Manufacturing process of seamless black steel pipe

Posted by zora li on October 13th, 2022

The production method of seamless black steel pipe is roughly divided into the cross-rolling method (Monnesmann method) and the extrusion method. In the cross-rolling method (Mennesmann method), the pipe is first pierced with a cross-roller and then extended with a rolling mill. This method has a high production speed, but has high requirements on the processing performance of the tube blank, and is mainly suitable for the production of carbon steel and low-alloy steel tubes. The extrusion method is to perforate the tube blank or ingot with a perforator, and then extrude it into a steel tube with an extruder. This method is less efficient than the skew rolling method and is suitable for the production of high-strength alloy steel pipes.

Both the skew rolling method and the extrusion method must first heat the tube blank or ingot, and the produced steel tube is called a hot-rolled tube. Steel pipes produced by hot working can sometimes be cold worked as required. There are two methods of cold working: one is cold drawing, that is, the steel pipe is pulled out through an extrusion die to make the steel pipe thinner and longer; the other method is cold rolling, invented by the Mennesmann brothers. A method of applying a hot rolling mill to cold working. The cold working of seamless steel pipe can improve the dimensional accuracy and processing finish of the steel pipe, and improve the mechanical properties of the material.

Production process of seamless steel pipe (hot-rolled steel pipe): The seamlessness of steel pipe is mainly achieved by reducing tension. The tension reduction process is a continuous rolling process of coreless hollow base metal. Under the condition of ensuring the welding quality of the parent pipe, the pipe tension reduction process is to heat the whole welded pipe to more than 950 degrees Celsius, and then heat it to various outer diameters and wall surfaces through the tension reducer (a total of 24 times the tension reducer). Thick finished tube.

The hot-rolled steel pipe produced by this process is essentially different from the ordinary high-frequency welded pipe. After heating in the heating furnace, the metallographic structure and mechanical properties of the weld bead and the parent body can be completely consistent. In addition, multiple passes of tension reduction are achieved. Machine rolling and automatic control make the dimensional accuracy of the steel pipe (especially the roundness and wall thickness accuracy of the pipe) better than that of similar seamless pipes. Among the fluid pipes produced in developed countries in the world, the seamless process of welded pipes has been widely used in boiler pipes. With the development of society, domestic hot-rolled welded pipes have gradually replaced seamless pipes.

Manufacturing process of seamless steel pipe:

①The main production process of hot-rolled seamless steel pipe (△main inspection process):
Tube blank preparation and inspection△→pipe heating→piercing→tube rolling→steel reheating→diameter determination (reduction)→heat treatment△→complete pipe straightening→finishing→inspection△ (non-destructive, physical and chemical, Taiwan inspection)

②The main production process of cold-rolled (drawn) seamless steel pipe:
Blank preparation→pickling lubrication→cold rolling (drawing)→heat treatment→straightening→finishing→inspection

Read more ：seamless vs welded pipe