The seamless steel pipe is made of perforated whole round steel, and the steel pipe without weld seam on the surface is called seamless steel pipe. According to the production method, seamless steel pipes can be divided into hot-rolled seamless steel pipes, cold-rolled seamless steel pipes, cold-drawn seamless steel pipes, extruded seamless steel pipes, and pipe jacking. According to the cross-sectional shape, the seamless steel pipe is divided into two types: round and special-shaped. The maximum diameter is 900mm and the minimum diameter is 4mm. According to different uses, there are thick-walled seamless steel pipes and thin-walled seamless steel pipes. Seamless steel pipes are mainly used as petroleum geological drilling pipes, cracking pipes for petrochemicals, boiler pipes, bearing pipes and high-precision structural steel pipes for automobiles, tractors and aviation.

No. 5 small diameter seamless steel pipe is divided into general boiler boiler steel pipe and high pressure boiler boiler steel pipe according to the high temperature performance. Regardless of the general boiler steel pipe or high pressure boiler steel pipe, it can be divided into various steel pipes according to their application requirements. The main production methods of small diameter seamless steel pipes are hot rolling (including extrusion), welding and cold working. Cold working is the secondary processing of steel pipes. The production process of hot-rolled small diameter seamless steel pipe is to pierce and roll a solid tube billet (or steel ingot) into a steel pipe with the required shape, size and properties.

There are three main deformation processes in the whole process:
1. Perforation - pierce and roll a solid billet (ingot) into a hollow capillary tube.
2. Tube rolling - rolling the capillary tube into a waste tube close to the required size;
3. Determining and reducing the diameter - rolling the waste pipe without mandrel into a finished pipe with the required dimensional accuracy and true circularity. In production, different types of pipe rolling mills are selected according to different conditions such as product varieties, specifications and production capacity.

   Due to the different kinematic conditions, stress state conditions, pass deformation, total deformation and productivity of the rolled piece when different types of tube rolling mills are rolled, it must be equipped with matching deformation and productivity. Perforators and other pre- and post-process equipment. In this way, different tube rolling mills constitute different tube rolling units accordingly. The production method of hot-rolled large-diameter seamless steel pipe is classified by the type of rolling mill in the unit. The production methods of hot-rolled large-diameter seamless steel pipe commonly used at present are shown in Table 1-9. The specific name of a unit is represented by the type and specification of the unit and the type of rolling mill. For example, the 168 continuous tube rolling mill refers to the unit whose maximum outer diameter of the product is about 168mm, and the tube rolling mill is a continuous tube rolling mill. The steel pipe hot extrusion unit uses the maximum technical pressure (tonnage) of the extruder or the product specification range to indicate its model