkilledsteels.

Othersulphidesincludetherare-earthmetal(REM)sulphidesandoxy-sulphideswhicharefoundin steelsspeciallytreatedto givehighRAz.Thesesulphidesarepredominantlysphericalinshape- seeFigB-lb.

.2 Silicates,metal-silicon-oxygencompounds.Inthestringerform,asinFigB-lc,thesehavea dominanteffect,particularlywhenRAzis lessthan15%(RefBl).

.3 Aluminates,A1203orcomplexaluminates.

.4 Mixedtypes,generallycombinationsofsul.phidesandsilicates(seeFigB-id)whichoftenarerelativelyshort.

WhilesilicatestringersandTypeII sulphideshavegreatesteffectonRAz,all-inclusionsmaybeinvolvedinLT.

B-2

...

‘.’

,-

b)REMsulphideandoxy-sulphide(inC-Mn-Nbsteel,Si-killedAlandREMtreated,with65%RA,z).

a)TypeIIsulphidestringer(inC-steel,Si-killed,Al-treated,with3%RA-~).

r...

● w.,..

d)Duplexstringers,Mn-Ssurroundedwithsilicatetails(inC+lnsteel,semi-killedwith50%RA~).

FigB-1 flicrogr~phsOf6.3

c)Silicatestringer(inC-Mnsteel,semi-killed,with8%RAz).

——

typicalinclusionsX400.

B-3 ORIGINOFINCLUSIONS

.1 SteelmakingControls.Inclusionsexistinallsteelsto someextentandorlglnateInsteelmakingfromimpuritiesinrawmaterialsandfromgasreactions.

Nearthefinalstageofsteelmaking,eitherinthebasicoxygenfurnaceorafterpouringintoladlesfromopenhearthorelectricsteelmakingfur-naces,thegeneralcompositionofthesteelis largelyfixed.Controlofsteelmakingoperationstothisstageenables,forinstance,sulphur- thecauseofMnSinclusions- tobe limitedfrequentlyto lessthan0.02%innormalconstructionalsteels.Specialcontrolsometimesenables0.01%tobeachieved- a levelwheretheriskofLTisgreatlyreduced.

Furthersteelmakingoperationswhichhavean importanteffectonthetype,distributionandgeometryofinclusionsmayinclude:

(a) de-oxidisation,and

(b) sulphurcontrol.

.2 SteelmakingProcess.Differentprocessesappearto haveno importanteffectonInclusionswhichpromoteLT.

.3 De-oxidisation.Thisoperationimprovespropertiesbyreducingoxygencontent,andiscarriedoutby:

(a) additionofde-oxidants(ie“killing”) to give semi-killedorfully-killedsteels.Thisistheusualmethodadoptedforcon-trollingoxygen.Siliconandaluminumaretheprincipalde-oxidantsused.

Infully-killedsteel,alloxygenintheladlereactswithaddedsiliconoraluminumtoformoxides.In semi-killedsteels,excessoxygenreactswithcarbontoformcarbonmonoxidewhichisevolvedduringsolidificationoftheingot.

(b) vacuumdegassingusingspecialhighcapitalcostequipmenttoremovegasesincludingoxygenwithouttheadditionofdeoxidants.Thismethodreducesoxide-typeinclusionsandisusedforspecialsteelsonly.

.4 FinalSulphurControl.Atthefinalstageofsteelmakingsulphurcanbefurthercontrolledbytheadditionofrare-earthmetals(REM),e.g.misch-metal,whichcontainscerium(Cc),orbycalciumcompoundssuchashypercal.

Thisaddition,whichmayalsobemadetotheingot-

(a) reducessulphurlevelbyremovingsulphurthroughtheslag,and

(b) tiesUD sul~hurinREMoxv-sulDhideswhichhavehiahmeltinc!.,points:resistdeformatio~globular,lessharmfulshape.

duringrollingandthus-retain~

,-.

B-4

J

:+

ThismethodisnowusedforspecialsteelswherehighRAzandresis-tancetoLTisrequired.

.5 IngotPouringandTreatment.Furthermethodsadoptedbythesteelmakertoreduceinclusions include:

(a) adjustmentofpouringtechnique,and

(b) hottoppingofingots.

