On 3-D crack problems in offshore pipeline with large plastic deformation

Offshore pipelines consist of short pipeline segments connected by girth welding method. Surface and embedded elliptical cracks are often observed at welding zone which pose a potential threat to the reliability of the offshore pipelines. In this paper, three-dimensional nonlinear elastic–plastic stress investigation for the fracture responses of such offshore pipeline with surface or embedded elliptical cracks has been carried out. Based on the reference strain method, strain-based estimation formulas for crack tip opening displacement (CTOD) are proposed for the flawed pipelines under pure bending. Furthermore, based on the proposed estimation formulations, two failure assessment diagrams (FADs) for strain-based fracture are established to perform fracture assessment on the specific pipelines.