1. Flat Face (FF) Flanges
2. Raised Face (RF) Flanges
3. Male-Female (M/F) Face Flanges
4. Tongue-Groove (T/G) Face Flanges
5. Ring Type Joint (RTJ) Flanges
6. Flanges based on Face Finish
7. Flanges based on Serrations
There are different types of pipe flanges used in the piping systems depending upon the fluid, PT rating, material of construction, connecting equipment etc. Below are the types of flanges used in piping based on facing
Based on Facing
1.1) Flat Face (FF) Flanges:
These pipe flanges are used when the counter flanges are flat face. They are mainly used at connection to cast iron equipment, valves and specialties. This flat face flange has a gasket surface in the same plane as the bolting circle face.
1.2) Raised Face (RF) Flanges:
These pipe flanges are the most commonly used flanges. The raised face thickness for 150# and 300# are included in the specified flange thickness and for higher rating they are not included in the flange thickness.
1.3) Male-Female (M/F) Face Flanges:
These pipe flanges are better version of Raised face flanges.
1.4) Tongue-Groove (T/G) Face Flanges:
1.5) Ring Type Joint (RTJ) Flanges:
These pipe flanges are most reliable type of flange joint but are costlier than the other type of flanges. The Ring Type Joint flanges are generally used in high pressure (Class 600 and higher rating) and/or high temperature services above 800°F (427°C).
2) Based on Face Finish:
2.1) Stock Finish: These flanges are used with non-metal gaskets. The allowable roughness for these type of Flanges is 250-500 or 500-1000 micro inch AARH.
2.2) Smooth/Serrated Finish: These flanges are used with metal or spiral wound gaskets. The allowable roughness for these type of Flanges is 125-250 micro inch AARH.
2.3) Extra Smooth Finish: These flanges are used with metal RTJ and T/G flanges. The maximum allowable roughness for these type of Flanges is 63 micro inch AARH.
3) Based on Serrations:
3.1) Concentric Serrations: These serrations are used where the conveying fluid is highly flammable or toxic or lower molecular weight gas.
3.2) Spiral Serrations: These are generally used type serrations.