Seamless steel tube mill hot rolling (extruded seamless steel tube): round billet → heating → piercing → three-roller oblique rolling, continuous rolling, or extrusion → tube drawing → sizing (or reduction) → cooling → straightening → hydrostatic testing (or flaw detection) → marking → storage. It is made from ingots or solid billets by piercing to form a blank tube, which is then hot rolled, cold rolled, or cold drawn to produce the final product. The specifications of large-diameter thick-walled steel tube mills are expressed in terms of outer diameter * wall thickness in millimeters. Seamless steel tubes are divided into hot-rolled and cold-rolled (drawn) seamless steel tubes. Hot-rolled seamless steel tubes include general-purpose tubes, low and medium-pressure boiler tubes, high-pressure boiler tubes, alloy steel tubes, stainless steel tubes, petroleum cracking tubes, geological tubes, and other steel tubes. In addition to general-purpose tubes, low and medium-pressure boiler tubes, high-pressure boiler tubes, alloy steel tubes, stainless steel tubes, petroleum cracking tubes, and other steel tubes, cold-rolled (drawn) seamless steel tubes also include carbon thin-walled steel tubes, alloy thin-walled steel tubes, stainless thin-walled steel tubes, and special-shaped steel tubes. The hot-rolled seamless steel tubes produced by Tongren large-diameter thick-walled steel tube mill generally have an outer diameter greater than 32mm, with wall thickness ranging from 2.5 to 75mm. The cold-rolled seamless steel tubes can reach an outer diameter of 6mm and a wall thickness of up to 0.25mm. The thin-walled tubes can have an outer diameter of up to 5mm with a wall thickness less than 0.25mm. Cold rolling offers higher dimensional accuracy compared to hot rolling.