Approximate J estimates for axial part-through surface-cracked pipes

This paper provides net-section limit pressures and a reference stress based J estimation method for pipes with constant depth, internal axial surface cracks under internal pressure. Based on systematic small strain finite element (FE) limit analyses using elastic perfectly plastic materials, net-section limit pressures are firstly determined, and based on FE results, a closed-form limit pressure solution is proposed. Furthermore, based on the proposed limit pressure solution, a method to estimate elastic-plastic J is proposed based on the reference stress approach. When the reference stress is defined by the proposed (global) limit pressure, estimated J values based on the reference stress approach are overall slightly lower than FE results, implying that the method is non-conservative. By re-defining the reference using optimised reference loads, resulting J estimates agree well with FE results.