3 Common Flange Sealing Faces
author: www.qishine.com
2026-03-05
Flange Sealing Face Selection Guide: A Comprehensive Analysis of FF, RF, and RTJ
In the world of pipeline connections, flanges act like joints, and the sealing face is the key to ensuring the system's "blood" does not leak. Choosing the right sealing face is not only crucial for the system's integrity but also directly impacts production safety and operational efficiency. Today, let's quickly explore the three most common flange sealing faces: FF, RF, and RTJ.
Flange Sealing Face: FF(flat) vs RF(raised) vs RTJ(circular groove)
1. Shape Characteristics of the Three Sealing Faces: Design Determines Function
1.1 FF Face (Flat Face Flange)
As the name suggests, the entire flange face is completely flat, without any protrusions or grooves. This simple design makes it the most basic member of the flange family. Its flat characteristic means it has the largest contact area, but it also imposes special requirements on sealing materials.
1.1 FF Face (Flat Face Flange)
As the name suggests, the entire flange face is completely flat, without any protrusions or grooves. This simple design makes it the most basic member of the flange family. Its flat characteristic means it has the largest contact area, but it also imposes special requirements on sealing materials.
Which Flange Face is Right for each Project?
1.2 RF Face (Raised Face Flange)
This is the most common type in industrial applications. It features a raised ring on the flange face, typically 1/6 inch (approximately 1.5 mm) in height. This raised part concentrates the sealing pressure, allowing the gasket to generate higher sealing force within a relatively small area, thereby improving sealing effectiveness.
This is the most common type in industrial applications. It features a raised ring on the flange face, typically 1/6 inch (approximately 1.5 mm) in height. This raised part concentrates the sealing pressure, allowing the gasket to generate higher sealing force within a relatively small area, thereby improving sealing effectiveness.
The RF flange has a convex surface.
1.3 RTJ Face (Ring Type Joint Flange)
This design adopts a completely different philosophy. The flange face is machined with precise ring grooves, typically with trapezoidal or oval cross-sections. It is paired with a metal ring gasket. During installation, the gasket embeds into the groove and undergoes plastic deformation under bolt tightening pressure, filling the entire ring groove space to form a hard metal-to-metal seal.
This design adopts a completely different philosophy. The flange face is machined with precise ring grooves, typically with trapezoidal or oval cross-sections. It is paired with a metal ring gasket. During installation, the gasket embeds into the groove and undergoes plastic deformation under bolt tightening pressure, filling the entire ring groove space to form a hard metal-to-metal seal.
The RTJ Flange has a Groove Ring
2. Installation Method Comparison: From Flat Alignment to Precise Embedding
2.1 FF Flange Installation
This is the most straightforward and simple method: place the gasket between the two flange faces and tighten the bolts evenly. However, due to the large contact area, special attention must be paid to the bolt tightening sequence and torque control to ensure even pressure distribution and avoid leaks caused by uneven force.
2.1 FF Flange Installation
This is the most straightforward and simple method: place the gasket between the two flange faces and tighten the bolts evenly. However, due to the large contact area, special attention must be paid to the bolt tightening sequence and torque control to ensure even pressure distribution and avoid leaks caused by uneven force.
Flat Face Flange VS Raised Face Flange
2.2 RF Flange Installation
This method leverages the advantage of the raised face design: the gasket is placed on the raised环形 surface. When bolts are tightened, pressure concentrates on the raised area, making it easier for the gasket to compress and deform to form an effective seal. During installation, ensure the gasket's inner diameter is slightly larger than the pipe's inner diameter, while its outer diameter is slightly smaller than the bolt hole circle diameter.
This method leverages the advantage of the raised face design: the gasket is placed on the raised环形 surface. When bolts are tightened, pressure concentrates on the raised area, making it easier for the gasket to compress and deform to form an effective seal. During installation, ensure the gasket's inner diameter is slightly larger than the pipe's inner diameter, while its outer diameter is slightly smaller than the bolt hole circle diameter.
2.3 RTJ Flange Installation
This requires the highest precision and skill. The metal ring gasket (usually soft iron or stainless steel) must precisely match the groove dimensions. During installation, first place the RTJ Flange gasket into the groove of one flange, then align the other flange and tighten the bolts slowly and evenly. During tightening, the metal gasket undergoes plastic deformation, filling every corner of the groove to form a reliable metal seal. This process must strictly follow the torque sequence, as over-tightening may cause excessive gasket deformation, adversely affecting the seal.
