Carbon steel pipe: basic supporting materials and technological innovation in the industrial field

1. Core classification and characteristics of carbon steel pipes
Classification by production process
Seamless carbon steel pipe
Made by perforated hot rolling or cold rolling process, the pipe wall has no weld seams, high strength and good pressure resistance. It is typically used in high-pressure pipeline systems (such as steam pipelines in oil refining units) and mechanical structural parts (such as hydraulic cylinder barrels). For example, 20# seamless carbon steel pipe has a carbon content of about 0.2%, good plasticity and weldability, and is often used to manufacture fluid transportation pipelines, with a working pressure of more than 10MPa.
Welded carbon steel pipe
Made of steel plate coil welding, it is divided into straight seam welded pipe (ERW) and spiral welded pipe (SSAW) according to the weld form. Straight seam welded pipe has high production efficiency and is suitable for low-pressure fluid transportation (such as building water supply and drainage pipes); spiral welded pipe has a spiral distribution of welds and better tensile strength than straight seam pipes, and is often used in large-diameter gas pipelines (such as natural gas long-distance pipelines, with a diameter of up to 1420mm).
Classification by carbon content and performance
Low carbon steel pipe (C≤0.25%)
Such as Q235B steel pipe, good plasticity, excellent weldability, but low strength. Mainly used for building scaffolding, furniture frames, low-pressure fluid pipelines (such as water and gas transportation). In a certain construction project, Φ48mm×3.5mm Q235B welded steel pipes are used as scaffolding poles, which can withstand a construction load of 200kg/m².
Medium carbon steel pipe (0.25%<C≤0.6%)
45# steel pipe is a typical representative. After quenching and tempering, it has excellent comprehensive mechanical properties (tensile strength ≥600MPa) and is often used for mechanical transmission shafts and automobile axle sleeves. For example, the drive axle axle of a heavy truck uses 45# seamless steel pipe. After quenching + tempering, the impact toughness reaches 35J/cm², which meets the anti-fatigue requirements under complex road conditions.
High carbon steel pipe (C>0.6%)
High carbon content, high hardness but poor toughness, mainly used for wear-resistant parts, such as chain sleeves of scraper conveyors in coal mines. T8 steel pipe (carbon content 0.8%) can reach HRC55 hardness after quenching, and is used to manufacture wear-resistant mining drilling pipes.
Classification by functional use
Structural carbon steel pipe: used for building steel structures (such as stadium trusses) and bridge supports, and must meet the tensile strength ≥345MPa, such as straight seam electric welded steel pipes specified in GB/T 13793.
Carbon steel pipe for fluid transportation: in accordance with GB/T 3091 standard, used for water, gas, and steam transportation, requiring weld tightness, and often undergoing water pressure tests (test pressure is 1.5 times the working pressure).
Carbon steel pipe for machining: such as gear sleeves and hydraulic cylinders, requiring high-precision dimensions (outer diameter tolerance ±0.5%) and surface roughness (Ra≤1.6μm).
2. In-depth analysis of key performance and application scenarios
Mechanical properties and engineering adaptability
Strength and pressure resistance limit: The strength of carbon steel pipes increases with the increase of carbon content, but the plasticity decreases. For example, Q355B steel pipes (yield strength 355MPa) can be used to manufacture compressed air pipes with a working pressure of 6MPa, while 40Cr steel pipes (alloyed medium carbon steel) have a yield strength of 785MPa after quenching and tempering, which is suitable for high-pressure hydraulic systems (such as engineering machinery cylinders).
Fatigue resistance: Carbon steel pipes for bridges need to withstand alternating loads. A Yangtze River Bridge uses Φ600mm×12mm Q390 steel pipes, which have no cracks after 2 million fatigue tests (stress amplitude 120MPa).
Corrosion resistance and protective measures
Carbon steel pipes have limited atmospheric corrosion resistance and are prone to rust in humid environments. In marine engineering, "hot-dip galvanizing + epoxy coating" double-layer protection is used. For example, a steel pipe pile of an offshore wind power foundation is first hot-dip galvanized (zinc layer thickness ≥ 85μm), and then coated with 300μm thick epoxy paint. The service life is expected to be more than 25 years.
Welding and processing characteristics
Key points of welding process: Low-carbon steel pipes can be directly welded by manual arc welding (E43 welding rod); medium-carbon steel pipes need to be preheated before welding (preheating temperature 150℃~250℃) to avoid cold cracks. For example, 45# steel pipes need to be stress-relieved annealed (temperature 600℃~650℃) after welding.
