1Cr-½Mo chrome-moly alloy steel buttweld pipe fittings for boiler headers, steam drums, and high-temperature piping to 540°C. The standard entry-level CrMo grade — lower silicon and chromium than WP11 — offering improved creep and oxidation resistance over carbon steel with straightforward welding and PWHT.
| 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) | 0.15–0.50 | 0.15–0.50 |
| 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 |
P12 carries lower silicon (0.15–0.50%) and chromium (0.80–1.25%) than P11. It is the standard 1Cr-½Mo CrMo grade for moderate-temperature boiler and steam service; P11's higher silicon gives it the edge in oxidising atmospheres.
| 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 | 0.50–1.00% | 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 | 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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