October 1, 2024
Flanges are essential components in piping systems, used to connect pipes, valves, pumps, and other equipment. One of the critical aspects of a flange is its facing, which plays a pivotal role in ensuring a secure and leak-free connection. This guide will delve into what flange facings are, the common types of flange facings, their uses, tolerances, and inspection guidelines.
What is a Flange Facing?
A flange facing is the surface on the end of a flange that makes contact with a gasket. The primary purpose of a flange facing is to create a seal when bolted together with a matching flange and gasket, ensuring no leaks in the connection. The type of facing determines the kind of gasket that can be used, the seal’s strength, and the flange’s overall performance in the piping system.
Common Types of Flange Facings
There are several flange facings, each designed to meet specific requirements of pressure, temperature, and sealing efficiency. Here are the most common types:
- Flat Face (FF) FlangesFlat Face flanges have a smooth, flat surface across the entire flange face. They have sealing surfaces that are on the same plane as the circumferential bolt surface. A flat face flange requires a full-face gasket, ensuring the entire contact surface is covered for a complete seal.
- Raised Face (RF) FlangesRaised Face flanges are the most commonly used type in process piping. These flanges have a sealing face higher than the circular bolt face, creating a better sealing surface by focusing pressure on a smaller area of the gasket. This design enhances the flange’s ability to hold pressure, making it suitable for a wide range of pressure classes.
- Ring-Type Joint (RTJ) FlangesRTJ flanges have a machined groove into which a metal gasket is seated. Gaskets are applied to the faces and then deform under pressure, being forced between the grooves to form a seal. The metal-to-metal seal provides excellent sealing performance under extreme conditions, making RTJ flanges ideal for critical service applications.
When to Use Raised Face, Flat Face or RTJ Flanges
Selecting the right flange facing depends on the application’s pressure, temperature, material compatibility, and sealing requirements:
- Flat Face (FF): Use in low-pressure, low-temperature environments or when dealing with cast iron or other brittle materials to avoid stress concentration.
- Raised Face (RF): Best suited for moderate to high-pressure applications, commonly used in refineries, chemical plants, and other industrial settings.
- Ring-Type Joint (RTJ): Ideal for high-pressure, high-temperature conditions such as oil and gas extraction, power generation, and other critical service environments.
Tolerances in Flange Facing
Flange facing tolerances are critical to ensure the flanges align properly and provide a secure seal. Tolerances for flange facings are specified by standards such as ASME B16.5 or EN 1092-1. Key tolerance aspects include:
- Flatness Tolerance: The flange face should be within a specific flatness range to ensure proper gasket seating.
- Surface Finish: The roughness of the flange face is controlled to ensure the gasket can effectively seal. Typical finishes range from 125 to 250 microinches.
- Facing Dimensions: The facing dimensions, including the raised face height or groove depth, must conform to specified standards to ensure compatibility with gaskets.
Flange Face Inspections
Proper inspection of flange faces is crucial to prevent leaks and ensure reliable connections. Here are the key steps in flange face inspection:
- Visual Inspection: Check for scratches, dents, corrosion, or any damage on the flange face that could impact sealing.
- Flatness Measurement: Use a straight edge and feeler gauge to verify the flatness of the flange face within acceptable tolerances.
- Surface Finish Inspection: Measure the roughness using a surface finish gauge to ensure it meets the required standards.
- Alignment Check: Ensure that mating flanges are properly aligned, with no misalignment that could cause sealing issues.
Whatever flanges you use in your application, you will need the appropriate gaskets to seal them. Durlon is one of the most recognizable brands when it comes to sealing solutions. We manufacture a wide variety of gaskets of different types, including PTFE, CNA, flexible graphite, and more. They are suited for several industrial applications, and all types of flange faces. Contact us for more information about our gaskets.