Residual strength of metallic pipelines subject to combined loads accounting for impact induced damage

Abstract

While the offshore pipelines are designed to withstand an extensive range of combined loads such as the internal/external pressure, axial force and bending moment, the residual strength of these structures accounting for impact induced damage is one of the most detrimental situations in limit state design. The impact might be caused by machinery such as trawl gears or anchors, which could introduce mechanical damage. One specific case is the interaction between the pipelines and fishing trawl boards when they are towed underwater. Depending on the pipe material properties and the impact forms, mechanical damage could be a dent, metal loss or even a crack. Therefore, the aim of this paper is to investigate the residual strength of metallic pipelines with impact induced dent or combined dent & crack subject to dominated bending moment with a combination of axial force and internal pressure under a certain level of absorbed energy. The nonlinear finite element method is deployed and the numerical models accounting for damage are developed. Simulation results are compared with each other and the most unfavorable damage pattern of the pipelines is determined. Research found that the combined dent & crack damage significantly decreased the residual strength of pipe structure under combined loads, and single dent damage had slight effect on pipe residual strength.