UNS S31803 vs. F51 Stainless Steel: Key Differences
Apr 07, 2026
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What is UNS S31803 material?
UNS S31803 (often referred to as 2205 duplex or F51) is a standard, 22% chromium duplex stainless steel with a ferritic-austenitic microstructure. It offers twice the yield strength of standard 316L/317L austenitic steels, high corrosion resistance, and excellent resistance to stress corrosion cracking (SCC) in chloride-rich environments. It can be processed into various practical product forms, including plates, coils, pipes, bars, and wires.
What is A182 F51 material equivalent to?
ASTM A182 F51 is primarily equivalent to UNS S31803 (2205 Duplex) and the Europeanstandard DIN 1.4462 (X2Cr Ni MoN22.5.3). It is a 22% Chromium duplex stainlesssteel frequently used for forged components, including high-pressure fittings and flanges,due to its high strength, good toughness, and excellent resistance to chloride-inducedstress corrosion cracking.
UNS S31803 vs. F51 Stainless Steel: Key Differences
Compositional Equivalence: The two grades are generally interchangeable; specifically, F51 refers to the forging specification, while S31803 is its corresponding UNS number.
Dual Certification: Products designated as S32205 (F60) may also be simultaneously certified as S31803 (F51), as their performance meets-and often exceeds the various requirements of S31803 (F51); however, the converse is not necessarily true.
Performance Characteristics: Both grades exhibit excellent resistance to pitting and crevice corrosion; nevertheless, due to the risk of embrittlement, their applicable service temperature range is restricted to between -50°C and 250°C (under specific specifications, the upper limit may be extended to 315°C).
UNS S31803 vs. F51 Stainless Steel: Chemical Composition
| Element | UNS S31803 (Standard Range) | ASTM A182 F51 (Forging Requirements) |
|---|---|---|
| Carbon (C) | ≤ 0.030 | ≤ 0.030 |
| Manganese (Mn) | ≤ 2.00 | ≤ 2.00 |
| Silicon (Si) | ≤ 1.00 | ≤ 1.00 |
| Chromium (Cr) | 21.0 – 23.0 | 21.0 – 23.0 |
| Nickel (Ni) | 4.5 – 6.5 | 4.5 – 6.5 |
| Molybdenum (Mo) | 2.5 – 3.5 | 2.5 – 3.5 |
| Nitrogen (N) | 0.08 – 0.20 | 0.10 – 0.20 |
| Phosphorus (P) | ≤ 0.030 | ≤ 0.030 |
| Sulfur (S) | ≤ 0.020 | ≤ 0.020 |
UNS S31803 vs. F51 Stainless Steel: Mechanical Properties
| Property | UNS S31803 / ASTM A182 F51 | Typical Test Values (Results) |
|---|---|---|
| Tensile Strength (Rₘ) | ≥ 620 MPa (90 ksi) | 680 − 800 MPa |
| Yield Strength (Rₚ0.2) | ≥ 450 MPa (65 ksi) | 500 − 600 MPa |
| Elongation in 2" (Aₐ) | ≥ 25% | 30% − 35% |
| Hardness (Brinell) | ≤ 293 HBW | 240 − 270 HBW |
| Charpy V-Notch Impact at −46°C | As per agreement (typically ≥ 60 J) | ≥ 100 J (Excellent Low-Temperature Toughness) |
Application : UNS S31803 vs. ASTM A182 F51
| Industry Sector | UNS S31803 Applications (Pipes, Plates, Tubes) | ASTM A182 F51 Applications (Forgings, Flanges, Valves) |
| Oil & Gas (Upstream) | Subsea flowlines, umbilical tubing, downhole production tubing. | Forged Christmas tree components, subsea wellhead housings, high-pressure valves. |
| Chemical Processing | Heat exchanger tubes, pressure vessel shells, chemical storage tanks. | Forged nozzles, heavy-duty flanges, pump casings, manifold fittings. |
| Desalination (RO) | High-pressure seawater piping, brine evaporation tubes. | High-pressure pump blocks, forged connectors, orifice flanges. |
| Marine & Offshore | Seawater cooling systems, cargo tanks for chemical tankers. | Propeller shafts (forged), rudder stocks, offshore platform structural connectors. |
| Pulp & Paper | Digesters, bleach washers, liquor tanks. | Forged valve bodies for corrosive liquor handling, heavy-duty pipe couplings. |
What is the difference between UNS S31803 and S32205?
