7/29/2019 Fatigue Life Extension by Peening of Welds in Hollow Section Connections PDF

1/5

HSS

Hollow

Structural

Sections

HSS:

TECHNICAL PAPER

by Jefrey A. Packer, Bahen/Tanenbaum Proessor o CivilEngineering, University o

Toronto, Ontario, Canada

2013 Steel Tube Institute

2516 Waukegan Road, Suite 172

Glenview, IL 60025

TEL: 847.461.1701

FAX: 847.660.7981

FATIGUE LIFE EXTENSION BY PEENING

OF WELDS IN HOLLOW SECTION

CONNECTIONS

7/29/2019 Fatigue Life Extension by Peening of Welds in Hollow Section Connections PDF

2/5

FatigueLifeExtensionbyPeeningofWeldsinHollowSectionConnectionsbyJeffreyA.Packer1

1Bahen/TanenbaumProfessorofCivilEngineering,UniversityofToronto,Ontario,Canada_____________________________________________________________________________________

It iswellknown,both internationallyand inNorthAmerica,thatpeeningofweldedjointsproducesan

extension of the fatigue life of welded connections. The position of American and Canadian

codes/standardson this topic is reviewedbelow, alongwith further international research evidence,

withparticularemphasisonmaterialpertainingtoweldedtubularstructures.Thewriter isamemberofboth theAWSD1.1 code technical committeeand theCSAW59 standardtechnicalcommittee,whicharecitedbelow.

1. USAThe current U.S. nationalwelding standard produced by the American Welding Society (AWS 2010)containsaSection8.4on Fatigue LifeEnhancement inwhich fivemethods for reconditioningwelddetails are listed: Profile Improvement; Toe Grinding; Peening (Shot peening of weld surface, orhammer peening of weld toes); TIG Dressing; Toe Grinding plus Hammer Peening. This sectionconcludeswiththegeneralstatementthatTheEngineershallestablishtheappropriate increase intheallowablestressrange.

Elsewhere in this code,however, inChapter2PartD SpecificRequirements forDesignofTubularConnections (StaticallyorCyclicallyLoaded),Clause2.21.6.6deals specificallywithFatigueBehaviorImprovementofwelded tubular connections.Herein, it states thatFor thepurposeofenhanced

fatiguebehavior,andwherespecified incontractdocuments,thefollowingprofile improvementsmay

beundertakenforweldsintubularT,Y,orKconnections:(3) The toe of the weld may be peened with a blunt instrument, so as to produce local plasticdeformationwhichsmoothsthetransitionbetweenweldandbasemetal,whileinducingacompressiveresidualstress.

Forregularweldedtubularconnections,withadiametertothickness(D/t)ratioofthechordmember

notexceeding48andwhereappropriate inspectionhasbeenperformed,Clause2.21.6.6(3)supportsa

fatiguecategory improvementfromX2toX1(ifactualstressconcentrationfactorsareknown),orfromK2toK1. Thesestresscategoriesaredescribed inTable2.7andrefertotheSNcurves inFigure2.13.Quantitatively,at2x107cycles forexample, this impliesan increase inpermissiblestress rangebyafactorofabout1.25(orconversely,about2.0oncyclelife).

2. CanadaThecurrentCanadiannationalweldingstandardproducedbytheCanadianStandardsAssociation(CSA2003)containsaClause9.5FatigueLifeEnhancementinwhichfourmethodsforreconditioningweldeddetailsare listed:ToeGrinding;Peening (Shotpeeningofweld surface,orhammerpeeningofweldtoes); TIG Dressing; Toe Grinding plus Hammer Peening. Thus, the mandatory part of CSA W59endorseshammerpeeningforfatiguelifeextension.

7/29/2019 Fatigue Life Extension by Peening of Welds in Hollow Section Connections PDF

3/5

2

CSAW59 also contains a nonmandatory Appendix R, inwhich Section R3.5Hammer Peening givesdetailed requirements for peening procedures and an applicable range of application (such as yieldstrengths 800MPa [116 ksi], and thicknesses 10mm). In CSAW59 Section R3.8Stress RangeIncrease the standard states The allowable stress range for cyclically loaded connectionsmaybe

increasedbyafactorof1.3alongtheSNdesigncurve,which isequivalenttoafactorof2.2oncycle

life,foranSNcurveslopeofapproximately1/3,whentoegrinding,hammerpeening,orTIGdressingis

used. Thus, although in an informative rather than normative Appendix of the code, the

permissible increase in fatigue life forsuch treatment isevenconservativelyquantified.AppendixR issupportedby12references,manyofwhicharedocumentsfromtheInternationalInstituteofWelding(IIW)andTheWeldingInstitute,U.K.

3. InternationalStudiesA review of relatively recent research literatureon peening treatments reveals that severalmodernmethodsofhighfrequencypeening,allofwhichhaveEuropeanorigins,areincurrentuse:

(i) PITPneumaticImpactTreatment(ii) HiFITHighFrequencyImpactTreatment(alsopneumatic)

(iii) UITUltrasonicImpactTreatment(iv) UPUltrasonicPeening(v) UNPUltrasonicNeedlePeening.

UseofPneumaticImpactTreatment(PIT)equipmentforweldpeening

These alloperate in a similarmanner toordinaryhammerpeening equipment,only at considerablyhigherfrequency,whichreducesvibrationandnoiseandgivesahighimprovementinfatiguestrength.Although theyaredifferentprocesses, theirpropertiesand resulting improvement in fatigue strengthappeartobesimilar(Pedersenetal.,2009). Weichetal.(2008)haveshownthatevenfatiguedamagedweldscanbetreatedwith thesamesuccessasnewwelds.Thecorrectexecutiontechnique,operatortraining and quality control for such weld treatment has also been emphasized (e.g. Gnther andKuhlmann,2009;WalbridgeandNussbaumer,2008).

