Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or strip after being rolled and formed. The production process of welded steel pipe is simple, the production efficiency is high, there are many varieties and specifications, and the equipment is small, but the general strength is lower than that of seamless steel pipe. Since the 30s of the 20th century, with the rapid development of high-quality strip continuous rolling production and the advancement of welding and inspection technology, the quality of welds has been continuously improved, and the varieties and specifications of welded steel pipes have increased, and seamless steel pipes have been replaced in more and more fields. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes according to the form of welds.

    The blank used in welded steel pipe is steel plate or strip, which is divided into furnace welded pipe, electric welded (resistance welded) pipe and automatic arc welded pipe due to its different welding processes. Due to its different welding forms, it is divided into two types: straight seam welded pipe and spiral welded pipe. Because of its end shape, it is divided into round welded pipe and special-shaped (square, flat, etc.) welded pipe. Welded pipes are divided into the following varieties due to their different materials and uses:

GB/T3091-1993 (galvanized welded steel pipe for low-pressure fluid transportation). It is mainly used to transport water, gas, air, oil and heating hot water or steam and other general lower pressure fluids and other use pipes. Its representative material is Q235A grade steel.

GB/T3092-1993 (galvanized welded steel pipe for low-pressure fluid transportation). It is mainly used to transport water, gas, air, oil and heating hot water or steam and other general lower pressure fluids and other use pipes. Its representative material is: Q235A grade steel.

GB/T14291-1992 (Welded steel pipe for mine fluid transfer). It is mainly used for longitudinal seam welded steel pipes for mine pressurized air, drainage and shaft gas. Its representative material Q235A and B grade steel. GB/T14980-1994 (large diameter welded steel pipe for low-pressure fluid transfer). Mainly used to transport water, sewage, gas, air, heating steam and other low-pressure fluids and other uses. Its representative material is Q235A grade steel.    

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

GB/T12771-1991 (stainless steel welded steel pipe for fluid transportation). It is mainly used to convey low-pressure corrosive media. Representative materials are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, etc.

The production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is relatively fast. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes, and larger welded pipes can be produced with narrower blanks, and welded pipes with different diameters can also be produced with the same width of blanks. However, compared with the straight seam pipe of the same length, the weld length is increased by 30~100%, and the production speed is lower.

    Therefore, most of the smaller diameter welded pipes use straight seam welding, and the large-diameter welded pipes mostly use spiral welding.