Machinability: 35# steel pipes are prone to strip chips when cutting, and sulfur-containing cutting fluid (sulfur content 0.08%~0.12%) is required to improve chip breaking performance. After a certain machining company adopted this process, the tool life was extended by 30%.
3. Technological innovation and industrial upgrading dynamics
Breakthrough in the development of high-performance carbon steel pipes
Carbon steel pipes for ultra-high pressure
The X70 grade carbon steel pipe (yield strength ≥ 485MPa) developed by a steel company uses controlled rolling and controlled cooling (TMCP) technology to refine the grains and is used for natural gas pipelines with a design pressure of 10MPa. The wall thickness is reduced by 20% and the weight is reduced by 15% compared with the traditional Q345 steel pipe.
Weather-resistant carbon steel pipe
Adding 0.2%~0.5% of copper and phosphorus elements to form a dense rust layer to prevent corrosion from spreading. For example, Q355NH steel pipes are used for outdoor steel structures (such as lighthouse brackets), which can save annual painting maintenance and reduce life cycle costs by 40%.
Green production process innovation
Short process rolling technology
Using the "continuous casting and rolling" process, the steel billet is heated to 1150℃ and directly rolled into a pipe, which reduces energy consumption by 18% compared with the traditional "ingot + billet opening" process. After a steel pipe plant applied this technology, it saved 23,000 tons of standard coal per year.
Chromium-free passivation surface treatment
Replacing traditional hexavalent chromium passivation, silane treatment (silane solution with pH value 5~6) is used, the film thickness is 0.5~1μm, and the salt spray test (GB/T 10125) is 720 hours without rust, and has been used for drinking water transportation steel pipes.
Intelligent manufacturing application
A steel pipe company introduced a digital twin system, and used ANSYS to simulate the temperature field and stress distribution during the steel pipe rolling process, shortening the new product development cycle from 10 months to 6 months, while reducing trial rolling waste by 30%. For example, when developing Φ114mm×4mm 20# high-pressure boiler tubes, the simulated predicted wall thickness deviation was ≤0.1mm, which was consistent with the actual production results.
IV. Market application and development trend
Demand explosion in key areas
New energy field
Photovoltaic support pipes: Double-sided galvanized carbon steel pipes (zinc layer thickness ≥ 55μm) are used in desert photovoltaic projects. The wind and sand wear resistance is 2 times higher than that of ordinary steel pipes. The domestic demand is expected to reach 800,000 tons in 2025.
Hydrogen energy pipelines: X65 grade carbon steel pipes (passed the hydrogen embrittlement test) are used for low-pressure hydrogen pipelines (pressure ≤ 4MPa). In a demonstration project, the Φ219mm×8mm pipeline transports 99.99% pure hydrogen with a leakage rate of < 0.01%.
Infrastructure and high-end manufacturing
Underground integrated pipeline corridors: Q355B plastic-coated steel pipes with a diameter of Φ800mm×10mm are used, and the inner wall is coated with a PE layer (thickness ≥1.5mm). They are used for laying power and communication cables with a service life of more than 50 years.
Aerospace tooling: 45# precision seamless steel pipe (straightness ≤ 0.1mm/m) is ground and polished to manufacture high-pressure oil pipes for aircraft engine fuel systems, with a working pressure of 35MPa.
Industry challenges and response strategies
Raw material price fluctuations: Iron ore prices will rise by 20% in 2024, and the production cost of carbon steel pipes will increase. Enterprises will reduce raw material costs by optimizing the charge structure (adding 30% scrap steel). After a steel pipe plant adopted this measure, the cost per ton of steel decreased by 120 yuan.
International trade barriers: After the EU launched an anti-dumping investigation on Chinese carbon steel pipes, domestic companies turned to high value-added products, such as Cr-Mo alloy carbon steel pipes exported to the Middle East (used in high-temperature refining units), with a unit price 35% higher than ordinary steel pipes.
V. Future Technology Development Direction
Adaptability to extreme environments: Research and develop -40℃ low-temperature tough carbon steel pipes (impact energy ≥34J) for Arctic oil and gas pipelines; develop 200℃ high-temperature resistant 15CrMo steel pipes for geothermal power station steam pipelines.
Functional integration: Composite graphene coating on the inner wall of carbon steel pipes to achieve the dual functions of "corrosion protection + drag reduction". After application in a certain oil pipeline, the friction resistance was reduced by 18% and the oil transportation volume increased by 10%.
