Small diameter welded pipe, also called a small-caliber welded steel pipe, is a steel pipe made of steel or strip steel after crimping and welding. The small-diameter welded pipe has a simple production process, high production efficiency, many varieties and specifications, and less equipment, but the general strength is lower than seamless steel pipe. Since the 1930s, 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 variety and specifications of small-diameter welded pipes have been increasing, and they have replaced them in more and more fields. Seamless steel pipe. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes according to the form of welds.