What is the purpose of the raised face or flat face on a blind flange

The raised face or flat face on a blind flange serves the purpose of creating a proper seal when the flange is installed in a piping system. The choice between a raised face (RF) and a flat face (FF) depends on the specific requirements of the application. Here's an explanation of the purpose and use of each:

1. Raised Face (RF) Blind Flange:

  - Sealing Enhancement: The raised face is a raised ring or surface around the bolt holes of the flange. This raised portion serves as a sealing surface for gaskets. When the blind flange is bolted in place, the gasket is compressed between the raised face of the blind flange and the mating flange or equipment, creating a tight and reliable seal.

  - Improved Sealing: The raised face design helps distribute the pressure from the bolts more evenly across the gasket, resulting in improved sealing performance. It also accommodates slight imperfections or misalignments in the flange faces of the mating components, which can be beneficial in achieving a leak-free seal.

2. Flat Face (FF) Blind Flange:

  - Compatibility: Flat face blind flanges have a smooth, flat surface around the bolt holes, and they are used when the mating flange or equipment also has a flat face. In such cases, a flat face-to-flat face connection does not require a raised sealing surface.

  - Gasket Requirement: When using flat face blind flanges, a gasket or other sealing method is typically necessary to create a seal. The flat face of the blind flange alone may not provide an adequate sealing surface, so the gasket compensates for this and ensures a secure seal.

In summary, the raised face (RF) on a blind flange is designed to provide a sealing surface that can directly contact and compress a gasket, resulting in an improved seal without the need for additional gasket materials. Conversely, the flat face (FF) on a blind flange is used when the mating flange or equipment has a flat face, and a gasket or other sealing method is employed to establish the seal. The choice between RF and FF depends on the design of the flange faces in the system and the sealing requirements of the application.