The steel pipe whose outer diameter to wall thickness ratio is less than 20 is called thick-wall steel pipe.

Mainly used as petroleum geological drilling pipes, cracking pipes for petrochemical industry, boiler pipes, bearing pipes and high-precision structural pipes for automobiles, tractors, and aviation.

Manufacturing process of seamless steel 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) → marking → warehousing.

The raw material for rolling seamless pipes is round pipe billet ,The round pipe billets are 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 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 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 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 rotates at a high speed through a conical drill bit to drill holes into the steel blank 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 straightening, the steel pipe 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 billet → heating → piercing → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening → water Compression test (flaw detection) → mark → warehousing.

Seamless pipe production classification-hot rolled pipe, cold rolled pipe, cold drawn pipe, extruded pipe, pipe jacking

1. Seamless steel pipe for structure (GB/T8162-1999) is a seamless steel pipe for general structure and mechanical structure.

2. Seamless steel pipes for fluid transportation (GB/T8163-1999) are general seamless steel pipes used to transport water, oil, gas and other fluids.

3. Seamless steel pipes for low and medium pressure boilers (GB3087-1999) are used to manufacture superheated steam pipes, boiling water pipes for low and medium pressure boilers of various structures and superheated steam pipes for locomotive boilers, large fire pipes, small fire pipes and arch bricks High-quality carbon structural steel hot-rolled and cold-drawn (rolled) seamless steel tubes for pipes.

4. Seamless steel pipes for high-pressure boilers (GB5310-1995) are high-quality carbon steel, alloy steel and stainless heat-resistant steel seamless steel pipes for the heating surface of water-tube boilers with high pressure and above.

5. High-pressure seamless steel pipes for fertilizer equipment (GB6479-2000) are high-quality carbon structural steel and alloy steel seamless steel pipes suitable for chemical equipment and pipelines with working temperature of -40~400℃ and working pressure of 10~30Ma.

6. Seamless steel pipes for petroleum cracking (GB9948-88) are seamless steel pipes suitable for furnace tubes, heat exchangers and pipelines in petroleum refineries.

7. Steel pipes for geological drilling (YB235-70) are steel pipes used for core drilling by geological departments. They can be divided into drill pipes, drill collars, core pipes, casing pipes and sedimentation pipes according to their purposes.

8. Seamless steel pipes for diamond core drilling (GB3423-82) are seamless steel pipes for drill pipes, core rods, and casings used for diamond core drilling.

9. Petroleum drilling pipe (YB528-65) is a seamless steel pipe used for thickening inside or outside at both ends of oil drilling. Steel pipes are divided into two types: wire and non-wired. Wired pipes are connected by joints, and non-wired pipes are connected with tool joints by butt welding.

10. Carbon steel seamless steel pipes for ships (GB5213-85) are carbon steel seamless steel pipes used in the manufacture of Class I pressure piping systems, Class II pressure piping systems, boilers and superheaters. The working temperature of carbon steel seamless steel pipe wall does not exceed 450℃, while that of alloy steel seamless steel pipe wall exceeds 450℃.

11. Seamless steel tubes for automobile axle sleeves (GB3088-82) are high-quality carbon structural steel and alloy structural steel hot-rolled seamless steel tubes for the manufacture of automobile axle sleeves and drive axle axle tubes.

12. High-pressure oil pipes for diesel engines (GB3093-86) are cold-drawn seamless steel pipes used to manufacture high-pressure pipes for diesel engine injection systems.

13. Precision inner diameter seamless steel pipes for hydraulic and pneumatic cylinders (GB8713-88) are cold-drawn or cold-rolled precision seamless steel pipes with precise inner diameters for the manufacture of hydraulic and pneumatic cylinders.

14. Cold-drawn or cold-rolled precision seamless steel pipe (GB3639-83) is a cold-drawn or cold-rolled precision seamless steel pipe with high dimensional accuracy and good surface finish for mechanical structure and hydraulic equipment. The use of precision seamless steel pipes to manufacture mechanical structures or hydraulic equipment can greatly save machining man-hours, increase material utilization, and at the same time help improve product quality.

