Last verified 19 August 2026.
The comparison
| Property | Duplex 2205 | 254 SMO | Evidence |
|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 500 MPa | 320 MPa | E3 E3 |
| PREN | 35 — | 43 — | E3 E3 |
| Modulus of elasticity | 200 GPa | 195 GPa | E3 E3 |
| Density | 7.8 g/cm³ | 8.0 g/cm³ | E3 E3 |
| Thermal conductivity | 15 W/(m·K) | 14 W/(m·K) | E3 E3 |
| Tensile strength Rm, minimum | 700 MPa | 650 MPa | E3 E3 |
| Elongation A80, minimum | 20 % | 35 % | E3 E3 |
| Proof strength Rp0.2, minimum (ASTM) | 450 MPa | not established here | E3 / — |
PREN — different documents — Outokumpu Forta range datasheet against Outokumpu Ultra range datasheet
Modulus of elasticity — different documents — Outokumpu Forta range datasheet against Outokumpu Ultra range datasheet
Density — different documents — Outokumpu Forta range datasheet against Outokumpu Ultra range datasheet
Thermal conductivity — different documents — Outokumpu Forta range datasheet against Outokumpu Ultra range datasheet
The trap on this comparison
Proof strength Rp0.2 is specified twice: 450 MPa (ASTM A240/A240M, plate, 20 °C) and 500 MPa (EN 10088-2, cold rolled strip, 20 °C) — 11% apart. Both correct. Which one governs is a question about your drawing and your product form, not about the material.
Where each side’s numbers come from
See Duplex 2205 and 254 SMO — each page lists every source, every demotion and every gap. Nothing on this page is derived from anything not on those two, and our coverage limits are stated separately.
Where a PREN appears above, read it as a ranking number rather than a qualification: what PREN can and cannot tell you.
When to choose which
Duplex 2205. Where strength sets the section or chlorides set the material. At the 450 MPa ASTM A240 minimum against 170 for 316L, a strength-driven part in 2205 is dramatically thinner, and for a plate in bending that compounds. The higher PREN also moves you out of the range where 316L is marginal in warm chloride service.
254 SMO. Seawater and strong chloride service where a single-phase austenitic is wanted rather than a duplex — because the part runs hot, because it must stay non-magnetic, or because the shop is set up for austenitic fabrication and not for phase-balance control. Desalination, seawater cooling, bleaching plant and offshore piping are the recurring uses.
Against Duplex 2205: Fabrication and supply, not properties. Duplex has a narrower heat-input window, needs procedures qualified for it, and is not on every stockist’s shelf in every thickness. A shop with qualified duplex procedures treats 2205 as ordinary; a shop without them faces a new PQR and an eight-week lead time, and that is frequently decisive regardless of what the property table says.
Against 254 SMO: Price and strength per unit cost. At six percent molybdenum the alloy content is expensive, and 2507 reaches the same pitting ranking with far more proof strength, so a strength-driven seawater part is usually cheaper in super duplex. Segregation on solidification also makes weld metal the weak point unless an overmatching filler is used.
What this comparison does not cover
- Crevice corrosion, the usual failure mode in seawater service, which PREN does not predict.
- Elevated temperature: 2205 has a service ceiling that 316L does not share, driven by 475 °C embrittlement and sigma-phase formation. Not sourced here.
- Cryogenic behaviour.
- Fatigue, fracture toughness and stress corrosion cracking.
- Cost, which moves with alloy surcharges and is not a fixed ratio.
- Composition limits, not established.
- Critical pitting and crevice temperatures are not established here, and they are what the alloy is selected on.
- Weld metal corrosion behaviour, which is where this alloy family usually fails first.
- Elevated temperature strength, fatigue and fracture toughness.
- Whether a super duplex is the better answer for your part. This page gives you the numbers, not the decision.
Generated from data/materials/2205.yaml and 254smo.yaml.