There are six types of flange faces which are flat (FF), raised (RF), lap joint, ring joint (RTJ), male and female (M&F), and tongue and groove (T&G). In various types of Flanges, different types of gaskets are required to make connections
Raised Face Flange (RF)
A Raised Face Flange (RF) is easy to categorize because the surface of the gasket is placed above the bolting line. A Raised Face Flange (RF) is suitable to use with different types of gaskets and also in many applications. These gaskets include flat, metallic, and semi-metallic types such as jacketed gaskets and spiral wound gaskets. To concentrate the pressure of the two mating flanges on a small surface and to enhance the strength of the seal is the main scope of RF.
Flat Face Flange (FF)
In Flat face flanges (FF), a contact surface is positioned at the equal height with the fastening line. Between Flat Face Flanges, full face gaskets are perfect to use. A flat face flange cannot be mated with a raised face flange to avoid a leak.
Ring Joint Flange (RTJ)
A ring joint flanges (RTJ) is perfect to create a seal in two metals between the mating flanges. It is suitable to use in high-pressure as well as high-temperature applications. A ring joint flange has a circular groove to connect with a ring joint gasket. To generate a tight seal between two metals, two ring joint flanges are first joined and then squeezed by applying bolting pressure.
Flange Face Finish
Roughness is required on the surface of Flanges to confirm that a flange combines with the gasket and the companion flange seamlessly. Flange face finish can be defined by roughness on the surface of flanges. There are common types of flange face finish, such as stock, spiral serrated, concentric serrated, and smooth flange finish. To make a high-quality seal, the face of the flange makes an excellent match between gasket, flange, and mating flange.
The stock finish is the most common type of finish, which is suitable for the majority of applications. Due to the friction present between the contacting parts, the pressure implants the soft face into the finish of the flange to make a good seal. To create a tight seal between two surfaces, the mating flanges are attached, and gaskets are enclosed into the flange face surface.
The spiral serrated finish is different from the spiral finish. It is a phonographic spiral groove in which a groove is crafted by a 90 degrees tool. This serrated finish in concentric or spiral has a minimum of 30 grooves to a maximum of 55 grooves per inch. It has roughness between 125 to 250 µinch.
The concentric serrated face finish of the flange has concentric grooves as an alternative to spirals grooves. The grooves are manufactured by the 90-degree tool, which is used for the spiral serrated finish. To get perfect concentric grooves, the device used with a depth of 0.079mm and a feed rate of 0.039mm per revolution.
Smooth Finish or Face
A smooth face finish of flanges removes the tool marks from the flanges and make it clean. This type of finishing and face of flanges is appropriate to utilize with metal facing gaskets, for example, jacketed style. This finish can be achieved by taking a machined contact surface with a constant spiral groove, which is formed by a radius of 0.8 mm, 0.3mm per revolution feed rate, and 0.05 mm of depth.