Welded steel pipe is a steel pipe with joints on the surface, which is welded by bending steel strip or steel plate into round, square and other shapes.

According to different welding methods, it can be divided into arc welding pipe, high frequency or low frequency resistance welding pipe, gas welding pipe, furnace welding pipe, etc.

According to the shape of the weld, it can be divided into straight seam welded pipe and spiral welded pipe. The strength of spiral welded pipe is generally higher than that of straight seam welded pipe. The welded pipe with larger diameter can be produced with narrower billet, and the welded pipe with different diameter can also be produced with billet of the same width. However, compared with the straight seam pipe of the same length, the weld length is increased by 30 to 100%, and the production speed is lower. Therefore, the smaller diameter welded pipe is mostly straight seam welding, and the large diameter welded pipe is mostly spiral welding.