Because long distance natural gas pipeline passes through long distance and complex geographical environment, various factors affecting normal pipeline service can be divided into external environment and pipeline quality. The quality of steel pipe is the most important factor affecting the quality of pipe material. The main aspects of the quality of steel pipe include the use of steel pipe and high-quality steel pipe manufacturing process.


The incomplete fusion of the filling metal base or the filling metal is not filled by the metal between the fuses. The main reasons for not fusing are that the trough is not clean, the wire drawing speed is too fast, the welding current is too small, the electrode angle is not appropriate, and so on. Slag: Residues or non-metallic inclusions in weld metal. The main causes of slag are too low welding current, too fast welding speed, clean, non-metallic inclusions floating in the slag or too late.  Cracks are the heat affected areas of welds or local fracture holes after or during welding. According to the causes of cracks, they can be divided into hot cracks, cold cracks and reheat cracks. Hot cracks are caused by improper welding technology during welding, and the main reasons hindering high frequency straight welded pipe are the deterioration of high speed welding seam and bottom cutting, the influence of welding parameters and control shape. Using double wire submerged arc welding wire (or more) is a reasonable welding method, which can ensure good welding quality and effectively improve welding speed. Therefore, the welding joint should be offset at the steel vertex and reverse rotation to make the molten metal pool close to the horizontal position in order to obtain a good weld shape.