Welded steel pipe refers to a steel pipe with seams on the surface that is welded by bending and deforming a steel strip or steel plate into a circular, square or other shape. The blanks used for welded steel pipes are steel sheets or strips. Since the 1930s, with the rapid development of strip rolling production and the advancement of welding and inspection technology, the quality of welds has been continuously improved, the varieties and specifications of welded steel pipes have been increasing, and they have replaced seamless steel pipes in more and more fields. Steel Pipe. Welded steel pipes have lower cost and higher production efficiency than seamless steel pipes.

Steel pipes are divided into seamless and welded pipes. Welded pipes are divided into straight seam steel pipes and spiral steel pipes. The straight seam welded pipe is divided into ERW (high frequency resistance welding) and LSAW (straight seam submerged arc welding). Spiral tube welding process is also submerged arc welding (SSAW for short) and LSAW. The difference is the form of the weld, and the difference from ERW is the welding process. Submerged arc welding (SAW) requires adding media (welding wire, flux), ERW does not If necessary, ERW is melted by intermediate frequency heating. Steel pipes can be divided into two categories according to the production method: seamless steel pipes and welded steel pipes. According to the production method, seamless steel pipes can be divided into: hot-rolled seamless pipes, cold-drawn pipes, steel pipes, hot-expanded pipes, cold-spinned pipes, and extruded pipes. Seamless steel pipes are made of carbon steel or alloy steel, and are divided into hot-rolled and cold-rolled (drawn).

The production process of the straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is fast. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe. However, compared with the same length of straight seam pipe, the length of the weld is increased by 30~100%, and the production speed is lower. Therefore, most of the welded pipes with smaller diameters use straight seam welding, and most of the welded pipes with large diameters use spiral welding.