Seamless steel pipe is a kind of strip steel with hollow section and no seam around it. Steel pipes have hollow cross-sections, which are widely used as pipelines for transporting fluids, such as oil, natural gas, coal gas, water and some solid materials.

Compared with solid steel such as round steel, steel pipe is a kind of economic cross-section steel with the same bending and torsional strength, which is widely used to manufacture structural parts and mechanical parts, such as petroleum drill pipes, automobile transmission shafts, bicycle racks and steel scaffolding used in construction.

Manufacturing annular parts with steel pipes can improve the utilization rate of materials, simplify the manufacturing process, and save materials and processing time, such as rolling bearing rings, jack sleeves, etc. At present, steel pipes have been widely used for manufacturing. Steel pipe is also an indispensable material for all kinds of conventional weapons, such as gun barrels, cannon barrels, etc. .

Steel pipes can be divided into round pipes and special-shaped pipes according to the shape of cross-sectional area. Because the circle 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 stress is relatively uniform, so most steel pipes are round pipes.

1. Classification by production method of seamless steel pipe.
Seamless pipe: hot tube, cold-rolled pipe, cold-drawn pipe, extruded pipe and jacking pipe.
Welded pipe.
According to the process: arc welded pipe, resistance welded pipe (high frequency, low frequency), gas welded pipe and furnace welded pipe.
According to the weld type: straight welded pipe and spiral welded pipe.

2. Classification by section shape.
Simple section steel pipes: round steel pipes, square steel pipes, oval steel pipes, triangular steel pipes, hexagonal steel pipes, diamond-shaped steel pipes, octagonal steel pipes, semicircular steel circles, etc.
Complex cross-section steel pipe: unequal hexagonal steel pipe, five-petal plum-shaped steel pipe, double convex steel pipe, double concave steel pipe, melon seed-shaped steel pipe, conical steel pipe, corrugated steel pipe, watch case steel pipe, etc.
Classified by wall thickness: thin-walled steel pipe and thick-walled steel pipe.
Classified by purpose: steel pipes for pipelines, thermal equipment, machinery industry, petroleum, geological drilling, container, chemical industry, special purpose, etc.