P9 Buttweld Pipe Fittings
9Cr-1Mo / EN 1.7386 (X12CrMo9-1) — highest sulfidic corrosion resistance among the plain (unmodified) CrMo grades, making it the top choice for high-temperature refinery service in crude distillation, atmospheric and vacuum units, FCC, coker, and visbreaker piping. ASME B16.9 and EN 10253-3 Type B.
⚠ P9 ≠ P91 — These grades are NOT interchangeable. P9 has no V, Nb, or N additions and has ~3× lower allowable stress than P91 at elevated temperature. See the comparison table below.
½″–48″
Size Range
600°C
Max Service Temp
420 MPa
Min Tensile (EN)
EN 10204
3.1 Std / 3.2 On Req.
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P9 Grade Equivalents
| ASTM | EN W.Nr. | EN Name | DIN | UNS | ASME P-No. |
|---|---|---|---|---|---|
| A234 WP9 | 1.7386 | X12CrMo9-1 | X12CrMo9-1 | K90941 | 5B, Gr 1 |
| A182 F9 (forged) | 1.7386 | X12CrMo9-1 | — | — | 5B |
| A335 P9 (pipe) | 1.7386 | X12CrMo9-1 | — | — | 5B |
Chemical Composition — P9 / 1.7386
| Standard | C | Cr | Mo | V | Nb | Mn | Si |
|---|---|---|---|---|---|---|---|
| ASTM A234 WP9 | ≤0.15 | 8.00–10.00 | 0.90–1.10 | None | None | 0.30–0.60 | 0.25–1.00 |
| EN 1.7386 (EN 10253-3) | 0.08–0.15 | 8.00–10.00 | 0.90–1.10 | None | None | 0.30–0.60 | 0.25–1.00 |
No V, Nb, or N — this is what distinguishes P9 from P91 (X10CrMoVNb9-1). P9 chemistry certificates will not show these elements; if you see V + Nb + N on a 9Cr certificate, it is P91, not P9.
P9 vs P91 — Critical Differences
P9 and P91 are NOT interchangeable — different ASME P-Numbers, different fillers, different WPS
P9 is ASME P-No. 5B, Group 1. P91 is P-No. 15E, Group 1. A WPS qualified for P91 does NOT cover P9, and vice versa. Never substitute one for the other based on Cr content alone.
| Property | P9 / EN 1.7386 | P91 / EN 1.4903 |
|---|---|---|
| V + Nb + N additions | None | Yes |
| ASME P-Number | 5B, Gr 1 | 15E, Gr 1 |
| Welding filler | ER80S-B8 | ER90S-B9 |
| PWHT temperature | 720–760°C | 745–775°C |
| Allowable stress at 600°C | ~40 MPa | ~114 MPa (~3×) |
| Primary use | Refinery sulfidic service | Power generation (creep) |
Mechanical Properties — P9 / 1.7386
| Standard | Min. UTS (MPa) | Min. YS (MPa) | Elongation (%) | Max. Hardness | HT Condition |
|---|---|---|---|---|---|
| ASTM A234 WP9 | 415 | 205 | ≥20% | 241 HBW | A or N+T |
| EN 1.7386 (EN 10253-3) | 420–600 | ≥220 | ≥20% | 241 HBW | N+T |
Welding & PWHT Requirements
Preheat Temperature
200–250°C minimum. P9 hardens rapidly on cooling — maintain preheat throughout.
Inter-pass Temperature
Maximum 350°C.
Filler Metal
ER80S-B8 (GTAW) or E9018-B8 (SMAW). 9Cr-1Mo matching composition. Do NOT use P91 filler (ER90S-B9) — it will introduce V+Nb into the weld and invalidate the WPS.
PWHT Temperature
720–760°C. Minimum 1 hour per 25mm wall. Different from P91 (745–775°C).
Cooling
Furnace cool to 300°C, then air cool. Temperature chart records mandatory.
Post-PWHT Hardness
Weld and HAZ ≤241 HBW after PWHT.
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