Engineering critical assessment for offshore pipelines with 3-D elliptical embedded cracks

• Fracture responses of pipeline girth weld are investigated numerically.
• Submodeling technique is adopted for 3-D finite element analysis.
• CTOD estimation schemes are proposed for the flawed pipelines.
• Strain-based defect assessment diagram is proposed for offshore pipelines.

Offshore pipelines are usually constructed by girth welding method, while weldments may naturally contain surface or embedded defects. Most existing fracture assessment procedures based on the load-controlled method are not explicitly designed for situations with large plastic strain. In this paper, the nonlinear elastic plastic fracture response of pipeline girth weld with embedded cracks is investigated through 3-D finite element analysis combined with submodeling technique. Strain-based estimation formulas for crack tip opening displacement are proposed for the pure bending load as well as the bending combined with the internal pressure. Furthermore, comparisons of fracture assessment between BS7910 and finite element analysis in the current study are made for various crack sizes.