X11CrMo9-1 · 1.25Cr-0.5Mo · EN 10253-2 Type B
Entry-level chromium-molybdenum grade for pressure service to 550°C. HRSG, refinery fractionation columns, moderate-temperature steam headers. PWHT mandatory on all P11 weld joints.
Post-weld heat treatment is mandatory for P11. Welding without PWHT produces a hard, brittle heat-affected zone susceptible to hydrogen cracking under service conditions. Time-temperature chart and HAZ hardness test results are included on the EN 10204 3.1 certificate for all P11 fitting orders.
P11 (EN designation: 13CrMo4-5 per EN 10216-2; material number 1.7335) is the entry point of the chromium-molybdenum alloy steel ladder. With 1.00–1.50% Cr and 0.44–0.65% Mo, it offers significantly better creep resistance and oxidation resistance than carbon steel above 450°C while remaining straightforward to weld with standard preheat and PWHT procedures.
The grade is used extensively in combined-cycle and steam-cycle power plant HRSG circuits, refinery fractionation column overhead piping, and moderate-temperature petrochemical steam services. Its relative simplicity compared to P22 and above makes it the default choice for applications up to approximately 550°C where the higher allowable stresses of P22 are not required.
| Element | Min | Max | Note |
|---|---|---|---|
| Carbon (C) | 0.08 | 0.15 | Low C for weldability |
| Silicon (Si) | — | 0.50 | — |
| Manganese (Mn) | 0.30 | 0.60 | — |
| Chromium (Cr) | 1.00 | 1.50 | Oxidation + creep |
| Molybdenum (Mo) | 0.44 | 0.65 | Creep resistance |
| Phosphorus (P) | — | 0.025 | — |
| Sulphur (S) | — | 0.010 | — |
| Grade | Cr% | Mo% | Max Temp | ASME P-No. | Primary Use |
|---|---|---|---|---|---|
| P11 (1.7335) | 1.00–1.50 | 0.44–0.65 | 550°C | 4 | HRSG, fractionation, steam headers |
| P22 (1.7380) | 1.90–2.60 | 0.87–1.13 | 580°C | 5A | Hydroprocessing, H₂ service |
| P5 (1.7362) | 4.00–6.00 | 0.44–0.65 | 650°C | 5B | Refinery furnaces, catalytic reforming |
| P91 (1.4903) | 8.00–9.50 | 0.85–1.05 | 650°C | 15E | Supercritical power, HP HRSG |
150–200°C minimum. Maintain interpass temperature ≤300°C. Preheat is critical to prevent hydrogen-assisted cold cracking in the HAZ.
ER80S-B2 (GTAW/GMAW) or E8018-B2 (SMAW). Match filler to base metal Cr-Mo chemistry.
690–730°C. Hold time per wall thickness — minimum 1 hour per 25 mm. Furnace or local PWHT acceptable.
HAZ hardness ≤248 HBW (per EN 15614). Reported on EN 10204 3.1 certificate.
| EN designation | 13CrMo4-5 |
| Material number | 1.7335 |
| ASTM equivalent | A234 WP11 |
| ASME P-Number | P-No.4 |
| Max temperature | ≤550°C (sustained) |
| Min yield strength | 205 MPa |
| PWHT | 690–730°C (mandatory) |
| Filler (GTAW) | ER80S-B2 |
| Standard | EN 10253-2 Type B |
| Certificate | EN 10204 3.1 standard |
PWHT time-temperature chart + hardness results on every 3.1 certificate. Third-party 3.2 (TÜV / Lloyd's) available. Tell us your fitting schedule, sizes, and delivery port.
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