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　　Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or steel strip after crimping and forming. The welded steel pipe has the advantages of simple production process, high production efficiency, more varieties and specifications, and less equipment, but its general strength is lower than that of seamless steel pipe. Since the 1930s, with the rapid development of high-quality strip continuous rolling production and the progress of welding and inspection technology, the weld quality has been continuously improved, the varieties and specifications of welded steel pipes have been increasing, and the seamless steel pipes have been replaced in more and more fields. Welded steel pipe is divided into straight welded pipe and spiral welded pipe according to the form of weld.

　　The straight welded pipe has the advantages of simple production process, high production efficiency, low cost and rapid development. The strength of ASTM A252 Spiral Welded Steel Pipe is generally higher than that of straight welded pipe. It can produce welded pipe with larger diameter with narrow blank and different diameter with the same width blank. However, compared with the same length of straight seam pipe, the weld length increases by 30-100%, and the production speed is low.

　　Therefore, most of the welded pipes with smaller diameter are straight seam welded, while most of the welded pipes with large diameter are spiral welded.

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