What Is A182 F11?
ASTM A182 Grade F11 is a 1-1/4 chromium, 1/2 molybdenum (1-1/4Cr-1/2Mo) forged alloy steel used for flanges, fittings, valve components, and other pressure parts in high-temperature service. It is the most commonly specified chrome-moly forging grade in refinery and power plant piping systems.
| Property | A182 F11 Class 2 |
|---|---|
| Specification | ASTM A182 / ASME SA-182 |
| UNS designation | K11572 |
| Alloy system | 1-1/4Cr-1/2Mo |
| Carbon | 0.05-0.15% |
| Chromium | 1.00-1.50% |
| Molybdenum | 0.44-0.65% |
| Manganese | 0.30-0.60% |
| Silicon | 0.50-1.00% |
| Tensile strength (min) | 485 MPa (70 ksi) |
| Yield strength (min) | 275 MPa (40 ksi) |
| Elongation (min) | 20% |
| Reduction of area (min) | 30% |
| Hardness (max) | 197 HBW (Class 2) |
| Max service temp | 565°C (1050°F) |
| Heat treatment | Normalize + temper, or quench + temper |
| Matching pipe | ASTM A335 P11 |
| Cast equivalent | ASTM A217 WC6 |
Why Chrome-Moly?
Carbon steel (ASTM A105) begins to lose strength above 425°C due to creep—the slow, permanent deformation under sustained stress at elevated temperature. The chromium in F11 provides oxidation resistance and resistance to sulfidation (high-temperature sulfur attack). The molybdenum increases creep rupture strength. Together, they extend reliable service to 565°C.
F11 Class Designations
ASTM A182 F11 has multiple classes with different mechanical property requirements:
| Class | Tensile (min) | Yield (min) | Hardness (max) |
|---|---|---|---|
| Class 1 | 415 MPa (60 ksi) | 205 MPa (30 ksi) | 187 HBW |
| Class 2 | 485 MPa (70 ksi) | 275 MPa (40 ksi) | 197 HBW |
| Class 3 | 515 MPa (75 ksi) | 310 MPa (45 ksi) | 235 HBW |
Class 2 is the standard grade for most piping applications. Class 3 provides higher allowable stress for high-pressure designs. Class 1 is rarely specified for new construction.
Applications
F11 serves wherever carbon steel cannot handle the temperature:
- Refinery piping: crude and vacuum distillation column overhead piping, FCC reactor effluent, reformer charge heaters
- Power generation: boiler superheater and reheater headers, main steam branch connections
- Petrochemical plants: high-temperature reactor piping, transfer lines
F11 pairs with ASTM A335 P11 seamless pipe, ASTM A234 WP11 buttweld fittings, and A217 WC6 cast valve bodies. All components in a chrome-moly piping class must match in alloy composition to avoid dissimilar-metal weld issues.
Testing and Welding
All F11 forgings must be heat-treated (normalize + temper or quench + temper). Mill test certificates per EN 10204 3.1 document chemistry, mechanical properties, and heat treatment condition. NDT (UT, MT) is commonly specified as supplementary. Hydrostatic testing follows the applicable flange or valve standard.
Welding F11 requires preheat (typically 150-200°C), matching filler metals (E/ER 8018-B2), and post-weld heat treatment (PWHT) at 690-750°C. The forging process delivers refined grain structure and uniform mechanical properties critical for high-temperature cycling.
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