Introduction to stainless steel seamless steel pipe

Introduction to stainless steel seamless steel pipe

Stainless steel seamless steel pipe is a long steel material with a hollow section and no seams around it. It is a steel pipe that is resistant to corrosion by weakly corrosive media such as air, steam, and water, and chemically corrosive media such as acids, alkali, and salts. Also known as stainless acid-resistant steel pipe.

Stainless steel seamless pipe production process

The manufacturing process and steps of stainless steel seamless pipes should be informed in advance. The manufacturing processes of stainless steel seamless pipes are different, and the corresponding manufacturing processes are also different. For example: Stainless steel seamless steel pipes are divided into cold-rolled pipes and hot-rolled pipes. For stainless steel sanitary seamless pipes with higher size and quality requirements, cold rolling, cold drawing or a combination of the two must be used.

1. The above operation is followed by a multi-pass cold drawing (cold rolling) process. Cold rolling of steel pipes is carried out on multi-roll mills. The stainless steel pipe is rolled using a circular pass consisting of a variable cross-section circular groove and a fixed cone head.

2. Cold-rolled stainless steel pipes have the advantages of large yield coefficient, no flaring, and no bending. In order to meet the health grade standards of stainless steel pipes, cold-rolled pipes should undergo bright annealing, demagnetization, pickling, straightening and other steps.

3. Pickling the stainless steel pipe, while the pipe is removing oil, rust, spot welding, oxide layer, free iron and other dirt, the surface becomes evenly pickled and passivated after silver treatment to prevent corrosion of the metal. and hydrogen embrittlement, inhibiting the production of acid mist.

4. After the above process, the next step is the polishing process of the stainless steel pipe. The standard for polishing nets on the inner and outer walls of the pipeline is 400 mesh, and the finish of the polished inner and outer surfaces of the pipeline reaches mirror standards (that is, sanitary standards).

5. The polished stainless steel pipes should undergo internal flaw detection and strict manual selection by the steel pipe quality inspector through a metal flaw detector (or hydraulic test), and qualified products will be packaged and delivered.

Production process: 1. Steelmaking → 2. Rolled round steel (peeling) → 3. Perforation (annealing) → 4. Cold drawing → 5. Cold rolling (annealing, demagnetization, pickling, cleaning) → 6. Inner wall polishing (400 mesh) → 7 .Exterior wall polishing (400 mesh) → 8. Air pressure test → 9. Surface test → 10. Attach trademark and certificate of conformity → 11. Packaging → 12. Delivery

Introduction to the characteristics of stainless steel seamless pipes

First, the thicker the wall thickness of the product, the more economical and practical it is. The thinner the wall thickness, the processing cost will increase significantly. Secondly, the process of the 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 pitting and black spots on the inside and outside that are difficult to remove; thirdly, its detection and shaping must be processed offline. Therefore, it reflects its superiority in terms of high pressure, high strength, and mechanical structural materials.
Stainless steel seamless pipes are steel pipes that are resistant to corrosion by weakly corrosive media such as air, steam, and water and chemically corrosive media such as acids, alkalis, and salts. Also known as stainless acid-resistant steel pipe.

The corrosion resistance of stainless steel seamless pipes depends on the alloying elements contained in the steel. Chromium is the basic element that makes stainless steel corrosion resistant. When the chromium content in steel reaches about 12%, chromium interacts with the oxygen in the corrosive medium to form a thin oxide film (self-passivation film) on the surface of the steel. , which can prevent further corrosion of the steel matrix. In addition to chromium, commonly used alloy elements for stainless steel seamless pipes include nickel, molybdenum, titanium, niobium, copper, nitrogen, etc. to meet the requirements for the structure and performance of stainless steel for various purposes.

Stainless steel seamless pipe is a hollow long circular steel material that is widely used in industrial transportation pipelines and mechanical structural components such as petroleum, chemical industry, medical, food, light industry, mechanical instrumentation, etc. In addition, when the bending and torsional strength are the same, the weight is lighter, so it is also widely used in manufacturing mechanical parts and engineering structures. It is also commonly used to produce various conventional weapons, gun barrels, artillery shells, etc.

