Nonlinear fracture analysis of misaligned clad pipes with semi-elliptical surface cracks under large deformation

The integrity of offshore oil pipes becomes increasingly important. The clad pipes are commonly used for oil transportation. These pipes often experience plastic deformations with a global strain of up to 2%, making the investigation of the weld crack flaws essential. Previous research has analyzed the failure responses and local buckling of clad pipes subjected to large deformation. This study uses validated 3D finite element (FE) models to investigate the nonlinear elastic-plastic fracture behavior of equal- and unequal-diameter misaligned clad pipes with semi-elliptical surface cracks subjected to large deformation. The effect of crack depth to wall thickness ratio, crack length to depth ratio, weld misalignment level, internal pressure, load condition, strength mismatch, and the location of crack on the crack tip opening displacement (CTOD) has been elaborated. The effectiveness of BS 7910 (2019) Option 2 assessment equations against FE models is evaluated, showing that the BS 7910 (2019) Option 2 assessment equations are more conservative than the results from FE models. Moreover, a failure assessment diagram (FAD) using the CTOD obtained by the FE models is developed to accommodate the effect of weld misalignment on the nonlinear fracture behavior of misaligned clad pipes with surface semi-elliptical cracks under large deformation.