15. Structural stainless steel seamless steel pipe (GB/T14975-1994) is a hot-rolled stainless steel made of corrosion-resistant pipes and structural parts and parts widely used in chemical, petroleum, textile, medical, food, machinery and other industries ( Extruded, expanded) and cold drawn (rolled) seamless steel tubes.

16. Stainless steel seamless steel pipes for fluid transportation (GB/T14976-1994) are hot-rolled (extruded, expanded) and cold-drawn (rolled) seamless steel pipes made of stainless steel for fluid transportation.

17. Special-shaped seamless steel pipe is a general term for seamless steel pipes with cross-sectional shapes other than round pipes. According to the different shape and size of the steel pipe section, it can be divided into equal-walled special-shaped seamless steel pipe (code D), unequal-walled special-shaped seamless steel pipe (code BD), and variable diameter special-shaped seamless steel pipe (code BJ). Special-shaped seamless steel pipes are widely used in various structural parts, tools and mechanical parts. Compared with round pipes, special-shaped pipes generally have larger moments of inertia and section modulus, and have greater bending and torsion resistance, which can greatly reduce structural weight and save steel.

Generally, seamless steel pipes are made of 10, 20, 30, 35, 45 and other high-quality carbon steels such as 16Mn, 5MnV and other low-alloy structural steels or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other composite steels by hot rolling or cold rolling. Seamless pipes made of low carbon steel such as 10 and 20 are mainly used for fluid transportation pipelines. Seamless tubes made of medium carbon steel such as 45 and 40Cr are used to manufacture mechanical parts, such as stressed parts of automobiles and tractors.　Generally, seamless steel pipes must be used for strength and flattening tests. Hot-rolled steel pipes are delivered in hot-rolled state or heat-treated state; cold-rolled steel pipes are delivered in hot-heated state. Seamless steel tubes for low and medium pressure boilers: used to manufacture various low and medium pressure boilers, superheated steam tubes, boiling water tubes, water wall tubes and superheated steam tubes for locomotive boilers, large smoke tubes, small smoke tubes and arched brick tubes.

　　 Use high-quality carbon structural steel hot-rolled or cold-rolled (dial) seamless steel pipe. It is mainly made of No. 10 and No. 20 steel. In addition to ensuring the chemical composition and mechanical properties, a hydraulic test, such as crimping, flaring, and flattening, must be performed. Hot-rolled products are delivered in a hot-rolled state, and cold-rolled products are delivered in a heat-treated state.

18.GB18248-2000 (Seamless steel pipe for gas cylinders) is mainly used to make various gas and hydraulic cylinders. Its representative materials are 37Mn, 34Mn2V, 35CrMo, etc.

Identify fake and inferior thick-walled steel pipes

1. Fake thick-walled steel pipes are easy to fold.

2. Fake thick-walled steel pipes often have pitting on the surface.

3. Fake thick-walled steel pipes are prone to scars.

4. The surface of fake and inferior materials is easy to crack.

5. Fake thick-walled steel pipes are easy to scratch.

6. Counterfeit thick-walled steel pipes have no metallic luster and are light red or similar to pig iron.

7. The cross ribs of counterfeit thick-walled steel pipes are thin and low, and often appear dissatisfied.

8. The cross section of the fake thick-walled steel pipe is oval.

10. The material of fake thick-walled steel pipe contains many impurities and the density of steel is too small.

11. The inner diameter of fake thick-walled steel pipe fluctuates greatly.

12. The trademarks and printing of high-quality tubes are relatively standardized.

13. For three large threads with a diameter of more than 16 steel pipes, the distance between the two marks is more than IM.

14. The longitudinal bars of shoddy steel rebar are often wavy.

15. Fake thick-wall steel pipe manufacturers do not drive, so the packaging is loose. The side is oval.