Gasket for FF and RF Flanges - Differences
Flanges play a key role in pipeline systems across many industries, from petrochemicals to construction. They provide the integrity and performance of piping systems by creating a safe, reliable, and leak-tight connection between pipes, valves, and other components.
What is a flange face?
The flange face is the surface that contacts the gasket and the corresponding surface of the mating flange or fitting. The flange face directly affects the tightness of a flange joint. Its selection depends on factors such as pressure, temperature, and maintenance requirements.
The most popular types include Flat Face (FF) flanges and Raised Face (RF) flanges. When choosing the appropriate flange, it is essential to understand their types and specifications. Each of them is used in different operating conditions — from low-pressure installations to high-pressure and high-temperature systems.
A properly selected flange face increases the durability of the joint and minimizes the risk of leakage.
Flat Face Flanges FF (Flat Face)
Features of the Flat Face FF flange
Construction and characteristics
A Flat Face (FF) flange provides a wide contact area with the gasket. Its contact surface is smooth, completely flat, and has no protruding elements. The entire flange face contacts the surface of the connected pipe or other components, which is particularly useful for large-diameter connections or connections made from fragile materials. The flat face ensures even distribution of compressive load on the gasket, providing a leak-tight joint. The design and manufacture of flat face flanges typically meet the requirements of ASME B16.5 and EN 1092-1 standards.
Flat face flanges should not be paired with raised face flanges, as this may cause leaks.
Sealing method
FF flanges use soft (non-metallic) full-face gaskets that cover the entire flange surface, increasing tightness by evenly distributing the load. They are installed between two flat face flanges, directly on the front sealing surface of the flange face, i.e., in the same plane as the bolt circle surface.
Operating pressure range
Due to their design, Flat Face flanges are commonly used in low-pressure applications, in ANSI pressure classes 125 and 150.
Gasket material compatibility
FF flanges are usually used with cast iron, copper, and plastics to avoid bending or cracking. They are ideally suited for use with non-metallic gaskets, such as rubber gaskets, which work effectively with the sealing surface.
Applications of Flat Face FF flanges
Flat face flanges are commonly used in low-pressure, non-critical applications and when connecting materials such as cast iron. Examples of applications:
- water treatment systems (HVAC systems, water mains, wastewater treatment pipes)
- connections of low-pressure equipment (connections between pumps, valves, or heat exchangers)
- low-pressure pipelines for conveying steam, air, natural gas
Raised Face Flanges RF (Raised Face)
Features of the Raised Face RF flange
Construction and characteristics
A Raised Face (RF) flange has a slightly elevated surface around the bore that protrudes beyond the bolting face of the flange. This provides a smaller, concentrated sealing surface, allowing a higher load to be applied to the gasket, effectively increasing its sealing performance and reducing the risk of leakage. This is especially important in high-pressure and high-temperature conditions. The design and manufacture of raised face flanges typically meet the requirements of ASME B16.5 and ASME B16.47 standards.
Sealing method
RF flanges use non-metallic or semi-metallic gaskets that fit the raised face. The smaller gasket area concentrates the pressure, which improves sealing and reduces the risk of leakage under high-pressure conditions.
Operating pressure range
The raised flange face allows a higher load to be applied to the gasket, providing reliable sealing in high-temperature and high-pressure conditions across all classes. The pressure rating of the flange determines the height of the raised face.
Gasket material compatibility
RF flanges can be made from various materials, including carbon steel, stainless steel, and alloy steel. They can be used with different gasket materials, from metallic to non-metallic, allowing them to be adapted to various piping systems and pressure conditions.
Applications of Raised Face RF flanges
Due to the concentrated sealing surface, raised face flanges are ideal for applications requiring resistance to high pressure and temperature. They effectively maintain tightness under variable pressure and temperature conditions, making them suitable for oil and gas pipelines, refineries, power plants, and chemical processing. Examples of applications:
- high-pressure and high-temperature pipeline systems
- pipeline connections for transportation and processing of oil and gas
- connections in industrial systems
- pipelines in chemical plants and power generation
What are the differences between FF and RF flanges?
As mentioned earlier, Flat Face (FF) flanges and Raised Face (RF) flanges are two flange types commonly used in piping systems.
Differences between FF (Flat Face) and RF (Raised Face) flanges
| Type | FF Flange (Flat Face) | RF Flange (Raised Face) |
|---|---|---|
| Construction | Flat sealing surface, without protruding elements | Slightly raised sealing surface, providing concentrated pressure |
| Pressure/temperature range | Designed for low-pressure and low-temperature environments | Ideal for medium and high-pressure environments and high temperatures |
| Pressure class | Most commonly 125, 150 | All classes |
| Sealing performance | Lower sealing performance, suitable for brittle materials such as cast iron | Provides higher sealing pressure, reducing the risk of leakage |
| Gasket type | Soft, non-metallic | Non-metallic or semi-metallic |
| Material suitability | Cast iron, copper, and similar | Carbon steel, stainless steel, alloy steel |
| Application areas | Water treatment, HVAC systems, low-pressure applications | Oil and gas industry, chemical industry, power generation, high-pressure systems |
| Installation method | The flat flange face contacts the gasket directly | The raised portion of the flange matches the gasket; even, concentrated pressure |
The choice of flange type depends on the environmental requirements of the specific application. As shown in the table above, FF flanges are suitable for low-pressure applications requiring simpler installation, while RF flanges perform well in high-pressure and high-temperature applications where the concentrated pressure helps to achieve a hermetic seal, reducing the risk of leakage.
More information on gasket types, materials, standards, and selection principles can be found in the complete guide to gaskets for flange connections.
Where can I buy gaskets for FF and RF flanges?
At the Power Rubber store we offer high-quality rubber gaskets designed for use under pressure, resistant to high temperatures and chemicals. Both standard gaskets and custom-made gaskets are available.
Our gaskets for FF flanges are ideal for low-pressure applications where effective sealing across the entire contact surface is required. On the other hand, our gaskets for RF flanges are made from materials resistant to high pressure, temperature, and compression, making them perfectly suited for applications where reliability and tightness are critical.
Production of rubber gaskets
Are you looking for a trusted manufacturer of rubber gaskets? At Power Rubber we specialize in the production of precision technical gaskets from high-quality rubber compounds. We manufacture gaskets to order based on technical documentation or a supplied sample.
We invite you to contact us by phone: +48 222 924 024 or +48 505 160 303, by email (power|powerrubber.com| rel="nofollow"|Power|PowerRubber.com) or via our contact form
