By When designing or maintaining an industrial piping system, choosing the right flange is only part of the decision. Flange facing is equally important because it determines how the flange connects with the gasket and mating flange to create a reliable, leak-resistant joint.
Three of the most commonly used flange facing types are Raised Face (RF), Flat Face (FF), and Ring Type Joint (RTJ). Each has different characteristics and is designed for specific pressure, temperature, material, and application requirements.
So, which flange facing should you choose? The answer depends on your operating conditions and piping requirements.
What Is Flange Facing?
Flange facing refers to the machined surface of a flange where the gasket sits and the connection is sealed.
The facing must work correctly with the corresponding flange and gasket. An unsuitable combination can result in poor sealing, leakage, flange damage, or premature maintenance issues.
The three commonly used options are:
- Raised Face (RF)
- Flat Face (FF)
- Ring Type Joint (RTJ)
Let’s understand how each one works.
1. Raised Face (RF) Flanges
Raised Face is one of the most widely used flange facing types across industrial piping systems.
As the name suggests, the gasket sealing area is slightly raised above the main flange surface. When the bolts are tightened, pressure is concentrated on the raised area, helping compress the gasket and create an effective seal.
Where Are RF Flanges Used?
RF flanges are commonly found in:
- Oil and gas facilities
- Chemical processing plants
- Petrochemical industries
- Power plants
- General industrial piping
- Water and process systems
They are available in a wide range of pressure classes and materials, making them suitable for many standard industrial applications.
Advantages of RF Flanges
RF flanges offer a practical balance between sealing performance, availability, and cost. They are also relatively straightforward to install and maintain.
However, the gasket selection must match the flange facing and operating conditions. The flange surface finish is also important for achieving reliable sealing.
2. Flat Face (FF) Flanges
A Flat Face flange has a completely flat sealing surface. Unlike an RF flange, there is no raised sealing area.
FF flanges are often used where the piping components are made from materials or equipment that could be damaged by the concentrated bolt loads associated with a raised face.
Where Are FF Flanges Used?
Flat Face flanges can commonly be found in:
- Lower-pressure piping systems
- Water treatment applications
- Cast iron piping
- Certain process systems
- Applications where equipment requires a flat mating surface
Why Choose a Flat Face Flange?
The flat design allows the gasket to cover the full face of the flange. This can help distribute the compressive load over a larger area.
However, FF and RF flanges should not be mixed casually. The flange arrangement, gasket, bolting, and equipment design should be evaluated together to ensure the connection is suitable.
3. Ring Type Joint (RTJ) Flanges
When operating conditions become particularly demanding, Ring Type Joint (RTJ) flanges are often considered.
Instead of using a conventional flat gasket, RTJ flanges have a specially machined groove that accommodates a metallic ring gasket. When the connection is properly assembled and tightened, the ring is compressed within the groove to create a highly reliable seal.
Where Are RTJ Flanges Used?
RTJ configurations are commonly associated with demanding applications such as:
- High-pressure oil and gas systems
- High-temperature applications
- Refineries
- Petrochemical facilities
- Offshore installations
- Critical process piping
RTJ flanges are particularly useful when leakage prevention is critical and the piping system operates under high pressure and temperature.
Advantages of RTJ Flanges
Their metallic sealing arrangement can provide excellent sealing performance under severe service conditions.
However, RTJ connections require greater attention during installation. The ring groove and sealing ring must be correctly matched, and the sealing surfaces should be protected from damage.
RF vs FF vs RTJ: Quick Comparison
| Feature | RF | FF | RTJ |
| Sealing Surface | Raised | Flat | Ring groove |
| Typical Applications | General industrial | Lower-pressure/special applications | High-pressure & critical service |
| Gasket Type | Various | Full-face gaskets commonly used | Metallic ring gasket |
| Pressure Capability | Wide range | Generally lower-demand applications | Excellent for severe service |
| Installation | Relatively simple | Relatively simple | Requires greater precision |
| Cost | Moderate | Generally economical | Higher |
| Maintenance | Straightforward | Straightforward | More specialised |
So, Which Flange Facing Should You Choose?
There is no single flange facing that is best for every application.
Choose RF When:
You need a versatile flange facing for a standard industrial piping application with moderate to high pressure and temperature requirements. RF is often a practical choice for general process and industrial systems.
Choose FF When:
You are working with compatible equipment or piping where a flat mating surface is required, particularly in lower-pressure applications or systems where concentrated loads could present a concern.
Choose RTJ When:
You are dealing with high-pressure, high-temperature, or critical applications where maximum sealing reliability is a priority and the system is designed specifically for RTJ connections.
Factors to Consider Before Selecting a Flange Facing
The flange facing should never be selected in isolation. Consider:
Operating pressure: Higher pressures may require specialised sealing arrangements.
Operating temperature: Temperature can affect gasket performance and material behaviour.
Fluid characteristics: Corrosive, toxic, flammable, or hazardous media may require enhanced sealing reliability.
Flange material: The material and mechanical properties of connected components must be considered.
Gasket compatibility: The gasket must be suitable for the selected facing and process conditions.
Applicable standards: Flanges should comply with the relevant dimensional, pressure, material, and manufacturing standards for the application.
Installation requirements: Some flange types require more precise assembly procedures and specialised inspection.
The Right Facing Makes a Difference
Flange facing may look like a small detail, but it has a major role in the performance of a piping connection. RF, FF, and RTJ each have their place, and choosing between them requires an understanding of the pressure, temperature, fluid, equipment, and sealing requirements of the system.
For most general industrial applications, RF offers excellent versatility. FF can be suitable for specific lower-pressure or compatible equipment applications, while RTJ is designed for demanding services where sealing performance is critical.
Ultimately, the best choice is not simply the most expensive or most robust option. It is the flange facing that matches the actual operating conditions and engineering requirements of the piping system.
When in doubt, consult the applicable piping standards and work with a qualified flange and piping specialist before finalising the selection.