254 SMO Buttweld Pipe Fittings
254 SMO / UNS S31254 / EN 1.4547 (X1CrNiMoCuN20-18-7) — a 20Cr-18Ni-6Mo-Cu-N super-austenitic stainless steel with a pitting resistance equivalent of about 43. Used where 316L and even 904L are inadequate: seawater cooling, reverse-osmosis desalination, FGD scrubbers and offshore chloride service. EN 10253-2 Type B and ASME B16.9. EN 10204 3.1 standard; 3.2 TPI on request.
½″–48″
Size Range
PRE ~43
Pitting Index
6% Mo
Super-austenitic
EN 10204
3.1 Std / 3.2 On Req.
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254 SMO Grade Equivalents
| Common Name | EN W.Nr. | EN Name | UNS | ASME P-No. |
|---|---|---|---|---|
| 254 SMO (fittings) | 1.4547 | X1CrNiMoCuN20-18-7 | S31254 | 8, Gr 4 |
| A182 F44 (flanges) | 1.4547 | X1CrNiMoCuN20-18-7 | S31254 | 8 |
| A312 TP S31254 (pipe) | 1.4547 | X1CrNiMoCuN20-18-7 | S31254 | 8 |
| A240 S31254 (plate) | 1.4547 | X1CrNiMoCuN20-18-7 | S31254 | 8 |
Chemical Composition — 254 SMO / 1.4547
| Standard | C | Cr | Ni | Mo | N | Cu |
|---|---|---|---|---|---|---|
| UNS S31254 (ASTM) | ≤0.020 | 19.5–20.5 | 17.5–18.5 | 6.0–6.5 | 0.18–0.22 | 0.50–1.00 |
| EN 1.4547 (X1CrNiMoCuN20-18-7) | ≤0.020 | 19.5–20.5 | 17.5–18.5 | 6.0–7.0 | 0.18–0.25 | 0.50–1.00 |
The 6% molybdenum plus nitrogen and copper give a PRE of roughly 43 — placing 254 SMO between the standard austenitic grades and the nickel alloys, with excellent resistance to chloride pitting, crevice corrosion and stress corrosion cracking.
Mechanical Properties — 254 SMO / 1.4547
| Standard | Min. UTS (MPa) | Min. YS (MPa) | Elongation (%) | Max. Hardness | HT Condition |
|---|---|---|---|---|---|
| UNS S31254 (ASTM) | 650 | 300 | ≥35% | 223 HBW | Solution annealed |
| EN 1.4547 (EN 10253-2) | 650–850 | ≥300 | ≥35% | 223 HBW | Solution annealed |
Welding & Corrosion Considerations
✓ No PWHT Required — supplied solution annealed.
254 SMO (UNS S31254 / EN 1.4547) is a fully austenitic grade supplied in the solution annealed condition; no post-weld heat treatment is required. Solution annealing at ~1150–1200°C after heavy forming restores full corrosion resistance.
Nickel-Base Filler Required
- Filler metal: over-alloyed nickel base — ERNiCrMo-3 (Alloy 625). A matching filler is not used because molybdenum segregates on solidification, reducing weld-metal pitting resistance.
- Corrosion resistance: PRE ~43 — resists chloride pitting, crevice corrosion and chloride SCC far beyond 316L / 904L.
- Typical service: seawater cooling & firewater, RO desalination, FGD scrubbers, bleach plants, offshore.
- ASME P-No.: 8, Group 4. WPQ per ASME IX or ISO 15614-1.
254 SMO Fitting Types Available
90° Elbow (LR & SR)
Long Radius & Short Radius
ASME B16.9
45° Elbow
Long Radius
ASME B16.9
Equal Tee
Straight tee, equal branch
ASME B16.9
Reducing Tee
Reduced branch outlet
ASME B16.9
Concentric Reducer
Inline bore reduction
ASME B16.9
Eccentric Reducer
Flat bottom / top configurations
ASME B16.9
End Cap
Pipe end closure
ASME B16.9
Stub End (Lap Joint)
For use with lap joint flanges
ASME B16.9
Cross / Lateral
Four-way and angled branch
ASME B16.9
316L vs 904L vs 254 SMO — Chloride Resistance
| Property | 316L | 904L | 254 SMO |
|---|---|---|---|
| Molybdenum | 2.0–3.0% | 4.0–5.0% | 6.0–6.5% |
| PRE (approx.) | ~24 | ~35 | ~43 |
| Typical limit | Low chloride | Sulphuric acid, moderate Cl | Seawater, FGD, desalination |
Ready to order 254 SMO super-austenitic fittings?
Specify size, schedule, fitting type, standard (ASME B16.9 or EN 10253-2 Type B), and required MTR (EN 10204 3.1 or 3.2). We respond within 1 business day.
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