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Welded pipes are common pipes in gas pipelines. Welded pipes with a diameter of more than 426mm (or 508mm) are generally called large-diameter welded pipes. Weld pipes can be classified into spiral welded pipes and straight welded pipes in accordance with the welding method.

A lsaw steel pipe is a cylindrical shape in which a hot rolled coil is formed by a forming machine and deforms the coil into a smooth shape, and is welded by using a skin effect and a proximity effect of a high-frequency current or an arc burning under a layer of the solder. The edge is heated and melted, and it is fused under a certain squeezing force and finally cooled to form. The edge of the tube, which is melted by a high-frequency current, is called a high-frequency straight welded tube (ERW), and the arc melting is called a LSAW (LSAW). The main raw materials of longitudinal welded pipe are low-carbon steel hot-rolled coils and hot-rolled strips. They are widely used in petroleum, natural gas, metallurgy, construction, coal mines, ports, and machinery industries for oil and gas transportation, low-pressure water gas transmission, mineral fluid transportation, and belt type. Conveyor rollers, car transmission shafts, etc.

Welded steel pipe, also called welded pipe, is a steel pipe made by welding a steel plate or strip after crimping. Welded steel pipe production process is simple, high production efficiency, variety specifications, equipment, less, but the general strength is lower than the seamless steel pipe. Since the 1930s, with the rapid development of high-quality strip continuous rolling production and the advancement of welding and inspection technologies, the quality of welds has been continuously improved, and the variety and specifications of welded steel pipes have been increasing, and they have been replaced in more and more fields. Steel pipe. Welded steel pipes are divided into lsaw steel pipes and ssaw steel pipe in the form of welds.

The blanks used for welded steel tubes are steel plates or strips, which are classified into furnaces, electric (resistance) tubes and automatic arc tubes because of their different welding processes. Because of its different welding methods, it is divided into two types: straight seam welded pipe and spiral welded pipe. Because of the shape of its end is divided into round welded pipe and shaped (square, flat, etc.) welded pipe. Welded pipes are divided into the following categories due to their different materials and uses:

GB/T3091-1993 (galvanized welded steel pipe for low pressure fluid delivery). Mainly used to transport water, gas, air, oil and heating water or steam and other general low pressure fluid and other uses. It stands for Q235A grade steel.

GB/T14291-1992 (mine fluid transport welded steel pipe). Mainly used for mine pressure wind, drainage, axial discharge gas with straight seam welded steel pipe. Its representative material Q235A, B grade steel. GB/T14980-1994 (large diameter welded steel pipe for low pressure fluid delivery). Mainly used for conveying water, sewage, gas, air, heating steam and other low-pressure fluids and other uses. It stands for Q235A grade steel.

GB/T12770-1991 (stainless steel welded pipe for mechanical structures). Mainly used for machinery, automobiles, bicycles, furniture, hotel and restaurant decoration and other mechanical parts and structural parts. Its representative material 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb and so on.

GB/T12771-1991 (stainless steel welded pipe for fluid transport). It is mainly used for conveying low-pressure corrosive media. Representative materials are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2 and so on.

The straight seam welded pipe has a simple production process, high production efficiency, low cost, and rapid development. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe. A narrower blank can be used to produce a larger diameter pipe, and a blank having a different diameter can be produced from a blank of the same width. However, compared with the straight seam pipe of the same length, the length of the weld seam increases by 30 to 100%, and the production speed is low. Therefore, the smaller diameter welded pipe mostly adopts the straight seam welding, and the large diameter welded pipe adopts the spiral welding.