What Is ASTM A217 WC9?
Chemical Composition and Properties
| Property | Value |
|---|---|
| Specification | ASTM A217 / ASME SA-217 |
| Grade | WC9 |
| Material type | Cast alloy steel (Cr-Mo) |
| Carbon | 0.05-0.18% |
| Chromium | 2.00-2.75% |
| Molybdenum | 0.90-1.20% |
| Manganese | 0.40-0.70% |
| Silicon | 0.60% max |
| Sulfur | 0.045% max |
| Phosphorus | 0.04% max |
| Tensile strength (min) | 485 MPa (70 ksi) |
| Yield strength (min) | 275 MPa (40 ksi) |
| Elongation (min) | 20% |
| Reduction of area (min) | 35% |
| Hardness | 241 HBW max |
| Max service temp | 595°C (1100°F) |
| Heat treatment | Normalize + temper, or quench + temper |
WC9 vs WC6: When to Upgrade
The higher chromium and molybdenum content in WC9 compared to WC6 delivers two critical advantages:
| Property | WC6 (1.25Cr-0.5Mo) | WC9 (2.25Cr-1Mo) |
|---|---|---|
| Max service temp | 565°C (1050°F) | 595°C (1100°F) |
| Hydrogen attack resistance | Moderate (Nelson curve) | Superior (Nelson curve) |
| Sulfidation resistance | Good | Better |
| Forged equivalent | A182 F11 | A182 F22 |
| Matching pipe | A335 P11 | A335 P22 |
WC9 is required in refinery environments where hydrogen partial pressures are high. Per API 941 (Nelson curves), 2.25Cr-1Mo steel resists hydrogen attack at significantly higher temperature-pressure combinations than 1.25Cr-0.5Mo.
Applications
- Hydroprocessing units: hydrotreater and hydrocracker reactor outlet valves, HP separator valves
- Hydrogen service: hydrogen reformer outlet piping, hydrogen recycle compressor suction/discharge valves
- Power plants: main steam and hot reheat valve bodies for advanced steam cycles above 565°C
- Refinery heaters: transfer line valves in crude and vacuum heater circuits
WC9 cast valve bodies pair with A182 F22 forged flanges and fittings, A234 WP22 buttweld fittings, and A335 P22 seamless pipe.
Testing and Welding
All WC9 castings require mandatory heat treatment. Mill test certificates per EN 10204 3.1 must report full chemistry, mechanical properties, and heat treatment records. Radiographic examination per ASME B16.34 is standard for valve castings; hydrostatic testing follows the applicable API standard.
Welding requires preheat (200-250°C minimum), matching E/ER 9018-B3 filler metals, and PWHT at 690-750°C. The casting process demands tight control of chromium and molybdenum segregation during solidification.
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