2205 is not a "higher-grade 316L"; it is **a different class of material**: a duplex structure (roughly half austenite and half ferrite), about twice the strength of 316L, significantly higher resistance to chloride pitting, but with stricter welding and forming requirements.
First, calculate PREN
PREN = Cr + 3.3 × Mo + 16 × N (pitting resistance equivalent).
| Grade | Cr / Mo / N | PREN | Upper limit of applicable chloride ions (60℃ reference) |
|---|---|---|---|
| 304 | 18 / 0 / 0 | ≈ 18 | < 100 ppm |
| 316L | 17 / 2.1 / 0 | ≈ 24–26 | ≈ 200 ppm |
| 2205 | 22 / 3.1 / 0.17 | ≈ 34–36 | ≈ 1000 ppm |
| 904L | 20 / 4.3 / 0 | ≈ 34 | High, but more costly |
Three signals to switch to 2205
- Chloride ions > 200 ppm and temperature > 60℃: the stress corrosion risk of 316L rises markedly; this is the most common switch point.
- Need to reduce thickness and weight: the yield strength of 2205 is about twice that of 316L; for the same pressure duty the thickness can be reduced by 30–40%, and the total cost is not necessarily higher.
- Strong erosion and corrosion coexisting: such as seawater piping and agitator blades; 2205 has better erosion-corrosion resistance than 316L.
The costs you must accept before switching
- High welding requirements: heat input and interpass temperature must be controlled, and the ferrite/austenite ratio must be ensured (usually 35–65% required), requiring qualified WPS and welders.
- No deep drawing: duplex steel has lower plasticity than austenitic steel; do not use it for complex deep-drawn parts.
- Not suitable for high temperatures: long-term exposure above 300℃ causes precipitation of σ phase and embrittlement, the opposite of the high-temperature use of 316L.
Conclusion: high chloride ions, need to reduce weight, need erosion resistance → 2205; if you just "want to be safer" and the medium is mild → 316L is more economical and easier to machine. Send us the medium report, and we will give recommendations based on PREN and note the welding precautions.