B-4 INFLUENCEOFROLLINGANDHEATTREATMENTONINCLUSIONS

.1 BasicEffect.Aftersolidification,theingotisreheatedto a hightemperatureandreducedhottoslabsandthentoplateorrolledsections.Thisdeformstheoriginallyglobularinclusionsto a flatandsometimeselongatedshape- thusinfluencingRAzvaluesandsusceptibilitytoLT. Thegrainsofthematrixarealsoelongatedinthedirectionofrolling.

Fromtheslabstagethechangeinshapeofinclusionsdependson:

(a) thedegreeofrollingorreductioninthickness,

(b) thedirectionofrolling,and

(c) thetemperatureofrolling.

Croppingattheslabstageremovesthepartof theslabcontainingpiping,grossinclusions,etc.

.2 EffectofThicknessReduction.Witha greaterdegreeof rollingandreductionofthickness,inclusionsbecomeflatandhavemoreinfluenceonRAzvalues.

.3 EffectofRollingDirection.Rollingpredominantlyinthedirectionofthe”originalingotaxis(l.e,straightrolling)elongatestheinclusionsintostringers.

Crossrolling,iewherethereisrollingbothtransverseandalongtheingotaxis,lessenselongationandgivesa roundershapeinplan. ThisleadstoreducedRAz(Ref132)butnotnecessarilyincreasedsusceptibilitytoLT.

.4 EffectofRollingTemperature.Thistemperatureis importantastheplasticityofmanganesesulphldeinclusionsrelativeto thesteelmatrixincreaseswithdecreasingtemperature,whilethatof silicateinclusionsdecreases.Thus,thelowerthetemperaturerangeofworking,thegreatertheflatteningofMnSinclusions.ForfurtherdetailsseeRefB2.

.5 InfluenceofHeatTreatment.Modificationtoshapeof inclusionsisnotposslble bynormalheattreatment.Diffusionannealinghashelped,butisnotpracticableforconstructionalsteels.Hence,thereisnocleardif-ferencebetweenas-rolledornormalisedcondition.

B-5

B-5 MATRIXFACTORS

.1 General.TheeffectofmatrixpropertiesonLTisprobablysmallwithusualconstructionalsteelswheninclusionsarenumerousandlarge.Re-searchandexperiencesuggestthematrixhasmoreeffectwithfewinclu-sions,butthentheproblemofLTisless.

.2can

.3but

GrainSize.ExperienceshowsthatbothcoarseandfinegrainedsteelsbesusceptibletoLT.

R“BandingofrolledplateandsectionsIsreasonablycommon,

t ISan othersegregationofalloyingelementsdo notappearto sub-stantiallyreduceZ-directionpropertiesorincreaseLT.

B-6 INFLUENCEOFINCLUSIONSONPROPERTIESANDLAMELLARTEARING

Theeffectofinclusionshape,distributionandsizeisdiscussedin2.3ofAppendixA. Usingthisandtheaboveinformationonvarioustypesofinclusionsitispossibleto givetheveryapproximaterelationshipsinTableB-6.

TABLEB-6 INFLUENCEOFINCLUSIONS

SteelTypesInclusionType UsuallyInvolved

1.

2.

3.

4.

5.

SilicatestringersDecreasingIncreasingSK,FK-Si,FK-Si+Alriskof RAz

TypeII manganese Lamellarsulphidestringers Tearing FK-Si,FK-S+A1

Duplexsulphideswithsilicatetails

1 “1

SK

Ellipsoidalsulphides FK-Si+Al(thickplate)

Sphericalsulphides REMtreatedsteels

SK= Semi-killed Si= SiliconkilledFK= Fully-killed Al= Aluminumtreated

B-7 REDUCTIONOFAREAASANINDICATOROFSUSCEPTIBILITYTOLT

.1 SelectionofReductionofArea.LTisclearlydependentonmaterialproperties,,particularlyInthel-direction.Itisnaturalthatconvention-al,well-establishedmechanicaltestshavesusceptibility.Through-thicknesstensileusedextensively,andtodaytheyareusedspecialsteels.

