Carbon Steel Pipe: Manufacturing Process, Application Scenarios and Development Trends

Carbon steel pipe is a tubular steel material made from carbon steel plates or coils through forming, welding, or piercing and rolling. It inherits the advantages of carbon steel: low cost, high strength, and ease of processing. Its tubular structure's pressure resistance and conveying capacity make it a core material for fluid transportation, structural support, and machinery manufacturing. A variety of manufacturing processes can be selected based on pressure requirements and media characteristics, serving a wide range of industries, including oil and gas, construction, chemicals, and municipal engineering. This article will comprehensively analyze the technical characteristics and practical value of carbon steel pipe from five perspectives: definition and classification, core characteristics, typical applications, selection criteria, and future trends.

I. Definition and Classification of Carbon Steel Pipe
Carbon steel pipe is made from carbon steel with a carbon content of 0.02%-2.11% and is manufactured through a process that progresses from raw material forming to joining/rolling to heat treatment and testing. Its core function is to convey fluids (liquids, gases, powders) or serve as structural load-bearing components. Based on manufacturing process, application, and performance, seamless carbon steel pipes are primarily categorized as follows:

Classification by Manufacturing Process

Seamless carbon steel pipes (Seamless Pipe): Made from solid carbon steel round billets, they are either heated and pierced (hot rolled) or cold drawn/cold rolled. They have no welded seams and offer strong pressure-bearing capacity. Further categorized by rolling process:

Hot-rolled seamless pipes: Round billets are heated to 1200-1300°C, then pierced and rolled. Wall thicknesses range from 2.5-100mm, and outer diameters range from 10-630mm. For example, 20# steel seamless pipes according to GB/T 8163 are suitable for high-pressure fluid transportation (e.g., hydraulic systems and steam pipelines). Cold-drawn/cold-rolled seamless pipes: These are drawn or rolled at room temperature using hot-rolled seamless pipes as billets. They offer high dimensional accuracy (OD tolerance ±0.1mm), a smooth surface (Ra ≤ 1.6μm), and can be as thin as 0.5mm. Cold-drawn pipes, such as those meeting the GB/T 17396 standard, are used for precision machinery parts (e.g., cylinders and spindle sleeves).
Welded carbon steel pipes: These are made from carbon steel coils/plates, formed by coiling and then welded. They are cheaper than seamless pipes and account for over 70% of the total carbon steel pipe production. By welding method:

ERW Pipe: Carbon steel coils are rolled into a cylindrical shape using a continuous forming machine, and the longitudinal seams are welded using high-frequency induction welding (ERW). These pipes have outer diameters ranging from 10-630mm and wall thicknesses ranging from 1.0-16mm. These pipes, such as Q235B ERW pipes in accordance with GB/T 3091, are used for low-pressure fluid transportation (such as tap water and natural gas branch pipes).

SSAW Pipe: Carbon steel coils are coiled in a helical direction, and the spiral seams are welded using submerged arc welding. These pipes offer strong lateral bending resistance. These pipes, such as Q345B SSAW pipes in accordance with SY/T 5037, are used for large-diameter oil and gas pipelines (such as the West-East Gas Pipeline). Classification by Application
Carbon steel pipes for fluid transportation, such as GB/T 8163 (seamless pipes for fluid transportation) and GB/T 3091 (welded pipes for low-pressure fluid transportation), require excellent sealing properties and are used for transporting water, oil, natural gas, steam, etc.
Carbon steel pipes for structures, such as GB/T 8162 (seamless pipes for structures) and GB/T 12770 (stainless steel pipes for mechanical structures, similar carbon steel), prioritize tensile strength and toughness and are used in building steel structures (such as trusses and columns) and mechanical supports.
Carbon steel pipes for high-pressure boilers, such as GB/T 5310 (seamless pipes for high-pressure boilers), are made of low-carbon alloy steels such as 20G and 15CrMoG. They must withstand temperatures exceeding 400°C and high pressures (≥3.82 MPa) and are used in boiler water walls and superheaters.​
II. Core Characteristics of Carbon Steel Pipes

Strong pressure and deformation resistance: Seamless carbon steel pipes have no welded weak points and boast a tensile strength of 400-900 MPa, capable of withstanding high pressures of 10-100 MPa (e.g., high-pressure oil pipelines). Spiral welded pipes disperse stress through the spiral weld seam, offering 20%-30% higher transverse load resistance than straight seam welded pipes, making them suitable for buried pipelines (to withstand soil pressure).

