316 vs 2205 Duplex Stainless
316 is the molybdenum-bearing austenitic stainless most people reach for when 304 is not enough. 2205 is a duplex grade, roughly half austenite and half ferrite, with 22% chromium, 3% molybdenum and a nitrogen addition. That gives it more than twice the minimum yield strength of 316, 450 against 205 MPa, a pitting resistance equivalent (PREN) of about 35 against about 24, and far better resistance to chloride stress-corrosion cracking, which attacks 316 in warm chloride water above about 60 °C (140 °F).
316 wins on fabrication and temperature range. It is easier to form, weld and machine, non-magnetic, tough at cryogenic temperatures, and usable to about 800 °C. 2205 is magnetic, must be welded with controlled heat input, and is limited to about -50 to 300 °C. Choose 2205 for warm chlorides and for pressure vessels, piping and tanks where its strength lets walls get thinner; choose 316 for everything else.
| Property | 316 | 2205 duplex |
|---|---|---|
| Structure | Austenitic | Duplex: ~50% austenite, ~50% ferrite |
| UNS | S31600 (S31603 for 316L) | S32205 (older S31803) |
| Composition | 16-18% Cr, 10-14% Ni, 2-3% Mo | 22-23% Cr, 4.5-6.5% Ni, 3.0-3.5% Mo, 0.14-0.20% N |
| PREN (Cr + 3.3Mo + 16N) | ~24 | ~35 |
| Yield, annealed | 205 MPa (30 ksi) min | 450 MPa (65 ksi) min |
| Tensile, annealed | 515 MPa (75 ksi) min | 655 MPa (95 ksi) min |
| Elongation | 40% min | 25% min |
| Chloride stress-corrosion cracking | Susceptible above ~60 °C (140 °F) | Much more resistant |
| Magnetic | No (annealed) | Yes |
| Service temperature | Cryogenic to ~800 °C | ~-50 to 300 °C (-60 to 570 °F) |
| Typical uses | Marine fittings, food and pharma equipment, valves, general chemical service | Oil and gas piping, chemical tanks, desalination, heat exchangers, seawater systems |
Typical values for the stated conditions. Confirm against the mill certificate and your spec.
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Decision matrix
A check marks the side with the edge on that dimension.
| Dimension | 316 | 2205 duplex |
|---|---|---|
| Machining | ✓ Fair; gummy, work-hardens | Fair to poor; stronger and tougher, more tool wear |
| Welding | ✓ Excellent; 316L filler, no special controls | Good; 2209 filler, controlled heat input and interpass temperature |
| Forming | ✓ Excellent; deep draws, tight bends | Fair; higher forces and more springback |
| Strength | 205 MPa yield min | ✓ 450 MPa yield min, over twice 316 |
| Corrosion resistance | Good; pits and stress-cracks in warm chlorides | ✓ Very good; PREN ~35, resists chloride stress-corrosion cracking |
| Finishing | ✓ Passivates, electropolishes, brushed and mirror finishes stocked | Pickles and passivates; usually mill or blasted finish |
| Material cost | ✓ Baseline | About 1.2-1.5x per pound; thinner walls can make the vessel cheaper |
| Availability | ✓ Every form, everywhere | Plate, pipe, fittings and bar from specialty stockists |
Choose 316 when
- General corrosion service, marine hardware, food, pharma and architectural parts in moderate chlorides
- Parts that are deep drawn, tightly bent, heavily machined or welded without procedure controls
- Cryogenic service, or temperatures above about 300 °C
- A non-magnetic part, or bar, sheet and tube from stock in small quantities
Choose 2205 duplex when
- Warm chloride exposure where 316 pits or stress-corrosion cracks: seawater, brine, process water above about 60 °C
- Pressure vessels, piping and tanks where twice the yield strength lets walls get thinner
- Offshore, desalination, pulp-and-paper and chemical-tanker work that already specifies duplex
- Erosion and abrasion in slurry service, where the higher strength and hardness help
Frequently asked questions
- Is 2205 duplex better than 316?
- Stronger and more corrosion resistant in chlorides, yes: about twice the yield strength, a PREN of about 35 against 24, and much better resistance to stress-corrosion cracking. It is not better everywhere. 316 is easier to fabricate, non-magnetic, works at cryogenic and high temperatures, and is stocked in more forms.
- Is 2205 duplex stainless magnetic?
- Yes. Its roughly 50% ferrite makes it clearly magnetic, so a magnet cannot tell 2205 from a ferritic or martensitic grade. Annealed 316 is essentially non-magnetic, though cold work and welds can make it slightly magnetic.
- Can you weld 2205 to 316?
- Yes. The usual filler is 2209, with 309LMo as an alternative. Keep heat input moderate and control interpass temperature on the duplex side so the weld and heat-affected zone keep a balanced austenite-ferrite structure.
- What is the maximum temperature for 2205?
- About 300 °C (570 °F) for long-term service. Above that the ferrite slowly embrittles, a problem known as 475 °C embrittlement, and at higher temperatures sigma phase can form. For hotter service use 316 or a heat-resistant austenitic grade.