beenusedto checkthematerialtestsofthematerialhavebeenforspecificationpurposesfor

B-6

—

Thesetensiletestsgiveyieldstress,tensilestrength,% elongation(onvariousgaugelengths)and% reductionof area(RAz).Variationofthesepropertiesisindicatedin2.3ofAppendixA andvariousresearchers(RefsB3andB4)haveshownRAztobethemostdiscriminatingandaccuratematerialmeasureatthelowductilitieswhereLT isencountered.It alsohasbeen-foundtocorrelatewellwithknownLTincidence(RefB5). ThisisnotunreasonableasRAzisa measureofthelocalstrainoccurringatfrac-tureandmorenearlyrepresentsthebehaviou~LT.

Toensurethatthefullthicknessofmaterialisassessed,standardpracticetodayistoweldextensionstubstotheplatebyfriction,studormanualarcweldingtoprovidegripsforthistensiletesting.

.2 InfluenceofTestSpecimenonRAz.testspecimendiameterissignificantin

(a) thesmallerdiameterspecimensthesizeandpositionoflarge

It is importantto notethatthequotingRAzvaluesas:

arelikelytobemoreinfluencedbyinclusions,ieminimumvaluesare

reducedandmaximumvaluesincreased.

(b) thelargerspecimens,uptoapproximately20mmdiameter,havemorelateralrestraintandthusgivelowermeanvaluesandreducedscatter.Thus,6.4mmdiameterspecimensgive,inabsoluteterms,approximately10%higherRAzmeansthan18mmspecimens.SeeFig.-

RAzoIo

50

40

30

20

10

00 5 6.4 10 15 2SpecimenDiametermm

FigB-2 TypicaleffectofspecimendiameteronRAz[forsteelwithapprox.25%Wlzon 6.4~ 4).RefsB5andB1O.

B-?—

.3 VariationofRAzinThicknessPosition.Testinghasshownthatthemaximumincidenceofinclusionsandfracturelocationmayvaryfromjustbelowthesurfacetothecentreoftheplateorsection,butusuallyismoreprevalentinthecentre.ExperiencealsoindicatesthatplatesmaybemoresusceptibletoLTatdifferentthicknesses.

Toprovideforthis,RAztestscheckthefullthickness.

.4 VariationofRAzinPlate.Investigations(RefsBl,B6andB7)shownoapparently-consistentvariationofRAzovervariouspositionsintheplate.Theonlygeneralindicationisthatfor.theplatestestedthere was aslightlygreaterprobabilityof lowerRAzinthetopcentral30%of theplate.

.5 RAzValuestoReduceRiskofLT. Farrar(RefB5)givescorrelationofRAzwith-knownLT,andIndicates:

(a) inallsteelswhichencounteredLT,themeanRAzvalues(6.4mm. diameter)wereequaltoorbelow15%andtheminimumvaluesofallwerebelow12%.

(b) inallsuccessfullyfabricatedsteels,themeanvaluesallex-ceeded13%andtheminimumvaluesofallexceeded5%.

AtthisstageitisnotpossibletostatethatsteelswithhighvaluesofRAzwillnotencounterLT,asmuch“dependsonrestraintfactors.As aguide,thevaluesgiveninFigB-3arerecommended.Thisdatatakesintoaccountrecommendationsfrom:

o ReferencesB1andB8,o IIW,ie15%to 20%minimummean,o ReferenceB9,30%fornodeplatesinoffshoredrillingrigs,o Currentpractice,25%minimummean(4or6 specimenstakenatthe

1/4platewidthposition)for.mostapplications,(35%by onemajoroilcompany)and10or15%individualminimum.

Asthescattercanbehighwithsmalldiameterspecimensthereis ariskthatanoccasionalspecimenwillfailbelowthespecifiedminimum.ThiswillhavelittleeffectonLT,butshouldbeallowedforbytheusualretestclause.

B-8 EFFECTOFOTHERMATERIALPROPERTIESONDESIGN

ThepossiblereductionoftensilestrengthandyieldstressintheZ-directionmayinfluencethedesignofthejointinadditiontoallowanceforreducedRAz.Thesereductionsarenormallynotgreat(see2.3of AppendixA)andcanalmostalwaysbeignoredindesign.

