There are different types of flange faces that are used as the contact faces sealing the gasket material. Both ASME B16.5 & B16.47 define various types of flange facings, include the raised face, large male & female facings that have identical dimensions in order to provide a relatively large contact area.
The other flanges are covered by all these standards that include the large & small tongue & groove facings & the ring joint facing that is specifically for ring-type joint metal gaskets.
Raised Face (RF)
This is one of the most common types – Raised Face is used in the process of plant applications, plus it is easy to identify. It is referred as the raised face due to the fact that the gaskets surfaces are raised above the bolting circle face. The type RF (Raised Face) allows the usage of wide combination of gasket designs as it includes flat ring sheet types & metallic composites, for instance, Spiral Wound & Double Jacked types.
The objective of RF (Raised Face) is to concentrate more pressure on the smaller gasket area. Therefore, increase the pressure containment capability of joint.
Diameter & height are in ASME B16.5 defined by pressure class & diameter. The pressure rating of flange determines the height of the raised face.
For ASME B16.5, the typical flange face finish is 125 μ in Ra
Flat Face (FF)
This type of flange face has a gasket surface in the sample plane as a bolting circle face. Flat Face (FF) are never be bolted to be a raised flat face.
ASME B31.1 : While connecting flat face cast iron flanges to carbon steel flanges, then the raised face flange on carbon steel flange must be removed & a full face gasket is required. You have to keep it thin, so bittle cast iron flange that is caused by the raised face of carbon steel flange, manufactured by carbon steel flanges manufacturers.
Ring-Type Joint Face
Typically, it is used in high pressure & high-temperature services above 800 degrees Fahrenheit. They include grooves cut into their faces that are steel ring gaskets. Ring-type joint flange face type is considered to be the most efficient one for use in pipeline design. This is one of increasing options with regards to flange connections. Also, it offers a good alternative to the standard face in particular applications.