by Joseph Bednarz, E.I.T. / May 01, 2019

Originally, the design fatigue curves were based on establishing a best-fit fatigue curve using data from smooth-bar fatigue tests, and then incorporating an adjustment for mean stress as well as margins on cycles and stress. Design fatigue curves are currently provided in the 2017 Edition of ASME B&PV Code, Section VIII, Division 2 (ASME VIII-2), Annex 3F and in the 2016 Edition of API 579-1/ASME FFS-1, Annex 14B in the form of higher order polynomial functions. These functions themselves do not clarify how the mean stress was accounted for or what margins were applied to stress and cycles.

In response to this concern, a procedure has been developed to reproduce the ASME smooth-bar curves using the original best-fit curves, correcting for mean stress, and applying explicit margins to stress and cycles.  (EEPub124)

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