ASTM A182 F51 Weld Neck Flange | Duplex S31803 WNRF
ASTM A182 F51 is a forged duplex stainless steel flange grade corresponding to UNS S31803, widely used in oil and gas, offshore, chemical processing and chloride-containing piping systems.
F51 combines a ferritic-austenitic duplex microstructure with high yield strength and good resistance to chloride stress-corrosion cracking, pitting and crevice corrosion.
We manufacture and supply ASTM A182 / ASME SA182 F51 weld neck flanges (WNRF), blind flanges, slip-on flanges and other forged duplex flanges to ASME B16.5, ASME B16.47 and project-specific dimensions.
ASTM A182 F51 Flange Specification
| Item | Specification |
|---|---|
| Material Standard | ASTM A182/A182M / ASME SA-182 |
| Grade | F51 |
| UNS | S31803 |
| Material Family | Duplex Stainless Steel |
| Common Name | Duplex 2205 family |
| Main Flange Type | Weld Neck / WNRF |
| Other Types | Blind / Slip-On / Threaded / Socket Weld |
| ASME B16.5 Size | NPS 1/2–24 |
| ASME B16.47 Size | NPS 26–60 |
| Facing | RF / FF / RTJ as applicable |
| Certification | EN 10204 3.1 / 3.2 when specified |
What Is ASTM A182 F51?
ASTM A182 F51 / UNS S31803 is a duplex stainless steel forging grade used for pressure-system components such as flanges, forged fittings, valves and valve parts.
Unlike conventional austenitic stainless steel, F51 has a mixed ferritic-austenitic microstructure after proper solution heat treatment.
This duplex structure provides a combination of:
- High yield strength
- Good ductility and toughness
- Resistance to chloride stress-corrosion cracking
- Good pitting resistance
- Good crevice-corrosion resistance
- Good general corrosion resistance
- Useful performance in many offshore and chemical environments
The actual phase balance depends on chemistry, forging conditions, heat treatment, cooling rate and subsequent welding.
ASTM A182 F51 Chemical Composition
| Element | ASTM A182 F51 / UNS S31803 |
|---|---|
| Carbon, C | 0.030% max |
| Manganese, Mn | 2.00% max |
| Silicon, Si | 1.00% max |
| Phosphorus, P | 0.030% max |
| Sulfur, S | 0.020% max |
| Chromium, Cr | 21.00–23.00% |
| Nickel, Ni | 4.50–6.50% |
| Molybdenum, Mo | 2.50–3.50% |
| Nitrogen, N | 0.08–0.20% |
The combination of chromium, molybdenum and nitrogen is important to the localized-corrosion resistance of F51 duplex stainless steel.
The actual chemical composition of each supplied heat should be confirmed by the Material Test Certificate.
ASTM A182 F51 Mechanical Properties
Typical ASTM A182 F51 minimum room-temperature mechanical requirements include:
| Property | Requirement |
|---|---|
| Tensile Strength, min. | 620 MPa / 90 ksi |
| Yield Strength, min. | 450 MPa / 65 ksi |
| Elongation, min. | 25% |
| Reduction of Area, min. | 45% |
The relatively high minimum yield strength is one of the major engineering advantages of duplex F51 compared with conventional 300-series austenitic stainless steels.
Design allowable stresses, however, must be taken from the applicable ASME Code rather than directly from room-temperature tensile values.
Solution Heat Treatment of F51
Proper heat treatment is critical to duplex stainless steel performance.
F51 forgings are supplied in a solution-annealed and rapidly cooled condition to develop the required ferritic-austenitic microstructure and minimize harmful intermetallic phases.
For 2205-type duplex material, solution annealing is typically carried out around 1020–1100°C, followed by rapid cooling or water quenching as applicable to the product specification and manufacturing route.
Heat-treatment records can be supplied when required by the project.
ASTM A182 F51 Weld Neck Flange
The weld neck raised face flange (WNRF) is one of the most commonly specified F51 flange types for high-integrity process piping.
Its long tapered hub provides a gradual transition between the flange and pipe, helping distribute mechanical stress through the connection.
Typical F51 weld neck flange applications include:
- Offshore process piping
- Oil and gas facilities
- Chemical-processing plants
- Chloride-containing piping systems
- Water-treatment systems
- Petrochemical equipment
- Pressure piping
- Selected marine applications
F51 WN flanges can be supplied with RF or RTJ facing, depending on pressure class and project requirements.
ASME B16.5 vs ASME B16.47 F51 Flanges
The dimensional standard depends primarily on flange size.
| Standard | Size Range | Pressure Classes |
|---|---|---|
| ASME B16.5-2025 | NPS 1/2–24 | 150 / 300 / 400 / 600 / 900 / 1500 |
| ASME B16.5 Class 2500 | NPS 1/2–12 | 2500 |
| ASME B16.47-2025 | NPS 26–60 | 75 / 150 / 300 / 400 / 600 / 900 |
ASME B16.47 includes Series A and Series B large-diameter flange configurations.
Therefore, a statement such as “F51 flange size 1/2–48 inch, Class 150–2500” should not imply that every size and pressure class belongs to one dimensional standard.
The correct size + class + flange standard should always be stated in the enquiry.
