Definition and classification of steel pipes

Steel pipe is a hollow, long strip of steel, widely used as a pipeline for transporting fluids such as oil, natural gas, water, coal gas, and steam. Additionally, it is lighter in weight while maintaining the same bending and torsional strength, making it widely used in the manufacture of mechanical parts and engineering structures. It is also commonly used in the production of various conventional weapons, gun barrels, and artillery shells.

Steel pipe classification: Steel pipes are broadly classified into seamless steel pipes and welded steel pipes (seamed pipes). Based on cross-sectional shape, they can be further divided into round pipes and shaped pipes. Round steel pipes are widely used, but there are also some square, rectangular, semi-circular, hexagonal, equilateral triangular, octagonal, and other shaped steel pipes.

Seamless steel pipes: Seamless steel pipes are made by piercing steel ingots or solid tube blanks to form a rough tube, which is then hot-rolled, cold-rolled, or cold-drawn. Seamless steel pipes are divided into hot-rolled and cold-rolled (drawn) seamless steel pipes. Hot-rolled seamless steel pipes are categorized into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes, and other steel pipes.

Cold-rolled (drawn) seamless steel pipes, in addition to general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, and other steel pipes, also include carbon thin-walled steel pipes, alloy thin-walled steel pipes, stainless thin-walled steel pipes, and special-shaped steel pipes.

Hot-rolled seamless pipes generally have an outer diameter greater than 32mm and a wall thickness of 2.5-75mm. Cold-rolled seamless steel pipes can have an outer diameter down to 6mm and a wall thickness down to 0.25mm. Thin-walled pipes can have an outer diameter down to 5mm and a wall thickness less than 0.25mm. Cold-rolled pipes have higher dimensional accuracy than hot-rolled pipes.

Seamless steel pipes are generally made from high-quality carbon structural steels such as 10, 20, 30, 35, and 45, low-alloy structural steels such as 16Mn and 5MnV, or alloy structural steels such as 40Cr, 30CrMnSi, 45Mn2, and 40MnB, through hot rolling or cold rolling. Seamless pipes made from low-carbon steels such as 10 and 20 are mainly used for fluid transportation pipelines. Seamless pipes made from medium-carbon steels such as 45 and 40Cr are used to manufacture mechanical parts, such as load-bearing components for automobiles and tractors.