Seamless steel tube factory cold drawn (rolled) seamless steel tubes: round billet → heating → piercing → upsetting → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening → hydrostatic testing (non-destructive testing) → marking → storage
Seamless steel tube mill hot rolled (extruded seamless steel tube): Round billet → Heating → Piercing → Three-roller oblique rolling, continuous rolling, or extrusion → Tube removal → sizing (or reducing sizing) → Cooling → Straightening → Hydrostatic testing (or flaw detection) → Marking → Storage. It is made from ingots or solid billets by piercing to form a blank, then hot rolled, cold rolled, or cold drawn to form. The specifications of large-diameter thick-walled steel tube mills are indicated by outer diameter * wall thickness in millimeters. Seamless steel tubes are divided into two categories: hot rolled and cold rolled (drawn) seamless steel tubes. Hot rolled seamless steel tubes include general steel tubes, low and medium pressure boiler tubes, high pressure boiler tubes, alloy steel tubes, stainless steel tubes, petrochemical cracking tubes, geological steel tubes, and other steel tubes. Cold rolled (drawn) seamless steel tubes at the Tongren large-diameter thick-walled steel tube mill generally have an outer diameter greater than 32mm, wall thickness of 2.5-75mm, cold rolled seamless tubes can reach 6mm in diameter, wall thickness can reach 0.25mm, thin-walled tubes can reach 5mm in outer diameter with wall thickness less than 0.25mm, and cold rolling has higher dimensional accuracy than hot rolling.