Study on cyclic plastic behaviour of sandwich pipelines subjected to cyclic thermo-mechanical loads

Subsea pipelines are generally used to transfer hydrocarbons from ultra-deep seawater to facilities on the shore. Typically, sandwich pipelines are filled with polymeric cores for thermal insulation, with structural reinforcements also used as a deep-water application. Sandwich pipelines are subjected to either monotonic or cyclic loads, such as bending moment, buckling, internal and external pressures during their installation or operation. It is necessary to evaluate the cyclic plasticity of sandwich pipelines under complex loading combinations to prevent structural failures caused by applied loads. In this research, limit load and shakedown analyses of sandwich pipes subjected to complicated cyclic thermo-mechanical loadings are conducted using a Linear Matching Method (LMM). Temperature-dependent material properties are employed to simulate actual pipeline behaviour, and an elastic perfectly plastic model is considered with regard to geometric non-linearity issues. Numerical results are validated via a full cyclic incremental analysis, also known as a step-by-step analysis. Moreover, comprehensive parametric studies are conducted with respect to changes in the geometry of sandwich pipelines. This research presents valuable insights into the most severe loading types and combinations affecting the structural integrity of sandwich pipelines. In addition, allowable load boundaries against existing geometric parameters can be determined.