GRADE PROFILE
254 SMO super austenitic — 1.4547 / X1CrNiMoCuN20-18-7
254 SMO carries 6 to 6.5% molybdenum and 0.18 to 0.25% nitrogen, for a PREN of 43 to 45. It is the seawater super austenitic: super duplex performance with austenitic fabrication.
- Super austenitic
- PREN 43–45
- Cost index 420
- Welded · Seamless · Heat exchanger
- Ø 10 to 273 mm
When to choose it
In seawater, on condensers, in desalination, in flue gas treatment, and in indoor swimming pools where the chlorinated atmosphere attacks structural components. It is also the rational choice where mechanical loading is not the issue and the fabricator has no qualified duplex procedure: at comparable performance, fabrication is markedly simpler.
Its temperature range is also wider than that of a duplex, which drops out around 300 °C.
When not to choose it
Where cost matters and a 2507 will do. At index 420 against 260, the gap is considerable for a marginally higher PREN. If the fabricator has duplex welding under control and mechanical strength is a bonus, 2507 wins.
Without an over-alloyed filler metal. An ordinary filler depletes the weld in molybdenum and creates a zone of far lower PREN than the parent metal: corrosion starts there, exactly where the best grade was thought to have been placed.
On any application where chlorides are moderate: paying for a PREN of 44 in brackish water makes no sense.
Composition
| Element | % |
|---|---|
| C | ≤ 0.02 |
| Cr | 19.5–20.5 |
| Ni | 17.5–18.5 |
| Mo | 6–6.5 |
| Cu | 0.5–1 |
| N | 0.18–0.25 |
| Mn | ≤ 1 |
Mechanical properties
We only publish mechanical properties tied to a specific standard and product form — welded tube, seamless tube and bar do not share the same values, and the gap routinely exceeds 30%. The figures that apply to your specification appear on the material certificate; ask us at enquiry stage.
Designations and standards
| Reference | Designation |
|---|---|
| EN (numeric) | 1.4547 |
| EN (symbolic) | X1CrNiMoCuN20-18-7 |
| ASTM / AISI | 254 SMO |
| UNS | S31254 |
| JIS | — |
| AFNOR | — |
Tube product standards :
- EN 10216-5
- ASTM A312
- ASTM A269
Availability
Welded, seamless and heat exchanger tube, Ø 10 to 273 mm, plus fittings, flanges and bar. Partner stock or mill depending on the size and quantity. EN 10204 3.1 material certificates carrying the heat chemistry supplied with the goods.
Related grades
- 2507 (1.4410) — the super duplex at similar PREN, cheaper and mechanically stronger, but more demanding to weld.
- 904L (1.4539) — the acid super austenitic, where the medium is reducing rather than saline.
- Titanium grade 2 — the non-stainless route for marine condensers, indifferent to chlorides.
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Frequently asked questions
- 254 SMO or 2507?
- 2507 if mechanical strength matters and duplex welding is mastered. 254 SMO if fabrication must stay simple, if service exceeds 300 °C, or if the geometry rules out duplex procedures. The PREN figures are too close to decide on that criterion alone.
- Why does the filler metal matter so much?
- Because molybdenum segregates on solidification: a weld made with filler matching the parent metal ends up depleted, and therefore lower in PREN. An over-alloyed filler, typically nickel-based, compensates for that segregation.
- Is it genuinely immune to seawater?
- It is highly resistant, not immune. Crevice corrosion remains possible under deposits or in a dead leg, and high temperature reduces the margin. Hydraulic design counts as much as the grade.