Welded steel pipe, also known as welded pipe, steel pipe is welded with steel plate or steel strip after forming. The production process is simple, the production efficiency is high, the variety specification is high, the equipment capital is little, but the general strength is lower than that of seamless steel tube. Since 1930s, along with the rapid development of high quality strip mill and the progress of welding and inspection technology, the quality of the welding seam has been improved, the varieties of welded steel pipe are increasing. According to the form of welded steel pipe weld is divided into longitudinal and spiral welded pipe.

Straight welded pipe production process is simple, high production efficiency, low cost, rapid development. Strength of spiral welded pipe is usually better than straight seam welded pipe is high, can use a narrow diameter of billet production larger pipe can also differ with the same width of the billet production diameter pipe. But with the same length of straight pipe, weld length of 30~100%, and the production rate is low.