According to the different metallographic structure of stainless steel, it can be divided into semi ferritic semi martensitic stainless steel seamless pipe, martensitic stainless steel seamless pipe, austenitic stainless steel seamless pipe, austenitic ferritic stainless steel seamless pipe, etc.
Specification and appearance quality
A. According to GB14975-2002 Seamless Stainless Steel Pipe, the steel pipe is usually 1.5~10m long (indefinite length) hot rolled steel pipe, and the hot extruded steel pipe is equal to or greater than 1m. The wall thickness of cold drawn (rolled) steel pipe is 0.5~1.0mm, 1.0~7m; If the wall thickness is greater than 1.0mm, it is 1.5-8m.
B. There are 45 kinds of hot-rolled (hot extruded) steel pipes with diameters of 54~480mm; The wall thickness is 4.5~45mm, totally 36 kinds. There are 65 kinds of cold drawn (rolled) steel pipes with diameters of 6~200mm; The wall thickness is 0.5~21mm, totally 39 kinds.
C. The inner and outer surfaces of steel pipes shall be free of cracks, folds, crazes, cracks, rolled folds, delaminations and scabs. These defects shall be completely removed (except for pipes for machining). After removal, the wall thickness and outer diameter shall not exceed the negative deviation. Other minor surface defects not exceeding the allowable negative deviation may not be removed.
D. Allowable depth of straight track. Hot rolled and hot extruded steel pipes with diameter less than or equal to 140mm shall not be greater than 5% of the nominal wall thickness, and the maximum depth shall not be greater than 0.5mm; The cold drawn (rolled) steel pipe shall not exceed 4% of the nominal wall thickness, and the maximum depth shall not exceed 0.3mm.
E. Both ends of the steel pipe shall be cut into right angles and burrs shall be removed.
Manufacturing process of stainless steel seamless pipe
1. Hot rolling (extrusion of seamless steel tubes): round tube blank → heating → piercing → three roll cross rolling, continuous rolling or extrusion → pipe stripping → sizing (or reducing) → cooling → straightening → hydrostatic test (or flaw detection) → marking → warehousing
The raw material for rolling seamless tubes is round tube blanks. The round tube blanks are cut by the cutting machine to process the blanks with a length of about 1 meter, and then sent to the furnace for heating by the conveyor belt. The billet is sent into the furnace for heating, and the temperature is about 1200 ℃. The fuel is hydrogen or acetylene. The temperature control in the furnace is a key problem. After the round billet is discharged from the furnace, it needs to be pierced by a pressure piercer. Generally, the more common piercer is the cone roll piercer. This kind of piercer has high production efficiency, good product quality, large piercing and diameter expansion, and can wear a variety of steel grades. After piercing, the round billets are successively cross rolled, continuously rolled or extruded by three rollers. After extrusion, the pipe shall be disconnected for sizing. The sizing machine rotates into the steel embryo at a high speed through a tapered drill bit to drill holes and form steel pipes. 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 being straightened, the steel pipe is sent to the metal flaw detector (or hydraulic test) 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 selected strictly by hand. After the steel pipe is inspected, the number, specification, production batch number, etc. shall be sprayed with paint. The crane shall be used to hoist it into the warehouse.
2. Cold drawn (rolled) seamless steel pipe: round pipe blank → heating → piercing → heading → annealing → pickling → oiling (copper plating) → multi pass cold drawing (cold rolling) → blank pipe → heat treatment → straightening → hydrostatic test (flaw detection) → marking → warehousing.
The rolling method of cold drawn (rolled) seamless steel tubes is more complicated than that of hot rolled (extruded) seamless steel tubes. The first three steps of their production process are basically the same. The difference starts from the fourth step. After the blank is punched, the blank shall be headed and annealed. After annealing, special acid liquid shall be used for pickling. After pickling, apply oil. Then it is followed by a series of cold drawing (cold rolling) to reblank the tube and special heat treatment. After heat treatment, it shall be straightened.