What is the material of ASTM A335 P9 boiler tube
Jul 10, 2025
1. Core material characteristics
ASTM A335 P9 is a chromium-molybdenum high-temperature alloy seamless steel pipe. Its chemical composition is designed with chromium (Cr) and molybdenum (Mo) as the core strengthening elements. The specific composition is as follows:
| Element | Content Range | Functions |
|---|---|---|
| Cr | 8.00%-9.50% | High temperature oxidation resistance (forming dense Cr₂O₃ film) |
| Mo | 0.90%-1.10% | Improved creep resistance and high temperature strength |
| C | ≤0.15% | Balanced strength and weldability |
| Mn | 0.30%-0.60% | Resilience Enhancement |
| Si | 0.25%-1.00% | Deoxidation and high temperature stability |
2. Performance advantages
High temperature performance:
Upper limit of applicable temperature: 650℃ (long-term service temperature ≤ 600℃), creep resistance is better than ordinary alloy steel;
Tensile strength ≥ 415 MPa at 600℃, yield strength ≥ 205 MPa.
Corrosion resistance:
High chromium content effectively resists hydrogen sulfide corrosion and high-temperature cyclohexane acid corrosion (typical environment of petrochemical cracking furnace);
Oxidation resistance meets the working conditions of 550~630℃ boiler reheater.
3. Comparison with other alloy steels
| Parameter | A335 P9 | A335 P91 |
|---|---|---|
| Core Ingredients | 9Cr-1Mo | 9Cr-1Mo-V-Nb |
| Strengthening Mechanism | Solid solution strengthening | Dispersion strengthening (V/Nb carbides) |
| Allowable stress | ≤ 600℃≈80 MPa | ≥110 MPa at 600°C (increased by 37.5%) |
| Applications | Medium and high pressure boiler superheater, petrochemical furnace tube | Main steam pipeline of supercritical unit |
