Ferralium 255 (UNS S32550) and Super Duplex 2507 (UNS S32750) are both super duplex stainless steel grades with PREN ≥ 40, used in seawater service, oil & gas, chemical processing and offshore applications. The defining difference is copper: Ferralium 255 contains 2% Cu (Cu-bearing super duplex); Super Duplex 2507 has no Cu addition, but slightly higher Cr and Mo. For full Super Duplex 2507 reference, see duplex2507.com (UNS S32750).
| Element | Ferralium 255 (S32550) | Super Duplex 2507 (S32750) |
|---|---|---|
| Chromium (Cr) | 24.0–27.0 | 24.0–26.0 |
| Nickel (Ni) | 4.5–6.5 | 6.0–8.0 |
| Molybdenum (Mo) | 2.9–3.9 | 3.0–5.0 |
| Nitrogen (N) | 0.10–0.25 | 0.24–0.32 |
| Copper (Cu) | 1.5–2.5 | max 0.5 (not specified) |
| Tungsten (W) | none | none |
| Carbon (C), max. | 0.04 | 0.030 |
Ferralium 255 PREN ≈ 40–42 typical per heat (25 Cr + 3.3×3 Mo + 16×0.2 N = 38.1 minimum, 41 typical). Super Duplex 2507 PREN ≈ 41–43 typical per heat (25 Cr + 3.3×4 Mo + 16×0.27 N = 42.5 typical). Super Duplex 2507 has marginally higher PREN due to higher Mo and N; both grades comfortably meet the PREN ≥ 40 super duplex threshold.
| Property | Ferralium 255 | Super Duplex 2507 |
|---|---|---|
| Yield strength (Rp0.2), min | 550 MPa | 550 MPa |
| Tensile strength (Rm), min | 760 MPa | 795 MPa |
| Elongation (A5), min | 15% | 15% |
| Hardness (NACE MR0175), max | 32 HRC | 32 HRC |
| Charpy at −46 °C, min (NORSOK) | 45 J | 45 J |
Choose Ferralium 255 when service involves reducing acids (dilute H2SO4, HCl, brines), chemical processing applications where the 2% Cu advantage matters, or when project specification requires a Cu-bearing super duplex grade.
Choose Super Duplex 2507 when service is dominated by chloride pitting alone (warm seawater, marine offshore), when the project specification calls out 2507 specifically (common in standard offshore EPC scopes), or when slightly higher PREN margin is preferred. Both grades are interchangeable for standard NACE MR0175 sour service and marine seawater.
Both grades are covered by the same ASTM specifications: ASTM A479 (bar), ASTM A789 (tube), ASTM A790 (pipe), ASTM A815 (fittings), ASTM A182 (forgings/flanges). Both qualify under NORSOK M-650 (Ferralium per MDS D55, 2507 per MDS D54), and NACE MR0175 / ISO 15156-3 for sour service. TorqBolt manufactures Ferralium 255 in Mumbai & Rajkot, India. Super Duplex 2507 sourcing detail at duplex2507.com.
