Research on Welding Process and Performance of Prefabricated Girth Welded Joints for Double-Connected Pipes of X80M Pipeline

The prefabricated welding of double-connected X80M pipeline steel pipes was completed with self-developed welding equipment, and the welding process used was GMAW + SAW. The key points of welding operation are summarized, hoping to guide site construction. After welding, the weld and heat-affected zone structure of the welded joint were observed by scanning electron microscopy, and the mechanical properties such as tensile, bending, impact, hardness, and CTOD of the joint were measured. The test results show that the welding equipment can efficiently complete the prefabrication welding of double-connected pipes of X80M pipeline steel. The welding joint has excellent performance, which meets the requirements of current standards and the performance at different welding positions was uniform. The GMAW+SAW welding process is a beneficial exploration for efficient welding of long-distance pipelines. Besides, the study shows that the accumulation of granular bainite in the weld zone and the existence of internal and external submerged arc welding boundaries will lead to a decrease in the toughness of the welded joint.