Stress analysis for an offshore pipeline containing an embedded crack

Abstract

Over the years, offshore pipelines played an important role in transporting oil and gas used for energy consumption. Carbon steels are one of the most common materials used to build an economical offshore pipeline. As offshore pipelines can go up to hundreds of kilometers, these pipelines are constructed by joining multiple shorter pipes through a welding process. In this process, defects such as cracks and porosity are unavoidable due to environmental effects and bending stresses. Such defects may shorten the lifespan of pipes and lead to failure of pipes due to fracture. In some cases, a crack may propagate faster due to the interaction with near-by cracks and start to coalesce with those cracks. This phenomenon that increases the rate of fatigue crack growth is crucial in failure analysis and prevention for offshore pipelines, as it can significantly shorten the lifespan of the pipes. The objective of this report is to understand how the interaction of two embedded cracks affect the lifespan of a carbon steel offshore pipe. Computational simulations have been carried out with a Finite Element Software, ANSYS Workbench 19.2. The focus is to study the influence of the distance between the two cracks on the fatigue life span of the pipe.