Seamless pipes is a long strip of steel with hollow section and no joint around it. Steel pipes have hollow sections and are widely used as pipelines for transporting fluids, such as pipelines for transporting oil, natural gas, gas, water and some solid materials. Compared with solid steel such as round steel, steel pipe is lighter in weight when its bending and torsional strength is the same. It is an economic section steel. It is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipe, automobile transmission shaft, bicycle frame and steel scaffold used in construction. Manufacturing ring parts with steel pipes can improve the utilization rate of materials, simplify the manufacturing process, and save materials and processing hours, such as rolling bearing rings, Jack sleeves, etc. at present, steel pipes have been widely used for manufacturing. Steel pipe is also an indispensable material for all kinds of conventional weapons. Gun barrel and barrel should be made of steel pipe. Steel pipe can be divided into round pipe and special-shaped pipe according to different cross-sectional area and shape. Because the circular area is the largest under the condition of equal circumference, more fluid can be transported by circular pipe. In addition, when the ring section is subjected to internal or external radial pressure, the force is more uniform. Therefore, the vast majority of steel pipes are round pipes. However, the circular pipe also has certain limitations. For example, under the condition of plane bending, the bending strength of the circular pipe is not as strong as that of the square and rectangular pipe. Square and rectangular pipes are commonly used in the framework of some agricultural machines and tools and steel and wood furniture. Special shaped steel pipes with other section shapes are also required according to different purposes.
At present, there are more than 5100 production plants under more than 1850 companies in more than 110 countries, including more than 260 plants under more than 170 companies in 44 countries. In 2000, the apparent consumption of seamless pipes in China was 4.18 million tons, including 3.821 million tons of domestic supply, accounting for 91.4% of the total domestic demand. The import was 359000 tons, accounting for 8.59% of the total domestic demand. In the same year, the consumption of oil pipes was about 910000 tons. The import is about 252000 tons. Imported pipes account for about 70% of the total domestic consumption, of which imported pipes account for 27.69% of the total domestic consumption, and oil pipes account for about 70% of the total imports of seamless steel pipes. Oil pipes imported from Japan account for more than half of the total imports. Tianjin steel pipe company, China’s largest oil casing production base, produced 522000 tons of steel pipe products in 2000, including 364100 tons of oil casing. Casing accounts for more than half of the national oil production. It ranks first in China’s casing Market in terms of output and sales volume.
From the international and domestic markets, the existing production capacity of seamless steel pipe (including special oil pipe) has exceeded the demand. Therefore, in the future, the focus should be on giving full play to the capacity of existing units and developing products such as oil pipes, high-pressure boiler pipes and gas cylinder pipes with high strength grade, high resistance to damage and high resistance to corrosion. It is also the content of optimizing the product structure of China’s steel market. This is also the key to increase the competitiveness of products at home and abroad and expand market share. In other words, improving the market competitiveness of domestic steel pipe enterprises is the long-term task and the key to the successful development of domestic enterprises after China’s accession to the WTO.
Seamless pipes is divided into hot rolled (extruded) seamless pipes and cold drawn (rolled) seamless pipes due to its different manufacturing processes. Cold drawn (rolled) pipe is divided into circular pipe and special-shaped pipe. Seamless pipes are divided into the following varieties due to their different uses:
1. GB / T8162-1999 (seamless pipes for structure). It is mainly used for general structure and mechanical structure. Its representative material (brand): carbon steel, 20#, 45# steel; Alloy steel Q345, 20Cr, 40Cr, 20CrMo, 30-35crmo, 42CrMo, etc.
2. GB / t8163-1999 (seamless steel pipe for fluid transportation). It is mainly used for conveying fluid pipelines on engineering and large equipment. The representative materials (brands) are 20#, Q345, etc.
3. GB3087-1999 (seamless steel pipe for low and medium pressure boiler) is a high-quality carbon structural steel hot-rolled and cold drawn (rolled) seamless steel pipe used for manufacturing superheated steam pipe, boiling water pipe, superheated steam pipe and arch brick pipe for low and medium pressure boiler of various structures. The representative materials are 10#, 20# steel.
4. GB5310-1995 (seamless steel pipe for high pressure boiler) is a high-quality carbon steel, alloy steel and stainless heat-resistant steel seamless steel pipe used to manufacture the heating surface of water tube boiler with high pressure and above. The representative materials are 20g, 12Cr1MoVG, 15CrMoG, etc.
5. Gb1479-2000 (seamless steel pipe for high-pressure chemical fertilizer equipment) is a high-quality carbon structural steel and alloy steel seamless steel pipe suitable for chemical equipment and pipelines with working temperature of – 40 ~ 400 ℃ and working pressure of 10 ~ 30mA. The representative materials are 20#, 16Mn, 12CrMo, 12cr2mo, etc.
6. GB9948-1988 (seamless steel pipe for petroleum cracking). It is mainly used for boilers, heat exchangers and fluid transmission pipelines in petroleum smelters. Its representative materials are 20#, 12CrMo, 1Cr5Mo, 1cr19ni11nb, etc.
7. The steel pipe for geological drilling (yb235-70) is the steel pipe used by the geological department for core drilling. According to the purpose, it can be divided into drill pipe, drill collar, core pipe, casing and sedimentation pipe.
8. Seamless steel pipe for diamond core drilling (gb3423-82) is a seamless steel pipe for drill pipe, rock core rod and casing used for diamond core drilling.
9. Oil drilling pipe (yb528-65) is a seamless steel pipe used for internal or external thickening at both ends of oil drilling. The steel pipe is divided into turning wire and non turning wire. The turning wire pipe is connected with the joint, and the non turning wire pipe is connected with the tool joint by butt welding.
