How many types of flange faces

What is flange face?

The process of flange facing (or flange refacing) involves the machining of flange mating surfaces so that they they produce a tight, leak-proof seal when assembled.

The frequently used term “flange face” refers to the shape of the flange surface area (i.e., the area where the gaskets are positioned and the two mating flanges are tightened). When making a flanged connection, operators should use two flanges with the same type of face, and never mate flanges with different surface areas, such as a flat face with a raised face or a ring joint with a male and female (in this case, the joint would not seal properly and leak).

Industry standards for flange facing
The American Society of Mechanical Engineers (ASME) are the go-to organisation for many standards for mechanical engineering around the world. They have the set the standards to which many engineers work to for flange facing surface finishes.
ASME set the standards for flange face surface finish types through the ANSI accredited ASME Standard B 16.5 ensuring all gasket and flange fittings are consistent and fit for purpose allowing a high quality seal.

Different types of flange faces are used as the contact surfaces to seat the sealing gasket material. ASME B16.5 and B16.47 define various types of flange facings, including the raised face, the large male and female facings which have identical dimensions to provide a relatively large contact area. The ASME B16.5 and ASME B16.47 norms mention a few different types of flange face types:

  • Flat face (“FF”)
  • Raised face (“RF”)
  • Ring joint (“RTJ”)
  • Lap joint
  • Male and female (“M&F”)
  • Large and small tongue-and-groove (“T&G”)

TYPES OF FLANGE FACE FINISH

FLAT FACE FLANGE (FF)

     1505913188 7834 FlatfaceflangeFF - How many types of flange faces

Flat face flanges (FF flanges) have a contact surface at the same height of the bolting line of the flange. Flat flanges should never be bolted to RF flanges according to ASME B31.1. Generally, soft gaskets are used for this type of flange surface area (flat, full face gaskets).

RAISED FACE FLANGE (RF)

    1505913188 2854 RFraisedfaceflange - How many types of flange faces

Raised face flanges (RF flanges) are widely used for oil & gas pipelines and are easy to recognize as the gasket surface is positioned above the bolting line of the flange. RF face flanges are compatible with a wide range of gaskets, from the flat cut types to the metallic and semi-metallic types (jacketed gaskets and spiral wound gaskets). The main goal of raised face flanges is to concentrate the contact pressure on a small area of the flange thus increasing the strength of the seal.

The height of the raised surface depends on the flange pressure rating and is defined by ASME B16.5 (for pressure classes 150 and 300, the height is 1.6 mm or 1/16 inch, whereas, for classes from 400 to 2500, the raised face height is approximately 6.4 mm, or 1/4 inch). The most common flange face finish for ASME B16.5 RF flanges is 125 to 250 micron Ra (3 to 6 micron Ra).

RING JOINT FLANGES (RTJ)

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Ring joint type flanges (RTJ) are used when a metal-to-metal seal between the mating flanges is required (high-pressure, as 600# and higher, and high-temperature, from 800 F° upward, applications). RTJ faced flanges have circular grooves where the ring joint gaskets (RTJ type) is accommodated. As the two RTJ flanges are bolted together and tightened, the applied bolting force compresses and deforms the metallic gaskets inside the grooves of the flanges and creates a very tight metal-to-metal seal (obviously, for this to happen, the material of the ring joint gaskets has to be softer than the material of the flanges).

RTJ flanges can be sealed by RTJ gaskets of different styles (R, RX, BX) and profiles (example: octagonal/oval for the R style). The most common RTJ gasket is the R style with an octagonal section, as it ensures a very strong seal (the oval section is an older type). A “flat groove” design, however, accepts both RTJ gaskets with an octagonal and oval section.

TONGUE AND GROOVE FLANGES (T AND G)

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Two tongue and groove flanges (T&G face) perfectly fit one into the other: one flange has a raised ring, the other a groove and they can be mated easily (the tongue enters the groove and seals the joint). T&G faced flanges are standardized in both large and small types.

MALE AND FEMALE FLANGES (M AND F)

1505913189 7522 M26Fmaleandfemaleflanges 300x107 - How many types of flange faces

Similarly to tongue and groove flanges, male and female flanges (M&F face type) match one to the other as well. One flange has an area extended beyond its face area, this is the male flange, whereas the other flange has a matching depression machined on the facing surface, and is the female flange. The female face is 3/16” deep, while the male face is 1/4″ high, and both of them are smooth finished. The outer diameter of the female face retains the gasket.

Advantages and disadvantages of T&G and M&F flange faces

ADVANTAGES:
Better sealing properties, more precise location and exact compression af sealing material, utilization of other, more suitable sealing and spezialized sealing material (O-rings).

DISADVANTAGES:
Commercial availabillity and cost. Normal raised faced is far more common and ready available both regarding Valves, flanges and sealing material. Another complexity is that some rigid rules must be applied to the piping design. Do you order Valves to be female end both sides, or on one side maybe, in which case do you point all male ends in the flow direction, or what. Same applies to any flanged joint / vessel connection of course.

Flange facing vs milling
Milling is the process of machining a surface using a multi-point cutting tool. While a milling machine is capable of getting a smooth surface finishes and cutting in a circular stroke (such as our range of orbital milling machines), they are not capable of getting the required surface finish needed to meet the ASME B 16.5 standard.
In order to reach some of the finishes required to meet ASME B 16.5, the flange should be machined using a single point cutting tool. The single point tool enables on-site machinists to achieve the grooves required to created surface finishes suitable of creating a strong leak-proof seal for gasket flanges, such as the serrated surface (see image). As such, single point cutting tools will be used with a flange facing machine.
For users that are happy simply to produce a flat finish on the flange (with no defined machine profile), machines can be supplied with milling heads rather than single-point cutters. This dramatically reduces the machining time which has made flange facing machines an ideal tool for use in wind turbine production.

Source: China Flanges Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com
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Reference:

  • http://www.wermac.org/flanges/flanges_raised-face_flat-face_ring-type-joint.html
  • https://www.yaang.com/types-of-flange-face.html

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