Elastic-plastic fracture response of multiple 3-D interacting cracks in offshore pipelines subjected to large plastic strains

Multiple cracks may be initiated in offshore pipelines due to imperfect manufacturing processes. Under complicated loading conditions, small closely cracks can grow and coalesce into a large one that may pose threats to the integrity and safety of the structures. One of the severe loading conditions is the large strain-controlled loading which exceeds the yield stress considerably. In this case, the existing codes such as the BS7910:2013 code will not be accurate in providing the failure assessment for re-characterized multiple cracks since they are derived based on the load-controlled method. Therefore, this study focuses on the nonlinear elastic-plastic fracture responses of a flawed pipeline with the interactions of a circumferential semi-elliptical surface crack and an elliptical embedded crack under the large plastic strains. It systematically explores the influence of the crack parameters and makes the comparison with the BS7910:2013 code. New strain-based CTOD estimation schemes are proposed with a user-friendly flowchart that could be helpful to easily perform the failure assessment of the 3-D multiple cracks in offshore pipelines.