Last verified 19 August 2026.
The comparison
| Property | 254 SMO | 904L | Evidence |
|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 320 MPa | 240 MPa | E3 E3 |
| Tensile strength Rm, minimum | 650 MPa | 530 MPa | E3 E3 |
| Elongation A, minimum | 35 % | 35 % | E3 E3 |
| PREN | 43 — | 34 — | E3 E3 |
| Density | 8.0 g/cm³ | 8.0 g/cm³ | E3 E3 |
| Modulus of elasticity | 195 GPa | 195 GPa | E3 E3 |
| Thermal conductivity | 14 W/(m·K) | 12 W/(m·K) | E3 E3 |
All shared rows compare like for like.
Where each side’s numbers come from
See 254 SMO and 904L — 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
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.
904L. Sulphuric and phosphoric acid service, and mixed acids with chlorides in them, where austenitic grades below it corrode generally rather than pit. The copper addition is specifically there for reducing acids. Pickling lines, acid plants, flue gas cleaning and some pharmaceutical process equipment are where it earns the price.
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.
Against 904L: Price, and the fact that a cheaper grade usually does the job. Where the problem is chlorides rather than acid, 2205 has a higher pitting ranking, twice the proof strength and a fraction of the alloy content; where the problem is severe chlorides, 254 SMO is the better answer. 904L gets specified out of habit more often than out of analysis.
What this comparison does not cover
- 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.
- Composition limits, not established.
- Whether a super duplex is the better answer for your part. This page gives you the numbers, not the decision.
- No corrosion rate data, which is the only reason to choose this alloy over a duplex.
- Critical pitting and crevice temperatures are not established here.
- Welding practice for high-alloy austenitics, including filler overmatching.
Generated from data/materials/254smo.yaml and 904l.yaml.