As contact surfaces for seating the sealing gasket material, various flange faces are useful. ASME B16.47 and B16.5 describe many types of flanges, such as raised face, male, and female face flanges, and matching facings are made with identical dimensions to give a large contact surface.
The small and big tongue-and-groove flange facings, as well as the ring joint face designed for ring joint-type metal gaskets, are also covered by these standards.
Raised Face (RF)
The raised face flange, also known as a standard type used in process plant applications, is easy to identify. It is referred to mainly as the raised face because the gasket surfaces are raised above the bolting circle face. The face type allows wide combinations of gasket designs, including flat ring sheet metallic composites and double jacketed and spiral wound types.
The purpose of the RF flange is to concentrate more pressure on the smaller gasket area. It thereby helps to increase the pressure containment capability of the joint. Height and diameter are in the ASME B16.5, defined by diameter and pressure class. Flange pressure ratings determine the height of the raised face.
The typical flange face finish for the ASME B16.5 RF flange is 125 to 250 µin Ra (3 to 6 µm Ra).
Raised face height
If we talk about the height measures which is H and B of all described flange dimensions, if we keep in mind the exception of the Lap Joint flange, it is crucial to remember the following things:
. In pressure classes 150 and 300, the height of the raised face is approximately 1.6 mm (1/16 inch). In the two pressure classes, almost all the flanges suppliers are shown in the brochure and catalog; the H and B dimensions include the raised face height.
. In pressure classes of 400, 600, 900, 1500, and 2500, the raised face flange height is approximately 6.4 mm (1/4 inch). Many suppliers show the H and B dimensions in these p
The flat face flange’s gasket surface is in the same plane as the bolting circular face. Flat face flanges are widely used in applications where the flanged fitting or mating flange is constructed of a casting. Bolting flat face flanges to raised face flanges is never a good idea.
According to the ASME B31.1, when connecting flat face cast iron flanges to carbon steel flanges, remember to remove the full-face gasket. It prevents the thin, fragile cast iron flange from being sucked into the gap created by the carbon steel flange’s elevated face.
Ring type joint
At high pressures, ring-type joint flanges are used. They have grooves carved into their faces, and steel ring gaskets are included. The flanges seal with the tightening of bolts to compress the gasket between the flanges into the grooves. This process will deform the gasket to make intimate contact inside the grooves and create metal to metal seal.
A ring-type joint flange may come with a raised face with a ring groove machined into it. However, the raised face does not serve any part in the sealing mechanism itself.
Ring-type joint gaskets
Ring-type joint gaskets are metallic sealing rings that suit high-temperature applications and high pressures. They are always applicable to special, accompanying flanges, which ensure good, reliable sealing with the right material and profiles.
Ring-type joint gaskets are designed to seal by “initial line contact” or welding action between the mating flange and gasket. Then, with the pressure on the seal interface through bolt force, the ‘softer’ metal of the gasket flows into the microfine structure of the more complex flange material and creates an efficient and tight seal.
The Tongue and Groove faces of the flanges need to match properly. One flange face has a raised ring (Tongue) machined onto the flange face, while the mating flange has a matching depression (Groove) machine into the face.
Tongue-and-groove facings are standardized in both small and large types. They differ from males and females in the inside diameter of the tongue, and the groove does not extend into the flange base. This helps in retaining the gasket on its outer and inner diameter.
A flange must match this flange category. For example, one flange face comes with an area that extends beyond the normal flange face (Male). However, the other flange or mating flange comes with a matching depression (Female) machined into its face.
The above description clearly shows the flange characterization based on their faces. If you want to learn more about flanges, can contact Texas Flange today!