Duplex vs Super Duplex Stainless Steel – Differences, Applications & Selection Guide
Duplex and super duplex stainless steels have become the materials of choice for demanding applications in the oil and gas, marine, desalination, and chemical processing industries. Their unique two-phase microstructure — approximately 50% austenite and 50% ferrite — delivers roughly double the yield strength of conventional austenitic grades like SS 304 or SS 316, combined with excellent resistance to stress corrosion cracking and pitting.
Metinox Overseas manufactures and exports both duplex and super duplex pipes, tubes, and flanges to global projects. Our Duplex Steel Pipes (UNS S31803 / S32205) and our Super Duplex Pipes in UNS S32750 and S32760 cover the full range of project requirements. Flanges in both grades are listed at our Duplex & Super Duplex Flanges page.
What Is Duplex Stainless Steel?
Duplex stainless steel — most commonly Grade 2205 (UNS S31803/S32205) — contains approximately 22% chromium, 5% nickel, and 3% molybdenum. Its dual-phase microstructure gives it:
- Yield strength of approximately 450 MPa — roughly twice that of SS 316L
- A PREN (Pitting Resistance Equivalent Number) of around 35
- Excellent resistance to stress corrosion cracking in chloride environments
- Good weldability with standard duplex filler metals
Duplex 2205 covers approximately 80% of duplex applications worldwide and is the default choice for most offshore, chemical, and marine projects requiring a step up from austenitic grades.
What Is Super Duplex Stainless Steel?
Super duplex grades push the alloy content significantly higher. The two most common super duplex grades are:
- UNS S32750 (2507): 25% chromium, 7% nickel, 4% molybdenum — PREN above 42
- UNS S32760 (Zeron 100): adds copper and tungsten on top of elevated Cr-Ni-Mo — PREN above 40
This elevated alloying provides superior performance over standard duplex in the most aggressive service conditions, including hot seawater, sour gas environments, and highly concentrated chloride streams.
Key Differences: Duplex vs Super Duplex
Corrosion Resistance
Standard duplex (PREN ~35) handles moderate chloride environments well. Super duplex (PREN >40) is specified for hot seawater service (above 25°C), brine environments, and highly corrosive process streams. In subsea and desalination applications, super duplex is almost universally required.
Mechanical Strength
Super duplex 2507 offers approximately 22% higher yield strength and 28% higher tensile strength than duplex 2205. This allows for thinner wall specifications in high-pressure applications, reducing weight — a significant benefit in offshore and subsea structures.
Weldability and Fabrication
Both grades require careful welding with controlled heat input and appropriate filler metals. Super duplex is more sensitive to intermetallic phase precipitation during fabrication, making strict process control essential. Always request material test reports (MTRs) and ferrite testing to confirm microstructure compliance.
Cost
Super duplex costs noticeably more than standard duplex due to its higher alloy content. Specify super duplex only when the operating conditions — high chloride concentration, elevated temperature, or sour gas service — genuinely require the additional performance. For general industrial service, duplex 2205 is the more cost-effective choice.
| Property | Duplex 2205 (S31803/S32205) | Super Duplex 2507 (S32750) |
|---|---|---|
| Chromium | ~22% | ~25% |
| Nickel | ~5% | ~7% |
| Molybdenum | ~3% | ~4% |
| PREN | ~35 | >42 |
| Yield strength | ~450 MPa | ~550 MPa |
| Best for | Offshore, chemical, marine | Hot seawater, sour gas, desalination |
Metinox Overseas Duplex and Super Duplex Range
- Duplex 2205 Pipes
- Duplex 2205 Tubes
- Super Duplex S32750 Pipes & Tubes
- Super Duplex S32760 Pipes
- Super Duplex S32750 Tubes
- Duplex 2205 Flanges
- Duplex 2507 Flanges
- S32760 Flanges
Frequently Asked Questions
Choose super duplex when operating temperatures exceed 25°C in seawater service, when chloride concentrations are very high, when sour gas (H₂S) is present at elevated partial pressures, or when design pressure requirements demand the higher strength of super duplex grades.
Yes. Metinox Overseas supplies both duplex and super duplex pipes in seamless and welded forms with full material traceability, PMI testing, and third-party inspection reports from TUV, SGS, or Bureau Veritas.
Common standards include ASTM A790 (seamless and welded), ASTM A789 (tubes), and ASTM A928 for welded pipes. Flanges are manufactured to ASTM A182 F51 (2205) and F53 (2507).
Looking for duplex or super duplex pipes and flanges? Contact Metinox Overseas at metinoxoverseas.com/contact-us — we supply to offshore, desalination, and petrochemical projects globally with competitive CIF pricing.
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