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 faces, their uses, tolerances, and inspection guidelines.
What is a Flange Face?
A flange face 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.
What is a Flange Face Finish, and Why is It Important?
Flange face finish refers to the roughness or texture of the flange surface. It’s important because it determines how well the gasket will seat and seal the connection. The finish must be smooth enough to prevent leaks but also provide adequate surface contact for the gasket material. Common finishes include smooth, serrated, or grooved finishes.
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) Flanges
Flat 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 gasket is required for a complete seal, ensuring the entire surface is covered.
Raised Face (RF) Flanges
Raised 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) Flanges
RTJ 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.
Learn more about flange alignment tolerance for proper gasket sealing and ensuring compatibility between flanges in our technical references section.
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:
What is the importance of flange face inspection?
Flange face inspection is essential to avoid leaks and ensure reliable connections. Inspection criteria include checking for surface finish, flatness, and proper alignment. Regular inspections help detect early signs of wear or damage, preventing more severe issues later. Here are the key steps in flange face inspection criteria:
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. This is critical for meeting flange alignment tolerance requirements.
Surface Finish Inspection
Measure the roughness using a surface finish gauge to ensure it meets the required standards.
Alignment Check
Learn how to check flange alignment by ensuring that mating flanges are properly aligned, with no misalignment that could cause sealing issues.
Choosing the Right Gasket for Your Flange Face Type
Choosing the right flange face is crucial for ensuring a reliable, leak-free connection in your piping systems. Whether you’re using flat face, raised face, or ring-type joint flanges, it’s essential to pair them with the appropriate gaskets to maintain sealing integrity.
At Durlon, we specialize in providing high-quality gasket solutions for all types of flange faces, including PTFE, CNA, flexible graphite, and more. Our gaskets are designed to handle a wide range of industrial applications and conditions, ensuring optimal performance and longevity.
If you need expert advice on selecting the right gasket for your flange face type or application, contact our team today to find the perfect sealing solution for your needs.