High fluid transport efficiency: Smooth inner wall (roughness Ra ≤ 6.3μm for seamless pipes, ≤ 12.5μm for welded pipes) reduces fluid resistance, resulting in a 15%-20% improvement in transport efficiency compared to cast iron pipes. The tubular structure also offers excellent sealing properties, effectively preventing leakage (leakage rate ≤ 0.1%) when connected via threads, flanges, or welds. Significant cost and processing advantages: Welded carbon steel pipes are made from carbon steel coils, and the manufacturing cost is only 1/2-2/3 that of seamless pipes, making them suitable for large-scale, low-pressure transmission applications. Furthermore, carbon steel pipes are easy to process, adapting to complex installation environments (such as bends in municipal pipelines) through cutting, drilling, and bending.

Suitable for a variety of media and environments: By selecting different materials (such as mild steel for neutral media resistance and low-alloy carbon steel for mild corrosion resistance) and applying anti-corrosion treatments (galvanizing or plastic coating), they can be used in environments such as fresh water, crude oil, natural gas, and soil, with a service life of 10-30 years (plastic-coated pipes have a lifespan of over 20 years). Typical Applications of Carbon Steel Pipes

Oil and Gas Transportation: Seamless carbon steel pipes (such as API 5L X65 seamless pipes) are used for high-pressure oil pipelines (withstanding pressures of 30-70 MPa) at oil and gas field wellheads and gathering pipelines. Spiral welded pipes (API 5L X70 spiral welded pipes) are used for long-distance oil and gas trunk lines (such as the China-Russia East Line Natural Gas Pipeline, with a diameter of 1420 mm). Cathodic protection (impressed current) is used to enhance soil corrosion resistance.

Municipal and Water Supply and Drainage: Longitudinal welded pipes (Q235B, GB/T 3091) are used for urban water mains (diameters 100-600 mm) and stormwater drainage pipes. Plastic-coated welded carbon steel pipes (with an epoxy resin coating on the inner wall and a polyethylene coating on the outer wall) are used for sewage pipes in chemical parks. They are resistant to acid and alkali corrosion (pH 2-12), preventing sewage leakage and soil contamination. In the construction and steel structure sector: Structural seamless pipes (20# steel, GB/T 8162) are used in steel columns for super-high-rise buildings (such as some support columns of the Guangzhou Tower, with diameters of 500-800mm). These pipes are welded together to form frames, combining strength and lightweight. Cold-drawn seamless pipes are used in curtain wall support keels, offering high dimensional accuracy (outer diameter tolerance ±0.05mm) and ensuring smooth installation.
In the machinery and equipment sector: Cold-drawn seamless pipes (45# steel, GB/T 3639) are used in hydraulic cylinder bodies, with a honed inner wall (Ra ≤ 0.8μm) to ensure smooth flow of hydraulic oil. Thick-walled seamless pipes (10-50mm thickness) are used in machine tool spindle sleeves and heavy machinery bases to withstand radial loads and vibration. Energy and Chemical Industry: High-pressure boiler seamless pipes (20G, GB/T 5310) are used for water-cooled wall tubes in power plant boilers (withstand 450°C, 10MPa steam). Low-alloy carbon steel pipes (15CrMoG) are used for jacketed pipes in chemical reactors, resistant to temperatures up to 350°C and corrosion from organic solvents, ensuring a stable reaction process.

IV. Key Points for Selecting Carbon Steel Pipes

Matching Pressure and Media Requirements: For high-pressure applications (such as oil and gas wellheads and boilers), seamless pipes (such as API 5L X65 and GB/T 5310) are preferred to eliminate weld leakage risks. For low-pressure applications (such as tap water and natural gas branch lines), welded pipes (GB/T 3091 and SY/T 5037) are preferred to reduce costs. For transporting corrosive media (such as sewage and acid and alkali solutions), plastic-coated/galvanized carbon steel pipes or low-alloy carbon steel (such as 16Mn) are recommended. Focus on key technical parameters:

Wall thickness and outer diameter: Calculate wall thickness based on pressure (for example, according to the API 5L standard, X65 steel transporting 10MPa natural gas requires a wall thickness of ≥12mm). The outer diameter must be adapted to the connecting components (such as the flange aperture), with tolerances controlled within ±1%.

