Fatigue failure analysis of dented pipeline and simulation calculation

Abstract

Natural gas pipeline leaks may cause considerable damage to people, properties, and the surrounding environment. This study investigates a dent leak in a gas pipeline in China that has operated for six years. The failure pipe section meets American Petroleum Institute (API) specification 5L-2012 standard for carbon steel pipelines. The cause of leakage is evaluated not only through visual examination, micromorphology observation, structural deformation analysis, and residual stress measure of the dented region near the leak point of the pipe body, but also through finite element analysis on the deformation and stress of the pipe under different loads. The dent formation is related to rocks during pipeline laying. Under the combined effect of external load and internal pressure, the maximum equivalent stresses of the dented edge at the outer wall, bulge top of the inner wall, and dented edge of the inner wall are greater than the yield stress of the material. Moreover, micro-crack formation occurs due to the maximum deformation at the bottom of the dent and the maximum equivalent stress on top of the inner surface bulge. Under alternating stress, microcracks gradually expand until they penetrate the wall thickness, and thereby cause pipeline leakages.