What Is A182 F51?
When to Specify A182 F51
ASTM A182 Grade F51 is the standard forged duplex stainless steel (UNS S31803 / 2205) for flanges, fittings, valve components, and other pressure parts in chloride-bearing and corrosive environments. F51 provides roughly double the yield strength of austenitic F316 with superior resistance to chloride stress corrosion cracking, pitting, and crevice corrosion.
| Property | Value |
|---|---|
| Specification | ASTM A182 / ASME SA-182 |
| Grade | F51 |
| UNS | S31803 |
| Common name | Duplex 2205 |
| Carbon | 0.030% max |
| Chromium | 21.0-23.0% |
| Nickel | 4.5-6.5% |
| Molybdenum | 2.5-3.5% |
| Nitrogen | 0.08-0.20% |
| Manganese | 2.00% max |
| Silicon | 1.00% max |
| Tensile strength (min) | 620 MPa (90 ksi) |
| Yield strength (min) | 450 MPa (65 ksi) |
| Elongation (min) | 25% |
| Hardness | 293 HBW max (31 HRC) |
| PREN | 34-36 (typical) |
| Ferrite | 40-60% |
| Heat treatment | Solution anneal 1020-1100°C, water quench |
| Max service temp | 315°C (600°F) |
| Cast equivalent | A995 Grade 4A |
F51 vs Austenitic Stainless
| Property | F316 (Austenitic) | F51 (Duplex 2205) |
|---|---|---|
| Yield strength | 205 MPa (30 ksi) | 450 MPa (65 ksi) |
| PREN | ~26 | ~35 |
| SCC resistance | Moderate | Excellent |
| Max chloride temp | ~60°C | ~100°C |
| Relative cost | Baseline | +20-40% |
| Weight for same pressure | Higher | Lower (thinner wall) |
The higher yield strength of F51 often allows thinner flanges and fittings, partially offsetting the per-kilogram cost premium over F316.
Applications
- Offshore platforms: topside piping flanges, manifold fittings, subsea wellhead components
- Seawater systems: fire water, cooling water, and injection system flanges
- Chemical plants: chloride-containing acid and brine service flanges and fittings
- Desalination: high-pressure reverse osmosis piping connections
- Oil and gas production: sour gas service compliant with NACE MR0175 when hardness is below 28 HRC
F51 forged components pair with A995 4A cast valve bodies, A790 S31803 seamless pipe, and A815 S31803 buttweld fittings.
Testing and Quality
ASTM A182 F51 requires solution annealing (1020-1100°C, water quench), ferrite content verification (40-60%), and corrosion testing per ASTM A923 Method C (ferric chloride pitting test). Mill test certificates per EN 10204 3.1 report chemistry, mechanical properties, ferrite content, and corrosion test results. Supplementary requirements cover impact testing at -46°C, ultrasonic and liquid penetrant examination, and intergranular corrosion testing. Hydrostatic testing follows the applicable flange or valve standard. The forging process produces a more uniform austenite-ferrite distribution than castings, with better mechanical properties and fewer defects.
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