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When do you need super duplex instead of duplex?
Short answer
Choose super duplex 2507 when the service is immersed seawater, warm brine or severe chlorides where crevice corrosion is a risk, because its PREN of 40 or more is the usual seawater threshold. Duplex 2205, with PREN about 35, covers brackish water, process piping and most chloride-SCC problems at lower cost.
Duplex 2205 vs Super Duplex 2507 at a glance
| Property | Duplex 2205 | Super Duplex 2507 |
|---|---|---|
| UNS | S32205 / S31803 | S32750 |
| EN | 1.4462 | 1.4410 |
| Family | Duplex stainless steel | Duplex stainless steel |
| C (%) | 0.030 max | 0.030 max |
| Cr (%) | 22.0 – 23.0 | 24.0 – 26.0 |
| Ni (%) | 4.5 – 6.5 | 6.0 – 8.0 |
| Mo (%) | 3.0 – 3.5 | 3.0 – 5.0 |
| N (%) | 0.14 – 0.20 | 0.24 – 0.32 |
| Cu (%) | — | 0.50 max |
| Tensile strength | 655 MPa (95 ksi) | 795 MPa (116 ksi) |
| Yield strength | 450 MPa (65 ksi) | 550 MPa (80 ksi) |
| PREN | 34 – 35 | ≥ 40 (typically 41 – 43) |
| Density | 7.8 g/cm³ | 7.8 g/cm³ |
| Magnetic | Magnetic, because of its ferrite content. | Magnetic, because of its ferrite content. |
| Typical use | Oil and gas flowlines, manifolds and process piping | Seawater cooling and firewater piping |
Which should you choose?
There's no universal "winner": the right choice depends on service conditions, codes and cost. Share your conditions with us for a recommendation.
Strength also changes the design
2507 has a minimum yield of about 550 MPa against 450 MPa for 2205. On high-pressure lines such as RO and injection systems, that allows thinner walls, which partly offsets the higher price per kilogram.
Fabrication needs more control
2507 is more prone to intermetallic phases if heat input or interpass temperature is too high. Welding procedures qualified with ferrite measurement and ASTM A923 testing are standard on projects using it.
Products in both grades
Related guides, comparisons and articles
Frequently asked questions
Can 2205 be used in seawater at all?
For short-term or cool, well-flushed service it sometimes is, but for permanent immersed seawater with crevices, super duplex is the safer choice.
Which specifications cover these grades?
Pipe to ASTM A790, tube to A789, plate to A240 and fittings to A815, with UNS S32205 and S32750.
What is the main difference between Duplex 2205 and Super Duplex 2507?
2507 raises chromium, molybdenum and nitrogen (PREN ≥ 40 against about 35) and yield strength (550 against 450 MPa). It's chosen for seawater and severe chlorides, while 2205 covers most brackish-water and process duties at lower cost.
When should I choose Duplex 2205?
Brackish water, process piping and chemical tankers.
When should I choose Super Duplex 2507?
Seawater, RO high-pressure and offshore systems.
Can Duplex 2205 replace Super Duplex 2507?
Only when the design, code and specification allow it. Strength, corrosion resistance and temperature limits differ, so substitution must be approved by the design authority.
Which has better pitting resistance, Duplex 2205 or Super Duplex 2507?
Typical PREN: Duplex 2205 34 – 35, Super Duplex 2507 ≥ 40 (typically 41 – 43). A higher PREN generally means better chloride pitting resistance.