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The corrosion resistance of stainless steel seamless steel pipe depends on the alloying elements contained in the steel. Chromium is the basic element for corrosion resistance of stainless steel. When the chromium content in steel reaches about 12%, chromium reacts with oxygen in corrosive media, thus forming a very thin oxide film (self-passivation film) on the steel surface, which prevents further corrosion of the steel substrate. In addition to chromium, common alloying elements of stainless steel seamless steel tubes include nickel, molybdenum, titanium, niobium, copper, nitrogen, etc. to meet the requirements of stainless steel structure and performance for various applications. The following is an introduction to the manufacturing process of stainless steel seamless steel tubes.

1. Hot rolling (seamless steel pipe): round billet → heating → perforation → three-roll cross-rolling, continuous rolling or extrusion → pipe removal → sizing (or reduction) → cooling → straightening → hydraulic testing → marking → storage.

Stainless steel seamless steel pipe

2. The raw material for rolling stainless steel seamless steel pipe is a round pipe billet. The round pipe billet is cut into billets of about 1 meter in length by a cutting machine and then sent to the heating furnace for heating via a conveyor belt. The billet is fed into the furnace and heated at a temperature of approximately 1200 degrees Celsius. The fuel is hydrogen or acetylene. Temperature control in the furnace is the key issue. After removing the round tube from the furnace, it must be pierced by means of a pressure punching machine. Usually, the more common piercing machine is the tapered roller piercing machine. This type of piercing machine has high productivity, good product quality, large expansion of piercing diameter and can grind a wide range of steel grades.
3. After piercing, the stainless steel seamless steel pipe billet is cross-rolled, rolled in tandem or extruded by three rollers in sequence. After extrusion, remove the test tube and calibrate it. The sizing machine uses a conical drill bit rotated at high speed into the billet to punch holes to form the steel pipe. The inside diameter of the seamless stainless steel pipe is determined by the length of the outside diameter of the sizing machine’s drill bit.

After the seamless stainless steel pipe is sized, it enters a cooling tower and is cooled by water jets. After the steel tube is cooled, it is straightened. After the tube is straightened, it is sent by conveyor belt to a metal detector (or hydraulic test) for internal inspection. If there are cracks, air bubbles, etc. inside the tube, they will be detected. After the quality inspection of the tubes, a strict manual selection is required. After quality inspection of stainless steel seamless steel pipe, serial number, specification, production lot number, etc. are painted with paint. The stainless steel seamless steel pipe is lifted to the warehouse by crane.