ExtensiveserviceexperiencehasindicatedthatconventionaldesignwhichisbasedonX-directionpropertiesisadequate.Thisis largelyduetothefollowing:

B-8

(a) steelswithverylowtensile oryieldstrengthoftenwillbe de-tectedbyLTduringfabrication,whereconditionsaremoreseverethanalmostallserviceconditions.

(b) tensilestrengthofmostconstructionalsteelsintheworstcondi-tionintheZ-directionisgreaterthantheyieldstressonwhichmostdesignsarebased.

(c) inmostweldedjointsthereisdiffusionof theserviceloadsthrougha greaterarea- thuseffectivelyreducingthestress;and

(d) theprobabilityof alremote.

In specialcriticalcasesspecialconsiderationmayneedto

1 factorsactingadverselyisextremely

whereveryhighstressesareinvolved,begiventodesignormaterial.

w-(J NegligibleRisk: 20x

CiIV-P SmallRisk‘Eg15mN .-

10

5

nu Low Mediurn HighJointRestraint

FigB-3 ApproximateRiskofLamellaxTeaxingforC andC-MnSteels.Specifiedminimumyieldstress<40.8kg/mm2

B-9

..

B1

B2

B3

B4

B5

B6

B7

B8

B9

B1O

LISTOFREFERENCESFORAPPENDIXB

Farrar,J.C.M.,“InclusionsandSusceptibilitytoLamellarTearingofWeldedStructuralSteels”,WeldingJournal,August,1974

Croll,synlpos

Croll,Journa”

Wilson.

J.E., “MaterialFactorsAffectingLamellarTearing”,AWRAurnonLamellarTearing,April,1976

J.E., “Through-ThicknessPropertiesofStructuralSteels”,ofAustralianInstituteofMetals,September,1975

W.G..“MinimizingLamellarTearing”,WeldingJournal,November1974

Farrar,J.C.M., etal,“UseofSmallScaleDestructiveTeststoAssesstheSusceptibilitytoLamellarTearing”,ProceedingsofInternationalConferenceonWeldinginOffshoreConstructions,February,1974

BritishSteelCorporation,“SteelPlatewithImprovedThrough-ThicknessDuctility”,October,1973

Takeski,Y:,“LamellarTearingandMarineStructures”,WeldingandMetalFabrication,December,1975

Schonherr,W.,“ ? th-V?IIUeasCriterionforJudgingLamellarTearingTendencyofSteelStructures”,IIWDOC.IX-948-76.

DetNorskeVeritas,“RulesforDesign,Construction,andInspec-tionofFixedOffshoreStructures”,1974

IIWDOC. IX-872-74: “JapaneseCommentsonThrough-ThicknessTensileTestforEvaluatingLamellarTearingSusceptibility”,1974

B-10

SHIP RESEARCH COMMITTEEMaritime Transportation Research Board

NationalAcademyof Sciences-NationalResearchCouncil

The Shipinteragency Ship

********

Research Committee has technical cognizance of theStructure Committee’s research program:

Mr. O. H.Mr. M. O.

Dr. J. N.Mr. D. P.Mr. W. J.Mr. A. C.Dr. W. Ft.

Oakley, Chairman, Co?;sultant,McLean, VABurkhart, Nava L Ocecmogaphu Division, Dep.zrtientof the N~Y,

Washington, b.C_.-Corciea, Senior Staff Metallurgist, ARMCO INC., MiddLetow, OHCourt Sal , Vice president, DPJVO Corporation, Pittsburgh, PALane, Consultant, Baltimorw, MDMcCIure, Akz C. McClure Associates, Inc., Houston, TXPorter, Vice ties. for Academ<c Affairs, State Univ. of N. Y.

