1. High-Temperature Limits of Carbon Steel Pipe

Carbon steel pipe has no single universal long-term service temperature. ASTM A106 covers seamless pipe for high-temperature service, ASTM A53 covers mechanical and pressure applications, including ordinary steam, water, gas, and air lines, and GB/T 8163 covers seamless steel pipe for fluid service. Allowable service conditions depend on the applicable design code, material grade, pressure, and wall thickness. Prolonged exposure above about 427°C (800°F) may cause graphitization in some carbon steels.

Note:

1.1 Effect of Carbon Content

Low-carbon steel (such as 20# steel) has better temperature resistance than high-carbon steel, as high-carbon steel is more susceptible to graphitization and embrittlement at high temperatures.

1.2 Standard Differences

Chromium-containing alloy steels such as ASTM A335 P11 can withstand temperatures exceeding 550°C, but strictly speaking, they are no longer considered ordinary carbon steel.

2. Factors Affecting the High-Temperature Performance of Carbon Steel Pipe

High-temperature performance depends on the material grade, service environment, design pressure, wall thickness, and heat treatment. Creep, graphitization, and oxidation can affect long-term service, so allowable conditions must be checked against the applicable design code.

2.1 Material Composition

Carbon increases steel strength, but higher carbon content generally reduces ductility and weldability. Manganese (Mn) contributes to strength and combines with sulfur to reduce the risk of hot shortness during hot working.
Silicon (Si) acts mainly as a deoxidizer and also contributes to strength.

Excessive sulfur (S) can reduce ductility and weldability, while phosphorus (P) can impair toughness and increase brittleness. Their contents are therefore limited by material specifications. For high-temperature pipe, the specified chemical composition must meet the requirements for the selected grade and service conditions.

2.2 Environmental Conditions

At high temperatures, oxygen reacts with the pipe surface to form oxide scale. Prolonged exposure and repeated heating and cooling can cause scale growth or spalling, gradually reducing the pipe wall thickness.

Sulfur-bearing environments can cause sulfidation, while high-temperature hydrogen service may lead to hydrogen attack under certain temperature and hydrogen partial-pressure conditions. In wet CO₂/H₂S environments, internal corrosion can also occur, depending on the fluid composition and operating conditions.

Internal corrosion and erosion can reduce the effective wall thickness and pressure-bearing capacity.

2.3 Pressure, Wall Thickness and Design Basis

Pressure and temperature jointly determine the required wall thickness and allowable stress under the governing design code. As design temperature rises, allowable stress generally decreases, requiring greater wall thickness at the same pressure. These factors must be evaluated together using the applicable code tables, such as ASME B31.3 for process piping.

2.4 Heat Treatment and Product Form

Normalizing can refine grain structure and improve toughness, but heat treatment alone does not determine a pipe's allowable service temperature.

Under ASTM A106, hot-finished pipe does not require heat treatment, while cold-drawn pipe must be heat-treated after the final drawing pass at 650°C (1200°F) or higher. For boiler pipe grades such as 20G, 12Cr1MoVG, and 15CrMoG, GB/T 5310 specifies heat-treatment requirements for each grade.

3. Comparison: Pipes Made of Other Materials

Compared to ordinary carbon steel pipes, pipes made of other materials have different high-temperature resistance characteristics.

3.1 Stainless Steel Pipes

Stainless steel pipes offer excellent corrosion resistance and good high-temperature resistance, with a temperature resistance of 600-900°C. They are suitable for environments requiring both corrosion resistance and heat resistance.

3.2 High-Temperature Alloy Pipe

Nickel-based high-temperature alloy pipes can withstand even higher temperatures, operating at temperatures exceeding 1000°C, making them an ideal choice for extremely high-temperature environments.

4. High-Temperature-Resistant Steel Pipe Grades

The grades in this section belong to two material families. 20G and ASTM A106 Grades B and C are carbon steels, while 12Cr1MoVG and 15CrMoG are low-alloy heat-resistant steels. Although 20G, 12Cr1MoVG, and 15CrMoG fall under GB/T 5310, their material properties and service applications differ. The Cr-Mo grades may require specific preheating, post-weld heat treatment, and hardness controls under the applicable welding procedure and code.

4.1 Carbon Steel Grades

4.1.1 20G — Seamless Carbon Steel Boiler Tube (GB/T 5310)

20G is the dedicated carbon steel grade for high-pressure boiler tubes in GB/T 5310, used for water walls, economizers and low-temperature superheater sections. It is not the same designation as 20# in GB/T 3087 or GB/T 8163, and the two are not interchangeable.

Standard: GB/T 5310 (Seamless steel tubes and pipes for high pressure boiler), current edition 2023

Typical metal temperature: up to about 450 °C

Tensile strength Rm: 410–550 MPa

Yield strength ReL: ≥ 245 MPa

Elongation A: ≥ 24 % longitudinal, ≥ 22 % transverse

Note that carbon steel offers no inherent corrosion resistance; in oxidizing flue gas the limit is set by scaling, not by the grade designation.

4.1.2 ASTM A106 Grade B and Grade C — Seamless Carbon Steel Pipe

A106 is a piping specification for high-temperature service, ordered to ASME B31.3 in design. It is not a boiler-tube specification, and it is not directly interchangeable with GB/T 5310 grades.

4.2 Low-Alloy Heat-Resistant Steel Grades (not carbon steel)

Both grades below are 1 % Cr low-alloy steels supplied under GB/T 5310. They carry the elevated-temperature strength that carbon steel cannot, and they are used where metal temperatures exceed the carbon steel limit.

4.2.1 12Cr1MoVG

Composition family: approximately 1Cr-0.3Mo-V low-alloy heat-resistant steel

Standard: GB/T 5310

Typical metal temperature: up to about 570 °C

4.2.2 15CrMoG

Composition family: approximately 1Cr-0.5Mo low-alloy heat-resistant steel (comparable to ASTM A213 T12 / A335 P12)

Standard: GB/T 5310

Typical metal temperature: up to about 550 °C

Both grades require preheat and post-weld heat treatment, and hardness limits apply to the weld and heat-affected zone.

Creep can affect both carbon and low-alloy steel pipes under sustained high-temperature stress. The need for remaining-life assessment depends on the material, service conditions, operating history, and applicable assessment criteria.

5. Precautions for Practical Applications

5.1 Temperature Monitoring

It is recommended to install thermocouples in the high-temperature section for real-time monitoring to prevent localized overheating.

5.2 Protective Measures

For pipes exposed to temperatures above 350°C for extended periods, heat-resistant coatings or insulation wrapping can be used.

5.3 Life Assessment

According to NACE SP0208, carbon steel pipes require a remaining life test after five years of continuous operation at 400°C.

6. Summary

The high-temperature resistance limit of carbon steel pipes is primarily between 400°C and 450°C. If higher temperatures (500°C to 600°C) are required, low-alloy heat-resistant steel pipes such as 15CrMoG and 12Cr1MoVG are recommended. For extreme environments exceeding 600°C, stainless steel or high-temperature alloy pipes should be considered.

When selecting a high-temperature carbon steel pipe, comprehensive consideration must be given to temperature, pressure, media properties, and operating cycle, and strict adherence to international standards such as ASME, API, and GB/T to ensure pipeline safety and cost-effectiveness.

Read more: What Is The Heat-resistant Temperature of Carbon Steel Pipe? or ASTM A106 Seamless Carbon Steel Pipe for High Temperature