Production of seamless steel pipes or other metal and alloy pipes by perforation and other methods. The outer diameter range of seamless pipe is 0.1 ~ 1425mm, and the wall thickness is 0.01 ~ 200mm. In addition to circular pipes, there are various special-shaped section pipes and cross-section pipes.

Production methods and brief history
There are many production methods of seamless pipe. According to the delivery requirements, seamless steel pipes can be produced by hot rolling (about 80 ~ 90%) or cold rolling and cold drawing (about 10 ~ 20%). The billets used for hot rolling pipes include round, square or polygonal ingots, rolled billets or continuous casting billets. The quality of billets has a direct impact on the quality of pipes.
There are three basic processes for hot rolling pipe: ① threading ingot or billet into hollow thick wall rough pipe on the piercer; ② The capillary tube is thinned on the extension machine and extended into a blank tube close to the wall thickness of the finished product; ③ The required finished pipe is rolled on the finishing mill. The pipe mill series is represented by the maximum outer diameter of the produced steel pipe.
The German Mannesmann brothers first invented the two roll cross rolling piercer in 1885, and the periodic pipe mill in 1891. In 1903, the Swiss R.C. stiefel invented the automatic pipe mill (also known as the top pipe mill). After that, various extension machines such as continuous pipe mill and pipe jacking machine appeared, which began to form the modern seamless steel pipe industry.
In the 1930s, due to the use of three roll pipe rolling mill, extruder and periodic cold rolling mill, the variety and quality of steel pipes were improved.
In the 1960s, due to the improvement of continuous pipe mill and the emergence of three roll piercer, especially the success of tension reducing mill and continuous casting billet, the production efficiency was improved and the competitiveness between seamless pipe and welded pipe was enhanced.
In the 1970s, seamless pipe and welded pipe were keeping pace, and the world steel pipe output increased at a rate of more than 5% per year.
Since 1953, China has attached importance to the development of seamless steel pipe industry, and has initially formed a production system for rolling all kinds of large, medium and small pipes.
Generally, copper pipe also adopts the processes of billet cross rolling and piercing, pipe mill rolling and coil stretching. Automatic pipe rolling is one of the ways to produce seamless steel pipe. The production equipment consists of piercer, automatic pipe mill, homogenizer, sizing mill and reducing mill.