Seamless steel pipe is a kind of long steel with hollow section and without seams. The steel pipe has a hollow section and is used as a pipeline for conveying fluids, such as pipelines for oil, gas, gas, water and certain solid materials. Compared to the steel pipe and round steel solid steel bending torsional strength phase at the same time, the weight is lighter, is a kind of economic cross section steel, widely used in the manufacture of structural and mechanical parts, such as petroleum drill pipe, auto transmission shaft, bicycle frame and construction of steel scaffolding is used. With steel pipe manufacturing annular parts, can improve material utilization, simplifying the manufacturing process, material saving and processing time, such as rolling bearing ring, jack sets, at present has been widely made from steel pipe. The steel pipe is also the indispensable material for all kinds of conventional weapons. The barrel and barrel are all made of steel tubes. The steel tube is divided into round tubes and special-shaped tubes according to the shape of cross-sectional area.
Because the circle area is the largest under the equal circumference, more fluid can be transported by the circular tube. In addition, the circular section is more uniform under internal or external radial pressure, so most of the steel tubes are round tubes. But, pipe also has some limitations, such as in the plane bending condition, the pipe is not square, rectangular tube bending strength is big, some agricultural machinery and skeleton, rectangular tube, steel wood furniture is commonly used. Special-shaped steel tubes with other cross-section shapes are needed for different purposes.