Mechanical properties: Fluid transport pipes must ensure a tensile strength of ≥400MPa and an elongation of ≥20%. Structural pipes must meet a yield strength of ≥235MPa (Q235) to avoid deformation under load.

Sealing: Welded pipes must pass a hydrostatic test (pressure ≥1.5 times the working pressure, maintained at this pressure for 30 minutes without leakage). Seamless pipes must undergo ultrasonic testing (UT) to detect internal wall defects. Confirm the standard and corrosion protection method: Choose according to industry standards, such as API 5L for the oil and gas sector and GB/T 3091 for the municipal sector. Outdoor or buried pipes require corrosion protection, such as galvanizing (zinc coating thickness ≥ 85μm) or 3PE (polyethylene + adhesive + epoxy powder coating, thickness ≥ 2.0mm) to extend service life.
Consider installation and maintenance costs: Spiral welded pipe is preferred for large-diameter pipes (diameter ≥ 1000mm). Single pipes can be up to 12m long, reducing the number of welded joints (reducing installation costs by 30%). For pipes that require frequent maintenance (such as branch pipes for chemical equipment), choose seamless pipe with flange connections for ease of disassembly.​
V. Future Development Trends of Carbon Steel Pipes

Upgrading to High Strength and Toughness: Through microalloying (adding Nb and V) and controlled rolling and cooling processes, high-strength seamless pipes (such as API 5L X90 and X100) are being developed. With a 15% reduction in wall thickness, the pressure-bearing capacity is increased by 30%, enabling deep-sea oil and gas transportation (withstanding seawater pressures exceeding 100 MPa). Simultaneously, optimized welding processes (such as laser welding) are being used to improve the weld strength of spiral welded pipes, bringing them closer to the performance of the base material.

Enhancing Corrosion Resistance: Alloyed carbon steel pipes (such as those with Cr, Mo, and Cu) are being promoted, achieving corrosion resistance 5-10 times higher than that of ordinary carbon steel. These pipes are being used in coastal oil and gas pipelines to protect against seawater corrosion. New anti-corrosion coatings (such as graphene composite coatings) are being developed and applied to the inner wall of welded pipes to reduce wax deposition during crude oil transportation and improve transportation efficiency. Green Manufacturing and Recycling: Carbon steel pipe raw materials are produced using a shortened steelmaking process (electric arc furnace), reducing carbon emissions by over 60% compared to the traditional long process. A closed-loop system has been established: scrap carbon steel pipes - recycled steel - new steel pipes. Qualified scrap pipes are sorted through non-destructive testing (eddy current testing), ensuring that the mechanical properties of recycled steel pipes are within 5% of those of virgin pipes.

Large Diameter and Intelligent Development: Ultra-large diameter spiral welded pipes (diameter ≥ 4000mm) are being developed for use in inter-basin water diversion projects (such as the South-to-North Water Diversion Project branch line), reducing the number of pipelines and footprint. Using IoT technology, sensors are installed on the inner walls of the pipes to monitor flow, temperature, pressure, and corrosion in real time, enabling intelligent operation and maintenance (e.g., automatic leak alarms).

Conclusion
As a "functional form" of carbon steel products, carbon steel pipes bridge the raw material base of carbon steel plates/coils with the transportation and structural requirements of the industrial sector, playing an irreplaceable role in energy security, urban construction, and equipment manufacturing. From high-pressure oil and gas seamless pipes to low-pressure municipal welded pipes, from building steel structure pipes to mechanical precision pipes, carbon steel pipes, with their diverse processes and performance, are adaptable to the differentiated needs of different scenarios. In the future, with the advancement of high-strength, corrosion-resistant improvements, and intelligent technologies, carbon steel pipes will further break through the limitations of pressure, environment, and efficiency, providing more reliable material support for industrial upgrading and sustainable development.