IBR Approved · Alloy Steel (CrMo)
ASTM A234 WP9 Buttweld Pipe Fittings
9Cr-1Mo chromium-molybdenum alloy steel fittings for refinery fired heaters and high-temperature hydrogen and sulphidic service. Elbows, tees, reducers and caps to ASME B16.9 / B16.28, IBR approved with Form III-C, EN 10204 3.1 / 3.2 traceable.
Grade Overview
ASTM / ASME A234 WP9 is the original 9Cr-1Mo chromium-molybdenum alloy steel. Its 9% chromium content places it high on the API 941 Nelson curves for resistance to high-temperature hydrogen attack (HTHA) and gives strong resistance to sulphidic corrosion — the standard grade for refinery fired heater coils and hot hydrogen/sulphur service beyond the range of WP5.
WP9 is not interchangeable with WP91 — it contains no vanadium, niobium or nitrogen and has lower creep strength. WP9 fittings are supplied IBR approved with Form III-C; the EN counterpart is X12CrMo9-1 (material number 1.7386).
PWHT is mandatory
All WP9 welds require post-weld heat treatment, typically 730–790°C, to temper the hardened heat-affected zone and avoid hydrogen cracking. Post-PWHT hardness and the time-temperature record are reported on the EN 10204 3.1 certificate. Filler metal: ER80S-B8. ASME P-No. 5B.
Chemical Composition — A234 WP9
| Element | Requirement | Note |
|---|---|---|
| Carbon (C) | ≤ 0.15% | — |
| Chromium (Cr) | 8.0 – 10.0% | HTHA / sulphidic resistance |
| Molybdenum (Mo) | 0.90 – 1.10% | Creep resistance |
| Mn / Si | Mn 0.30–0.60, Si 0.25–1.00 | — |
| P / S | ≤ 0.030% each | Impurity limits |
Mechanical Properties — A234 WP9 (Class 1)
| Property | Requirement |
|---|---|
| Tensile Strength | 415 – 585 MPa (60 – 85 ksi) |
| Yield Strength (min) | 205 MPa (30 ksi) |
| Elongation (min) | ≥ 20% (per specification formula) |
| Heat Treatment | Annealed or normalised & tempered; PWHT after welding |
Equivalent Grades
| Product Form | Specification |
|---|---|
| Buttweld fittings | ASTM / ASME A234 WP9 |
| Seamless pipe | ASTM A335 P9 |
| Forgings / flanges | ASTM A182 F9 |
| EN designation | X12CrMo9-1 (W.Nr. 1.7386) |
Fitting Types Available in WP9
- Elbows — 45° / 90° / 180°, LR & SR
- Tees — equal & reducing
- Reducers — concentric & eccentric
- Caps — buttweld end closures