The flange face is the surface area that receives the gaskets. The material of the gasket seats over the flange face and creates an effective sealing under pressure.
The flange face is designed per the ASME B16.6 for flanges up to 24 inches and ASME B16.47 for 26-inch flanges and larger. To prevent leakage problems, many kinds of flange faces are produced.
Meaning of flange face finish
The ASME B16.5 code needs the flange face (flat face and raised face) to come with a specific roughness. It ensures that the surface is compatible with the gasket.
It helps provide a high-quality seal. A serrated finish, either spiral or concentric, is required, with 30 to 55 groves every inch.
It comes with a resultant roughness between 125 and 500 micro inches. It allows for many grades of surface finish that should be available by the flange manufacturers for the gasket contact surface of the metal flanges.
In this blog, we will learn about various flange faces and types of flange face finishes.
Types of Flange Faces
The ASME B16.47 and ASME B16.5 standards refer to 6 different flange faces. These are:
Lap joint flange
The lap joint flange comes with a flat side that is not useful in sealing the flange. Instead, the joint accommodates the back of the stub end. The sealing surface has a stub end and can be either raised or flat.
Ring joint flange (RTJ)
Ring-type connection flanges come with high pressure (class 600 and above) and high-temperature applications above 800°F (427°C). They come in a groove cut into the faces that are steel ring gaskets.
As the tightened bolts force the gaskets between the flanges in the groove, the flanges seal and deform the gasket to seal it in the groove. It creates a metal-to-metal seal.
The RTJ flange comes with a raised face with a machined annular groove. The raised surface doesn’t act as a sealant.
In the case of O-ring sealing RTJ flanges, the raised faces of the flanges are clamped and mated together that may come into contact.
In this case, the compressed gasket doesn’t usually carry the load beyond the bolt tension, movement, or vibration. It will also not crush the gasket and reduce joint stress any further.
Raised face flange (RF)
Raised face flanges are the most common in the identifiable and plant application process. It is called raised face, as the sealing face is higher than the circular bolt face.
The face type enables a wider range of gasket design combinations such as double wall type, spiral wound type, flat ring sheet type, and other metal composite materials.
Flat face flange (FF)
Flat-face flanges have a sealing surface in the same plane as the circumferential bolt surface. Therefore, flat face flanges need to come with bolted-to-raised face flanges.
In addition, a soft type (non-metallic) full-face gasket is usually useful in the two flat-face flanges while it makes a joint connection. The type of flange face is also known as the plain face.
Flat-face flanges are preferable in low-pressure applications. These flanges are not suggested to mate with the RF flange.
Male and female flange (M&F)
Male and female flanges need flange adjustments. The flange face possesses an area beyond the normal (male) flange face. The mating or other flange comes with a matching recess (female) machined in the face.
The female face is 3/16” deep, and the male face is ¼” high. It comes with a smooth finish. The outer diameter of the female face is used to hold and locate the gasket.
The two available versions are large and small M&F flange. In addition, custom male and female shrouds are often found on the heat exchanger shells that cover and channel the flanges.
Large and small tongue-and-groove flange (T&G)
The groove and tongue surfaces of the flanges are essential to match. For example, one flange face has raised ring (Tongue) machined into the flange face. The mating flange has a matching recess (groove) machined into the face.
Tongue and groove facings come in both small and large sizes. They differ from female and male threads in the inner diameter of the groove and tongue. It does not protrude into the flange base by retaining the seal at its outer and inner diameters. These are found commonly on cam and pump covers.
Contact Texas Flange today if you have any questions about Flange’s face.