When it comes to piping systems and industrial connections, selecting the right type of flange is essential to ensure leak-proof, pressure-resistant, and structurally sound joints. One of the key factors in flange selection is the flange facing type. The two most common facing types are raised face (RF) and flat face (FF) flanges.

Understanding the difference between flange raised face vs flat face is critical for engineers, procurement teams, and maintenance professionals. In this article, we will explain the characteristics of each flange face type, their advantages, applications, and how to choose the right one for your project.

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What Is a Flange Face

Before diving into the differences, it’s important to understand what a flange face is. The flange face is the surface area that comes into direct contact with a gasket. It plays a vital role in sealing the connection between two pipe flanges. The design of the face affects how well the joint seals under pressure and how the gasket behaves during tightening.

At sasaflange, we manufacture a wide range of flanges with different facing types to meet global standards and industry demands. Whether you require RF or FF flanges, choosing the right face type is crucial to the safety and efficiency of your system.

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What Is a Raised Face Flange

A raised face (RF) flange is the most widely used flange facing in industrial applications. In this design, the sealing surface is slightly raised above the flange’s bolt circle area. The standard height of the raised face depends on the pressure class:

• For flanges in pressure classes 150 and 300, the raised face height is 1.6 mm (1/16 inch)

• For pressure classes 400 and above, the height increases to 6.4 mm (1/4 inch)

The raised face allows the gasket to be concentrated on a smaller surface area, which improves the sealing capability under high pressure.

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Benefits of Raised Face Flanges

• Better sealing performance due to concentrated gasket compression

• Suitable for higher pressure and temperature applications

• Widely available and compatible with standard gasket types

• Ideal for critical systems such as refineries, chemical plants, and oil and gas pipelines

Raised face flanges are designed to work with spiral wound, ring, or flat gaskets and are the preferred choice for most industrial applications requiring tight, high-pressure seals.

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What Is a Flat Face Flange

A flat face (FF) flange has a flat, even gasket surface that is level with the bolt circle area of the flange. There is no raised section, and the entire face is used for sealing.

Flat face flanges are typically used in low-pressure applications, such as water treatment systems, low-pressure steam lines, and cast iron piping systems. The design helps distribute the load evenly across the entire gasket surface and is ideal where flange deformation must be avoided.

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Benefits of Flat Face Flanges

• Suitable for use with cast iron equipment and fittings, which are brittle and sensitive to uneven pressure

• Helps prevent flange warping or cracking

• Ideal for systems operating at low pressure and low temperature

• Compatible with full-face gaskets for even load distribution

At sasaflange, we offer flat face flanges specifically designed for municipal and water works projects where safety and simplicity are prioritized.

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Key Differences Between Raised Face and Flat Face Flanges

1. Design

   • Raised face flanges have a small elevated surface for sealing

   • Flat face flanges have a flat, continuous sealing surface

2. Gasket Type

   • Raised face: spiral wound, ring type, or flat ring gaskets

   • Flat face: full-face gaskets covering the entire flange surface

3. Application

   • Raised face: used in high-pressure, high-temperature systems

   • Flat face: used in low-pressure, non-critical systems

4. Material Compatibility

   • Raised face flanges are compatible with most metallic piping systems

   • Flat face flanges are typically used with cast iron or brittle materials

5. Installation Considerations

   • Raised face flanges require proper torque to compress the gasket in a smaller area

   • Flat face flanges require careful bolting to avoid uneven stress and potential breakage

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Choosing the Right Flange Face Type

The choice between raised face and flat face flanges depends on several factors:

• Pressure and temperature rating: RF is better for high-pressure systems

• Piping material: Use FF when connecting to cast iron or fiberglass

• Gasket type: RF allows more gasket material flexibility

• Application: Critical industrial systems often require RF, while municipal piping may use FF

For systems involving different flange face types, always match the same facing types on both ends of the connection. Mixing RF with FF can lead to gasket failure and joint leakage.

At sasaflange, we help clients choose the correct flange face based on their technical requirements, industry standards, and operating conditions.

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Conclusion

Understanding the difference between flange raised face vs flat face is key to building safe and effective piping systems. Raised face flanges offer high sealing efficiency for demanding industrial environments, while flat face flanges are ideal for low-pressure systems and connections involving brittle materials.

Choosing the correct flange face type ensures proper gasket performance, system integrity, and long-term reliability. Always consult with a qualified flange supplier or engineer before making a final decision.

For premium flange solutions tailored to your project needs, trust sasaflange — your reliable partner for high-quality flange products and expert guidance in the piping industry.