Industry News

Introduction of Seamless Stainless Steel Tube

Seamless Stainless Steel Tube is a long strip of steel with a hollow section and no joints on the periphery. The thicker the wall thickness of the product, the more economical and practical it is, and the thinner the wall thickness, its processing cost will rise substantially.
The process of this product determines its limited performance. Generally, seamless steel pipes have low precision: uneven wall thickness, low brightness on the inside and outside of the pipe, high cost of sizing, and there are pitting and black spots on the inside and outside that are not easy to remove; its detection and Shaping must be processed offline. Therefore, it embodies its superiority in terms of high pressure, high strength, and mechanical structure materials.

According to the rolling method, it is divided into hot rolled, hot extruded and cold drawn (rolled) stainless steel tubes.
According to the metallographic structure of stainless steel, it can be divided into semi-ferritic and semi-martensitic stainless steel seamless pipes, martensitic stainless steel seamless pipes, austenitic stainless steel seamless pipes, austenitic-ferritic iron stainless steel seamless pipes, etc. .
Specifications and appearance quality
A. According to the provisions of GB14975-2002 "Stainless Steel Seamless Steel Tubes", steel tubes usually have a length (indefinite length) of hot-rolled steel pipes of 1.5-10m, and hot-extruded steel pipes are equal to and greater than 1m. For cold drawn (rolled) steel pipes with a wall thickness of 0.5~1.0mm, 1.0~7m; for those with a 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; a total of 36 kinds with a wall thickness of 4.5-45mm. There are 65 kinds of cold drawn (rolled) steel pipes with a diameter of 6~200mm, and 39 kinds with a wall thickness of 0.5~21mm.
C. There must be no cracks, folds, cracks, cracks, rolling, delamination and scarring defects on the inner and outer surfaces of the steel pipe. These defects should be completely removed (except the pipe for mechanical processing). The diameter exceeds the negative deviation. Other minor surface defects that do not exceed the allowable negative deviation may not be removed.
D. Allowable depth of straights. Hot-rolled and hot-extruded steel pipes, with a diameter less than or equal to 140mm, not greater than 5% of the nominal wall thickness, and the maximum depth is not greater than 0.5mm; cold drawn (rolled) steel pipes are not greater than 4% of the nominal wall thickness, and the maximum depth is not greater than 0.3 mm.
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 tube billet → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → pipe removal → sizing (or reducing) → cooling → straightening → hydraulic test (Or flaw detection)→mark→warehousing
The raw material for rolling seamless pipes is round pipe blanks. The round pipe blanks are cut by a cutting machine into a billet with a length of about 1 meter, and then sent to the 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. The temperature control in the furnace is a key issue. After the round tube is out of the furnace, it must be pierced through a pressure piercing machine. Generally, the more common piercing machine is the tapered roller piercing machine. This type of piercing machine has high production efficiency, good product quality, large perforation diameter expansion, and can wear a variety of steel types. After piercing, the round tube billet is successively cross-rolled, continuously rolled or extruded by three rolls. After squeezing, take off the tube and calibrate. The sizing machine uses a conical drill bit to rotate at a high speed into the steel blank to punch holes to form a steel pipe. The inner diameter of the steel pipe is determined by the length of the outer diameter of the drill bit of the sizing machine. After the steel pipe is sized, it enters the cooling tower and is cooled by spraying water. After the steel pipe is cooled, it will be straightened. After the steel pipe is straightened, it is sent to the metal flaw detector (or hydraulic test) by the conveyor belt for internal flaw detection. If there are cracks, bubbles, etc. inside the steel pipe, it will be detected. After the quality inspection of steel pipes, strict manual selection is required. After the quality inspection of the steel pipe, paint the serial number, specification, production batch number, etc. with paint. It is hoisted into the warehouse by a crane.
2. Cold drawn (rolled) seamless steel pipe: round tube blank → heating → piercing → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening →Hydraulic test (flaw detection)→Marking→Warehousing.

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 needs to be headed and annealed. After annealing, use a special acid liquid for pickling. After pickling, apply oil. Then it is followed by multiple passes of cold drawing (cold rolling) and then billeting, and special heat treatment. After heat treatment, it is straightened.