1. Core classification and characteristics of carbon steel pipes
Classification by production process
Seamless carbon steel pipe
Made by perforated hot rolling or cold rolling process, the pipe wall has no weld seams, high strength and good pressure resistance. It is typically used in high-pressure pipeline systems (such as steam pipelines in oil refining units) and mechanical structural parts (such as hydraulic cylinder barrels). For example, 20# seamless carbon steel pipe has a carbon content of about 0.2%, good plasticity and weldability, and is often used to manufacture fluid transportation pipelines, with a working pressure of more than 10MPa.
Welded carbon steel pipe
Made of steel plate coil welding, it is divided into straight seam welded pipe (ERW) and spiral welded pipe (SSAW) according to the weld form. Straight seam welded pipe has high production efficiency and is suitable for low-pressure fluid transportation (such as building water supply and drainage pipes); spiral welded pipe has a spiral distribution of welds and better tensile strength than straight seam pipes, and is often used in large-diameter gas pipelines (such as natural gas long-distance pipelines, with a diameter of up to 1420mm).
Classification by carbon content and performance
Low carbon steel pipe (C≤0.25%)
Such as Q235B steel pipe, good plasticity, excellent weldability, but low strength. Mainly used for building scaffolding, furniture frames, low-pressure fluid pipelines (such as water and gas transportation). In a certain construction project, Φ48mm×3.5mm Q235B welded steel pipes are used as scaffolding poles, which can withstand a construction load of 200kg/m².
Medium carbon steel pipe (0.25%<C≤0.6%)
45# steel pipe is a typical representative. After quenching and tempering, it has excellent comprehensive mechanical properties (tensile strength ≥600MPa) and is often used for mechanical transmission shafts and automobile axle sleeves. For example, the drive axle axle of a heavy truck uses 45# seamless steel pipe. After quenching + tempering, the impact toughness reaches 35J/cm², which meets the anti-fatigue requirements under complex road conditions.
High carbon steel pipe (C>0.6%)
High carbon content, high hardness but poor toughness, mainly used for wear-resistant parts, such as chain sleeves of scraper conveyors in coal mines. T8 steel pipe (carbon content 0.8%) can reach HRC55 hardness after quenching, and is used to manufacture wear-resistant mining drilling pipes.
Classification by functional use
Structural carbon steel pipe: used for building steel structures (such as stadium trusses) and bridge supports, and must meet the tensile strength ≥345MPa, such as straight seam electric welded steel pipes specified in GB/T 13793.
Carbon steel pipe for fluid transportation: in accordance with GB/T 3091 standard, used for water, gas, and steam transportation, requiring weld tightness, and often undergoing water pressure tests (test pressure is 1.5 times the working pressure).
Carbon steel pipe for machining: such as gear sleeves and hydraulic cylinders, requiring high-precision dimensions (outer diameter tolerance ±0.5%) and surface roughness (Ra≤1.6μm).
2. In-depth analysis of key performance and application scenarios
Mechanical properties and engineering adaptability
Strength and pressure resistance limit: The strength of carbon steel pipes increases with the increase of carbon content, but the plasticity decreases. For example, Q355B steel pipes (yield strength 355MPa) can be used to manufacture compressed air pipes with a working pressure of 6MPa, while 40Cr steel pipes (alloyed medium carbon steel) have a yield strength of 785MPa after quenching and tempering, which is suitable for high-pressure hydraulic systems (such as engineering machinery cylinders).
Fatigue resistance: Carbon steel pipes for bridges need to withstand alternating loads. A Yangtze River Bridge uses Φ600mm×12mm Q390 steel pipes, which have no cracks after 2 million fatigue tests (stress amplitude 120MPa).
Corrosion resistance and protective measures
Carbon steel pipes have limited atmospheric corrosion resistance and are prone to rust in humid environments. In marine engineering, "hot-dip galvanizing + epoxy coating" double-layer protection is used. For example, a steel pipe pile of an offshore wind power foundation is first hot-dip galvanized (zinc layer thickness ≥ 85μm), and then coated with 300μm thick epoxy paint. The service life is expected to be more than 25 years.
Welding and processing characteristics
Key points of welding process: Low-carbon steel pipes can be directly welded by manual arc welding (E43 welding rod); medium-carbon steel pipes need to be preheated before welding (preheating temperature 150℃~250℃) to avoid cold cracks. For example, 45# steel pipes need to be stress-relieved annealed (temperature 600℃~650℃) after welding.
Machinability: 35# steel pipes are prone to strip chips when cutting, and sulfur-containing cutting fluid (sulfur content 0.08%~0.12%) is required to improve chip breaking performance. After a certain machining company adopted this process, the tool life was extended by 30%.
