I. Introduction to High-Pressure Seamless Steam Pipes
High-pressure seamless steam pipes are high-performance steel pipes specifically designed for high-temperature and high-pressure steam pipeline systems. They are widely used in power generation, petrochemicals, metallurgy, boilers, and industrial steam transportation.
These pipes are manufactured from high-quality carbon steel or low-alloy steel (such as ASTM A106 Gr.B/C, ASTM A335 P11/P22/P91, or GB 5310 20G/15CrMoG/12Cr1MoVG) using hot rolling or cold drawing processes, ensuring uniform wall thickness, precise dimensions, and superior resistance to high temperatures and pressures.
II. Chemical Composition and Mechanical Properties of Commonly Used Steel Grades for High-Pressure Seamless Pipes
i. Chemical Composition Table
| Steel grade | C (%) | Si (%) | Mn (%) | P (%) | S (%) | Cr (%) | Mo (%) | V (%) |
| 12Cr1MoV | 0.10-0.15 | ≤0.35 | 0.40-0.70 | ≤0.025 | ≤0.025 | 0.90-1.20 | 0.45-0.60 | 0.15-0.25 |
| 15CrMoG | 0.10-0.18 | ≤0.35 | 0.40-0.70 | ≤0.025 | ≤0.025 | 0.80-1.10 | 0.40-0.50 | – |
| 20G / Q345R | 0.17-0.24 | ≤0.35 | 0.40-0.70 | ≤0.035 | ≤0.035 | 0.25-0.35 | 0.08-0.15 | – |
| ASTM A335 P11 | 0.05-0.12 | 0.10-0.50 | 0.30-0.60 | ≤0.035 | ≤0.035 | 0.90-1.10 | 0.45-0.65 | – |
| ASTM A335 P22 | 0.05-0.15 | 0.10-0.50 | 0.30-0.60 | ≤0.035 | ≤0.035 | 2.00-2.50 | 0.90-1.00 | – |
| ASTM A335 P91 | 0.08-0.12 | 0.20-0.50 | 0.40-0.70 | ≤0.020 | ≤0.010 | 8.00-9.50 | 0.85-1.05 | 0.18-0.25 |
ii. Mechanical Properties Table
| Steel Grade | Allowable Temperature (℃) | Yield Strength σs (MPa) | Tensile Strength σb (MPa) | Elongation δ5 (%) | Impact Energy KV (J) |
|---|---|---|---|---|---|
| 12Cr1MoV | ≤ 550 | ≥ 235 | 410 – 540 | ≥ 20 | ≥ 27 |
| 15CrMoG | ≤ 540 | ≥ 235 | 410 – 550 | ≥ 20 | ≥ 27 |
| 20G / Q345R | ≤ 450 | ≥ 215 | 375 – 530 | ≥ 20 | ≥ 27 |
| ASTM A335 P11 | ≤ 540 | 240 – 275 | 415 – 550 | ≥ 20 | ≥ 27 |
| ASTM A335 P22 | ≤ 580 | 275 – 310 | 415 – 550 | ≥ 20 | ≥ 27 |
| ASTM A335 P91 | ≤ 620 | 415 – 485 | 585 – 690 | ≥ 20 | 34 |
III. Selection Guide for High-Pressure Seamless Steam Pipes
| Step | Operation | Reference Criteria / Description | Remarks |
|---|---|---|---|
| 1. Define operating conditions | Determine the working pressure, temperature, medium, and flow rate of the steam pipeline | Pressure (MPa), temperature (℃), presence of corrosive media | Directly affects steel grade and wall thickness selection |
| 2. Select steel grade | Choose pressure- and temperature-resistant steel grade based on operating conditions | Domestic: 12Cr1MoV, 15CrMoG, 20G / Q345RInternational: P11, P22, P91 | High-temperature and high-pressure service requires heat-resistant steels |
| 3. Determine pipe diameter and wall thickness | Calculate flow rate and pressure loss; determine pipe diameter; calculate wall thickness using formulas or standards | Wall thickness: t = P·D / (2·[σ]·φ + P·y), or refer to GB/T 5310 and ASTM A335 tables | Corrosion allowance should be considered |
| 4. Verify pipe material quality | Check chemical composition, mechanical properties, NDT results, and dimensional tolerances | Chemical elements: Cr, Mo, V contentMechanical properties: yield strength, tensile strength, elongation, impact toughnessNDT: RT / UT / MT | Manufacturer shall provide MTC (Mill Test Certificate) |
| 5. Select pipe end type | Determine pipe end according to connection method | Plain end (welding), threaded end (threaded connection), flanged end (flange installation) | Ensure ease of installation and reliable sealing |
| 6. Verify applicable standards | Ensure the pipe complies with design and application standards | Domestic: GB/T 5310, GB/T 6479, GB/T 8162International: ASTM A335, ASTM A213, EN 10216-2 | Can be used as basis for procurement and acceptance |
| 7. Consider safety margin and cost efficiency | Increase steel grade or wall thickness appropriately considering corrosion, wear, and temperature fluctuation | Balance between safety margin and economic efficiency | Avoid safety risks or material waste caused by under- or over-design |
IV. Applications of High-Pressure Seamless Steel Pipes for Steam
1. Thermal Power Generation and Power Plant Boilers
Application Description:
Used for main steam pipes, superheated steam pipes, and reheat steam pipes in boilers, withstanding high-temperature and high-pressure steam to ensure the long-term safe and stable operation of power plants.
Selection Recommendations and Reasons:
Steel Grade Selection: 12Cr1MoV, 15CrMoG, or ASTM P11/P22.
Reason: These steel grades are resistant to high temperatures, high pressure, and creep, capable of withstanding long-term high-temperature and high-pressure steam, reducing pipe fatigue and leakage risks.
Wall Thickness Recommendation: Calculated based on design pressure and corrosion allowance to ensure a safety margin.
2. Chemical, Petrochemical, and Petroleum Industries
Application Description:
Used in high-temperature and high-pressure reactors, steam heating pipelines, and heat exchange systems. Also suitable for steam injection oil recovery and heating devices, ensuring process safety and reliability.
Selection Recommendations and Reasons:
Steel Grade Selection: 15CrMoG, P11, P22, or P91 high-temperature pipes if necessary.
Reason: Chemical and petrochemical steam pipelines may come into contact with corrosive media. High-temperature and high-pressure conditions require corrosion-resistant and creep-resistant steel to ensure long-term stable operation.
Pipe Diameter and Wall Thickness: Calculated based on flow rate and pressure, while considering the corrosion allowance of the medium.
3. Metallurgy, Industrial Boilers, and Other Industries
Application Description:
Used in hot rolling, heat treatment, and process heating pipelines, also suitable for paper manufacturing, food processing, and industrial boiler steam distribution, providing a stable steam supply.
Selection Suggestions and Reasons:
Steel Grade Selection: 20G/Q345R or 12Cr1MoV; ordinary low-alloy steel can be selected for low-corrosion environments.
Reason: The temperature and pressure in metallurgy and industrial boilers are relatively low, and ordinary low-alloy steel is both economical and meets the requirements; low corrosion requirements save costs.
Wall Thickness and End Form: Determined according to working pressure and steam flow rate; welded or flanged connections are selected for the ends for easy installation and maintenance.
4. Selection Principles:
Select the steel grade according to the working temperature and pressure; use high-temperature resistant steel for high temperatures and pressures, and ordinary low-alloy steel for low pressures and temperatures.
Calculate the wall thickness and pipe diameter according to the working conditions, considering corrosion and wear allowances.
Select the end form (welded, threaded, flanged) according to the piping system to ensure safety and reliability.
