1¼Cr-½Mo silicon-bearing alloy steel buttweld pipe fittings for boiler headers, superheater piping, and refinery service to 540°C. The elevated silicon content (0.50–1.00%) improves scale and oxidation resistance over WP12 in high-temperature oxidising atmospheres.
| Element | WP11 Cl.1 % | WP11 Cl.2/3 % |
|---|---|---|
| Carbon (C) | 0.05–0.15 | 0.05–0.15 |
| Manganese (Mn) | 0.30–0.60 | 0.30–0.60 |
| Silicon (Si) | 0.50–1.00 | 0.50–1.00 |
| Chromium (Cr) | 1.00–1.50 | 1.00–1.50 |
| Molybdenum (Mo) | 0.44–0.65 | 0.44–0.65 |
| Phosphorus (P) | ≤0.045 | ≤0.045 |
| Sulphur (S) | ≤0.045 | ≤0.045 |
The elevated silicon content (0.50–1.00%) and higher chromium (1.00–1.50%) are the distinguishing features of P11 vs P12 — they improve scale and oxidation resistance at service temperatures approaching 540°C.
| Property | Class 1 | Class 2 |
|---|---|---|
| Tensile Strength (min) | 415 MPa | 485 MPa |
| Yield Strength (min) | 205 MPa | 275 MPa |
| Elongation (min) | 30% | 20% |
| Hardness (max) | 197 HBW | 241 HBW |
| Heat Treatment | Normalised + Tempered or Annealed | |
| PWHT Required | Yes — 690–750°C | |
| Property | WP11 | WP12 |
|---|---|---|
| Cr content | 1.00–1.50% | 0.80–1.25% |
| Mo content | 0.44–0.65% | 0.44–0.65% |
| Si content | 0.50–1.00% | 0.15–0.50% |
| EN W.Nr. | 1.7337 | 1.7335 |
| Max service temp | 540°C | 540°C |
| Oxidation resistance | Better (higher Si) | Standard |
| Weld filler | ER80S-B2 (Si-matched) | ER80S-B2 |
Available in elbows, tees, reducers, and caps. PWHT certificates and hardness reports included. EN 10204 3.1 standard. See also ASTM A234 WP12.
Get Quote