Straight seam high frequency (ERW) welding and induction welding can be divided into two types of welding contacts. Hot rolled wide coil is used as raw material. The spiral welding steps, such as pre-bending, continuous forming, welding, heat treatment, sizing, straightening and cutting, are short, with high dimensional accuracy, uniform thickness, good surface quality and high pressure. However, the disadvantage is that only small diameter thin-walled pipe can be produced and gray leaves can easily be produced. Spot welding, incomplete fusion groove corrosion defects. At present, the transportation of petroleum products such as urban gas and crude oil is widely used.
 
The volume of the spiral submerged arc tube (SSAW) is that its central line forms an angle (adjustable) in the forward direction of the pipe and forms a side welding. The advantages of the same specification are that it can produce steel of various diameters, adapt to a wider range of raw materials, avoid stress in the main seam, and have better stress. The disadvantage is that the geometric shape is poor, the length of the straight seam is longer than the pipe, easy to crack, gas holes, welding slag and welding. Medium welding defects, welding stress and tension state. General design code for oil and gas pipelines Spiral submerged arc is only used in grade 3 and 4 areas. This process will improve the quality of foreign raw materials to steel plate, separate forming and welding, thin pre-welding and post-weld cold expansion. Its quality is close to UOE welded pipe. At present, there is no such process, which is the improvement of factory direction. "Oriental" is still used in the traditional production process, but the pipe end has been expanding. The general SSAW of the United States, Japan and Germany was rejected, believing that SSAW should not be used for the main line; Canada and Italy partially used SSAW, while Russia cautiously used SSAW, and very stringent additional conditions had been established. For historical reasons, most of the backbone in China still used SSAW.
 
Longitudinal submerged arc welding (LSAW) is a method of double-sided submerged arc welding and expanding production with veneer as raw material and pressure plate (volume) in die or forming machine. Its product specifications are complete, weld toughness, ductility, uniformity and compactness are good. It has the advantages of large diameter, large wall thickness, high pressure resistance, low temperature resistance and corrosion resistance. When long distance oil and gas pipelines with high strength, high toughness and high quality are constructed, most of the large diameter thick-walled pipelines required are straight seam submerged arc. According to API standards, in large oil and gas pipelines, when passing through alpine zone, sea area, densely populated urban areas such as type 1 and type 2 areas, vertical submerged arc pipe is the only applicable designation.