UNS S31803 represents the original specification for Duplex Steel 2205, whereas UNS S32205 is its enhanced version, imposing stricter minimum requirements for key alloying elements: Cr (22.0% vs. 21.0%), Mo (3.0% vs. 2.5%), and N (0.14% vs. 0.08%). This upgrade raises the minimum Pitting Resistance Equivalent Number (PREN) from 31 to above 35. Today, most high-quality materials are supplied with dual certification to both the S31803 and S32205 standards.
What is the difference between ASTM A182 F51 and F60?
Within the ASTM A182 standard system for forgings, Grade F51 corresponds to UNS S31803, while Grade F60 corresponds to UNS S32205. The primary technical distinction between the two lies in the threshold levels for nitrogen and molybdenum: F60 mandates a minimum molybdenum (Mo) content of 3.0% and a minimum nitrogen (N) content of 0.14%, whereas F51 permits lower content levels (2.5% for Mo and 0.10% for N). Although F51 remains prevalent in certain legacy specifications, F60 has emerged as the industry benchmark for high-reliability forged flanges and valve products within the offshore oil and gas sector.
As a specialized global supplier of Duplex stainless steel, GNEE provides a comprehensive range of UNS S31803 and ASTM A182 F51 products. While S31803 is the general alloy designation for flat and long products, F51 is the specific standard for our high-integrity forgings.
GNEE Product Range: UNS S31803 & F51 Stainless Steel
| Product Form | Applicable Standards | Size / Dimension Range |
| Hot Rolled Plate | ASTM A240 / EN 10088-2 | Thickness: 3mm – 100mm; Width: up to 3000mm |
| Cold Rolled Sheet | ASTM A240 / EN 10088-2 | Thickness: 0.3mm – 6.0mm; Width: 1000/1219/1500mm |
| Seamless Pipe | ASTM A790 / ASME SA790 | OD: 1/2" – 24" (21.3mm – 610mm); WT: SCH 10S – SCH XXS |
| Welded Pipe | ASTM A792 / ASME SA792 | OD: 2" – 48" (60.3mm – 1219mm); WT: SCH 5S – SCH 80S |
| Forged Flanges (F51) | ASTM A182 F51 / EN 1092-1 | DN15 – DN2000 (Class 150 – 2500) |
| Round Bar | ASTM A276 / ASTM A479 | Diameter: 5mm – 500mm |
| Pipe Fittings | ASTM A815 WP-S / WP-W | 1/2" – 48" |
Lead Time
**Stock Inventory:** 3 – 7 business days.
**Custom Processing:** 15 – 30 business days.
**Large-scale Projects / Direct Mill Shipments:** 45 – 60 calendar days.
Packaging
**Surface Protection:** Tubes are individually sleeved in plastic tubing or bundled into hexagonal packages using textile strapping; plates are interleaved with protective paper or covered with a PE film designed for laser-cutting protection.
**End Protection:** Both ends of the tubes are fitted with High-Density Polyethylene (HDPE) caps to prevent the ingress of debris and internal oxidation.
**Crates & Supports:** Forgings (e.g., F51 material) and small-diameter tubes are packed in fumigated plywood crates (compliant with IPPC standards) or reinforced steel-frame wooden crates.
**Accompanying Documentation:** Each package includes a waterproof document pouch containing the MTC 3.1 Material Test Certificate (compliant with EN 10204), a packing list, and a PMI test report.
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