The production methods of seamless steel pipes can be roughly divided into oblique rolling method (Mannesmann method) and extrusion method. The oblique rolling method (Mannesmann method) first uses an oblique rolling mill to pierce the tube blank, and then extends it using a rolling mill. This method has a fast production speed, but requires high processability of the pipe blank, and is mainly suitable for producing carbon steel and low-alloy steel pipes.

Production process: The extrusion method involves piercing the billet or steel ingot with a perforating machine, and then extruding it into a steel pipe using an extruder. This method is less efficient than the oblique rolling method and is suitable for producing high-strength alloy steel pipes.

Both the oblique rolling method and the extrusion method require heating the billet or steel ingot first, and the produced steel pipe is called hot-rolled pipe. Steel pipes produced by hot processing can sometimes be cold processed as needed. There are two methods for cold processing: one is the cold drawing method, which is to pull the steel pipe through a pipe drawing die, gradually making the steel pipe thinner and elongated; Another method is the cold rolling method, which applies the hot rolling mill invented by the Mannesmann brothers to cold processing. Cold processing of seamless steel pipes can improve the dimensional accuracy and processing smoothness of steel pipes, and enhance the mechanical properties of materials.

Production process: Seamless steel pipes are mainly achieved through tension reduction, which is a continuous rolling process of hollow base materials without core rods. Under the condition of ensuring the welding quality of the main pipe, the tension reducing process of welded pipe is to heat the welded pipe as a whole to above 950 degrees Celsius, and then roll it into finished pipes with various outer diameters and wall thicknesses through a tension reducing machine (which has 24 passes). The hot-rolled steel pipes produced by this process have essential differences from ordinary high-frequency welded pipes. After heating in a heating furnace, the metallographic structure and mechanical properties of the weld seam and the main body can be completely consistent. In addition, the dimensional accuracy of the steel pipe (especially the roundness and wall thickness accuracy of the pipe body) is better than that of similar seamless pipes through multiple passes of tension reducing machine rolling and automatic control.