Production Process of Hot-rolled Seamless Steel Pipe

Hot-rolled seamless steel pipe: Hot rolling is relative to cold rolling, cold rolling is rolling below the recrystallization temperature, and hot rolling is rolling above the recrystallization temperature.

The basic processes of the production process of hot-rolled seamless steel pipes include:

Tube blank preparation and inspection ³→Tube heating→Perforation→Rolling pipe→Steel pipe reheating→fixed (reduced) diameter→Heat treatment³→Finished pipe straightening→Finishing→Inspection³(Non-destructive, physical and chemical, bench inspection)→Warehousing

There are generally three main deformation processes in the production of hot-rolled seamless steel pipes: piercing, pipe rolling, and sizing and reducing. The respective process objectives and requirements are as follows.

1. Piercing

Perforation is to pierce a solid tube into a hollow capillary. The equipment is called a piercing machine: The requirements for the piercing process are:
(1) Ensure that the wall thickness of the capillary that passes through is uniform, the ovality is small, and the geometrical dimension accuracy is high;
(2) The inner and outer surfaces of the capillary tube are relatively smooth, and there must be no defects such as scars, folds, cracks, etc.;
(3) There must be a corresponding piercing speed and rolling cycle to adapt to the production rhythm of the entire unit, so that the final rolling temperature of the capillary tube can meet the requirements of the tube rolling mill.

2. Rolling pipe

The rolled pipe is to press the perforated thick-walled capillary tube into a thin-walled waste tube to achieve the required thermal size and uniformity of the finished tube. That is, the wall thickness of the waste pipe in this process is determined according to the reduction amount of the subsequent process and the empirical formula to process the wall thickness. This equipment is called a pipe rolling mill.

The requirements for the rolling process are:
(1) When turning thick-walled capillaries into thin-walled waste pipes (reduced-wall extension), first ensure that the waste pipes have a high uniformity of wall thickness;
(2) The waste pipe has good internal and external surface quality. The selection of the tube mill and the reasonable matching of its deformation with the piercing process are the key to determining the quality, output and technical and economic indicators of the unit.

3. Fixed (reduced) diameter

The main function of sizing and reduction is to eliminate the difference in the outer diameter of the waste pipe caused by the rolling process in the previous process, so as to improve the outer diameter accuracy and roundness of the hot-rolled finished pipe. Diameter reduction is to reduce the large pipe diameter to the required size and accuracy. Tension reduction is to reduce the diameter under the action of the front and rear frame tension, while reducing the wall. The equipment used for sizing and reducing is a sizing (reducing) machine. The requirements for the sizing and reducing process are:

(1) To achieve the purpose of sizing under the conditions of a certain total reduction rate and a smaller single frame reduction rate;
(2) It can realize the task of using one size tube blank to produce multiple sizes of finished tubes;
(3) Further improve the outer surface quality of the steel pipe.

At the end of the 1980s, there was a tendency to abolish the pipe rolling process, and only use the method of perforation plus diameter reduction to produce seamless steel pipes, referred to as CPS, and it was held in Tosa, South Africa from March 1990 to July 1991. The factory has carried out industrial tests and produced steel pipes with an outer diameter of φ33.4^φ179.8mm and a wall thickness of 3.4^25mm. The minimum diameter of the fixed diameter is 101.6mm. Through practical tests, the process has acceptable quality when producing steel pipes with wall thickness greater than 10mm, but sizing and tension reduction cannot completely eliminate the spiral line of the perforated capillary when producing steel pipes with a wall thickness of less than 8mm, which affects the appearance quality of the steel pipe. 

Tips: ASTM A53 covers seamless and welded steel pipe with nominal wall thickness. The surface condition is usually black and hot-dipped galvanized. ASTM A53 is produced mainly for pressure and mechanical applications, and is also used for transport of steam, water, gas line pipes. ASTM A53 Grade B is more popular than other grades. These pipes can be bare pipes without any coating, or it may be Hot-Dipped or Zinc-Coated and manufactured by Welding or by a Seamless manufacturing process.