Available F51 Flange Types
We supply ASTM A182 F51 forged flanges including:
- Weld Neck Flange / WNRF
- Blind Flange / BLRF
- Slip-On Flange / SORF
- Threaded Flange
- Socket Weld Flange
- RTJ Flange
- Large-diameter flanges
- Custom forged flanges according to drawings
Available facing configurations include:
- Raised Face – RF
- Flat Face – FF where applicable
- Ring Type Joint – RTJ
Project-specific drilling, machining and facing can be supplied according to the required dimensional standard.
Corrosion Resistance of Duplex F51
F51 offers significantly better resistance to chloride stress-corrosion cracking than many conventional austenitic stainless steels.
Its Cr-Mo-N composition also provides good resistance to:
- Pitting corrosion
- Crevice corrosion
- Chloride environments
- Many process chemicals
- Selected sour-service environments subject to specification requirements
A commonly used indicator for localized corrosion resistance is PREN:
PREN = %Cr + 3.3 × %Mo + 16 × %N
Typical F51 / S31803 material is associated with PREN values around 33 or higher, depending on actual heat chemistry.
PREN is useful for comparing alloy chemistry but should not be treated as a complete corrosion-design criterion.
Continuous seawater exposure, high temperatures, stagnant crevices, biofouling and severe chloride conditions may require a higher-alloy duplex or super duplex grade.
ASTM A182 F51 vs F60
F51 and F60 are both commonly associated with the Duplex 2205 family, but their UNS designations and chemistry limits differ.
| Item | ASTM A182 F51 | ASTM A182 F60 |
|---|---|---|
| UNS | S31803 | S32205 |
| Cr | 21.0–23.0% | 22.0–23.0% |
| Mo | 2.5–3.5% | 3.0–3.5% |
| N | 0.08–0.20% | 0.14–0.20% |
| Alloy Family | Duplex 2205 | Duplex 2205 |
| Chemistry Control | Broader | Tighter Cr/Mo/N limits |
F60 / S32205 was developed with tighter chromium, molybdenum and nitrogen limits within the 2205 composition range.
As a result, material meeting S32205 can often also satisfy S31803 requirements and may be dual-certified, while S31803 material does not automatically meet S32205.
The purchase order should specify the required grade and whether dual certification is acceptable.
Complete Duplex S31803 Piping System
ASTM A182 F51 flanges can form part of a complete UNS S31803 duplex piping system.
| Component | Related Specification |
|---|---|
| Flange | ASTM A182 F51 |
| Pipe | ASTM A790 UNS S31803 |
| Tube | ASTM A789 UNS S31803 |
| Butt-Weld Fitting | ASTM A815 S31803 |
| Plate | ASTM A240 UNS S31803 |
For more demanding chloride environments, related higher-alloy products include:
- ASTM A182 F60 / UNS S32205 Duplex Flanges
- ASTM A182 F53 / UNS S32750 Super Duplex Flanges
- ASTM A182 F55 / UNS S32760 Super Duplex Flanges
Inspection & Certification
ASTM A182 F51 flanges can be supplied with:
- EN 10204 Type 3.1 MTC
- EN 10204 Type 3.2 certification when specified
- Chemical composition analysis
- Mechanical test results
- Heat-treatment records
- PMI
- Dimensional inspection
- Surface inspection
- Hardness testing
- Ferrite / phase-balance testing when specified
- Ultrasonic examination when required
- Dye penetrant examination
- Impact testing when specified
- Third-party inspection
Additional corrosion or project-specific testing can be arranged according to the applicable material specification and purchaser requirements.
Frequently Asked Questions
What is ASTM A182 F51?
ASTM A182 F51 is a forged duplex stainless steel grade corresponding to UNS S31803. It is used for flanges, forged fittings, valves and other pressure-system components requiring high strength and good chloride-corrosion resistance.
What is the UNS number for ASTM A182 F51?
The UNS designation for ASTM A182 F51 is S31803.
It belongs to the Duplex 2205 alloy family.
Is ASTM A182 F51 the same as Duplex 2205?
F51 / UNS S31803 is part of the Duplex 2205 family. However, S32205 / F60 has tighter Cr, Mo and N chemistry limits and is also widely referred to as Duplex 2205.
For procurement, the exact ASTM grade and UNS designation should be stated.
What is the difference between F51 and F60?
F51 is UNS S31803, while F60 is UNS S32205. F60 has tighter minimum Cr, Mo and N limits, providing more consistent localized-corrosion resistance within the 2205 alloy family.
What standard covers F51 weld neck flange dimensions?
For standard forged flanges, ASME B16.5 covers NPS 1/2–24, while ASME B16.47 covers large-diameter flanges from NPS 26–60.
The pressure class, facing and dimensional standard should all be stated when ordering.
ASTM A182 F51 Weld Neck Flange Manufacturer
We manufacture and supply ASTM A182 / ASME SA-182 F51 duplex stainless steel flanges for oil and gas, offshore, petrochemical, chemical and industrial piping projects.
Available products include WNRF, blind, slip-on and RTJ flanges in standard and customized dimensions, with PMI, NDE, heat-treatment records, EN 10204 certification and third-party inspection when required.
For quotation, please specify:
Grade + Flange Type + NPS + Pressure Class + Facing + Standard + Quantity + Inspection Requirements
Example:
ASTM A182 F51, WNRF, NPS 8, Class 600, RF, ASME B16.5
