Welded steel pipe: A steel pipe with a seam on the surface of a steel strip or steel plate that is bent and deformed into a circular shape or a square shape. The inner wall of the welded pipe has welding ribs. The main products include: ERW steel pipe, LSAW steel pipe and SSAW steel pipe. Steel pipe is a kind of hollow long steel, which is used as a conduit for conveying fluids, such as oil, natural gas, water, gas, steam, etc.