Analysis of Flange Facing Types and Applications in Industrial Piping Systems

In today's discussion, we're covering the various flange-facing options commonly found in industrial piping systems. The flange face is the surface opposite the hub that makes contact with the corresponding flange or fitting during bolted connections. Here’s a summary of the key points:

1. Raised Face (RF)

• Description: The raised face is the most common flange face type, with the surface slightly elevated (raised) from the rest of the flange. This helps concentrate the applied surface pressure during bolting, resulting in a stronger seal.
• Class 150: Raised face height is typically 1/16 inch.
• Class 400 and higher: Raised face height increases to 1/4 inch.
• Usage: Typically paired with raised face-to-raised face flanges, creating a stronger, more efficient seal.

2. Flat Face (FF)

• Description: A flat face, sometimes referred to as a full face, has a smooth, machined surface across the flange. It’s typically used in situations where the flanges are made from different materials or for applications where a raised face may cause issues.
• Serrated Finish: Flat face flanges also feature a serrated finish, similar to the raised face, to improve gasket sealing.

3. Phonographic and Concentric Serrations

• Phonographic Serrations: These are spiral grooves, similar to a vinyl record, running from the outer edge to the inner diameter of the flange. This design improves gasket sealing by allowing it to "bite" into the surface.
• Concentric Serrations: Often used in vacuum applications, these grooves are circular and form a bull’s-eye pattern. They are typically required for more specialized applications and seal configurations.

4. Protecting Flange Faces

• Face Protectors: To avoid damage during transport or installation, face protectors can be used. These include plastic snap-on protectors that fit into the bolt holes, preventing dents and scratches on the serrated flange faces. Damaged flange faces can result in derating of the flange, so it's crucial to protect them.

5. Ring Type Joint (RTJ)

• Description: The RTJ is used for high-pressure and high-temperature applications, where a metal-to-metal seal is required. The RTJ gasket sits in a groove on the flange face. When the flanges are bolted together, the gasket is crushed, forming a metal seal.
• Available Pressure Classes: These are available in various pressure classes, including the Class 150, which uses an R-15 gasket.

6. Alternate Flange Facings:

• Tongue and Groove: This type involves a "tongue" on one flange that fits into a "groove" on the other flange, providing a secure connection.
• Male and Female: Similar to the tongue and groove, but with the male side fitting into the female side for a more rigid connection.
• Special Gaskets: These alternate flange faces require specialized gaskets designed for their unique geometries.

7. Considerations When Ordering Flanges

• When specifying flange facings, it’s crucial to include all necessary descriptors:
  • Size: e.g., 1/2" or 12".
  • Pressure Class: e.g., 150#, 600#, etc.
  • Flange Type: e.g., weld neck, slip-on, blind, etc.
  • Schedule: Depending on the pipe’s thickness and material.
  • Material of Construction: For example, A105, 316, F11, Inconel 625, etc.

Summary:

Flanges are crucial components in piping systems, and choosing the correct flange facing is essential for ensuring a proper seal. Whether you need a Raised Face, Flat Face, Ring Type Joint, or Alternate Flange Faces, it's important to understand the specific requirements of your application, including pressure class, size, material, and flange type.

By taking these factors into account, you can ensure that the flange you choose will perform effectively under the required conditions.