According to the rolling method, it is divided into hot rolled, hot extruded and cold drawn (rolled) stainless steel pipe.
According to the metallographic structure of stainless steel, it is divided into semiferritic and semi-martensitic stainless steel seamless pipe, martensitic stainless steel seamless pipe, austenitic stainless steel seamless pipe, austenitic-ferritic stainless steel seamless pipe, etc.
Specifications and appearance quality
A. According to the provisions of GB14975-2002 "Stainless Steel Seamless Steel Pipe", the length of the steel pipe is usually 1.5~10m of hot-rolled steel pipe, and the hot-extruded steel pipe is equal to and greater than 1m. Cold-drawn (rolled) steel pipe wall thickness 0.5~1.0mm, 1.0~7m; wall thickness greater than 1.0mm, 1.5~8m.
B. There are 45 kinds of hot-rolled (hot-extruded) steel pipes with a diameter of 54~480mm; There are 36 types of wall thickness 4.5~45mm. There are 65 kinds of cold-drawn (rolled) steel pipes with diameters of 6~200mm; There are 39 kinds of wall thickness 0.5~21mm.
C. There shall be no cracks, folds, cracks, cracks, rolling, delamination and scarring defects on the inner and outer surfaces of the steel pipe, and these defects should be completely removed (except for the pipe for machining), and the wall thickness and outer diameter shall not exceed the negative deviation after removal. Other minor surface defects that do not exceed the permissible negative deviation may not be removed.
D. The allowable depth of the straight. Hot-rolled and hot-extruded steel pipes, diameter less than or equal to 140mm not more than 5% of the nominal wall thickness, maximum depth not more than 0.5mm; cold-drawn (rolled) steel pipe not more than 4% of the nominal wall thickness, maximum depth not more than 0.3mm.
E. Both ends of the steel pipe should be cut at right angles and burrs should be removed.
Manufacturing process of stainless steel seamless pipe
1. Hot rolling (extruded seamless steel pipe): round pipe blank→ heating→perforated→ three-roll oblique rolling, continuous rolling or extrusion→ de-sizing→ sizing (or reducing diameter), →cooling → straightening→ hydrostatic test (or flaw detection) → marking → storage
The raw material for rolling seamless pipe is round pipe blank, and the round tube preform is cut by the cutting machine to process a blank with a length of about 1 meter, and sent to the furnace for heating through the conveyor belt. The billet is fed into a furnace for heating at a temperature of about 1200 degrees Celsius. The fuel is hydrogen or acetylene. Temperature control in the furnace is a key issue. After the round tube blank is out of the oven, it is pierced by a pressure perforating machine. Generally, the more common perforating machine is the conical roller perforating machine, which has high production efficiency, good product quality, large perforation and diameter expansion, and can penetrate a variety of steel grades. After perforation, the round tube blank is successively obliquely rolled, continuously rolled or extruded by three rolls. After extrusion, it should be de-pipe and sized. The sizing machine rotates into the steel embryo at high speed through a conical drill bit to punch holes to form a 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 the steel pipe is sized, it enters the cooling tower, cooled by water spray, and the steel pipe is straightened after cooling. After straightening, the steel pipe is sent by the conveyor belt to the metal flaw detector (or hydraulic test) for internal flaw detection. If there are cracks, bubbles and other problems inside the steel pipe, it will be detected. After the quality inspection of steel pipes, they must also pass strict manual selection. After the quality inspection of the steel pipe, spray the number, specification, production batch number, etc. with paint. And hoisted into the warehouse by crane.
2. Cold-drawn (rolled) seamless steel pipe: round pipe billet → heating→ perforation→ heading→ annealing→ pickling→ oiling (copper plating), →multi-pass cold-drawn (cold-rolled) →billet pipe→ heat treatment→ straightening→ hydrostatic test (flaw detection) → marking → storage.
The rolling method of cold-drawn (rolled) seamless steel pipe is more complicated than that of 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 emptied, it is hit with the head and annealed. After annealing, pickling with a special acidic liquid is used. After pickling, apply oil. This is followed by several passes of cold drawing (cold rolling) and re-billet with special heat treatment. After heat treatment, it is straightened.
