25MnG high-pressure boiler steel tubes

SA-210C (25MnG) is a seamless carbon-manganese steel tube specified under the ASME SA-210 standard, designed primarily for use in boilers and superheaters. As a pearlitic heat-resistant steel, it offers an excellent balance of strength, ductility, and thermal stability. In 1995, China incorporated this material into the GB5310 standard under the designation 25MnG, refining its chemical limits to enhance weldability and structural stability. By controlling carbon content (≤0.30%) and increasing manganese levels, 25MnG achieves superior mechanical strength while maintaining good plasticity, making it a core material for high-pressure boiler applications.

1. Chemical Composition Optimization

Carbon ≤ 0.30%: Lower carbon content minimizes embrittlement in the weld heat-affected zone, improving weld integrity.

Manganese 0.29%–1.06%: Provides solid solution strengthening, increasing yield strength by about 20% compared with 20G steel, while maintaining high ductility (elongation ≥ 30%) and toughness.

Phosphorus, Sulfur ≤ 0.035%: Strict impurity control prevents brittle fracture and degradation of high-temperature performance.

This optimized chemical design ensures the material maintains excellent mechanical balance and high-temperature resistance, essential for demanding boiler environments.

2. Mechanical Properties and Performance

Tensile Strength ≥ 485 MPa

Yield Strength ≥ 275 MPa

Hardness ≤ 89 HRB

These properties meet the rigorous requirements of high-pressure boiler systems, providing strength while retaining good machinability and formability for cold bending and hot expansion processes.

3. High-Temperature Stability

25MnG’s pearlitic microstructure offers outstanding creep resistance, ensuring reliable operation at sustained temperatures below 500°C (or below 450°C in specific conditions).
It also provides:

Excellent oxidation resistance, minimizing oxide scale spalling at elevated temperatures.

Stable mechanical performance, extending service life in components such as economizers, water walls, and low-temperature superheaters.

4. Applications and Economic Advantages

Typical Applications:

Power industry: Water-cooled walls, economizers, and low-temperature superheater piping in 300 MW–600 MW boiler units.

Chemical industry: High-pressure reactors and heat exchangers requiring both corrosion and thermal fatigue resistance.

Economic Benefits:

Wall Thickness Reduction: Compared with 20G steel, 25MnG can reduce pipe wall thickness by 15–30%, saving up to 100 tons of steel per 300 MW boiler.

Enhanced Heat Transfer Efficiency: Thinner walls reduce thermal resistance, improving boiler efficiency and lowering fuel consumption.

Lower Processing Costs: Excellent cold and hot workability simplifies fabrication and shortens production cycles.

5. Manufacturing Process and Quality Control

Production Process:

Hot Rolling: Ensures accurate dimensions and superior surface finish.

Cold Drawing / Continuous Rolling: Provides small-diameter, high-precision pipes for complex components.

Heat Treatment: Stress relief and microstructure stabilization improve long-term performance and reliability.

Quality Assurance:

Hydrostatic Testing: Every pipe undergoes pressure testing to ensure sealing integrity.

Flaring and Flattening Tests: Validate plasticity and processing safety.

Microstructure and Grain Size Control: Maintains consistent high-temperature mechanical behavior.

6. Selection Guidelines and Maintenance

Operating Temperature: Should remain below 500°C to prevent pearlite spheroidization and loss of strength.

Welding Precautions: Use low-hydrogen electrodes and control interpass temperature to avoid cracking.

Routine Inspection: Regularly check for oxide scale, corrosion pits, or microcracks, and replace aging parts as needed.

Alternative Materials: For higher strength or corrosion resistance, SA-213 T22 (Cr-Mo steel) or TP347H (austenitic stainless steel) can be selected, though at a higher cost.

Conclusion

25MnG (SA-210C) high-pressure boiler steel tubes have become a benchmark material in the medium and low-pressure boiler sector due to their ideal combination of strength, ductility, thermal stability, and cost efficiency. Their optimized composition enhances reliability, improves heat transfer, and reduces overall production costs—making them the preferred choice for power and chemical industries seeking both performance and economy.