Production process of hot rolled seamless steel pipe
The production process of hot-rolled seamless steel pipe includes several basic procedures such as preparation of billet before rolling, heating of billet, piercing, rolling, fixed reduction, and cooling and finishing of steel pipe.

There are three general deformation processes for the production of hot-rolled seamless steel pipes: steel pipe perforation, Rolled tube, and fixed reduction; their respective process objectives and requirements are:

 
1.Steel pipe Perforated
The solid tube blank is turned into a hollow capillary tube; we can understand it as shaping, that is, the cross section of the rolled product is set into a ring shape; its equipment is called a puncher.
Requirements for the perforation process:
(1) Ensure that the thickness of the capillary tube is uniform, the ellipse is small, and the geometrical accuracy is high;
(2) The inner and outer surfaces of the capillaries should be smooth and free from defects such as scarring, folding, and cracking;
(3) There must be corresponding piercing speed and rolling cycle to adapt to the production rhythm of the whole unit, so that the final rolling temperature of the capillary can meet the requirements of the rolling mill.
 

2.Rolled tube
The thick-walled capillary tube is changed to a thin-walled (close to the thickness of the finished product) waste pipe; we can regard it as a fixed wall, that is, determine the wall thickness value of the waste pipe in this process according to the subsequent process diameter reduction and empirical formula; this equipment It is called a tube mill.
The requirements for the rolling process are:
(1) When turning thick-walled capillary tubes into thin-walled waste tubes (reduced wall extension), first ensure that the waste-tubes have a high wall thickness uniformity;
(2) The waste pipe has good internal and external surface quality.
 
 
3. Fixed reduction
Large circle becomes small circle, referred to as sizing; the corresponding equipment is a sizing (reduction) machine.
The requirements for the fixed reduction process are:
(1) Under the condition of a certain total reduction rate and a smaller single frame reduction rate, the purpose of sizing is achieved,
(2) It can realize the task of producing a variety of finished product pipes with one specification pipe blank,
(3) The outer surface quality of the steel pipe can be further improved.
 
 
At the end of the 1980s, there had been attempts to cancel the pipe rolling process and use only the method of perforation addition and subtraction to produce seamless steel tubes, referred to as CPS, and conducted industrial tests at the Tosa plant in South Africa to produce outer diameters: 33. The steel pipe with a thickness of 4 to 17.9mm and a wall thickness of 3.4 to 25mm has a minimum outer diameter of 101.6mm for sizing and a maximum outer diameter of 101.6mm for tension reduction. After practical tests, the quality of this process is acceptable when producing steel pipes with a wall thickness of more than 10mm, but when producing steel pipes with a wall thickness of less than 8mm, the helix of the perforated capillary cannot be completely eliminated by sizing and stretching, which affects the appearance quality of the steel pipe . In the subsequent transformation, a MINI-MPM had to be added between the punching machine and the fixed reducer to ensure product quality.