ASTM A182 F51 Slip On Flange – Duplex UNS S31803 SORF / SOFF
ASTM A182 F51 slip on flange is a forged duplex stainless steel flange made from UNS S31803, commonly known as part of the Duplex 2205 material family. It provides high mechanical strength and good resistance to pitting, crevice corrosion and chloride stress corrosion cracking.
When manufactured to ASME B16.5, F51 slip on flanges are commonly supplied as:
- SORF – Slip On Raised Face
- SOFF – Slip On Flat Face
They are widely used in oil & gas, offshore, chemical processing, desalination, water treatment and marine piping systems.
ASTM A182 F51 Slip On Flange Specifications
| Item | Specification |
|---|---|
| Material | ASTM A182 F51 |
| UNS | S31803 |
| Material Type | Duplex Stainless Steel |
| Dimensional Standard | ASME B16.5 |
| Size Range | NPS 1/2–24 |
| Pressure Class | 150 / 300 / 400 / 600 / 900 / 1500 / 2500, subject to size and configuration |
| Facing | RF / FF |
| Type | SORF / SOFF |
| Certificate | EN 10204 3.1 when specified |
| Optional Inspection | PMI, PT, MT, UT, Ferrite Test, ASTM G48, Third-Party Inspection |
What Is ASTM A182 F51?
ASTM A182 F51 corresponds to UNS S31803 duplex stainless steel for forged piping components such as flanges and fittings.
F51 combines a ferritic-austenitic duplex microstructure with chromium, nickel, molybdenum and nitrogen alloying, providing:
- Higher strength than many austenitic stainless steels
- Good resistance to chloride stress corrosion cracking
- Good pitting and crevice corrosion resistance
- Good performance in many corrosive process environments
ASTM A182 F51 vs F60
F51 and F60 are often both described commercially as Duplex 2205, but they are different ASTM grades.
| Grade | UNS | Key Difference |
|---|---|---|
| ASTM A182 F51 | S31803 | Standard duplex grade |
| ASTM A182 F60 | S32205 | Tighter chemistry control |
F51 = UNS S31803
F60 = UNS S32205
Some heats may meet both S31803 and S32205 requirements and may be dual-certified, but this should be verified from the Material Test Certificate (MTC).
SORF vs SOFF
| Type | Facing | Typical Use |
|---|---|---|
| SORF | Raised Face | General process, oil & gas and chemical piping |
| SOFF | Flat Face | Flat-face mating flange or equipment connections |
The correct facing should follow the mating flange, gasket arrangement and project piping specification.
Chemical Composition
Typical ASTM A182 F51 / UNS S31803 chemistry:
| Element | Requirement |
|---|---|
| Cr | 21.0–23.0% |
| Ni | 4.5–6.5% |
| Mo | 2.5–3.5% |
| N | 0.08–0.20% |
| C | ≤ 0.030% |
| Mn | ≤ 2.00% |
| Si | ≤ 1.00% |
| P | ≤ 0.030% |
| S | ≤ 0.020% |
Actual chemistry should be verified against the MTC.
Mechanical Properties
| Property | Minimum |
|---|---|
| Tensile Strength | 620 MPa |
| Yield Strength | 450 MPa |
| Elongation | 25% |
| Reduction of Area | 45% |
The relatively high yield strength is one of the key advantages of duplex stainless steel.
Heat Treatment
ASTM A182 F51 forgings are supplied in a solution heat-treated and rapidly cooled condition.
Correct heat treatment is important for maintaining the required duplex microstructure, mechanical strength and corrosion resistance.
Corrosion Resistance
ASTM A182 F51 provides good resistance to:
- Pitting corrosion
- Crevice corrosion
- Chloride stress corrosion cracking
- General corrosion in many process environments
F51 is commonly used in chloride-containing environments, but it should not automatically be considered suitable for every seawater condition.
For severe seawater or highly aggressive chloride service, Super Duplex F53 / UNS S32750 or F55 / UNS S32760 may be more appropriate.
Testing and Inspection
Standard material verification normally includes chemical composition, mechanical properties, dimensional inspection, visual inspection and material traceability.
Additional project requirements may include:
- PMI
- PT / MT / UT
- Ferrite measurement
- Hardness test
- ASTM G48 corrosion test
- EN 10204 3.1 / 3.2
- Third-party inspection
These additional tests should be specified in the RFQ and should not automatically be considered mandatory ASTM A182 requirements.
ASTM A182 F51 for Sour Service
ASTM A182 F51 should not automatically be described as NACE compliant.
For sour-service applications, specify:
NACE MR0175 / ISO 15156
Compliance should be evaluated according to material condition, hardness, heat treatment and actual service environment.
ASTM A182 F51 Slip On vs Weld Neck Flange
| Feature | Slip On Flange | Weld Neck Flange |
|---|---|---|
| Connection | Fillet welded | Butt welded |
| Installation | Easier | More precise fit-up |
| Cost | Generally lower | Generally higher |
| Stress Distribution | Lower | Better |
| Typical Use | General piping | Critical / cyclic piping |
The final flange type should follow the piping code and project specification.
How to Specify ASTM A182 F51 Slip On Flange
A complete RFQ should normally include:
NPS + Class + Flange Type + Facing + Material + Standard + Quantity + Inspection Requirements
Example:
FLANGE, SLIP-ON, RF, NPS 4, CLASS 300, ASME B16.5, ASTM A182 F51 / UNS S31803, EN 10204 3.1, PMI 100%, QTY: 20 PCS
Frequently Asked Questions
Is ASTM A182 F51 the same as UNS S31803?
Yes. ASTM A182 F51 corresponds to UNS S31803 for forged piping components.
Is F51 the same as Duplex 2205?
F51 / S31803 belongs to the Duplex 2205 family. However, “2205” may also refer to S32205, so the exact ASTM grade and UNS number should be stated in procurement documents.
Is F51 the same as F60?
No.
F51 = UNS S31803
F60 = UNS S32205
What is SORF?
SORF means Slip On Raised Face flange.
What is SOFF?
SOFF means Slip On Flat Face flange.
Is F51 suitable for seawater?
F51 provides good chloride resistance, but suitability depends on temperature, chloride concentration, flow conditions and crevice exposure.
ASTM A182 F51 Slip on Flange
ASTM A182 F51 Slip on Flange ASME B16.5
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ASTM A182 F51 Slip On Flange Manufacturer & Supplier
As a professional ASTM A182 F51 slip on flange manufacturer and supplier, we provide Duplex UNS S31803 SORF and SOFF flanges manufactured to ASME B16.5 requirements for oil & gas, offshore, chemical, marine and water treatment projects.
We can supply F51 duplex stainless steel flanges with project-specific requirements for EN 10204 3.1 certification, PMI, NDT, ferrite testing, corrosion testing and third-party inspection.
Send us your NPS, pressure class, facing, quantity and technical specification for quotation.
