Seamless pipe for fluid is a kind of pipe with hollow section and no weld from beginning to end. Steel pipe has hollow section, which is widely used as pipeline to transport oil, natural gas, gas, water and some solid materials. 
Compared with solid steels such as round steel, steel pipe has lighter weight when its bending and torsional strength is the same. It is an economic section steel. It is widely used in manufacturing structural and mechanical parts, such as oil drill pipe, automobile transmission shaft, bicycle frame and steel scaffolding used in construction. Manufacturing ring parts with steel pipes can improve material utilization, simplify manufacturing process, save material and processing time, such as rolling bearing rings, Jack sleeves, etc. Steel pipes have been widely used in manufacturing. Steel pipe is also an indispensable material for all kinds of conventional weapons. Tubes, barrels, etc. are made of steel pipe. Pipe can be divided into circular pipe and special-shaped pipe according to the shape of cross-section area. Because the circular area is the largest under the condition of equal circumference, more fluid can be transported by the circular pipe. In addition, when the ring section is subjected to internal or external radial pressure, the force is more uniform, so the vast majority of steel tubes are circular tubes.