Seamless steel pipes whose outer diameters are small can be called seamless steel pipes with small diameters. Seamless steel pipes with small diameters can also be classified into seamless steel pipes with small diameters and welded pipes with small diameters. Generally, steel pipes whose outer diameters are smaller than 89mm but bigger than 4mm are collectively called seamless steel pipes with small diameters.

The could-drawn seamless steel pipe with small diameters is a kind of steel product whose cross section is hollow, and it has round, square and rectangular shapes without seams. Seamless steel pipes are made of steel ingots or solid tubes, and then hot roll, cold roll or cold drawn them. Seamless steel pipes have cross sections, and they are mainly used for transporting fluids. Compared with solid steel products such as round bar steel, seamless steel pipes have lighter weight when they have the same bending and torsional strength. Seamless steel pipes are widely used for manufacturing structural parts and machinery parts such as oil drill stems, automotive drive shafts, bicycle stands and steel scaffolding in the construction.

Seamless steel pipes can be divided into hot-rolled pipes, cold-rolled pipes, cold-drawn pipes and extruded pipes according to different manufacturing processes. Usually, hot-rolled seamless pipes are produced by the automatic pipe mill.

Check the solid tube and deal with its surface defect, and cut the solid tube into the required length. Make the center point on the piercing surface of the solid tube; send the solid tube to the heating furnace to be heated; use a piercing mill to bore a hole in the solid tube; the inner part of the solid tube will gradually form a cavity under the effect of the mill roller and the piercing plug; the solid tube with a cavity will be processed by the automatic pipe mill; use a reeling mill to make the wall thickness of the pipe even; the pipe is processed by a sizing mill or reducing mill to meet the specifications. Manufacturing hot-rolled seamless steel pipes by continuous pipe mills is a relatively advanced method.

If you want to get smaller and better quality seamless pipes, you must adopt cold-rolled processes, cold-drawn processes or a combination of the two processes. Cold-rolled processes are carried out in two-roll mills and cold-drawn processes are carried out in single chain or double chain cold drawing machines.