Welded steel pipe, also called welded pipe, is a steel pipe made by welding steel plates or strips after rolling. Welded steel pipe production process is applied to seamless steel pipes. Since the 1930s, with the rapid development of high-quality strip continuous rolling production and the improvement of welding and inspection technology, more and more fields have replaced seamless steel tubes. Welded steel pipe is divided into straight seam welded pipe and spiral welded pipe according to the form of weld.

 The blanks used for welding steel pipes are steel plates or strip steels, which are divided into furnace-welded pipes and electric-welded (resistance-welded) pipes due to their different welding processes. Because of its end shape, it is divided into round welded pipes and special-shaped (square, flat, etc.) welded pipes. Welded pipes are classified according to their materials and uses.

GB / T3091-2001 (galvanized welded steel pipe for low-pressure fluid transportation). Mainly used to transport water, gas, air and oil.

GB / T14291-2006 (Mining fluid transport welded steel pipe). It is mainly used for large diameter electric-welded steel pipes for mines for air pressure, drainage, shaft gas discharge, and straight seam welding fluid transportation). It is mainly used to transport low-pressure fluids such as water, sewage, gas, air, and heating steam.

GB / T12770-2002 (stainless steel welded steel pipe for mechanical structure). Mainly used in machinery, automobiles, bicycles, furniture, representative materials are 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb and so on.

GB / T12771-1991 (stainless steel welded steel pipe for fluid transportation). Mainly used to transport low-pressure corrosive media. Representative materials are 0017Cr17Ni14Mo2 and so on.

In addition, welded stainless steel pipe for decoration (GB / T 18705-2002), welded stainless steel pipe for building decoration (JG / T 3030) and welded steel pipe for heat exchanger (YB4103-2000).

The production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is fast. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. Billets with different strengths produce welded pipes with different pipe diameters. However, compared with the straight seam pipe of the same length, the weld seam length is increased by 30 to 100%. Therefore, the smaller-diameter welded pipes are mostly straight seam welded, and the large-diameter welded pipes are mostly spiral welded.