1¼Cr-½Mo-Si alloy steel buttweld pipe fittings for boiler headers, steam drums, and high-temperature piping to 540°C. Silicon addition improves oxidation resistance and creep rupture strength compared to standard WP11 at the same temperature range.
| Element | WP12 Cl.1 % | WP12 Cl.2 % |
|---|---|---|
| Carbon (C) | 0.05–0.15 | 0.05–0.15 |
| Manganese (Mn) | 0.30–0.61 | 0.30–0.61 |
| Silicon (Si) | 0.60–1.00 | 0.60–1.00 |
| Chromium (Cr) | 0.80–1.25 | 0.80–1.25 |
| 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 (0.60–1.00%) is the distinguishing feature of P12 vs P11 — it improves scale resistance and oxidation resistance at service temperatures approaching 540°C.
| Property | Class 1 | Class 2 |
|---|---|---|
| Tensile Strength (min) | 415 MPa | 485 MPa |
| Yield Strength (min) | 220 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% | 0.60–1.00% |
| EN W.Nr. | 1.7335 | 1.7337 |
| Max service temp | 540°C | 540°C |
| Oxidation resistance | Good | Better (higher Si) |
| Weld filler | ER80S-B2 | ER80S-B2 (Si-matched) |
Available in elbows, tees, reducers, and caps. PWHT certificates and hardness reports included. EN 10204 3.1 standard.
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