This requires the highest precision and skill. The metal ring gasket (usually soft iron or stainless steel) must precisely match the groove dimensions. During installation, first place the RTJ Flange gasket into the groove of one flange, then align the other flange and tighten the bolts slowly and evenly. During tightening, the metal gasket undergoes plastic deformation, filling every corner of the groove to form a reliable metal seal. This process must strictly follow the torque sequence, as over-tightening may cause excessive gasket deformation, adversely affecting the seal.
How is the RTJ flange installed?
3. Applicable Environments: The Art of Selection Matching Operational Requirements
3.1 FF Flanges
Most suitable for low-pressure, low-temperature, non-critical applications, commonly found in cast iron flanges or low-pressure stainless steel flanges. Their flat design makes them particularly suitable for use with full-face gaskets, such as rubber gaskets or compressed non-asbestos fiber gaskets. However, due to their relatively low sealing pressure, they are not recommended for high-temperature, high-pressure, or hazardous media.
3.1 FF Flanges
Most suitable for low-pressure, low-temperature, non-critical applications, commonly found in cast iron flanges or low-pressure stainless steel flanges. Their flat design makes them particularly suitable for use with full-face gaskets, such as rubber gaskets or compressed non-asbestos fiber gaskets. However, due to their relatively low sealing pressure, they are not recommended for high-temperature, high-pressure, or hazardous media.
3.2 RF Flanges
These are the true "all-rounders," suitable for most industrial applications, including medium- to high-pressure systems. Their raised face design improves sealing efficiency and can be paired with various gasket materials, such as flexible graphite, polytetrafluoroethylene (PTFE), or metal wound gaskets. RF flanges are widely used in chemical, petroleum, natural gas, and power industries, serving as the backbone of industrial piping systems.
These are the true "all-rounders," suitable for most industrial applications, including medium- to high-pressure systems. Their raised face design improves sealing efficiency and can be paired with various gasket materials, such as flexible graphite, polytetrafluoroethylene (PTFE), or metal wound gaskets. RF flanges are widely used in chemical, petroleum, natural gas, and power industries, serving as the backbone of industrial piping systems.
3.3 RTJ Flanges
Designed specifically for harsh conditions: high-temperature and high-pressure systems, hazardous media, or critical applications requiring zero leakage. The metal-to-metal seal design enables them to withstand extremely high pressures and temperature fluctuations. They are commonly found in high-pressure petrochemical units, high-temperature steam systems, and offshore platforms. Their initial cost is higher, and installation requirements are strict, but their reliability and safety under extreme conditions are irreplaceable.
Designed specifically for harsh conditions: high-temperature and high-pressure systems, hazardous media, or critical applications requiring zero leakage. The metal-to-metal seal design enables them to withstand extremely high pressures and temperature fluctuations. They are commonly found in high-pressure petrochemical units, high-temperature steam systems, and offshore platforms. Their initial cost is higher, and installation requirements are strict, but their reliability and safety under extreme conditions are irreplaceable.
4. Summary: Correct Selection for Safe Operation
Choosing a flange sealing face is an art of balance: it requires comprehensive consideration of pressure rating, temperature range, media characteristics, cost budget, and installation conditions.
Choosing a flange sealing face is an art of balance: it requires comprehensive consideration of pressure rating, temperature range, media characteristics, cost budget, and installation conditions.
For low-pressure, ambient-temperature, non-critical systems, FF flanges provide an economical and practical solution. For most industrial applications, RF flanges are the preferred choice, offering the best balance between performance and cost. For extreme conditions involving high temperature and pressure, hazardous media, or zero-leakage requirements, RTJ flanges are the unequivocal choice to ensure system safety.
Mastering the characteristics of these three basic sealing faces is the first step toward becoming a pipeline connection expert. The right choice not only enhances system reliability but also significantly reduces maintenance costs and safety risks.
If you wish to delve deeper into more details about flange connections, you can contact our technical team.
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Email: qishine@qishine.com
Tel: 0592-5225595
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