Abstract Scope |
Spiral submerged arc welded (SSAW) linepipes with large diameter and thick wall have been widely used in long distance oil and gas transmission pipeline projects due to their many advantages. However, SSAW linepipes have a distinct disadvantage, i.e., saddle-shaped formation defect on the inner wall. In this work, a developed generator for producing the transverse assistant magnetic field (TAMF ) is put at the outside of the linepipes and moves along with the torch during the welding processing. An optimized match between the welding parameters and the intensity of the TAMF is beneficial to inhibit or even eliminate the saddle-shaped formation defect. The tested results show that the influence of the TAMF on the weld seam morphology, the microstructure and performance of welded joints, and the fluid flow behavior in the molten pool. According to the simulated results and analysis, it was found that the force produced by the TAMF is conducive to breaking the crystallization nucleation and stirring their growth in the solidification process of molten pool, and the microstructure composition is optimized and their distribution is uniform. Therefore, the mechanical properties and resistance to corrosion of the welded joint are improved. This work provides an effective solution for overcoming the saddle-shaped formation defect and enhances the service performance of the welded joints for multi-wire SSAW linepipes. |