On the influence of interacting dual defects on the collapse pressure of pipes under external pressure

Abstract

Metal loss due to corrosion poses a severe threat to the safety of thick-walled pipe in deep-water applications. In the present study, the interaction between defects in the event of collapse under external pressure was examined. Experiments were conducted on a set of small-scale pipes with three families of dual defects positioned longitudinally (LPDD), circumferentially (CPDD), and diagonally (DPDD). The collapse mode of LPDD tubes was dominated by a U-shaped mode, while for CPDD and DPDD families, the prevalent collapsed shape changed from a U-shaped mode to a mode similar to the classical ovalization. Finite element models were also developed to reproduce the experimental results, and good agreement was reached. With the established numerical framework, sensitivity studies on the interaction rules to various parameters of the problem were carried out. It was found that with increasing defect spacing, the normalized collapse pressure increased monotonically for the LPDD group, while the response of CPDD and DPDD families exhibited an increase first, and then a reduction followed it. Overall, the interaction between dual defects was primarily affected by the defect alignment direction, the defect size, as well as the initial ovality and the diameter-to-thickness ratio.