When hot-rolling seamless steel pipes, the centering of the tube blank is to make the plug correspond accurately to the axis of the tube blank during perforation, and the center position of the tube blank section is along the axis of the tube blank. A circular hole of a certain size is machined like a funnel.

Low and medium pressure boiler tubes are made of steel ingots or solid tube billets through perforation into capillary tubes, which are then hot-rolled, cold-rolled or cold-drawn.It is suitable for the manufacture of high-quality carbon structural steel hot-rolled, hot-extruded, hot-expanded and cold-drawn, cold-rolled seamless steel pipes for various low and medium pressure boilers.

Galvanized steel is widely used in all walks of life. The advantage of using galvanized steel is to protect the internal steel structure with metallic zinc that can form a dense oxide protective layer in the air. In the case of being welded or scratched, due to the existence of Zn-Fe primary battery, the relatively active galvanized part can be used as a sacrificial anode, delaying the corrosion of steel and having good corrosion resistance. However, due to the existence of the galvanized layer, cracks, pores, and slag inclusions are easily generated during welding, and it is difficult to obtain good welding quality.

ERW steel pipes may have various defects, and the names of defects are not completely uniform. Combined with the production characteristics of ERW welded pipes, it is concluded that there are the following defects.

Rolling seamless steel pipes should focus on operating in strict accordance with the construction specifications and technical requirements related to indirect technology, rather than processing and repairing after cracks.For metals of special materials and new steel grades, tests should be carried out before rolling to find a more practical probe technology for review to ensure the welding quality.

DIN 2391 standard specifies the Seamless steel tubes used for Mechanical and Automobile.The main products of steel / steel grade: DIN2391-1(ST35, ST45, ST52).