Welded pipe is a common pipe in gas pipelines. Welded pipes with a diameter greater than 426mm (or 508mm) are generally called large-diameter welded pipes. According to the welding method, they can be divided into spiral welded pipes and straight seam welded pipes.

Spiral welded pipe is made by rolling low-carbon carbon structural steel or low-alloy structural steel strip into a pipe blank at a certain spiral angle (also called forming angle), and then welding the pipe seam. It can produce large-diameter steel pipes with narrower strip steel. Spiral welded pipes are mainly spiral submerged arc welded pipes (SSAW), which are widely used in the construction of various gas pipelines in my country. Its specifications are expressed by outer diameter * wall thickness. Spiral welded pipes are single-sided welded and double-sided welded. Welded pipes should ensure that the water pressure test, tensile strength of the weld and cold bending performance meet the requirements.

Straight seam welded pipe is formed by hot-rolled coils through a forming machine, so that the steel coils are deformed into a smooth cylindrical shape, and the skin effect and proximity effect of high-frequency current or the arc burning under the flux layer are used for welding, so that the edge of the tube is heated and melted, and fused under a certain extrusion force, and finally cooled and formed. Among them, the edge of the tube melted by high-frequency current is called high-frequency straight seam welded pipe (ERW), and the one melted by arc is called straight seam submerged arc welded pipe (LSAW).

The main raw materials of straight seam welded pipe are low-carbon steel hot-rolled coils and hot-rolled strips. They are widely used in oil and natural gas transportation, low-pressure water-gas transportation, mining fluid transportation, belt conveyor rollers, automobile transmission shafts, etc. in the petroleum, metallurgy, construction, coal mining, ports, machinery and other industries.
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