Raised Face vs Flat Face Flange: Know the Differences

When choosing between raised face vs flat face flanges, the key differences lie in their design, performance, and applications. A raised face flange is suited for high-pressure, high-temperature environments, while a flat face flange is better for lower-pressure systems. 

However, these distinctions aren’t the only factors to consider—there’s more to selecting the right flange than meets the eye. Let’s explore the essential details of each type to help you make an informed decision.

What is a Flange Face?

A flange face refers to the surface area of the flange where the sealing element (gasket) is placed. It plays a crucial role in ensuring a proper seal and preventing leaks in a piping system.

The design of the flange face impacts how the flange can contain pressure. It also defines how well it can maintain a strong and secure connection.

Two of the most common types of flange faces are the raised face flange and the flat face flange. Both follow standard finishes outlined by ASME B16.5 and ASME B16.47, which specify a 125-250 RMS (Root Mean Square) surface finish.

Each of these is designed for different operating conditions and requirements. Choosing between these two depends on factors like pressure, temperature, and the type of piping system.

Understanding a Raise Face Flange

The raised face flange (RF flange) is one of the most widely used flange types. You can typically find this type of flange in industries that require high-pressure and high-temperature containment.

This flange design features a raised surface around the bore. For smaller flanges, the raise is typically 1/16 inch. On the other hand, the raise of larger ones is 1/4 inch.

Advantages of Raised Face Flanges:

• Enhanced Sealing: The raised area compresses the gasket more effectively, providing a stronger seal, especially in high-pressure systems.
• Pressure and Temperature Capability: Raised face flanges are designed to handle high-pressure and high-temperature environments, making them ideal for industries like oil and gas, petrochemical plants, and power generation.
• Gasket Size: The raised surface allows for the use of smaller, more specialized gaskets, such as spiral wound or metallic gaskets, which are well-suited for industrial use.

Applications of Raised Face Flanges:

• High-Pressure Environments: Industries such as oil and gas, petrochemicals, and power generation often use raised face flanges. The reason for this is that they are designed to handle extreme pressure and temperature.
• Industrial Piping: In scenarios where piping systems are subjected to significant stress, raised face flanges provide a secure, leak-proof connection.

In the debate of raised face flange vs flat face, the raised face option is more suitable when superior sealing and higher pressure tolerance are required. However, its higher cost and installation complexity must also be considered.

Understanding a Flat Face Flange

A flat face flange has a completely flat surface, which contrasts with the raised face design. This type of flange is generally used in lower-pressure applications. The flat face is most common in systems where materials like cast iron or plastic are used.

Advantages of Flat Face Flanges:

• Cost-Effective: Flat-face flanges are typically less expensive than raised-face flanges due to their simpler design and the use of full-face gaskets.
• Even Load Distribution: Since the entire surface of the flange face is flat, it distributes the load more evenly across the gasket, which is especially beneficial for softer materials like ductile iron or plastic piping.

Applications of Flat Face Flanges:

• Low-Pressure Systems: Flat-face flanges are ideal for plumbing, waterworks, and HVAC systems where the risk of leaks is lower and the pressure is moderate.
• Material-Sensitive Systems: Flat-face flanges are preferable when the connecting pipes or valves are made from materials like cast iron, which are prone to warping under high tension.

In flat face flange vs raised face comparisons, flat face flanges are typically used in less demanding environments, particularly where budget constraints or lower pressure and temperature levels are factors.

So, Which Should You Choose?

When deciding between a raised face vs flat face flange, several factors should be taken into account, including pressure, temperature, material compatibility, and cost.

Pressure and Temperature:

• Raised Face Flanges: A raised face flange is the best option if the piping system operates under high pressure or high temperature. Its design enhances the sealing capability, reducing the risk of leaks in demanding environments.
• Flat Face Flanges: For low-pressure, low-temperature systems, especially those made of ductile iron or cast iron, flat face flanges are more suitable. These materials are prone to damage under high bolt pressure, and the flat face provides an even load distribution, preventing warping or cracking.

Cost Considerations:

• Flat Face Flanges: More cost-effective and easier to install, flat face flanges are ideal for projects where budget constraints are a priority and the system does not require high-pressure resistance.
• Raised Face Flanges: While more expensive due to the smaller gasket and enhanced sealing capabilities, raised face flanges are necessary in high-stress applications where safety and reliability are paramount.

Material Compatibility:

• Flat Face Flanges: These are ideal for systems using materials such as cast iron or plastic, where the risk of over-tightening and warping is significant.
• Raised Face Flanges: These are more commonly used with metallic systems and are capable of withstanding more intense environments where higher sealing performance is required.

Gasket Compatibility:

• Raised Face Flange: Uses smaller, more specialized gaskets, which offer better performance in high-pressure systems.
• Flat Face Flange: Requires full-face gaskets, which distribute the sealing force across a wider surface area, offering protection against leaks in low-pressure applications.

Conclusion

In summary, the raised face flange is ideal for high-pressure, high-temperature environments. Their design offers enhanced sealing and durability. The flat face flange provides a cost-effective solution for lower-pressure systems. Each of these flanges has its strengths. 

You must consider the application, pressure, temperature, and material compatibility to determine which flange is best for your requirements.For those seeking reliable, high-quality raised face flanges, Longan Flange is a trusted manufacturer, providing durable, precision-engineered flanges for various industrial needs.

References:

Flange Face – an overview (1)

Calculations and Evaluation of Sealing Performance in Comparison of Raised Face and Flat Face Flange Connections (2)