1.As the long-distance natural gas pipeline through the long distance, complex geographical environment, therefore, a variety of factors affect the normal pipeline services, but the most important factor can be divided into the external environment and the quality of the pipeline itself. Steel pipe, quality is the most important factor affecting the quality of the tube and the main aspects of the quality of the steel pipe include the use of steel and steel pipe quality steel pipe manufacturing process.
2.The incomplete fusion of the filled metal base or the filling metal is not filled with metal between the fusions. The main reason for the absence of fusion is when the tank is not clean, the drawing speed is too fast, the welding current is too small, the improper electrode angle, and so on. Slag: refers to the residual residue in the weld metal or non-metallic inclusions. The main reason for the slag is the welding current is too small, the welding speed is too fast, clear and clean, non-metallic inclusions floating in the slag or too late. Cracks are the heat affected area of the weld or the local fracture hole after welding or during the welding process. According to the cause of the crack can be divided into hot cracks, cold cracks and reheat cracks. Thermal cracking is due to improper welding technology when welding occurs; the main reason for hindering high frequency straight seam welded pipe is the impact of defects such as the deterioration of high-speed welding welds and undercutting, the welding process parameters and the external shape of the control. The use of double wire submerged arc welding wire (or more) is a reasonable way of welding can guarantee and good welding quality while effectively improving the welding speed. Therefore, the solder joint should be in the steel vertex and reverse rotation offset distance, so that the molten metal pool close to the horizontal position, in order to get a good weld shape.