A steel with a hollow section that is much longer than its diameter or circumference. It is divided into round, square, rectangular and special-shaped steel pipes according to the cross-sectional shape; it is divided into carbon structural steel pipe, low-alloy structural steel pipe, alloy steel pipe and composite steel pipe according to the material; it is divided into conveying pipe and engineering structure according to its purpose. For thermal equipment, petrochemical industry, machinery manufacturing, geological drilling, steel pipe for high pressure equipment, etc.; according to the production process is divided into seamless steel pipe and welded steel pipe, which seamless hot steel and cold rolling (pulling) Two kinds of welded steel pipes are divided into straight seam welded steel pipes and spiral welded steel pipes.
Steel tubes are not only used for conveying fluids and powdered solids, exchanging heat energy, making mechanical parts and containers, but also an economic steel. The use of steel pipes for the manufacture of architectural structure grids, pillars, and mechanical supports can reduce weight, save 20 to 40% of metal, and enable industrialized mechanized construction. The use of steel pipes to manufacture road bridges not only saves steel and simplifies construction, but also significantly reduces the area of the protective coating and saves investment and maintenance costs.