Flange faces types and function

In this post we will explain all the types and uses of the flange faces

What are flange faces?

Flange face standards define the exact geometry and dimension of the part of the flange that is in contact between faces. As a general rule, the most commonly used are flat face flanges (Flat Face Flanges -FF), raised face flanges (Raised Face Flanges – RF) or ring type joint (Ring Type Joint Flanges -RTJ or R-JF). There are also two less commonly used types of faces: flanges with tongue and groove faces and flanges with male and female faces.

As a general rule of thumb, the smaller the contact surface area between the flange faces, the harder the material of the sealing surface of the gasket and flange. This is because a smaller sealing area means it can take more pressure with less force (pressure = force/area). Harder materials require higher pressure to seal than softer materials, even if surfaces are ground and lapped prior to mating. To achieve higher pressures without the need to apply excessive torque to the bolts, it is better to reduce the size of the contact patch.

For this reason, flat-faced flanges have gaskets that extend from the inside diameter of the flange to the outside diameter of the flange; these types of gaskets are known as “full face” gaskets and have a large contact sealing area. Flanges with raised face have only one gasket in the raised area; these types of joints are known as “flat ring” joints. For ring-type joint flanges, the sealing area is comparatively small and the gasket material comparatively hard (metal).

TYPES OF FACES AND FEATURES

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FLAT FACE – FF

Flat Face (FF) Flanges usenon-metallic gaskets (soft gaskets) and should always have a serrated sealing surface. This type of flange is highly suitable for low-pressure applications and is used for pressure classes 125 and 250.

Gaskets are installed directly on the front sealing face of the flange sheet, i.e. in the same plane as the circle face of bolting The gasket sealing area is from the inner flange diameter to the outer flange diameter. Typical soft gasket materials are typically rated for 100 ⁰C (212 ⁰F) and no more than 20 bar (290 psi) pressure . Because flat faced flanges use such a large sealing area, they are made to fit. Flat Face Flange Gaskets cannot rotate once installed due to bolt hole penetrations through the gasket. Due to the large size of the sealing face, flat-faced flanges are resistant to mechanical distortion (bending, warping, etc.).

Flat face flanges should never be mated with raised face flanges, especially if the raised face flange is made of a harder material.

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FACE WITH RING TYPE JOINT – RTJ

Ring Type Joint (RTJ) Flanges are a variation of the raised face flange design. RTJ flanges are generally used for more severe applications, particularly for high pressure systems and/or high temperature systems (>750 ⁰C / 1382 ⁰F). It is possible to use RTJ flanges in all pressure classes, but they are generally used for class 900 and above.

The difference between an RTJ flange and a raised face flange is the way the seal is obtained. Metal (hard) gaskets are used with RTJ flanges, while raised face gaskets use soft or semi-metal gaskets. There are three main groups of ring type joints: R, RX and BX; we will focus on the type R joint because it is by far the most common.

RTJ type R gaskets are circular in shape with an oval or octagonal shaped profile/body; the octagonal profile obtains the most efficient seal and is the most modern design. A groove is machined into the face of an RTJ flange and the associated gasket is installed in this groove. When the flange is assembled, the two mating faces compress the gasket until it deforms and forms a metal-to-metal seal. If the flange is assembled correctly, the two mating RTJ flanges should not come into physical contact with each other.

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TONGUE AND RIBBED FACE – T&G

Tongue and groove cable ties are made up of two faces. The one with the raised side is called the tongue and the other end is called the groove. The advantage of this is that it self aligns and acts as a reservoir for the adhesive. The tongue and groove have been designed to create a seal between the flange and the pipe as the cones approach the same diameter. Tongue and groove flanges are used for special circumstances, with the main advantage that they can be attached to the pipe without welding.

Stainless steel tongue and groove cable ties are known for their excellent performance, corrosion resistance and durability. These ANSI B16.47 tongue and groove flanges meet the requirements of various industries such as automotive, heavy engineering, railways, and pipeline engineering.

DIN 2512 flange tongue groove dimensions are designed in accordance with DIN 2512. The size is compact and saves space. It is very cost effective and only requires one butt weld to install.

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FACE WITH FEMALE-MALE – M&F

The flanges Female-Macho or Male and Female Flange in English, are very similar to the Tongue Groove, with the difference that they do not have enclosure or limit inside the flange. In this case, the gasket is in direct contact with the fluid unlike the Tab Groove, which is completely enclosed in the flange.