3. Technological innovation and industrial upgrading dynamics
Breakthrough in the development of high-performance carbon steel pipes
Carbon steel pipes for ultra-high pressure
The X70 grade carbon steel pipe (yield strength ≥ 485MPa) developed by a steel company uses controlled rolling and controlled cooling (TMCP) technology to refine the grains and is used for natural gas pipelines with a design pressure of 10MPa. The wall thickness is reduced by 20% and the weight is reduced by 15% compared with the traditional Q345 steel pipe.
Weather-resistant carbon steel pipe
Adding 0.2%~0.5% of copper and phosphorus elements to form a dense rust layer to prevent corrosion from spreading. For example, Q355NH steel pipes are used for outdoor steel structures (such as lighthouse brackets), which can save annual painting maintenance and reduce life cycle costs by 40%.
Green production process innovation
Short process rolling technology
Using the "continuous casting and rolling" process, the steel billet is heated to 1150℃ and directly rolled into a pipe, which reduces energy consumption by 18% compared with the traditional "ingot + billet opening" process. After a steel pipe plant applied this technology, it saved 23,000 tons of standard coal per year.
Chromium-free passivation surface treatment
Replacing traditional hexavalent chromium passivation, silane treatment (silane solution with pH value 5~6) is used, the film thickness is 0.5~1μm, and the salt spray test (GB/T 10125) is 720 hours without rust, and has been used for drinking water transportation steel pipes.
Intelligent manufacturing application
A steel pipe company introduced a digital twin system, and used ANSYS to simulate the temperature field and stress distribution during the steel pipe rolling process, shortening the new product development cycle from 10 months to 6 months, while reducing trial rolling waste by 30%. For example, when developing Φ114mm×4mm 20# high-pressure boiler tubes, the simulated predicted wall thickness deviation was ≤0.1mm, which was consistent with the actual production results.
IV. Market application and development trend
Demand explosion in key areas
New energy field
Photovoltaic support pipes: Double-sided galvanized carbon steel pipes (zinc layer thickness ≥ 55μm) are used in desert photovoltaic projects. The wind and sand wear resistance is 2 times higher than that of ordinary steel pipes. The domestic demand is expected to reach 800,000 tons in 2025.
Hydrogen energy pipelines: X65 grade carbon steel pipes (passed the hydrogen embrittlement test) are used for low-pressure hydrogen pipelines (pressure ≤ 4MPa). In a demonstration project, the Φ219mm×8mm pipeline transports 99.99% pure hydrogen with a leakage rate of < 0.01%.
Infrastructure and high-end manufacturing
Underground integrated pipeline corridors: Q355B plastic-coated steel pipes with a diameter of Φ800mm×10mm are used, and the inner wall is coated with a PE layer (thickness ≥1.5mm). They are used for laying power and communication cables with a service life of more than 50 years.
Aerospace tooling: 45# precision seamless steel pipe (straightness ≤ 0.1mm/m) is ground and polished to manufacture high-pressure oil pipes for aircraft engine fuel systems, with a working pressure of 35MPa.
Industry challenges and response strategies
Raw material price fluctuations: Iron ore prices will rise by 20% in 2024, and the production cost of carbon steel pipes will increase. Enterprises will reduce raw material costs by optimizing the charge structure (adding 30% scrap steel). After a steel pipe plant adopted this measure, the cost per ton of steel decreased by 120 yuan.
International trade barriers: After the EU launched an anti-dumping investigation on Chinese carbon steel pipes, domestic companies turned to high value-added products, such as Cr-Mo alloy carbon steel pipes exported to the Middle East (used in high-temperature refining units), with a unit price 35% higher than ordinary steel pipes.
V. Future Technology Development Direction
Adaptability to extreme environments: Research and develop -40℃ low-temperature tough carbon steel pipes (impact energy ≥34J) for Arctic oil and gas pipelines; develop 200℃ high-temperature resistant 15CrMo steel pipes for geothermal power station steam pipelines.
Functional integration: Composite graphene coating on the inner wall of carbon steel pipes to achieve the dual functions of "corrosion protection + drag reduction". After application in a certain oil pipeline, the friction resistance was reduced by 18% and the oil transportation volume increased by 10%.
Deepening of intelligent manufacturing: Promote "5G + industrial robot" welding to achieve fully automatic tracking of carbon steel pipe welds (tracking accuracy ±0.5mm). After a certain enterprise applied this technology, the welding qualification rate increased from 89% to 99.5%.