Finite Element Simulation and Process Optimization of JCO Forming for Extreme-Specification X80 Steel Line Pipes

The current internationally largest-diameter and thickest-wall oil and gas transmission line pipe of X80 grade (API Spec 5L) manufactured by longitudinal submerged arc welding (LSAW) is the X80 OD 1422 mm × 32.1 mm straight-seam LSAW pipe, which approaches the limit of manufacturing equipment capability. To overcome the 29-pass limitation of the conventional JCO (J-forming, C-forming, O-forming) forming process for steel pipes, this study conducts a three-dimensional finite element numerical simulation analysis based on ABAQUS 2022/Explicit (explicit dynamic finite element solver within the commercial finite element software Abaqus) to investigate the JCO forming process of this extreme-specification pipe. An innovative involute lower die is designed, enabling a reduction in the forming process to 25 passes. The residual stress and plastic strain distributions in the formed pipes from both the 25-pass and 29-pass processes exhibit consistent patterns, characterized by higher values at the surface layers and lower values in the core region, with the inner surface showing higher stress and strain levels than the outer surface. The maximum residual stress (231.7 MPa) and maximum plastic strain (0.03787) of the 25-pass pipe are slightly lower than those of the 29-pass pipe (231.9 MPa and 0.03859, respectively). In terms of geometric accuracy, the 25-pass process yields an opening gap of 118.8 mm, marginally better than the 118.98 mm of the 29-pass process, and produces a smoother outer circumference profile after forming. These results demonstrate the superiority of the 25-pass process with the novel involute die configuration. The subsequent engineering application validates that the established finite element model possesses high predictive accuracy and practical guidance value. This study provides a breakthrough solution to the technical challenge of excessive forming passes in the JCO forming of the extreme-specification X80 OD 1422 mm × 32.1 mm pipe, achieving a reduction in forming passes while maintaining forming quality, significantly improving efficiency, and reducing manufacturing costs.