Scope
ASTM A182 covers forged or rolled alloy and stainless steel pipe flanges, forged fittings, valves, and similar parts for high-temperature service across dozens of grades. Grade F51 is the duplex (austenitic-ferritic) stainless steel grade within that specification, offering roughly double the yield strength of standard austenitic grades such as F304 or F316 along with superior resistance to chloride stress-corrosion cracking and pitting.
Chemical Composition (UNS S31803 / S32205)
| Element | Composition, % |
|---|---|
| Carbon | 0.030 max |
| Manganese | 2.00 max |
| Phosphorus | 0.030 max |
| Sulfur | 0.020 max |
| Silicon | 1.00 max |
| Chromium | 21.0 – 23.0 |
| Nickel | 4.50 – 6.50 |
| Molybdenum | 2.50 – 3.50 |
| Nitrogen | 0.08 – 0.20 |
| Iron | Balance |
Mechanical Properties
| Property | Requirement |
|---|---|
| Tensile Strength | 90 ksi (620 MPa) min |
| Yield Strength (0.2% offset) | 65 ksi (450 MPa) min |
| Elongation in 2 in. (50 mm) | 25% min |
| Hardness | 293 HBW max / 30 HRC max |
Heat Treatment of ASTM A182 Grade F51
Grade F51 forgings must be solution annealed and water quenched (or rapidly cooled by other means) to develop the balanced austenitic-ferritic microstructure that gives duplex stainless steel its combination of strength and corrosion resistance. Improper heat treatment can result in harmful intermetallic phases that reduce both toughness and corrosion performance.
Why Duplex 2205 (F51)
- Approximately double the yield strength of austenitic grades 304/316, allowing thinner-wall, lighter components
- High resistance to chloride pitting and crevice corrosion – suited to seawater and brackish water service
- Strong resistance to chloride stress-corrosion cracking, a common failure mode for standard austenitic stainless in hot chloride environments
- Frequently specified with NACE MR0175 / ISO 15156 compliance for sour (H2S-containing) oil & gas service
Equivalent and Related Grades
| Standard | Designation |
|---|---|
| UNS | S31803 / S32205 |
| ASTM A182 | Grade F51 |
| ASTM A240 (plate) | Grade S31803 / S32205 – see our plate & sheet specifications |
| ASTM A276 / A479 (bar) | Duplex 2205 round bar equivalent |
| EN 1.4462 | European material number equivalent |
| ASTM A182 F53 | Super duplex step-up grade (UNS S32750) for more severe service – see our super duplex round bars |
Applications of ASTM A182 F51 Material
Duplex 2205 / F51 forgings are widely specified for offshore oil & gas platforms, subsea and topside piping, desalination plants, seawater cooling systems, chemical processing, and pulp & paper equipment, wherever standard austenitic stainless lacks sufficient chloride resistance but full duplex-grade corrosion performance at a lower cost than nickel-based alloys is required.
Frequently Asked Questions
1. What is the difference between F51 and F53?
2. Is ASTM A182 F51 the same as UNS S31803?
3. Does F51 require NACE compliance for oil & gas service?
Need Duplex 2205 / F51 forgings, fittings, or round bar to a specific project specification? Contact our technical team or view the full Specifications hub.
