GRADE PROFILE
Super duplex 2507 — 1.4410 / X2CrNiMoN25-7-4
2507 raises chromium to 25%, molybdenum to 4% and nitrogen to 0.3%. PREN 42.5. It is the seawater and offshore grade — and one of the most demanding in the catalogue to fabricate.
- Super duplex
- PREN 42–43
- Cost index 260
- Welded · Seamless · Heat exchanger
- Ø 10 to 406 mm
When to choose it
When the medium is genuinely marine. Seawater, offshore, high-salinity desalination, acidic chlorinated media, umbilicals. Above a PREN of 40 you enter the range where 2205 no longer offers margin and the cost of super duplex is justified by the risk avoided.
On pressurised marine circuits, the high yield strength allows reduced wall thickness, which counts twice offshore where carried weight is paid for.
When not to choose it
Above 300 °C in continuous service, like any duplex: sigma phase precipitates and the embrittlement is irreversible. Super duplex, more heavily alloyed in chromium and molybdenum, is if anything more susceptible than 2205.
Without a qualified welding procedure. This is not a recommendation but a condition of function: phase balance and nitrogen retention on cooling are controlled through heat input. A poorly executed weld does not have the properties of the parent metal, and the defect is invisible.
Where 2205 is enough. The cost difference is around 50%, and in brackish water 2205 is the rational answer.
Composition
| Element | % |
|---|---|
| C | ≤ 0.03 |
| Cr | 24–26 |
| Ni | 6–8 |
| Mo | 3–4.5 |
| N | 0.24–0.35 |
| Mn | ≤ 2 |
| Si | ≤ 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) | 1.4410 |
| EN (symbolic) | X2CrNiMoN25-7-4 |
| ASTM / AISI | 2507 |
| UNS | S32750 |
| JIS | — |
| AFNOR | — |
Tube product standards :
- EN 10216-5
- ASTM A790
- ASTM A789
Availability
Welded, seamless and heat exchanger tube, Ø 10 to 406 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 — on this kind of application, ask for them before despatch if you want to verify the actual PREN.
Related grades
- 2205 (1.4462) — the step below, for brackish water.
- 254 SMO (1.4547) — the super austenitic at comparable PREN, easier to weld but less strong.
- CuNi 70/30 — the copper route, where biological fouling matters as much as corrosion.
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Frequently asked questions
- 2507 or 254 SMO for seawater?
- The PREN figures are close, 42.5 against 44. 2507 offers far higher yield strength and allows thinner walls; 254 SMO welds like an austenitic and handles intermediate temperatures better. The choice turns on mechanical loading and on the fabricator's competence.
- Why is welding so critical?
- Because duplex properties come from a balance between austenite and ferrite achieved by heat treatment. The welding thermal cycle disrupts it locally, and only controlled heat input with an over-alloyed filler restores it. A weld that is too ferritic loses both corrosion resistance and toughness.
- Does a PREN of 42.5 guarantee seawater performance?
- No. PREN ignores temperature, flow velocity and crevice corrosion. Hot stagnant seawater is more aggressive than cold flowing seawater in the same grade. The index rules candidates out; it does not validate a choice.