1. Cold-drawn (rolled) seamless steel tube: round tube blank → heating → piercing → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → blank tube → heat treatment → straightening → hydrostatic test (flaw detection) → marking → warehousing.

The rolling method of cold-drawn (rolled) seamless steel pipe is more complicated than hot-rolled (extruded) seamless steel pipe. 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 hollowed out, it should be headed and annealed. After annealing, use special acidic liquid for pickling. After pickling, oil is applied. Then it is followed by multi-pass cold drawing (cold rolling) and re-blank tube, and special heat treatment. After heat treatment, it will be straightened.

2. Hot rolling (extrusion of seamless steel tube): round tube blank → heating → piercing → three-roll skew rolling, continuous rolling or extrusion → tube stripping → sizing (or reducing) → cooling → straightening → hydrostatic test (or flaw detection) → marking → warehousing. The raw material for rolling seamless tubes is round tube blank, which is cut by a cutting machine and processed into blanks with a length of about 1 meter, and sent to the furnace for heating by a conveyor belt. The billet is sent to the furnace for heating, and the temperature is about 1200 degrees Celsius. The fuel is hydrogen or acetylene. The temperature control in the furnace is a key problem. After the round tube blank is discharged from the furnace, it should be pierced by a pressure piercer. The common piercer is the cone roller piercer, which has the advantages of high production efficiency, good product quality, large hole diameter expansion and can pierce a variety of steel grades. After piercing, the round tube blank is successively rolled by three rollers, continuously rolled or extruded. After extrusion, take off the tube and size. The sizing machine rotates the conical drill bit at high speed into the steel blank to punch holes, thus forming the steel pipe.

The inner diameter of the steel pipe is determined by the outer diameter length of the drill bit of the sizing machine. After sizing, the steel pipe enters the cooling tower and is cooled by spraying water. After cooling, the steel pipe will be straightened. After straightening, the steel pipe is sent to a metal flaw detector (or hydraulic test) by a conveyor belt for internal flaw detection. If there are cracks and bubbles in the steel pipe, they will be detected. After the quality inspection of steel pipes, they have to pass strict manual selection. After quality inspection, the steel pipe shall be painted with the number, specification and production batch number, etc. And hoisted into the warehouse by a crane.

The above points are the analysis and explanation of the manufacturing process of stainless steel seamless pipe.