Welded steel pipe

　　Welded steel pipe, also known as welded pipe, is a steel pipe made of rolled steel plates or strips. The production process of welded steel pipe is simple, the production efficiency is high, there are many varieties and specifications, and the equipment investment is small, but the general strength is lower than that of seamless steel pipe. Since the 1930s, with the rapid development of continuous rolling production of high-quality strip steel and the progress of welding and inspection technology, the quality of welding seam has been continuously improved, and the variety and specification of welded steel pipes have increased day by day, and they have replaced seamless steel pipes 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 production process of longitudinal welded pipe is simple, the production efficiency is high, the cost is low, and the development is fast. The strength of spiral welded pipe is generally higher than that of straight seam welded pipe. It can be used to produce welded pipe with larger pipe diameter with narrower blank, and can also be used to produce welded pipe with different pipe diameter with the same width blank. However, compared with the straight seam pipe with the same length, the weld length increases by 30~100%, and the production speed is low. Therefore, straight seam welding is mostly used for small diameter welded pipe, and spiral welding is mostly used for large diameter welded pipe.