Investigation of Torsional Stress Intensification Factors and Stress Indices for Girth Butt Welds in Straight Pipe

The basis for fatigue evaluation of ASME Section III Class 2, 3 and B31.1 piping is the girth butt weld where the Stress Intensification Factor (SIF) is defined to be 1.0. The SIFs for other components are based on comparison to the butt welds. This SIF of 1.0 for butt welds is based on extensive bending tests on carbon steel straight pipe which are reviewed and summarized in this study. The results of new test data, including torsional test data, are presented. The authors are unaware of any previous torsional tests on carbon steel straight pipe. This new data leads to suggested changes in the codes taking into account the directionality of the loading.