Super Duplex Stainless Steel
Super duplex stainless steel (such as 2507 / UNS S32750, S32760) has higher chromium, molybdenum and nitrogen than duplex, giving a PREN above 40 and outstanding resistance to seawater, chlorides and aggressive process fluids. It is used in offshore, subsea and severe chemical service.
What it is
With about 25% chromium, 7% nickel and 3.5–4% molybdenum plus nitrogen, super duplex resists pitting and crevice corrosion in warm seawater where 316 and standard duplex may fail, while offering very high strength.
It is costly and demanding to machine and weld, so it is used where its corrosion performance is essential.
Typical applications
- Offshore and subsea components
- Seawater pumps and valves
- Firewater and ballast systems
- Chemical process equipment
- Desalination high-pressure parts
Materials & grades
- Super duplex 2507 (S32750)
- Zeron 100-type (S32760)
- Cast super duplex (CE3MN, 5A/6A)
Points to consider
- Strict welding procedures and heat input control are essential.
- Material certification with corrosion testing (e.g. ASTM G48) may be required.
- Slow machining and high tool wear; plan cost accordingly.
- Verify genuine material with PMI testing for critical service.
Frequently asked questions
What is the difference between duplex and super duplex?
Super duplex has more chromium, molybdenum and nitrogen, giving higher strength and a PREN above 40 for much better seawater resistance.
Where is super duplex used?
Offshore, subsea, seawater and severe chemical service where standard stainless steels would corrode.
What is PMI testing?
Positive material identification, a quick check of alloy composition to confirm the correct material is supplied.