Evaluation of Torsion and Bending Collapse Moments for Pipes With Local Wall Thinning

Abstract

ASME B&PV Code Section XI provides fully plastic bending fracture evaluation procedures for pressurized piping components containing flaws subjected to bending and membrane loads. The piping components in power plants may experience only bending moments but also occasionally small torsion moments, simultaneously. Currently, there is a lack of guidance in the Section XI for combined loading modes including torsion. Finite element analyses were conducted in this paper for 24-inch diameter straight pipes with local wall thinning. The pipe was subject to combined bending and torsion moments. It is shown that the effect of torsion moment on plastic collapse bending moment for the pipes depends on the local wall thinning sizes. In addition, it is found that the equivalent moments defined as the root of the sum of the squares (RSS) of the torsion and bending moments is equal to pure bending moments, when wall thinning depth is shallow.