What Is ASTM A182 F51?
F51 is a duplex (austenitic-ferritic) stainless forging (22Cr-5Ni-3Mo-N, matching UNS S31803 / S32205). Duplex microstructures combine higher strength with better chloride stress-corrosion cracking resistance than standard 304/316 austenitic grades.
Temperature Range
Per ASME B16.5-2025 Table 2-2.13 and its notes, F51 must not be used above 316°C — duplex steels may become brittle after service at moderately elevated temperatures. Below that, the Group 2.13 pressure-temperature rating applies.
Material Group (per ASME B16.5)
Per ASME B16.5-2025 Table 1A, F51 (22Cr-5Ni-3Mo-N) belongs to Material Group 2.13, together with F60, F53 and F55 duplex/super-duplex grades.
Corrosion Resistance
In the Schweitzer corrosion tables, F51 / Alloy 2205 is rated excellent (E) in the media where it is listed; local table coverage is limited, so send us your exact service medium for confirmation. In practice duplex is specified where 316 suffers chloride pitting or stress-corrosion cracking — seawater, brines, chloride process streams.
Typical Applications
- ASME B16.5 flanges for seawater, desalination and offshore piping
- Chemical-processing fittings resistant to chloride stress-corrosion cracking
- Heat-exchanger and pulp & plant components
Chemistry & Mechanical Properties
Duplex composition and mechanical properties (including the higher yield strength) per ASTM A182 — consult the standard for exact limits. 3.1 mill certificates supplied.
Related Standards
- ASME B16.5 — Pipe Flanges (NPS 1/2–24)
- ASME B16.11 — Socket-Welding & Threaded Fittings
- ASTM A182 F316 — Molybdenum-Bearing Stainless
- ASTM A182 F316L — Low-Carbon 316
- Our Flange Range
FAQ
Why is F51 limited to 316 C?
Duplex stainless steels can become brittle after long service at moderately elevated temperatures — ASME B16.5 note (1) for Group 2.13 sets the ceiling at 316°C.
What is the advantage of duplex over 316?
Higher yield strength and better resistance to chloride stress-corrosion cracking and pitting — the reason duplex is specified for seawater and brine service.
Is F51 the same as 2205?
Yes — F51 corresponds to the 22Cr-5Ni-3Mo-N duplex family (UNS S31803 / S32205, Alloy 2205).
Can F51 replace F316 at lower cost?
Often at reduced wall thickness thanks to its higher strength, but it is a more expensive raw material — compare total weight and design conditions.
Can F51 be used above 316°C?
No — ASME B16.5 notes that duplex steels may become brittle at moderately elevated temperatures, and Group 2.13 material is not to be used over 316°C.
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