Multi-wire submerged arc welding technology for LSAW pipes

As the core process of straight seam steel pipe production is welding, especially for high quality oil and gas steel pipe, the quality requirement is high and the welding quantity is large, so it is required to improve the welding efficiency as much as possible while ensuring the excellent welding quality. The straight straight seam steel pipe weld length is large (usually a single length of about 12m) and the weld is in a horizontal position, thus giving rise to the application and development of multi-wire submerged arc welding.

At present, the number of wires in the pipe making industry has been developed to 4~5 wires. Compared with the traditional single-wire submerged arc welding, it has the following advantages:

Single wire submerged arc welding due to the welding pool small size, small quality, the existence of a short period of time, the crystallization of the cooling rate is fast, in a certain welding specifications, the welding speed is limited, generally 300 ~ 600mm / min, LSAW pipe too fast welding speed is very easy to lead to the molten pool cooling crystallization speed and welding defects, too slow speed leads to heat input is too large, the heat-affected zone widening the joints degradation of performance, production efficiency Low. The multi-wire submerged arc welding is mostly multi-wire longitudinal series, in the welding process to form a common molten pool, three-wire welding when the length of the molten pool can reach more than 80 ~ 100mm, the molten pool exists for a long time, the metallurgical reaction is sufficient, there is ample time for the gas and impurities to float out. Welding quality is good, as long as the process and specification control is good, welding defects are rare. Welding speed can reach more than 1.0~2m/min, high productivity. It is 3~5 times higher than single wire submerged arc welding. 30mm or less products can be completed with one internal and one external weld. At the same time through the use of reasonable bevel form, matching high toughness wire and high toughness high-speed sintering flux and reasonable welding process specification parameters, fully able to meet the quality requirements of high-quality welded pipe joints, welding process is mainly dependent on the ability of the equipment and technology to ensure that the large-caliber straight-seam steel pipe on the welder's skill level is not required, to facilitate the realization of the mechanization of the assembly line production.