Duplex Steel S32205
Duplex Stainless Steel S32205 (UNS S32205) is a tighter-controlled version of the S31803 duplex grade. It has a higher nitrogen floor (0.14-0.20%) and a narrower chromium minimum. This stricter nitrogen control produces more consistent pitting resistance and phase balance, and S32205 is now the preferred standard for structural and corrosion-critical duplex applications.
1. Chemical Composition
The table below shows the elemental composition of S32205. The narrower nitrogen range is what separates it from S31803, directly raising its PREN and improving microstructural consistency.
| Grade | C | Mn | P | S | Si | Cr | Ni | Mo | N | Cu |
| S32205 | 0.03 | 2.0 | 0.03 | 0.02 | 1.0 | 22.0–23.0 | 4.5–6.5 | 3.0–3.5 | 0.14–0.2 | — |
Note: Compared to S31803, S32205 raises the nitrogen minimum from 0.08% to 0.14% and the molybdenum minimum from 2.5% to 3.0%. This gives a minimum PREN approximately 3-4 points higher than S31803 and more reproducible corrosion performance across heats.
2. Mechanical Properties
The following minimum mechanical property values apply to S32205 in the solution-annealed condition per ASTM A790 and A789.
| Grade | Condition | Tensile Strength Min, MPa (ksi) | Yield Strength Min, MPa (ksi) | Elongation Min, % | PREN |
| S32205 | Annealed | 655 (95) | 450 (65) | 25 | ≥34 |
Note: The tensile strength minimum of 655 MPa for S32205 is slightly higher than S31803 (620 MPa). This reflects the added solid-solution strengthening from the higher nitrogen floor, though both grades share the same yield strength minimum of 450 MPa.
3. Equivalent Grade
This table cross-references S32205 across major international designation systems. S32205 and S31803 share the EN 1.4462 designation but differ in their UNS-level compositional requirements.
| GRADE | UNS | GB | JIS | ISO | DIN/EN | GOST | |
| ISC | NEW | ||||||
| 2205 | S32205 | S22253 | 022Cr22Ni5Mo3N | SUS329J3L | X2CrNiMoN22-5-3 | 1.4462 | 02Х22Н5АМ3 |
Note: ASTM / UNS formally distinguishes S32205 from S31803 through its stricter compositional envelope, even though both correspond to EN 1.4462. Engineers specifying EN 1.4462 should confirm the UNS number with the mill to verify which composition band applies.
4. Key Technical Advantages
- Higher Minimum Nitrogen for Consistent PREN: By increasing the minimum nitrogen content to 0.14%, S32205 consistently achieves a PREN (Pitting Resistance Equivalent Number = %Cr + 3.3×%Mo + 16×%N) of about 34–35 in all heats that meet the specification. In comparison, low-nitrogen heats of S31803 (with 0.08% nitrogen) can have PREN values as low as about 30.5. This more consistent, higher PREN is important for applications that demand reliable performance in seawater and chloride-containing process environments.
- Stricter Molybdenum Minimum for Crevice Corrosion Resistance: Because S32205 has at least 3.00% molybdenum (compared to 2.50% in S31803), it offers better protection against crevice corrosion in chloride-rich environments. This is especially important in tight spots like under deposits and at bolted flange joints, which are common failure points in offshore and coastal systems.
- Identical Mechanical Performance with Higher Compositional Assurance: S32205 meets the same 450 MPa yield strength minimum as S31803 while producing more reproducible corrosion test results (e.g., in ASTM G48 Method A pitting tests) due to its tighter compositional control. This reduces the risk of specification rejection on corrosion qualification tests.
- Technical Note: S32205 has mostly replaced S31803 in modern engineering standards and purchasing specifications (including NORSOK and offshore structural design codes). The main reason is that S32205 avoids the variability in corrosion resistance that can occur with the lower-end composition of S31803.
In practice, when you have to choose between these two grades, S32205 is usually the better choice.
5. Common Manufacturing Standards
- A790: Standard specification for seamless and welded ferritic/austenitic stainless steel pipe. This is the primary standard for S32205 duplex pipe, covering both seamless and longitudinally welded configurations.
- ASTM A789: Standard specification for seamless and welded ferritic/austenitic stainless steel tubing for general service. This is the primary standard for S32205 duplex tubing in heat exchanger and process applications.
- ASTM A928: Standard specification for ferritic/austenitic (duplex) stainless steel pipe welded with the addition of filler metal, applicable for S32205 large-diameter welded pipe in structural and subsea applications.
- DIN EN 10216-5: Seamless steel tubes for pressure purposes, stainless steel (Grade 1.4462 equivalent).
- DIN EN 10217-7: Welded steel tubes for pressure purposes, stainless steel (Grade 1.4462 equivalent).
- JIS G3459: Stainless steel pipes, SUS329J3L for duplex designation.
- GB/T 14976: Seamless stainless steel tubes for fluid transport, 022Cr23Ni5Mo3N designation.
- GOST R 53364: Duplex stainless steel pipes, 03X22H5AM3 equivalent.
- NORSOK M-630: Material data sheets for piping. S32205 is listed as the preferred duplex grade for offshore North Sea service.
Manufacturing Standards Comparison Table:
| Standard | ASTM | EN/DIN | JIS | GB/T | GOST |
| Seamless Pipe | A790 S32205 | EN 10216-5 (1.4462) | G3459 SUS329J3L | GB/T 14976 | GOST R 53364 |
| Seamless Tube | A789 S32205 | EN 10216-5 (1.4462) | G3463 SUS329J3L | GB/T 13296 | GOST R 53364 |
| Welded Pipe | A790 / A928 S32205 | EN 10217-7 (1.4462) | G3459 SUS329J3L | GB/T 12771 | GOST R 53364 |
6. Primary Applications
- NORSOK-Compliant Offshore Piping: Topside and subsea piping systems on North Sea platforms and FPSOs where NORSOK M-630 specifies S32205 as the standard duplex grade. It has replaced S31803 in new field developments because of its more consistent corrosion performance.
- High-Pressure Oil and Gas Gathering Lines: Onshore and offshore gathering lines transporting crude oil and gas with associated formation water containing chlorides, CO2, and H2S within NACE MR0175 / ISO 15156 permissible hardness and strength limits.
- Seawater Cooling Systems: Seawater lift pump casings, cooling water headers, and condenser water boxes in coastal power generation and industrial plants where the higher PREN of S32205 over S31803 gives a measurable safety margin against pitting initiation.
- Chloride-Bearing Chemical Process Piping: Heat exchanger shells, tube bundles, and process piping in chloride-rich chemical processes, including sodium hypochlorite, ferric chloride, and HCl service at low concentrations, where 316L would fail by SCC.
- Structural Applications in Marine Environments: Structural tubes, hollow sections, and handrail systems on offshore structures and coastal infrastructure, where the 450 MPa minimum yield strength reduces structural section sizes and weight compared to austenitic alternatives.