UNS S31803 (2205 duplex stainless steel) and S31600 both belong to the category of stainless steel, but they have fundamental differences in microstructure, chemical composition, mechanical properties and corrosion resistance. Our manufacturers can produce seamless and welded pipes to meet industry requirements. Contact us market@htpipe.com for more information and a free quote!
stainless steel 2205 s31600 Chemical Composition Comparison
| Element | SS316 / 316L | UNS S31803 (2205) |
|---|---|---|
| Chromium (Cr) | 16.0 - 18.0 | 21.0 - 23.0 |
| Nickel (Ni) | 10.0 - 14.0 | 4.5 - 6.5 |
| Molybdenum (Mo) | 2.0 - 3.0 | 2.5 - 3.5 |
| Nitrogen (N) | ≤ 0.10 | 0.08 - 0.20 |
| Carbon (C) | ≤ 0.030 (316L) | ≤ 0.030 |
| Manganese (Mn) | ≤ 2.0 | ≤ 2.0 |
| Silicon (Si) | ≤ 0.75 | ≤ 1.0 |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.030 |
| Sulfur (S) | ≤ 0.030 | ≤ 0.020 |
| PREN Value | 24 - 29 | 34 - 39 |
super duplex s31803 and ss316 Physical Properties Comparison
| Property | SS316 / 316L | UNS S31803 (2205) |
|---|---|---|
| Density (g/cm³) | 8.0 | 7.8 |
| Thermal Expansion (μm/m·°C, 20-100°C) | 16.0 | 13.0 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 19.0 |
| Modulus of Elasticity (GPa) | 200 | 200 |
| Magnetic Properties | Essentially Non-magnetic | Magnetic |
Mechanical Properties s31803 and s316
| Property | SS316 / 316L | UNS S31803 (2205) |
|---|---|---|
| Yield Strength (MPa) | ≥ 205 | ≥ 450 |
| Tensile Strength (MPa) | ≥ 515 | ≥ 655 |
| Elongation (%) | ≥ 40 | ≥ 25 |
| Hardness (HB) | ≤ 217 | ≤ 293 |
Corrosion Resistance Comparison of s31803 and s316
General Corrosion: In a variety of acidic media, UNS S31803 typically exhibits superior resistance to general corrosion compared to SS316 due to its higher chromium, molybdenum, and nitrogen content.
Pit Corrosion and Crevice Corrosion: Resistance to pitting and crevice corrosion is usually measured using the pitting corrosion equivalent value.
- SS316 has a PREN value of approximately 24-29.
- UNS S31803 has a PREN value of approximately 34-39.
Stress Corrosion Cracking: This is one of the most critical differences between the two. In chloride-containing environments, especially at elevated temperatures (typically above 60°C), austenitic stainless steels such as SS316 are susceptible to stress corrosion cracking. The dual-phase microstructure of UNS S31803 gives it significant resistance to chloride stress corrosion cracking.
Intergranular Corrosion: Both materials exhibit good resistance to intergranular corrosion in the supplied condition. However, improper welding or heat treatment can lead to carbide precipitation in certain sensitive temperature ranges (e.g., 450-850°C), resulting in increased susceptibility to intergranular corrosion.
Welding Metallurgy
S31600 (316 SS): Highly forgiving during welding. It possesses excellent weldability using all standard fusion processes (GTAW, GMAW, SMAW, SAW). It does not require pre-heating, and post-weld heat treatment is rarely necessary unless heavy sections are prone to stress accumulation.
UNS S31803 (Duplex 2205): Requires precise thermal control. The goal during welding is to maintain the critical 50/50 austenite-to-ferrite balance in the weld metal and Heat Affected Zone (HAZ). If the cooling rate is too fast, excessive ferrite forms, reducing toughness; if too slow, detrimental intermetallic phases precipitate, destroying corrosion resistance.
Filler Metal Requirement: Unlike 316, which can be welded autogenously (without filler), UNS S31803 almost always requires over-alloyed filler wire (typically enriched with 7–9% Nickel, such as ER2209) to ensure sufficient austenite forms upon cooling. Interpass temperatures must be strictly limited to a maximum of 150°C (300°F).
Solution Annealing Thresholds
When full recrystallization is required to relieve stress or dissolve precipitates, their heat treatment temperatures differ:
S31600: Annealed at 1010°C to 1150°C (1850°F to 2100°F), followed by rapid cooling or water quenching to prevent chromium carbide precipitation.
UNS S31803: Requires a higher, narrower soaking window of 1020°C to 1100°C (1868°F to 2012°F), followed by immediate, rapid water quenching. Slow cooling through the 450°C–850°C range will cause immediate embrittlement.
Application Guide: When to Choose S31600 vs. UNS S31803
Choose S31600 (316 Stainless Steel) if: Your project involves standard architectural structures, commercial food processing, pharmaceutical production, or applications requiring cryogenic operations (where austenitic steel retains superior impact toughness down to extreme sub-zero temperatures). S31600 also provides greater cold-forming flexibility.
Choose UNS S31803 (Duplex 2205) if: You are designing for high-pressure oil and gas pipelines, marine desalination infrastructure, petrochemical processing equipment, sour gas handling wells, or heavy load-bearing structural elements exposed to marine splash zones where high strength and chloride protection are mandatory.
