A steel pipe has a hollow section, the length of which is much longer than the diameter or circumference of steel. According to the section shape is divided into round, square, rectangular and special-shaped steel pipe; According to the material is divided into carbon structural steel pipe, low alloy structural steel pipe, alloy steel pipe and composite steel pipe; According to its use, it is divided into pipe transportation, engineering structure, thermal equipment, petrochemical industry, machinery manufacturing, geological drilling, high pressure equipment and so on. According to the production process, it is divided into seamless steel pipe and welded steel pipe, among which seamless steel pipe is divided into hot rolled and cold rolled (drawing) two kinds, welded steel pipe is divided into straight welded steel pipe and spiral welded steel pipe.
Steel pipe is not only used to transport fluids and powdery solids, exchange heat, and make machine parts and containers, it is also an economic steel. Using steel pipe to make building structure grid, pillar and mechanical support, can reduce weight, save 20 ~ 40% metal, and can realize the factory mechanized construction. Using steel pipe to make highway bridge can not only save steel, simplify construction, but also greatly reduce the area of protective coating, save investment and maintenance costs.