Duplex 2205 and super duplex 2507 share the same two-phase structure, but 2507 carries more chromium, nickel, molybdenum and nitrogen for tougher chloride and seawater service.
| Property | Duplex 2205 | Super Duplex 2507 |
|---|---|---|
| UNS number | S31803 / S32205 | S32750 |
| Chromium | 21.0–23.0% | 24.0–26.0% |
| Nickel | 4.5–6.5% | 6.0–8.0% |
| Molybdenum | 2.5–3.5% | 3.0–5.0% |
| Nitrogen | 0.08–0.20% | 0.24–0.32% |
| PREN (approx.) | 33–36 | 40 or more |
| Min yield | 450 MPa | 550 MPa |
| Min tensile | 620 MPa | 795 MPa |
| Continuous service limit | About 300°C | About 250°C |
The Pitting Resistance Equivalent Number (PREN) estimates resistance to pitting in chloride environments, calculated from chromium, molybdenum and nitrogen. Super duplex grades are generally defined as having a PREN of 40 or more. A higher PREN means more margin in warm or high-chloride service.
2205 roughly doubles the yield strength of 316L and resists chloride stress-corrosion cracking far better. It suits heat exchangers, pressure vessels, pumps and general marine and chemical equipment with moderate chloride levels.
Choose super duplex 2507 or S32760 for subsea equipment, seawater cooling systems, offshore oil and gas and high-chloride process lines, where 2205 would be marginal. The higher strength also allows lighter sections.
S32760 is another super duplex grade, with added tungsten and copper. Its corrosion performance is comparable to 2507, but the two UNS numbers are not interchangeable on certified work, so check which one your specification names.
Both grades need controlled heat input when welding to protect the austenite-ferrite balance, and super duplex is the more demanding. Avoid long exposure above the temperature limits shown, because of embrittlement. Projects commonly specify ferrite content and ASTM A923 testing to confirm freedom from harmful intermetallic phases.
