Super duplex stainless · UNS S32750 · EN 1.4410
In short: 2507 is a super duplex stainless steel with 25% chromium, 7% nickel, 4% molybdenum and high nitrogen, giving a pitting resistance number above 40 and a minimum yield of 550 MPa (80 ksi). That combination is why it is the standard material for seawater cooling, firewater, offshore topsides and reverse-osmosis desalination piping.
Overview
With 24–26% chromium, 3–5% molybdenum and 0.24–0.32% nitrogen, super duplex reaches a PREN of at least 40, the threshold usually taken for resistance to pitting in ambient seawater. Its yield strength of 550 MPa is higher than 2205, which allows thinner, lighter piping and vessels.
Super duplex is used for seawater cooling and firewater systems, offshore process piping, reverse-osmosis desalination high-pressure piping, subsea equipment and chemical plant. Its fabrication window is narrow: welding and heat treatment must avoid sigma and other intermetallic phases. "SAF 2507" is a trademark of Alleima; generic material is specified as UNS S32750.
Available as
Select a form for its specification, sizes and weights.
Where it's used
Strength
ASTM A240: room-temperature specification values for the annealed condition.
Offshore orders
Super duplex is sensitive to heat treatment and fabrication, so specifications check the microstructure as well as the chemistry.[2]
Confirms the austenite-ferrite balance.
Detects embrittlement from intermetallic phases.
Corrosion test at a specified temperature.
NORSOK M-650 where the project requires it.
Chemistry
| Element | Limit, % | Why it matters |
|---|---|---|
| C | 0.030 max | |
| Mn | 1.20 max | |
| P | 0.035 max | |
| S | 0.020 max | |
| Si | 0.80 max | |
| Cr | 24.0 – 26.0 | 24–26% |
| Ni | 6.0 – 8.0 | 6–8%: phase balance |
| Mo | 3.0 – 5.0 | 3–5% |
| Cu | 0.50 max | |
| N | 0.24 – 0.32 | 0.24–0.32%: strength and pitting resistance |
Limits per ASTM A240 (S32750); other product forms and specifications differ slightly. Your order's specification and edition govern.
Supply
| Product form | Specification and designation |
|---|---|
| Super Duplex 2507 pipes | ASTM A790 / ASME SA790 S32750; A928 EFW |
| Super Duplex 2507 tubes | ASTM A789 / ASME SA789 S32750 |
| Super Duplex 2507 plates | ASTM A240 S32750 |
| Super Duplex 2507 sheets | ASTM A240 S32750 |
| Super Duplex 2507 bars | ASTM A276 / A479 S32750 |
| Super Duplex 2507 fittings | ASTM A815 WPS32750 |
| Super Duplex 2507 flanges | ASTM A182 F53 |
| Super Duplex 2507 bolts | Super duplex S32750 bolting (to order) |
| Super Duplex 2507 nuts | S32750 nuts |
| Super Duplex 2507 washers | S32750 washers |
Ordering
Getting these on the enquiry avoids the usual back-and-forth and makes sure the certificate matches your specification.
2507 questions
Above 40 by definition of "super duplex"; Alleima specifies a minimum of 42.5 for its seamless 2507 tube, with equal PRE in the ferrite and austenite phases.[1] Duplex 2205 is about 34–35, so 2507 is the usual step up for warm or chlorinated seawater.
Its high PREN resists pitting and crevice corrosion in seawater, it has excellent resistance to chloride stress corrosion cracking, and its yield strength (550 MPa (80 ksi) minimum) allows thinner, lighter piping.[1]
Like other duplex grades it is normally limited to below about 300 °C because of 475 °C embrittlement of the ferrite.[2]
Ferrite content, Charpy impact at low temperature and ASTM G48 pitting tests are common, plus NORSOK M-650 mill qualification on many North Sea and international projects. See our UK page for NORSOK.
Pipe: ASTM A790 / ASME SA790 S32750; A928 EFW. Tube: ASTM A789 / ASME SA789 S32750. Plate: ASTM A240 S32750. Flanges: ASTM A182 F53. Fittings: ASTM A815 WPS32750.
Sources
Trade rules and project schedules change. Confirm current requirements with your customs broker or project authority before shipment.
Send sizes, specification and test requirements (ferrite, impact, G48, NORSOK).