Analytical Ratcheting Limits of Straight Pipeline under Internal Pressure and Reversed Bending Moments

Abstract

Excessive ratcheting deformation is a typical failure mode of pressurized pipeline under repeated loads in practice. There are still very few studies regarding the analytical ratcheting limits of pressurized pipes subjected to reversed biaxial loads. In this work, the ratcheting limits of straight pipes under combined constant internal pressure and repeated bending moment were deduced and verified. Moreover, the effects of the radius ratio and strain hardening were discussed in detail. The results show that the proposed ratcheting limits are better than those obtained from the KTA/ASME and RCC-MR codes. However, the analytical ratcheting limits are still very conservative compared with those experiment data owing to the strain hardening effect of the material. The flow stress was introduced to involve the strain hardening effect, and the results show that the flow stress can be used to estimate the ratcheting limits of strain hardening pipes with high accuracy. Correspondingly, a Bree-like diagram of strain hardening pipeline under combined internal pressure and reversed bending moment was further established for engineering design.