10. Gb5312-1999 (carbon steel and carbon manganese steel seamless pipes for ships) is a carbon steel seamless pipes for manufacturing class I pressure pipe system, class II pressure pipe system, boiler and superheater. The working temperature of carbon steel seamless pipes wall shall not exceed 450 ℃, and the working temperature of alloy steel seamless pipes wall shall exceed 450 ℃. The representative materials are 360, 410 and 460 steel grades.
11. Seamless pipes for automobile half axle sleeve (gb3088-82) is a hot-rolled seamless pipes made of high-quality carbon structural steel and alloy structural steel for automobile half axle sleeve and drive axle housing.
12. High pressure oil pipe for diesel engine (gb3093-86) is a cold drawn seamless steel pipe for manufacturing high pressure pipe of diesel injection system.
13. Precision inner diameter seamless pipes for hydraulic and pneumatic cylinder barrel (GB8713-88) is a cold drawn or cold-rolled precision seamless pipes with precision inner diameter for manufacturing hydraulic and pneumatic cylinder barrel.
14. Cold drawn or cold rolled precision seamless pipes (gb3639-83) is a cold drawn or cold rolled precision seamless pipes with high dimensional accuracy and good surface finish for mechanical structure and hydraulic equipment. Selecting precision seamless steel pipe to manufacture mechanical structure or hydraulic equipment can greatly save machining hours, improve material utilization rate and improve product quality.
15. Stainless steel seamless steel pipe for structure (GB / T14975-1994) is a hot-rolled (extruded, expanded) and cold drawn (rolled) seamless steel pipe made of stainless steel for corrosion-resistant pipes, structural parts and parts widely used in chemical, petroleum, light textile, medical, food, machinery and other industries.
16. Stainless steel seamless steel pipe for fluid transportation (GB / t14976-1994) is a hot-rolled (extruded, expanded) and cold drawn (rolled) seamless steel pipe made of stainless steel for fluid transportation.
17. Special shaped seamless steel pipe is the general name of seamless steel pipe with other section shapes except circular pipe. According to the shape and size of steel pipe section, it can be divided into equal wall thickness special-shaped seamless steel pipe (code D), unequal wall thickness special-shaped seamless steel pipe (code BD) and variable diameter special-shaped seamless steel pipe (code BJ). Special shaped seamless steel pipe is widely used in various structural parts, tools and mechanical parts. Compared with circular pipe, special-shaped pipe generally has larger moment of inertia and section modulus, and has greater bending and torsion resistance, which can greatly reduce the structural weight and save steel.
18. GB18248-2000 (seamless pipes for gas cylinder). It is mainly used to make all kinds of gas and hydraulic cylinders. Its representative materials are 37Mn, 34Mn2V, 35CrMo, etc.
In addition, there are GB / t17396-1998 (hot rolled seamless pipes for hydraulic prop), gb3093-1986 (high pressure seamless pipes for diesel engine), GB / t3639-1983 (cold drawn or cold rolled precision seamless pipes), GB / t3094-1986 (cold drawn seamless steel pipe, special-shaped steel pipe), GB / t8713-1988 (precision inner diameter seamless steel pipe for hydraulic and pneumatic cylinder) GB13296-1991 (stainless steel seamless pipes for boiler and heat exchanger), GB / T14975-1994 (stainless steel seamless pipes for structure), GB / t14976-1994 (stainless steel seamless pipes for fluid transmission), GB / t5035-1993 (seamless pipes for automobile axle sleeve pipe), API Spec 5ct-1999 (Specification for casing and oil pipe), etc.
1. Hot rolled (extruded seamless steel pipe): round tube blank → heating → perforation → 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 tube is round tube blank. The round tube blank shall be cut and processed by the cutter, and the blank with a growth of about 1m shall be sent to the furnace for heating through the conveyor belt. The billet is sent to the furnace for heating at a temperature of about 1200 degrees Celsius. The fuel is hydrogen or acetylene. Temperature control in furnace is a key problem After the round tube blank is discharged from the furnace, it shall be pierced through the pressure piercer. Generally, the more common piercer is the cone roll piercer. This kind of piercer has high production efficiency, good product quality, large perforation diameter expansion, and can wear a variety of steel grades. After perforation, the round tube blank is successively rolled by three roll cross rolling, continuous rolling or extrusion. After extrusion, take off the pipe for sizing. The sizing machine rotates into the steel embryo at high speed through the conical drill to form a steel pipe. The inner diameter of the steel pipe is determined by the outer diameter length of the sizing machine bit. After sizing, the steel pipe enters the cooling tower and is cooled by water spray. After cooling, the steel pipe will be straightened. After straightening, the steel pipe is sent to the metal flaw detector (or hydrostatic 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. Steel pipes should be strictly selected by hand after quality inspection. After the steel pipe is inspected, the number, specification, production batch number, etc. shall be sprayed with paint. And hoisted into the warehouse by 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) → blank tube → heat treatment → straightening → hydrostatic test (flaw detection) → marking → warehousing.
The rolling method of cold drawn (rolled) seamless steel pipe is more complex 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 started and annealed. After annealing, special acid liquid shall be used for pickling. After pickling, apply oil. Then it is followed by multi pass cold drawing (cold rolling) and special heat treatment. After heat treatment, it will be straightened. After straightening, the steel pipe is sent to the metal flaw detector (or hydrostatic 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. Steel pipes should be strictly selected by hand after quality inspection. After the steel pipe is inspected, the number, specification, production batch number, etc. shall be sprayed with paint. And hoisted into the warehouse by crane.