Cold-drawn seamless steel pipe and hot-rolled seamless steel pipe

　　Generally, the production process of seamless steel pipe includes hot rolling and cold drawing.

　　1. Hot rolled seamless steel pipes include general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes. Hot-rolled steel pipes are delivered in hot-rolled state or heat-treated state;

　　The production process of hot-rolled seamless steel pipe: tube blank → heating → piercing → three-roll cross rolling and continuous rolling → tube stripping → sizing → cooling → straightening → hydraulic test → marking → warehousing. The raw material for rolling seamless steel pipe is round tube blank. The round tube blank needs to be cut and processed by the cutting machine with a length of about 1 meter, and then sent to the furnace for heating by the conveyor belt. The tube blank is sent into the furnace and heated to about 1200 ℃. The fuel for heating the tube blank is hydrogen or acetylene. The temperature control in the furnace is a key problem. After the tube blank is discharged from the furnace, it needs to be perforated by a piercing machine.

　　Generally, the more common piercer is the conical roll piercing steel pipe piercer. This kind of piercer has high production efficiency, good product quality, large perforation and diameter expansion, and can pierce a variety of steel grades. After piercing, the tube blank is successively cross-rolled and continuously rolled by three rollers. After extrusion, the pipe shall be removed for sizing. The sizing machine rotates the conical drill bit into the steel embryo at high speed to form a steel pipe (the inner diameter of the steel pipe is determined by the outer diameter length of the sizing machine drill bit). After sizing, the steel pipe enters the cooling tower and is cooled by water spray. After cooling, the steel pipe will be straightened. After straightening, the steel pipe is sent to the metal flaw detector by the conveyor belt for internal flaw detection. If there are cracks, bubbles and other problems inside the steel pipe, they will be detected. After quality inspection, the steel pipes shall be strictly selected by hand. After quality inspection, the steel pipe shall be painted with number, specification, production batch number, etc. The crane shall be lifted into the warehouse.

　　2. The cold-drawn seamless steel pipe includes carbon thin-wall steel pipe, alloy thin-wall steel pipe, stainless steel pipe, stainless steel pipe, oil cracking pipe and other steel pipes in addition to general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel thin-wall steel pipe and special-shaped steel pipe. Cold rolling is delivered in heat treatment condition.

　　Production process of cold-drawn seamless steel pipe: tube blank → heating → piercing → heading → annealing → pickling → oiling → multi-pass cold drawing → tube blank → heat treatment → straightening → hydraulic test → marking → warehousing. The rolling method of cold-drawn seamless steel pipe is more complex than hot-rolling, and the first three steps of their production process are basically the same. The difference starts from the fourth step. After the round tube blank is punched, it needs to be headed and annealed. After annealing, special acid liquid shall be used for pickling. After pickling, apply oil. Then it was followed by many cold-drawn sessions. After heat treatment, it should be straightened. After straightening, the steel pipe is sent to the metal flaw detector by the conveyor belt for internal flaw detection. If there are cracks in the steel pipe, bubbles and other problems will also be picked out.

　　From the appearance, the length of cold-drawn seamless pipe is generally shorter than that of hot-rolled seamless pipe. In terms of wall thickness, cold-drawn seamless pipe is more uniform than hot-rolled seamless pipe. The precision of hot-rolled pipe is lower and the surface is rough, while the precision of cold-drawn pipe is higher and the surface roughness is also better.