The fluid pipe is a steel pipe with a hollow section and no welds from beginning to end. The steel pipe has a hollow section and is used as a pipe for transporting oil, natural gas, gas, water and certain solid materials in large quantities. Compared with solid steel such as round steel, steel pipe is lighter when the bending and torsion strength is the same. It is a kind of economical cross-section steel, which is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, and bicycles. And steel scaffolding used in construction.