| Abstract Scope |
The fatigue evaluation procedures were developed for weld toe and weld root failures under torsion-dominant loading using the equilibrium-based structural stress method, which was adapted by ASME BPVC VIII-2 and API 579-1/FFS-1.
To express the multiaxial loading effect, the effective equivalent structural stress parameter, which is a Mises form on equivalent structural stress developed for general multiaxial loading, was applied to the investigation for weld toe and weld root failures. Taking the damage due to out-of-phase combined loading into account, the path-dependent maximum range concept was employed.
For the investigation of residual stress effects on fatigue under torsion-dominant loadings, widely accepted literature data sets were used. The model configurations investigated were tube-to-flange joints/tube-to-tube joints, and loadings of interest were mainly pure torsion, and combined bending and torsion.
From the observations of the weld toe and root fatigue failures, the design S-N curves were constructed for weld toe and root failure under torsion-dominant loading. At the same fatigue life, the effective equivalent structural stress range for root failure was quite a bit reduced compared with the design S-N curve for toe failure under torsion-dominant loading. The trend of the fatigue reduction for root failure under torsion was similar to that under normal loading.
The residual stress effects on fatigue under torsion-dominant loading were also investigated. The fatigue characteristics of residual stress effects on fatigue between welded plate joints and welded tubular joints are compared and discussed in this study. |