Seamless steel pipe is made of whole metal without any seams on its surface. Seamless steel pipe is mainly used for petroleum geological drilling pipe, cracking pipe for petrochemical industry, boiler pipe, bearing pipe and high-precision structural steel pipe for automobiles, tractors and aviation. The production methods of seamless steel pipe are roughly divided into skew rolling (Mannesmann method) and extrusion method.
Skew rolling (Mannesmann method) is to pierce the pipe with a skew roll, and then extend it with a rolling mill. This method has a fast production speed, but requires a high machinability of the billet. It is mainly suitable for the production of carbon steel and low alloy steel pipes.
The extrusion method is to use a piercing machine to pierce the billet or ingot and then extrude it into steel pipe. This method is less efficient than the skew rolling method and is suitable for the production of high strength alloy steel pipe.
Both skew rolling and extrusion methods must first heat the billet or ingot. The produced steel pipe is called hot-rolled pipe. Steel pipes produced by hot-working method can sometimes be cold-processed as needed. There are two methods for cold-drawing: one is cold-drawing, which is to draw the steel pipe through the drawing die to make the steel pipe thinner and elongate gradually; the other is cold-rolling, which is the method of applying the hot-rolling mill invented by Mannesmann Brothers to cold-processing. Cold processing of seamless steel pipe can improve the dimensional accuracy and processing smoothness of steel pipe, and improve the mechanical properties of materials.