Maritime Co1logeProf. S. T. RO1fe, Civil Engineering Dept., University of XuwasMr. R. W. Rumke, Ezecutive Secretary, ship Research Committee

********

The.ShipMaterials, Fabrication, & Inspection Advisory Groupprepared the project prospectus, evaluated the proposals for this project,provided the liaison technical guidance, and reviewed the project reportswith the investigator:

Dr. J. N. Cordea, Chairman, Senior .sti~ffMetallurgist, ARMCO INC., Middletown, OHMr. W. C. Brayton , Asst. to General Manager, Bethl.shamSteel corp., Spari-otisPoint,;,~Mr. T. E. Koster, Naval Architect, AMOCO International Oil Co., Chicago, ILDr. W. C. Leslie, Dept. of Materia2s & Met. Eng?g., Univ. of Michigan, Ann Arbor, MlDr. H. 1. McHenry , cryogenics Division, Nationa L Bweau of Standards, Boulder, COMr. P. W. Narshal 1, Senior sti~ffcivilEng?., SHELL OIL CO., .Youston,TXPt_Of.P. F. Packman, C’man, Dept. of Civil 4 Mech. hg?g. , Southern Methodist’Univ.

Dallas, TXPrOf. G. C. Sih, Inst. of Fracture & Solid Mechanics, Lehigh Univ., Bethlahern,PA

SHIP STRUCTURE COMMITTEE PUBLICATIONS

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These documents me distributed by the National TechnicalInfomnation Service, Springfield, Va. 22151. Those oh-wnents have been announced in the Clearinghouse journalU. S. Govezwnent Research & Development Reports (USGRDR)under the indicated AL nwnbers.

The Effect of Strain Rate on the Toughness of Ship Steels by P. H. Franci S,T. S. Cook, and A. Nagy. 1978. AO-A059453.

Fracture Be??wviorCharacterization of Ship Stee1s and Weldments byP. H. Francis, T. S. Cook, and A. Nagy. 1978. AO-A058939.

@iginal Radar and Standard Tucker Wavt?meterSL-7 Containarship DataReduction and Correlation Sample by J. F. Dal zel 1. 1978. AD-A062394.

Wavemeter Data Reduction Method and Initial Data for the SL-7Contairwrship by J. F. Dalzel1. 1978. AO-A062391.

Modified Radar and Standard Tucker Wavemetez’SL-7 Containership Databy J. F. Dalzel 1. 1978. AD-A062393.

Results and Evaluation of the SL-7 Containership Radar and Tucker Wave-meter Data by J. F. Oalzell . 1978. AD-A062392.

Bibliography for the Study of I+opelZer-Induced Vibration in HullStructural Elements by O. H. 8urnside and D. O. Kana. 1978. AO-A062996.

Comparison of Stresses Calculated Using the DAISY System to ThoseMeasured on the SL-7 Containership Frogrm by H. Y. Jan, K. T. Chan9, andM. E. Wojnarowski . 1979. AD-A069031

; L~~ture Survey on the ColZieion and Grounding Protection of Ships by1979. AD-A069032

Critical Evaluation of Lou-Energy Ship Collision-Damage Theories andDesign Methodologies - Volume I - Evaluation and RoconnnendationsbyP. R. Van Mater, Jr. , and J. G. Giannotti. 1979. AD-A070567

Critical Sval?.zztionof Low-Energy Ship Collision-Damage Theories andDesign Methodologies - Vol%nw?II - Literaiur%?Search and Review byP. R. Van Mater, Jr. , and J. G. Giannotti. 1979. AD-A070568

Results of the First Five “Data Years” of ErctremeStress Scratch GaugeData Colbaction Aboard Sea-Land’s SL-7 ‘.sby R. A. Fain and E. T. Booth.1979.

SSiC-287, Ezanination of Service and Stress Data of Three Ships for DeveLopment

of HULL Girder Load Criteria by J. F. Oalzell , N. M. Maniar, andM. W. tisu. 1979.

SSC-288, The Effeet.sof Varging Ship Hull Proportions and Hull Materials on HullFlexibility Banding and Vibratory Stresses by P. Y. Chang. 1979.

SSC-289, A Method for Econotie Trade-Offs of Alternate Ship Structural Materialsby C.:R. Jordan, J. 8. Montgomery, R. P. Krumoen, and D. J. Woodley. 1979.

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