Female-Male Flanges are manufactured in 2 types of series: the Long Male Female series, and the Female Short Male. The difference between the two is the nominal pressure for which they are designed to work.

This type of flange uses spirated metal gaskets, which bear the same name, Male Female Gasket, or are also called “RIR” type.

Female-Male spiral wound gaskets are the same as spiral wound tongue-groove type gaskets, and differ by having an internal ring that prevents  that the coil is sucked or pushed by the pressures carried by the flange.

Likewise, this flange can use soft gaskets made of aramid fibers , graphite reinforced with stainless steel or PTFE , provided they have an inner ring type eyelet made of 316 stainless steel that covers the inside of the joint similar to a casing.

 

FLANGE FACE TYPE
CharacteristicsFlat faceRaised faceRing-Type JointTongue and GrooveMale and female
Sealing areaBigMediumLittleLittleLittle
Face sealing areaInner to outer diameterInside diameter to outside diameter of highlighted areaGroove in the faceGroove in the faceGroove in the face
Pressure rangeLow pressureGeneralGeneral. High pressureSpecific. High pressureSpecific. High pressure
Pressure class125#, 250# All. Up to 2500#.900#All. Up to 2500#.900#
Temperature rangeLow temperaturesGeneralGeneralGeneral. Extreme conditions.General. Extreme conditions.
Type of jointSoft. non metallicNon-metallic, semi-metallic.Hard. Metal-metal.Non-metallic, semi-metallic.Non-metallic, semi-metallic.

In this post we will explain all the types and uses of the flange faces

Types of flange faces and function

What are flange faces?

Flange face standards define the exact geometry and dimension of the part of the flange that is in contact between faces. As a general rule, the most commonly used are flat face flanges (Flat Face Flanges -FF), raised face flanges (Raised Face Flanges – RF) or ring type joint (Ring Type Joint Flanges -RTJ or R-JF). There are also two less commonly used types of faces: flanges with tongue and groove faces and flanges with male and female faces.

As a general rule of thumb, the smaller the contact surface area between the flange faces, the harder the material of the sealing surface of the gasket and flange. This is because a smaller sealing area means it can take more pressure with less force (pressure = force/area). Harder materials require higher pressure to seal than softer materials, even if surfaces are ground and lapped prior to mating. To achieve higher pressures without the need to apply excessive torque to the bolts, it is better to reduce the size of the contact patch.

For this reason, flat-faced flanges have gaskets that extend from the inside diameter of the flange to the outside diameter of the flange strong>; these types of gaskets are known as “full face” gaskets and have a large contact sealing area. Flanges with raised face have only one gasket in the raised area; these types of joints are known as “flat ring” joints. For ring-type joint flanges, the sealing area is comparatively small and the gasket material comparatively hard (metal).

 

TYPES OF FACES AND FEATURES

FLAT FLANGE FACE TYPE – FF

Flat Face (FF) Flanges use non-metallic gaskets (soft gaskets) and should always have a serrated sealing surface. This type of flange is highly suitable for low-pressure applications and is used for pressure classes 125 and 250.

Gaskets are installed directly on the front sealing face of the flange sheet, i.e. in the same plane as the circle face of bolting The gasket sealing area is from the inner flange diameter to the outer flange diameter. Typical soft gasket materials are typically rated for 100 ⁰C (212 ⁰F) and no more than 20 bar (290 psi) pressure . Because flat faced flanges use such a large sealing area, they are made to fit. Flat Face Flange Gaskets cannot rotate once installed due to bolt hole penetrations through the gasket. Due to the large size of the sealing face, flat-faced flanges are resistant to mechanical distortion (bending, warping, etc.).

Flat face flanges should never be mated with raised face flanges, especially if the raised face flange is made of a harder material.

RAISED FLANGE FACE TYPE – RF

A raised-face (RF) flange has a circular-shaped sealing face that projects beyond the plane of the flange’s bolt circle. Raised face flanges are available in all pressure classes and therefore for a wide range of pressure and temperature ratings. RF flanges are the most common type of flange used in the chemical engineering and oil and gas industries.

