Stress analysis for an offshore pipeline containing embedded cracks

Abstract

Offshore pipelines have been crucial in the transportation of oil and gas for energy purposes over time. Carbon steels have emerged as a popular material for constructing cost-effective offshore pipelines. Given that these pipelines can span hundreds of kilometers, the welding of multiple shorter pipes is often necessary. However, the welding process can result in defects like cracks and porosity, which are difficult to avoid. These defects may reduce the lifespan of the pipes and even cause pipe failure under stress loadings underwater. In certain instances, the presence of cracks that are close to each other may cause a crack to propagate at a faster rate and ultimately merge with adjacent cracks. This phenomenon can significantly accelerate the growth of fatigue cracks and has important implications for the failure analysis and prevention of offshore pipelines, potentially reducing their lifespan. The objective of this report is to examine how the different directional stress loading could affect the propagation of the cracks. In addition, to compare the material properties that are commonly used for subsea pipelines. To achieve this objective, computational simulations were conducted using ANSYS Workbench 19.2, a Finite Element Software. The primary focus was to investigate the fatigue lifespan of the pipeline.