Seamless UNS S31803 Duplex Stee Tube, commonly known as Duplex 2205, is a premium-grade stainless steel celebrated for its unique dual-phase microstructure—combining approximately 50% austenite and 50% ferrite. This composition delivers a remarkable balance of high strength, exceptional corrosion resistance, and durability, making it ideal for demanding industrial applications. With chromium (21.0–23.0%), nickel (4.5–6.5%), molybdenum (2.5–3.5%), and nitrogen additions, Duplex 2205 offers twice the yield strength of conventional austenitic steels like 304 or 316, while resisting chloride-induced stress corrosion cracking (SCC).
Manufactured to standards such as ASTM A789, ASTM A790, and EN 10088-3, these seamless pipes and tubes undergo precision processing to ensure uniform wall thickness, consistent mechanical properties, and superior surface finish. The alloy’s duplex structure makes it a go-to solution for industries where high-strength, corrosion-resistant materials are non-negotiable.
Zhejiang Xintongda Special Steel Manufacturing Co., Ltd. delivers UNS S31803 products that meet the highest quality benchmarks, providing reliable solutions for offshore, chemical, and energy sectors.
| Element | C | Mn | Si | P | S | Cr | Ni | Mo | N |
| Content | ≤0.03 | ≤2.00 | ≤1.00 | ≤0.030 | ≤0.020 | 21.0–23.0 | 4.5–6.5 | 2.5–3.5 | 0.08–0.20 |
| Property | Value |
| Tensile Strength | ≥620 MPa (90 ksi) |
| Yield Strength (0.2% offset) | ≥450 MPa (65 ksi) |
| Elongation | ≥25% |
| Hardness (HBW) | ≤290 |
| Hardness (HRC) | ≤30 |
| Property | Value |
| Density | 7.805 g/cm³ |
| Thermal Conductivity | 19.0 W/m·K |
| Thermal Expansion | 13.7×10⁻⁶/K (20–100°C) |
| Electrical Resistivity | 0.85×10⁻⁶ Ω·m |
| Melting Point | 1400–1450°C |
| Parameter | Duplex 2205 (S31803) | Austenitic 316L (S31603) | Super Duplex 2507 (S32750) |
| Microstructure | 50% Austenite/50% Ferrite | 100% Austenite | 45% Austenite/55% Ferrite |
| Yield Strength | ≥450 MPa | ≥170 MPa | ≥550 MPa |
| Cr Content | 21–23% | 16–18% | 24–26% |
| Mo Content | 2.5–3.5% | 2.0–3.0% | 3.0–5.0% |
| N Content | 0.08–0.20% | – | 0.24–0.32% |
| Chloride SCC Resistance | Good | Poor | Excellent |
| Cost Ratio | 1.5x 316L | 1x | 2.5x 316L |
| Typical Applications | Offshore, chemical | General corrosion | Extreme marine, oil & gas |
Key Differences:
Duplex 2205 offers 2.5x the strength of 316L, enabling thinner wall designs.
Super Duplex 2507 excels in severe chloride environments but at a higher cost.
Chloride Stress Corrosion Cracking (SCC): Resists SCC in seawater, brine, and chloride-rich media, outperforming austenitic steels like 316L in marine and offshore applications.
Pitting & Crevice Corrosion: High chromium, molybdenum, and nitrogen content provide a Pitting Resistance Equivalent (PRE) of ≥34, making it suitable for harsh chemical environments.
Acid & Alkali Resistance: Performs well in mild sulfuric, phosphoric, and alkaline solutions, ideal for chemical processing and wastewater treatment.
Mechanical Advantage: With yield strength ≥450 MPa, Duplex 2205 reduces material thickness by 50% compared to 316L, cutting weight and transportation costs.
Fatigue Resistance: Maintains ductility and impact resistance at low temperatures (-40°C), preventing brittleness in cryogenic systems.
Weldability: Can be welded by TIG, MIG, or stick welding using ER2209 filler metal; minimal risk of carbide precipitation with proper heat input control.
Machinability: Requires slightly slower machining speeds than austenitic steels but offers good formability for complex pipe configurations.
Life Cycle Cost: Reduced maintenance and replacement needs due to superior corrosion resistance, especially in high-chloride environments.
Temperature Resistance: Performs reliably up to 250°C, exceeding the thermal limits of many ferritic steels.
Subsea Systems: Seawater pipelines, subsea valves, and wellheads exposed to saltwater and corrosive hydrocarbons.
Marine Platforms: Support structures, hull components, and desalination plant heat exchangers.
Reactors & Vessels: Equipment for handling acids, chlorides, and organic chemicals in refineries and chemical plants.
Heat Exchangers: High-efficiency heat transfer tubes resistant to fouling and corrosion in sulfuric acid applications.
Flue Gas Desulfurization (FGD): Scrubbers, ducts, and stacks in coal-fired power plants, resisting sulfuric acid condensation.
Geothermal Energy: Tubing for high-temperature, acidic geothermal brine extraction.
Strength: Duplex 2205 offers 2.5x the yield strength of 316L, making it ideal for high-pressure applications.
Corrosion Resistance: 2205 excels in chloride environments, while 316L performs better in oxidizing acids.
Cost: 2205 costs ~1.5x more than 316L but offers longer-term reliability.
Yes, Duplex 2205 resists seawater corrosion up to 250°C. For higher temperatures or extreme chlorides, Super Duplex 2507 is recommended.
Nitrogen Content: S32205 has higher nitrogen (0.14–0.20%) for enhanced strength and corrosion resistance.
Molybdenum: S32205 contains 3.0–3.5% molybdenum (vs. 2.5–3.5% in S31803), improving pitting resistance.
Yes, due to its ferritic phase, Duplex 2205 is slightly magnetic, unlike fully austenitic steels like 316L.
Use ER2209 filler metal and control heat input to avoid excessive ferrite growth.
Post-weld heat treatment is rarely needed, but annealing may optimize toughness for thick sections.
Continuous use is recommended up to 250°C. Above this, the duplex microstructure may degrade, reducing corrosion resistance.
Corrosion Resistance: 2205 far outperforms carbon steel, which rusts rapidly in seawater.
Strength: 2205 allows thinner walls, while carbon steel requires thicker sections for equivalent strength.
