Numerical study of deformation inhomogeneity and its effect on mechanical properties of the heavy-wall offshore pipeline fabricated by different processes

The large-diameter pipes in offshore applications are mainly produced through two cold-forming fabrication processes, namely UOE or JCOE processes. The increasing design thickness of offshore pipelines has exacerbated deformation inhomogeneity across the thickness during fabrication, which significantly affects the ultimate performance of the pipelines. In this paper, the deformation behavior and mechanical property changes in each thickness layer of heavy-wall offshore pipelines during different fabrication processes were quantitatively investigated via numerical simulation. A kinematic hardening model was adopted to describe the Bauschinger effect in heavy-wall plates. The results revealed distinct regionalization in the circumferential plastic deformation along the thickness direction of the pipe during the UOE process, and homogeneous sinusoidal fluctuations occurred during the JCOE process. UOE pipes exhibited more uniform residual stresses than JCOE pipes. This characteristic enhances the geometric integrity and improves the resistance to collapse in pipes. However, the circumferential yield stress of the UOE pipe exhibited three vulnerable points across each thickness layer, which affected its longevity. The yield stress of each layer for the JCOE process was higher than the yield stress of the initial plate, and the final strength was more homogeneously distributed along the circumference. This work is essential for selecting and controlling the fabrication of high-strength, high-strain offshore pipelines.