Reviewoffatiguedesignproceduresforpressurevessels H.Mayer a, * ,H.L.Stark a ,S.Ambrose b,1 a University of New South Wales, Sydney, Australia b Welding Technology Institute of Australia, Australia Abstract Whenapplyingdetailedfatigueanalysistoweldsinpressurevessels,designersencounterpracticaldif®cultieswiththemethodsrequired bynationalstandardssuchasASMEBPVSectionVIIIDiv.2,BS5500andAS1210. Thispaperdiscussesthemainfatiguedesignstressparameters,being:a)thestressintensityrangeandb)theprincipalstressrange,and evaluatesthesefortheirvalidityoverthescopeoffatigueconditionstheyarerequiredtopredict. Itisconcludedthatapracticalandconservativeapproachforagivenwelddetailistocalculategeometricstressparametersatthecritical location,evaluateandselectthelargerofthetwoparametersabove,andtocomparethistoafatiguecurvebasedonundressedwelded specimens.Itisfurtherconcludedthatanadditionalfatiguestrengthreductionfactorof2besuperimposedwhentheprincipalstressdirection changessigni®cantly. q 2001PublishedbyElsevierScienceLtd. Keywords:Fatiguedesign;Pressurevessels;Stressintensityrange;Principalstressrange 1. Introduction Fatiguedesignofpressurevesselstoday,isbroadlybased ontwonationalstandards,thosebeingtheASMEBoiler and Pressure Vessel Code Section 8 Div. 2, and Section 3) [1], and BS5500:1997, Annex C [2]. Until recently the Australian national standard AS 1210 Supplement 1) [3] has been based on the ASME Code. Dif®culties in the application in practice of both the American and British approaches have caused thoseresponsiblefortheAustraliancodetodraftastandard thatdivergesinimportantaspectsfromboththeAmerican and British approaches. It is the purpose of this paper to raisethesedifferencesfordiscussion. TheASMEapproachrequiresfordesign,knowledgeof the peak alternating stress intensity, that is the peak local value no matter how small the location) of amplitude of ¯uctuation of the Tresca stress intensity half the magnitude of ¯uctuation in difference in principal stres- ses). This is compared with material property data, based on strain cycling experimental data of plain, unwelded plate. Of particular note is the requirement that the ¯uctuations in all three of the principal stresses need to be known, and those need to be known for the most localised of peak stress intensity locations. For machined shapes of known geometry this provides no insuperable barriers given the advent of ®nite element analysis FEA), however for welds, and speci®cally undressed toes of welds, the designer has little or no hopeofdeterminingsuchlocalisedpeaksgiventhevari- able geometry of same. Also for the toes of welds which are the most likely of the stress concentrations to initiate fatigue cracking in practice) there is the further issueofmetallurgicaldamagecoincidentwiththegeometric stress concentration. Accordingly the material property approachusedinASME,whilereadilyapplicabletode®ned geometriesremotefromwelds,isnotreadilyappliedtoweld details. By comparison BS5500:1997 Annex C [2] speci®cally addresses the weld issue and requires knowledge of the maximum range in principal stress at the weld, which is then used with fatigue data based on a range ofdifferentweldjointgeometriesthathavebeensubjected to uniaxial strain cycling. This weld detail categorisation approach considers only ¯uctuations in one of the three principalstressesattheweld.Thatis,ifthelargest¯uctua- tioninprincipalstressisacrossthetoe,theprincipalstress alongtheweldisignored. Houston[4]appliedeachoftheseprocedurestoasingle exampleandfoundthesetwoapproachestodifferinfatigue lifeestimationbyafactorof50.WhenHouston'scalcula- tionswererepeatedusingthecurrentlyvalidrules[1,2],this factorwasreducedto15. InternationalJournalofPressureVesselsandPiping772000)775±781 0308-0161/00/$-seefrontmatter q 2001PublishedbyElsevierScienceLtd. PII:S0308-016100)00069-7 www.elsevier.com/locate/ijpvp * Correspondingauthor. 1 Presentaddress:1AWoodsSt.,NorthEpping,NSW2121,Australia.