RF flanges use serrated sealing surfaces with non-metallic or semi-metallic type gaskets. The sealing face of an RF flange is from the inside diameter of the flange to the outside diameter of the raised face. A typical gasket for RF flanges would be a composition graphite steel gasket with a temperature rating of up to 400⁰C (750⁰F) and a nominal pressure up to 250 bar (3625 psi).

The height of the raised face above the bolted face plane is dictated by the flange class and the standard from which it is taken. To the ASME B16.5 standard, Class 150 and 300 steel flanges have a raised face height of 1/16 inch (1, 6mm); Steel flanges exceeding Class 300 use a 1/4-inch (6.4 mm) raised face. In an ideal world, the height of a raised face would increase as the class increases, but this is not the case in most standards; however, it is a logical generalization.

RING TYPE JOINT FLANGE FACE TYPE – RTJ

Ring Type Joint (RTJ) Flanges are a variation of the raised face flange design. RTJ flanges are generally used for more severe applications, particularly for high pressure systems and/or high temperature systems (>750 ⁰C / 1382 ⁰F). It is possible to use RTJ flanges in all pressure classes, but they are generally used for class 900 and above.

The difference between an RTJ flange and a raised face flange is the way the seal is obtained. Metal (hard) gaskets are used with RTJ flanges, while raised face gaskets use soft or semi-metal gaskets. There are three main groups of ring type joints: R, RX and BX; we will focus on the type R joint because it is by far the most common.

RTJ type R gaskets are circular in shape with an oval or octagonal shaped profile/body; the octagonal profile obtains the most efficient seal and is the most modern design. A groove is machined into the face of an RTJ flange and the associated gasket is installed in this groove. When the flange is assembled, the two mating faces compress the gasket until it deforms and forms a metal-to-metal seal. If the flange is assembled correctly, the two mating RTJ flanges should not come into physical contact with each other.

TONGUE AND GROOVED FLANGE FACE TYPE – T&G

Tongue and groove cable ties are made up of two faces. The one with the raised side is called the tongue and the other end is called the groove. The advantage of this is that it self aligns and acts as a reservoir for the adhesive. The tongue and groove have been designed to create a seal between the flange and the pipe as the cones approach the same diameter. Tongue and groove flanges are used for special circumstances, with the main advantage that they can be attached to the pipe without welding.

Stainless steel tongue and groove cable ties are known for their excellent performance, corrosion resistance and durability. These ANSI B16.47 tongue and groove flanges meet the requirements of various industries such as automotive, heavy engineering, railways, and pipeline engineering.

DIN 2512 flange tongue groove dimensions are designed according to DIN 2512. The size is compact and saves space. It is very cost effective and only requires one butt weld to install.

FEMALE-MALE FLANGE FACE TYPE – M&F

The flanges Female-Macho or Male and Female Flange in English, are very similar to the Tongue Groove, with the difference that they do not have enclosure or limit inside the flange. In this case, the gasket is in direct contact with the fluid unlike the Tab Groove, which is completely enclosed in the flange.

Female-Male Flanges are manufactured in 2 types of series: the Long Male Female series, and the Female Short Male. The difference between the two is the nominal pressure for which they are designed to work.

This type of flange uses spirated metal gaskets, which bear the same name, Male Female Gasket, or are also called “RIR” type.

Female-Male spiral wound gaskets are the same as spiral wound tongue-groove type gaskets, and differ by having an internal ring that prevents strong> that the coil is sucked or pushed by the pressures carried by the flange.

Likewise, this flange can use soft gaskets made of aramid fibers , graphite reinforced with stainless steel or PTFE , provided they have an inner ring type eyelet made of 316 stainless steel that covers the inside of the joint similar to a casing.

FLANGE FACE TYPE
CharacteristicsFlat faceRaised faceRing-Type JointTongue and GrooveMale and female
Sealing areaBigMediumLittleLittleLittle
Face sealing areaInner to outer diameterInside diameter to outside diameter of highlighted areaGroove in the faceGroove in the faceGroove in the face
Pressure rangeLow pressureGeneralGeneral. High pressureSpecific. High pressureSpecific. High pressure
Pressure class125#, 250# All. Up to 2500#.900#All. Up to 2500#.900#
Temperature rangeLow temperaturesGeneralGeneralGeneral. Extreme conditions.General. Extreme conditions.
Type of jointSoft. non metallicNon-metallic, semi-metallic.Hard. Metal-metal.Non-metallic, semi-metallic.Non-metallic, semi-metallic.

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