Flange Facing Types
According to ASME Standards we have the following codes for flanges with different usage:
The ASME B16.5 and ASME B16.47 tell us the different types of flange faces:
And now, let's see some small details about these facing types:
RAISED FACE FLANGE (RF)
The Raised Face flange is the most common type used in process plant applications, and is easily to identify. It is referred to as a raised face because the gasket surfaces are raised above the bolting circle face.?Raised face flanges are the most sold type of flanges.
A raised face flange is compatible with a wide range of?flange gaskets, ranging from flat to semi-metallic and metallic types (as, for ex: jacketed gaskets and spiral wound gaskets).
The main scope of a raised face flange design is to concentrate the pressure of the two mating flanges on a small surface and increase the strength of the seal.
The height of the raised face depends on the?flange pressure rating?as defined by the?ASME B16.5?specification (for pressure classes 150 and 300, the height is 1.6 mm or 1/16 inch, for classes from 400 to 2500, the raised face height is approximately 6.4 mm, or 1/4 inch).
FLAT FACE FLANGE (FF)
???
Flat face flanges (FF) have a contact surface?having the same height as the bolting line of the flange. Full face gaskets, generally of the soft type, are used between two flat face flanges.
According to ASME B31.3(used for process piping), a flat face flange should never be mated with a raised face flange as the resulting flanged joint would definitely leak.
领英推荐
RING JOINT FLANGE (RTJ)
???
A ring joint flanges (RTJ) is used when a metal-to-metal seal between the mating flanges is required (which is a condition for high-pressure and high-temperature applications, i.e. above 700/800°C).
A ring joint flange features a circular groove to accommodate a ring joint gasket (oval, or rectangular).
As the two ring joint flanges are bolted together and then tightened, the applied bolting force deforms the gaskets?inside the flange groove creating a very tight?metal-to-metal seal. To make this happen, the material of the ring joint gasket has to be softer (more ductile) than the material of the flange.
RTJ flanges can be sealed by?RTJ gaskets of different styles (R, RX, BX)?and profiles (example: octagonal/oval for the R style).
The most common RTJ gasket is the R style with an octagonal section, as it ensures a very strong seal (the oval section is an older?type). A “flat groove”?design, however,?accepts both RTJ gaskets having an octagonal or oval section.
LAP JOINT FLANGE
A lap joint flange has a flat face, which is not used to seal the flanged joint but simply hosts the back of a?stub end. The sealing surface is actually on the stub end itself and may be either flat face or raised face.
MALE AND FEMALE FLANGE (M AND F)
One flange has an area extended beyond its face area, the male flange, the other flange has a matching depression machined on the facing surface, the female flange.
The female face is 3/16” deep, while the male face is 1/4″ high, and both of them are smooth finished.
References
Mechanical Engineer at Hargrove Engineers + Constructor
1 年Where in ASME B31 does it refer to never mate a RF and FF flange?
Senior Engineer - Hydraulic Projects
1 年Can we mate the RF flange with the flat face flange?