Assessing defect safety of girth welds in X80 pipeline under internal pressure and axial loading

Onshore oil and gas pipelines are usually composed of steel pipe segments linked to each other using the arc welding method on site during construction. Internal surface and embedded cracks may occur during the welding process. Geological movement during service can cause significant axial-direction plastic deformations in the pipeline. In this study, a three-dimensional elastic-plastic finite element analysis of X80 steel pipe girth welds with surface and embedded cracks under biaxial loading is carried out, focusing on the influence of crack sizes on structural safety, and an empirical formula for the crack leading-edge driving force and crack size parameters is proposed based on the reference strain method, which can facilitate engineers to make a quick assessment of pipeline safety.