In themost recent comprehensive fatigue design guidance by the International Institute ofWelding(Hobbacher,2008),hammerpeeningiscoveredinSection3.5.3.5. Thisdocumentlimitstheapplicationto steelswithayield strength 900MPa [130.6ksi], to50mm thickness 10mm,andnotes theinfluenceoftheappliedstress ratio (R)onthe fatigue lifebenefit. (Forexample, ifR>0.4there isno

7/29/2019 Fatigue Life Extension by Peening of Welds in Hollow Section Connections PDF

4/5

3

benefit). Themaximumstressrangebenefitthatcanbeclaimed fromhammerpeening, forusewiththenominalstressapproach,isgivenbytheTablebelow.

Steelyieldstress25mm).

Amongst the many fatigue studies on high frequency hammer peening of welds, some have beenspecificallyperformedonweldedhollowsectionconnections (Kudryavtsevetal.,2006;Walbridgeand

Nussbaumer, 2008; Ummenhofer et al., 2011) and demonstrated the applicability to hollow sectionstructures. Importantly,Ummenhoferetal. (2011)showedthatthe fatiguestrengthwas increasedbyapproximately50%relativetountreatedtubularconnections(i.e.astressrangeenhancementfactorof

1.5),aswellas7090%comparedtoCIDECTDesignGuideNo.8(Zhaoetal.,2000)orISO14347(2008)

(i.e.astressrangeenhancementfactorof1.7to1.9beyonddesignlevels). Furthermore,highfrequency

hammerpeenedtestsbyUmmenhoferetal.(2011)indicatedSNcurveswithaslopeofm=4,basedon

themeanof the testdata.Thus, relative to typicalSNdesigncurvesutilizingm=3 the fatigue line isflatter,producinganevengreaterbenefitfromweldtreatmentataveryhighnumberofloadcycles.

4. ConclusionHammer peening and high frequency hammer peening of weld toes in welded joints is aninternationallyacceptedmethodforfatiguelifeenhancement. ThetechniqueisrecognizedinCanadianandAmericancodes/standardsandhasbeenusedon railwayandhighwaybridges inNorthAmerica.Whenperformedbyproperly trainedoperators,a fatigue stress range improvement factorof1.3 (oralternativelyafactorof2.2onfatiguelife)can,ingeneral,beconservativelyassumedforweldedtubularsteelconnections.

5. ReferencesAWS. 2010. Structural Welding Code Steel, AWS D1.1/D1.1M:2010, American Welding Society,Miami,Florida,U.S.A.

CSA. 2003. Welded Steel Construction (Metal Arc Welding), CSA W5903, Canadian Standards

Association,Mississauga,Ontario,Canada.

Gnther,H.P.andKuhlmann,U.2009. Nachweiskonzepte zurBemessungermdungsbeanspruchterBauteile unter Bercksichtigung von Schweinahtnachbehandlungsverfahren durch hherfrequentesHmmern,Stahlbau,Vol.78(9),pp.613621.

7/29/2019 Fatigue Life Extension by Peening of Welds in Hollow Section Connections PDF

5/5

4

Hobbacher,A. (Ed.)2008.Recommendations forFatigueDesignofWelded JointsandComponents,IIW Doc. 182307, IIW Doc. XIII125107, IIW Doc. XV1254r407, International Institute of Welding,Paris,France.

ISO. 2008. FatigueDesign Procedure forWeldedHollowSection Joints Recommendations, ISO

14347:2008(E),InternationalStandardsOrganisation,Geneva,Switzerland.

Kudryavtsev, Y., Kleiman, J., Lugovskoy, A. and Prokopenko, G. 2006. Fatigue Life Improvement ofTubular Welded Joints by Ultrasonic Peening, IIW Doc. No. XIII211706, International Institute ofWelding,Paris,France.

Pedersen,M.M.,Mouritsen,O.O.,Hansen,M.R.,Andersen,J.G.andWenderby,J.2009.ComparisonofPostWeldTreatmentofHighStrengthSteelWeldedJointsinMediumCycleFatigue,IIWDoc.XIII227209,InternationalInstituteofWelding,Paris,France.

Ummenhofer,T.,Herion,S.,Weidner,P.,Hrabowski,J.,Schneider,M.andJosat,O.2011.ExtensionoftheFatigueLifeofExistingandNewWeldedHollowSectionJoints,CIDECTReport7BY7/11,Karlsruhe

InstituteofTechnology,Germany.

Walbridge, S. and Nussbaumer, A. 2008. A Probabilistic Assessment of the Effect of PostWeldTreatmenton theFatiguePerformanceofTubularTrussBridges,EngineeringStructures,Vol.30,pp.247257.

Weich,I.,Ummenhofer,T.,NitschkePagel,Th.,Dilger,K.andEslami,H.2008.InfluenceofTreatment

andLoadingConditionson theFatigueStrengthofWelds ImprovedbyHighFrequencyPeening, IIW

Doc.XIII221808,InternationalInstituteofWelding,Paris,France.

Zhao,X.L.,Herion,S.,Packer,J.A.Puthli,R.S.,Sedlacek,G.,Wardenier,J.,Weynand,K.,vanWingerde,

A.M.andYeomans,N.2000.DesignGuideforCircularandRectangularHollowSectionWeldedJointsunderFatigueLoading,CIDECTDesignGuideNo.8,TV,Kln,Germany.

September2012