Stress intensity factors of pipe-in-pipes with circumferential through-wall cracks based on elastic finite element analyses

Any defects and cracks in pipe-in-pipes (PIPs) applied to deep-water and harsh environment are potential threats that can cause terrible economic damage or environmental pollution as triggering failures. In the present study, stress intensity factors (SIFs) of PIPs with circumferential through-wall cracks (TWCs) were investigated via detailed 3-dimensional (3-D) elastic finite element (FE) analyses. In terms of the crack location, the cracks are postulated in the inner pipe which is considered as mainly important part to assess the integrity of PIPs. In the present FE analyses, the effects of cross-sectional shapes of both inner and outer pipes on the SIFs of PIPs were systematically evaluated. As for loading conditions, internal pressure, axial tension and bending moment were considered. The FE results of the SIFs of PIPs were also compared with the existing solution of single-walled pipes with circumferential TWCs to evaluate the restraint effect by the outer pipe on the SIFs of PIPs, where the dimensions of single-walled pipes are assumed to be identical to those of the inner pipe of PIPs.