Types of stainless steel seamless pipes

The rolling methods are divided into hot rolling, hot extrusion and cold drawn (rolled) stainless steel pipes.
According to the different metallographic structures of stainless steel, it can be divided into semi-ferritic and semi-martensitic stainless steel pipes, martensitic stainless steel pipes, austenitic stainless steel pipes, austenitic-ferritic stainless steel pipes, etc.

Specifications and quality of stainless steel seamless pipes

A. According to the provisions of GB14975-94 "Stainless Steel Seamless Steel Pipe", the usual length of steel pipes (indeterminate length) is 1.5 to 10m for hot-rolled steel pipes and equal to or greater than 1m for hot-extruded steel pipes. Cold drawn (rolled) steel pipes with a wall thickness of 0.5 to 1.0mm, 1.0 to 7m; those with a wall thickness greater than 1.0mm, 1.5 to 8m.

B. There are 45 types of hot-rolled (hot extruded) steel pipes with diameters ranging from 54 to 480mm; and 36 types with wall thicknesses ranging from 4.5 to 45mm. There are 65 types of cold-drawn (rolled) steel pipes with diameters ranging from 6 to 200mm; and 39 types of wall thickness ranging from 0.5 to 21mm.

C. There shall be no cracks, folds, cracks, cracks, folds, delamination and scarring defects on the inner and outer surfaces of the steel pipe. These defects shall be completely removed (except for pipes for mechanical processing). After removal, the wall thickness and appearance shall not be changed. diameter exceeds the negative deviation. Other minor surface defects that do not exceed the allowable negative deviation do not need to be removed.

D. Allowable depth of straight track. Hot-rolled and hot-extruded steel pipes with a diameter less than and equal to 140mm shall not exceed 5% of the nominal wall thickness, and the maximum depth shall not exceed 0.5mm; cold-drawn (rolled) steel pipes shall not exceed 4% of the nominal wall thickness, and the maximum depth shall not exceed 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 blank → heating → perforation → three-roll cross rolling, continuous rolling or extrusion → detubing → sizing (or diameter reduction) → cooling → straightening → hydraulic test (or flaw detection) → Mark → Warehouse

The raw material for rolling seamless pipes is round tube billet. The round tube billet must be cut by a cutting machine into a billet with a length of about 1 meter and sent to the furnace for heating via a conveyor belt. The billet is fed into the furnace and heated to a temperature of approximately 1,200 degrees Celsius. The fuel is hydrogen or acetylene. Temperature control in the furnace is a key issue. After the round tube comes out of the furnace, it must be pierced through a pressure punching 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 penetrate a variety of steel types. After perforation, the round tube blank is successively cross-rolled, continuous rolled or extruded by three rollers. After extrusion, the pipe must be removed and calibrated. The sizing machine rotates a tapered drill bit at high speed into the steel blank to drill 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 and is cooled by spraying water. After the steel pipe is cooled, it will be straightened. After straightening, the steel pipe is sent to the metal flaw detector (or hydraulic test) by a 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, steel pipes must undergo strict manual selection. After the quality inspection of the steel pipe, spray the serial number, specification, production batch number, etc. with paint. And it is hoisted into the warehouse by a crane.

2. Cold drawn (rolled) seamless steel pipe: round tube blank → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening →Hydraulic test (flaw detection)→Marking→Storage.

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 needs to be headed and annealed. After annealing, special acidic liquid should be used for pickling. After pickling, apply oil. Then it is followed by multiple passes of cold drawing (cold rolling) and then special heat treatment. After heat treatment, it is treated in the same way as the steel pipe cooling process.

Scope of application of stainless steel seamless pipes

Because stainless steel seamless pipes have good comprehensive properties, they are widely used in chemical industry, construction, water supply, drainage, petroleum, light and heavy industry, refrigeration, sanitation, plumbing, fire protection, electric power, aerospace, shipbuilding and other basic projects.