Plastic Limit Loads for Pipe-in-Pipes with Circumferential Through-Wall Cracks Based on Finite Element Analyses

Pipe-in-pipes (PIPs) are generally applied to the extreme environments such as deep-sea and next-generation reactors due to their functionality and robustness. Thus, it is important to estimate the fracture behaviors of PIPs for integrity assessment of this unique piping system. In this work, the plastic collapse behaviors of PIPs with circumferential through-wall cracks (TWCs) are investigated based on three-dimensional finite element (FE) limit analysis, where the crack is assumed to be located at the inner pipe of PIPs. As for loading conditions, internal pressure, axial tension, and global bending moment are considered. In particular, the bending restraint effect induced by interconnection between the inner and outer pipes of PIPs is quantified through the FE analyses considering a practical range of geometries of PIPs. Based on the FE analysis results, the tabular and closed-form solutions of the plastic limit loads of the circumferential through-wall cracked PIPs are proposed, and then, validated against numerical simulations.