Innovation and Practice in CRC Automatic Welding Process for Large-Diameter Thick-Wall Subsea Pipelines with Geometric Deviations

　　
　　In the Engineering, Procurement and Construction (EPC) of Lawe-Lawe Facilities RDMP RU-V Balikpapan project, the offshore section involving 13.9km of 52-inch diameter, 25.4mm wall thickness API 5L X65MO steel line pipes, a major challenge of "pipe geometric deviations" was encountered in the welding process. This study explores the innovative application of CRC automatic welding technology to address this issue. The steel line pipes, which did not undergo cold expansion after JCO forming, exhibited severe deviations in ovality and squareness, posing risks of misalignment and root weld quality issues with traditional welding methods. Through the optimized design of a "U"-type compound bevel, the formulation of a dynamic micro-adjustment strategy for root welding parameters, and precise control of heat input and oscillation parameters, an adaptive welding process system tolerant of pipe geometric deviations was developed. Procedure Qualification Record (PQR) results demonstrated excellent mechanical properties of the welded joints, with the average Charpy impact energy at 0°C in all positions exceeding 169J. Field application achieved a high first-pass qualification rate of 99.2%, with welding efficiency approximately 15 times that of traditional shielded metal arc welding 1. This study provides a reliable process solution and a practical reference for similar subsea pipeline projects affected by pipe manufacturing imperfections.