Prewelding method of thin-wall longitudinal submerged-arc welded (LSAW) pipes with small bore diameter

The invention discloses a prewelding method of thin-wall longitudinal submerged-arc welded (LSAW) pipes with a small bore diameter, and relates to the technical field of steel products welding. The prewelding method lies in that prewelding is carried out by adopting CO2 and Ar mixed gas protective automatic welding, and further comprises the following steps: firstly, determining welding technological parameters, determining the diameter of a welding wire as 2.0 mm and the welding speed as 1.8-2.9 m/min, and determining the proportion and flow of mixed gas, then carrying out preparation before welding, preparing a groove, determining the grade of the welding wire and the welding parameters. During the process of producing thin-wall steel pipes with a small bore diameter, prewelding is carried out by utilizing a shielding welding wire with the diameter of 2.0 mm, welding is carried out by adopting low current, the prewelding seam is plump, the overlaps of an internal groove are greatly reduced, the occurrence probability of defects like burning through and weld misalignment is reduced, and at the same time, the prewelding failure discharge regulation times is reduced, the prewelding once-shaping ratio is increased, and the production efficiency is improved.