Multi-wire submerged arc welding technology for LSAW pipes

As welding is the main process in the production of straight seam steel pipes, particularly for high-quality oil and gas pipes, it is necessary to ensure high quality while also improving welding efficiency. The length of the weld for straight seam steel pipes is typically quite long, usually around 12 metres. The weld is in a horizontal position, which has led to the development and application of multi-wire submerged arc welding.

Currently, the pipe making industry typically uses 4-5 wires, which offers several advantages over traditional single-wire submerged arc welding.
Single wire submerged arc welding has a small welding pool size and short existence time, resulting in fast cooling and crystallization rates. To ensure quality, welding speed is limited to 300-600mm/min for certain specifications. Welding too fast can lead to defects, while welding too slow can widen the heat-affected zone and degrade joint performance, resulting in low production efficiency for LSAW pipes. Multi-wire submerged arc welding is typically done in a longitudinal series, creating a shared molten pool. In three-wire welding, the length of the molten pool can reach 80-100mm, allowing for ample time for gas and impurities to escape and ensuring sufficient metallurgical reaction. With proper process and specification control, welding defects are rare. The welding speed can reach more than 1.0-2m/min, resulting in high productivity. This is 3-5 times higher than single wire submerged arc welding. Products with a thickness of 30mm or less can be completed with one internal and one external weld. By using a reasonable bevel form, matching high toughness wire and high-speed sintering flux, and following a logical welding process with specific parameters, the quality requirements of high-quality welded pipe joints can be fully met. The welding process mainly depends on the equipment and technology, rather than the welder’s skill level, to ensure the production of large-caliber straight-seam steel pipes is mechanized and assembly line production is facilitated.