When 316L is not enough, buyers often look at Duplex 2205. It offers roughly double the yield strength and much better resistance to chloride corrosion — but it also needs more care in welding and fabrication. For pipe, fitting and flange suppliers, knowing when to recommend duplex can open higher-value orders in oil & gas, desalination, chemical and marine projects.
What "duplex" means
Duplex stainless steels have a mixed microstructure of roughly 50% austenite and 50% ferrite. This combination gives them high strength and good resistance to stress corrosion cracking. 316L, by contrast, is fully austenitic.
2205 is the most widely used duplex grade. It is covered by UNS S31803 and the tighter UNS S32205, with EN number 1.4462. Many mills supply dual-certified S31803/S32205 material.
Chemistry compared (typical, weight %)
| Element | Duplex 2205 (S32205) | 316L |
|---|---|---|
| Chromium | 22.0 – 23.0 | 16.0 – 18.0 |
| Nickel | 4.5 – 6.5 | 10.0 – 14.0 |
| Molybdenum | 3.0 – 3.5 | 2.0 – 3.0 |
| Nitrogen | 0.14 – 0.20 | 0.10 max |
| Carbon (max) | 0.030 | 0.030 |
Duplex has more chromium, molybdenum and nitrogen but much less nickel.
Strength
| Property (plate, ASTM A240) | Duplex 2205 | 316L |
|---|---|---|
| Yield strength, min | 450 MPa | 170 MPa |
| Tensile strength, min | 655 MPa | 485 MPa |
Higher strength means designers can often use thinner walls for the same pressure, which reduces weight and can offset the material price difference.
Corrosion resistance
Pitting and crevice corrosion
The PREN (Cr + 3.3 Mo + 16 N) is about 35 for 2205 and about 24 for 316L. Duplex resists chlorides much better — useful in seawater-cooled systems, brackish water and chloride-containing process streams.
Stress corrosion cracking
Austenitic grades like 316L can suffer chloride stress corrosion cracking at elevated temperatures. Duplex has much better resistance, a key reason it is chosen for hot chloride environments.
Temperature limits
Duplex is not ideal for every temperature. Above roughly 300 °C, it can become brittle over time, so design codes limit its use at high temperatures. At very low temperatures, its toughness also drops compared with austenitic grades. 316L remains the better choice for cryogenic service.
Fabrication and welding
- Duplex needs controlled heat input and suitable filler metals (such as 2209) to keep the right ferrite–austenite balance.
- Ferrite content is often measured after welding.
- Buyers may require extra tests such as ASTM A923 (detrimental intermetallic phases) and ASTM G48 (pitting).
316L is easier to weld and form, which keeps fabrication costs lower.
Typical applications
Duplex 2205
- Desalination plants and seawater systems
- Offshore and onshore oil & gas piping
- Chemical tankers and storage tanks
- Pulp and paper equipment
- Heat exchangers with chloride-containing water
316L
- Food, dairy and pharmaceutical plants
- General chemical and process piping
- Marine fittings and architectural work
- Low-temperature and cryogenic service
Product standards to quote
- Pipe: ASTM A790 (seamless and welded duplex pipe)
- Tube: ASTM A789
- Plate: ASTM A240 UNS S32205
- Fittings: ASTM A815 WPS32205
- Flanges and forgings: ASTM A182 F51 / F60
Compare with 316L standards such as A312 TP316L and A182 F316L. Background on 304 and 316 is in our SS 304 vs SS 316 guide.
How to advise buyers
- Ask about chloride levels, temperature and pressure.
- Check if the project specification names duplex or allows 316L.
- Offer both grades if the application is unclear, with weights for each wall thickness.
- Confirm testing requirements (ferrite, A923, G48) before quoting.
- Supply a precise mill test certificate — MTCMitra checks every value against grade limits.
Cost comparison in practice
Buyers often compare duplex and 316L only by price per kilogram. A fairer comparison looks at the whole line:
- Wall thickness — with roughly twice the yield strength, duplex can often meet the same design pressure with a thinner wall, which reduces weight per metre.
- Service life — in chloride environments, 316L may need earlier replacement or more maintenance.
- Fabrication — duplex welding procedures, ferrite checks and extra tests add cost.
- Availability — 316L is stocked in more sizes, which can shorten lead times.
Offer the buyer both options with weights per metre and total cost, and let the application decide. Our pipe weight calculator makes the comparison quick.
Frequently asked questions
Is duplex 2205 magnetic?
Yes. Because of its ferrite content, duplex stainless steel is magnetic, unlike annealed 316L.
Is duplex more expensive than 316L?
Per kilogram it is often similar or higher, depending on nickel and molybdenum prices. Thinner walls can make the overall cost competitive.
Can duplex replace 316L everywhere?
No. Duplex is not suitable for high-temperature service or cryogenic use, and it needs more careful welding.
What is super duplex?
Grades such as 2507 (UNS S32750) have even higher PREN and strength, for very aggressive seawater and offshore service.
Key takeaways
- Duplex 2205 offers about twice the yield strength of 316L and better chloride resistance.
- 316L is easier to fabricate and better for cryogenic and some high-temperature uses.
- Quote the right standard, testing and certificate for each grade.
