Duplex Stainless Steel 2205: Physical Properties, PREN and Industrial Applications
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What Makes 2205 a Duplex Grade
Duplex stainless steel 2205 (UNS S32205, EN 1.4462) is a 22% chromium duplex grade supplied in the solution-annealed condition with a balanced microstructure of roughly equal proportions of austenite and ferrite. That two-phase structure is the source of its defining behaviour: it combines the toughness and weldability of austenitic stainless steel with the strength and chloride resistance of ferritic grades. The grade is also available under the earlier UNS S31803 designation; S32205 is the tightened-composition version with a controlled nitrogen range, and it is the grade most often quoted for new projects.
The high chromium, molybdenum and nitrogen content produces a Pitting Resistance Equivalent Number of 33 - 34, calculated from the standard expression PREN = Cr + 3.3 Mo + 16 N. That value places 2205 well above Alloy 316L and Alloy 317L and makes it a standard choice wherever chlorides, sour gas or seawater drive corrosion.
Chemical Composition and Standards
| Element (%) | UNS S32205 / EN 1.4462 |
|---|---|
| Chromium | 22.0 - 23.0 |
| Nickel | 4.5 - 6.5 |
| Molybdenum | 3.0 - 3.5 |
| Nitrogen | 0.14 - 0.20 |
| Carbon | max. 0.030 |
| Manganese | max. 2.00 |
| Silicon | max. 1.00 |
| Pitting Resistance Equivalent Number | 33 - 34 |
Plate, sheet and strip are covered by ASTM A240, seamless and welded tube by ASTM A789 and A790, and the European product standard is EN 10088-2 with the material number 1.4462. Corrosion testing methods for duplex product are described in ASTM A923.
Physical Properties
| Property | Typical value |
|---|---|
| Density | 7.8 g/cm³ |
| Thermal expansion, 20 - 100 °C | about 13.7 x 10⁻⁶ / °C |
| Thermal conductivity at 20 °C | about 19 W/m·K |
| Specific heat capacity | about 480 J/kg·K |
| Electrical resistivity | about 0.80 μΩ·m |
| Young's modulus | about 200 GPa |
| Magnetic behaviour | ferromagnetic, because of the ferrite phase |
Compared with austenitic stainless steel, 2205 expands less when heated and conducts heat better. Lower thermal expansion reduces distortion and thermal stress in heat exchangers and welded assemblies, while higher thermal conductivity improves heat transfer per unit of surface area in process equipment.
Mechanical Properties
| Property (solution annealed) | Typical value |
|---|---|
| 0.2% yield strength | min. 450 MPa, roughly twice that of Alloy 316L |
| Tensile strength | min. 620 MPa |
| Elongation | min. 25% |
| Hardness | about 31 HRC maximum |
| Impact toughness (Charpy V, 20 °C) | typically above 100 J |
The high yield strength allows designers to reduce wall thickness, which frequently offsets the higher price per kilogram and makes 2205 more cost-competitive than Alloy 316L or Alloy 317L in pressure-containing equipment. Machining behaviour is controlled through composition balance and inclusion type, which improves chip formation and reduces tool wear compared with older duplex chemistry.
Corrosion and Temperature Limits
Pitting and crevice corrosion: superior to Alloy 316L and Alloy 317L in almost all chloride-bearing media, including flowing and stagnant seawater.
Stress corrosion cracking: highly resistant in chloride environments where austenitic grades crack.
Sour service: suitable for oil and gas production containing hydrogen sulphide, subject to hardness and stress limits in the applicable specification.
Acid resistance: good resistance to sulphuric, phosphoric and nitric acid media under moderate conditions.
Temperature: design codes normally limit long-term service to about 316 °C, above which the ferrite phase can embrittle; avoid prolonged exposure in the 300 - 500 °C range.
Typical Industrial Applications
Process equipment for sulphuric, nitric and phosphoric acid production, ethylene oxide, polypropylene and PVC plants.
Heat exchangers, chemical storage tanks, tankers and evaporators handling organic and fatty acids.
Marine and shipbuilding components: propellers, shafts, rudders, shaft seals, pumps, fasteners, valves and instrumentation.
Oil and gas equipment: pumps, valves, line pipe, pressure vessels, wellhead and subsea equipment, separators and heat exchangers.
Pollution control: flue gas desulphurization systems, wastewater scrubbing and acid water purification.
Pulp and paper: pulp liquor heaters, bleach tower liners, digesters and brown stock washers.
Food and beverage: brewery piping, evaporators, hot wine tanks and presses.
Frequently Asked Questions
Q: How does 2205 compare with Alloy 316L?
2205 offers roughly twice the yield strength, a much higher PREN and better chloride pitting and stress corrosion resistance, at a higher cost per kilogram that is often recovered through reduced wall thickness.
Q: Is duplex stainless steel 2205 magnetic?
Yes. The ferrite phase makes 2205 ferromagnetic, unlike fully austenitic grades such as Alloy 316L.
Q: What is the difference between UNS S31803 and UNS S32205?
S32205 is the later specification with a narrower, nitrogen-controlled composition within the S31803 range, giving more consistent corrosion resistance and mechanical properties.
Q: What is the maximum service temperature of 2205?
Continuous service is normally limited to about 316 °C to avoid embrittlement of the ferrite phase; higher temperatures require a different grade.
Q: Can 2205 be welded?
Yes. It is welded with GTAW, GMAW, SMAW, FCAW, SAW and plasma processes using matching duplex filler metals, with controlled heat input and interpass temperature.
Q: Why is 2205 preferred for sour gas service?
Its combination of high yield strength, PREN above 33 and resistance to chloride stress corrosion cracking allows it to handle produced fluids containing chlorides and hydrogen sulphide where austenitic grades would fail.
