How is the corrosion resistance of boiler tubes?

Boiler tubes are subjected to high temperatures, high pressure, and corrosive media such as steam, flue gases, and chemicals. Therefore, corrosion resistance is a critical factor that determines their safety, durability, and performance.

1. Factors Affecting Corrosion Resistance

1.1 Material Selection
The corrosion resistance of boiler tubes is primarily influenced by their material composition. Common materials include:

Carbon Steel (e.g., 20G, SA210): Offers basic resistance to steam but is vulnerable to oxygen corrosion and acidic environments.

Low Alloy Steel (e.g., 15CrMoG, 12Cr1MoVG): Enhanced oxidation and sulfur corrosion resistance due to added Cr and Mo.

Stainless Steel (e.g., 304H, 321H, 316L): High Cr/Ni content provides excellent resistance to acid, alkali, and chloride corrosion. However, cost is relatively high.

Duplex Steel (e.g., 2205): Excellent resistance to chloride stress corrosion cracking (Cl-SCC), ideal for seawater or saline environments.

Special Alloys:

Titanium Alloys: Resistant to acid, alkali, and seawater corrosion.

Nickel Alloys: High corrosion and heat resistance, suitable for high-temperature steam applications.

1.2 Operating Environment

Temperature: High temperatures (>400°C) accelerate oxidation and sulfidation.

Pressure: Elevated pressures increase the risk of stress corrosion cracking (SCC).

Medium Composition:

Acidic (H₂S, CO₂): Can lead to sulfide corrosion or hydrogen embrittlement.

Alkaline (e.g., NaOH): May cause caustic embrittlement.

Chloride Ions (Cl⁻): Can trigger pitting and Cl-SCC in stainless steel.

1.3 Protective Measures

Surface Treatments: Galvanizing, sandblasting, and coating improve resistance.

Internal Coatings/Linings: Enamel or epoxy coatings protect against acid and alkali.

Water Treatment: Maintaining pH between 8.5–9.2 and reducing oxygen levels (<7 ppb).

Cathodic Protection: Commonly used for seawater or buried pipelines.

2. Common Corrosion Types and Solutions

3. Causes and Remedies for Boiler Tube Rust

Common Causes:

Poor Water Quality: High oxygen or CO₂ levels accelerate corrosion.

Scale Deposits: Long-term scale buildup creates rust spots and reduces heat exchange efficiency.

Inferior Materials: Defects or poor-quality tubes are more susceptible to rusting.

Solutions:

Improve Water Quality: Reduce dissolved gases and impurities.

Regular Cleaning: Remove scale deposits to prevent corrosion.

Material Replacement: Replace corroded tubes with high-quality, corrosion-resistant materials.

4. Boiler Tube Material Recommendations

5. Key Measures to Enhance Corrosion Resistance

Control medium composition (e.g., Cl⁻, O₂, pH levels).

Apply protective coatings or internal linings.

Conduct regular inspections and preventive maintenance.

Conclusion:
Corrosion resistance is essential for the safe and long-term operation of boiler systems. By selecting appropriate materials, managing operating conditions, and implementing protective strategies, the integrity and service life of boiler tubes can be significantly improved.