A strain-based fracture assessment for offshore clad pipes with ultra undermatched V groove weld joints and circumferential surface cracks under large-scale plastic strain

Bimetal clad pipes are the most widely used transportation media for submarine oil and gas. Inner clad alloy is commonly used to prevent corrosion by the transportation media. Reel-lay is one of the most efficient approaches to pipeline installation. During the reel and lay process, pipelines are subjected to large-scale plastic strain, and there are many complexities for the fracture assessment of bimetal-clad pipes. The ultra-low mismatch ratio (below 0.8) between the weld and base metal increases the difficulty of engineering critical assessment. In this work, an ultra-low mismatch weld and clad is considered as an assessment condition. The analysis matrix involves various clad thicknesses, weld root gaps, weld groove angles, crack depth ratios, crack aspect ratios, and pipe diameter ratios. An independently developed model generator based on Python language is used to generate a large number of models. An optimized reference strain approach is used to make the fracture assessment.