What Are Flange Facing Types?
The facing is the machined surface of a flange that meets the mating flange with a gasket between them. The facing type determines how the gasket is contained, how bolt load is distributed, and how the joint performs under pressure and temperature. Facing finish, dimensions, and surface roughness all affect seal performance. ASME B16.5 specifies a surface finish of 125 to 250 microinches RMS for standard flange facings, typically produced with concentric or spiral serrations.
| Facing Type | Abbreviation | Gasket Type | Typical Class Range | Primary Application |
|---|---|---|---|---|
| Raised Face | RF | Flat sheet, spiral wound | 150 - 2500 | General purpose |
| Flat Face | FF | Full-face | 125 - 300 | Cast iron equipment |
| Ring Type Joint | RTJ | Metal ring | 600 - 2500 | High-pressure, high-temp |
| Male & Female | M&F | Flat, contained | 150 - 2500 | Chemical processing |
| Tongue & Groove | T&G | Flat, contained | 150 - 2500 | Hazardous fluids |
Raised Face (RF)
The raised face is the most common flange facing type, used across all pressure classes and material grades. The raised surface concentrates bolt load onto the gasket area, improving sealing efficiency. The typical raised face height is 1/16 inch for Class 150 and 300 flanges, and 1/4 inch for Class 400 through 2500. RF facings are compatible with virtually all gasket types including non-metallic, semi-metallic, and metallic gaskets. The surface finish is typically serrated in a concentric or spiral pattern to provide grip and prevent gasket extrusion.
Flat Face (FF)
The flat face extends across the entire flange face with no raised portion. It is used primarily with cast iron or flat-faced equipment to prevent flange breakage from bolt stress on brittle materials. Full-face gaskets are used with flat face flanges to distribute the bolt load evenly across the entire face area. Flat face flanges are typically found in low-pressure applications (Class 125 or 250 in cast iron, or Class 150 in steel) connected to cast iron valves, pumps, and compressors.
Ring Type Joint (RTJ)
The ring type joint facing features a precision-machined groove in the flange face that accepts a metal ring gasket. When the bolts are tightened, the ring gasket deforms into the groove walls, creating a metal-to-metal seal. RTJ facings are designed for high-pressure and high-temperature service, typically Class 600 and above. The groove dimensions are standardized per ASME B16.5, and three ring profiles are available: oval, octagonal, and RX. RTJ flanges require careful handling to avoid damaging the groove sealing surfaces.
Male & Female (M&F)
Male and female facing pairs provide self-centering alignment during assembly. The male face on one flange fits into the female recess on the mating flange, keeping the gasket fully contained within the female recess. This design reduces gasket extrusion under high pressure and is commonly used in chemical processing applications. M&F facings are available across all pressure classes and are often specified for applications where gasket blowout prevention is critical.
Tongue & Groove (T&G)
Tongue and groove facings are similar to M&F but feature a deeper interlocking engagement. The tongue on one flange fits precisely into the groove on the mating flange, providing positive alignment and anti-blowout protection. The gasket sits fully contained within the groove, making T&G facings ideal for high-pressure chemical and hazardous fluid service. They are commonly used in heat exchanger and pressure vessel nozzle connections where leak-tight integrity is paramount.
Facing Surface Finish Requirements
ASME B16.5 specifies that flange facings shall have a surface finish of 125 to 250 microinches RMS (3.2 to 6.3 micrometers Ra). The finish can be produced by either concentric or spiral serration, with the serration tool radius specified by the standard. The surface finish affects gasket seating and sealing reliability: smoother finishes are required for soft gaskets like elastomers and PTFE, while rougher finishes work well with metallic and semi-metallic gaskets that need to grip the surface.
How to Select the Right Facing
For most applications, raised face is the default and recommended choice. Specify flat face when connecting to cast iron or flat-faced equipment to prevent flange breakage. Use RTJ for high-pressure and high-temperature service, particularly at Class 900 and above. M&F and T&G facings should be specified for chemical and hazardous services where gasket containment and anti-blowout protection are critical. Always ensure both mating flanges have compatible facing types.
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