What is Flange: Flanges are generally used to connect with the pipe, pipe fittings, valves, and other specialty items (Strainer) to complete the piping system. Joining Connection by Flange is mostly used after welding and is considered as a reliable technique.
Flange connections typically comprise three parts:
- Pipe flanges
- Gasket (for leakage protection)
- Bolted connection
Design Codes: Standards that are used for the design of flanges are classified as:
- For the flange size ½” to 24” NPS dimension, refer design code standard ASME B16.5
- For the flange size ½” to 60” NPS dimension, refer design code standard ASME B16.47
Material Selection: Material selection for flanges depends on the Design condition applicable, in general cases C.S (SA 105) and S.S (SA 182). Other types of material for flanges are Monel, Inconel, chrome Moly and list continues.
Types of Flange: Common types of flanges used in industrial applications are listed below:
Weld Neck Flange (WN): Weld neck flange construction consists of a long tapered hub for pipe welding during the joining procedure. Single penetration butt weld (V shape) is used for flange connection. For connection purpose dimension of the flange (Nominal pipe size and schedule) is matching with the dimension of the pipe to be connected. Refer to the below-attached figure for the weld neck type flange.
Key benefits of Weld neck flange:
- Suitable for low and high-temperature applications
- Long tapered helps in the distribution of stress uniformly between pipe and weld neck flange.
- Used in all pressure class applications.
- Due to the absence of Pressure drop throughout the flange, thus there is no restriction for the fluid flowing in the piping system.
Long Weld Neck (LWN): Long weld neck flanges are similar to the Weld neck type flanges except the tapered hub extension becomes slightly longer. Long weld neck flanges are available in equal (E) and heavy barrel (HB). Generally, long weld neck flanges are used for pressure vessels, columns, etc. Refer to the below figure for the long weld neck-type flange.
Key benefits of long weld neck flange:
- Suitable for High-pressure applications.
- Mechanically strong and reliable.
- Easy to install and long neck enables the integrity of welds through RT (radiographic test) purpose.
Slip-on flange: procedure for connection Slip-on flange by inserting the pipe into the cavity of the flange and filler material is required on both sides of the flange. The outside bore of the flange is larger than the pipe size, for proper insertion of the pipe and fillet welding on the joints. Slip-on flanges have a shorter life than weld neck flanges. Refer to the below figure for the slip-on type flange.
Key benefits of Slip flange:
- Suitable for low-pressure applications.
- Leakage chances are quite less.
- Easy to align during installation, low installation cost.
Socket weld flanges: Joining of the flange to the pipe with the help of fillet weld, flanges consist of sockets into which the pipe is inserted and fitted. Refer to the attached figure for the Socket weld flange.
Key benefits of Socket weld flange:
- Applicable for high-pressure applications.
- Easy to align.
- Minimum chances of leakage in comparison to threaded fittings.
Threaded flange: Threaded flange consists of a female thread so that the male thread of the pipe can insert into the female thread. Threaded-type flanges do not require welding for joint connection. Refer to the attached figure for reference.
Advantage of threaded flange:
- Installation is possible where welding is not possible because of the explosive atmosphere.
- Do not require welding which makes threaded flange time and cost-saving.
- Possibilities of leakage.
Blind flange: Blind flange does not have a hub and center hole. The blind flange is typically used to close the vessel or open the end of the piping system.
Advantages of blind flange:
- Installation for cleaning and maintenance purposes.
- Suitable for high-pressure applications.
Types of flange face: Flanges are designed according to the type of flange face. Flange faces are the part where the gasket is placed. Three types are Flat Face, Raised Face (RF), and Ring Type Joint Face (RTJ).
Please refer below Image for flange face understanding…
- Flat Face: In the flat face of the flange has a large sealing area. Used in low-pressure and temperature applications up to 150# Class. Non-metallic – soft gaskets are used.
- Raised Face (RF): Raised face in which face is based on the internal diameter whereas raised face is the outer diameter. RF flanges in which the Sealing area is reduced in comparison to the flat face. Raised face flanges can be used for intermediate pressure and temperature application up to 150 – 900#class. Non-metallic – soft or semi-metallic gaskets are used.
- Ring Type Joint: The sealing area for RTJ type face is smallest in comparison to other faces it is because of the groove on the flange face. RTJ type flanges used for High pressure – Temperature application class greater than 900# class. Hard metallic gaskets are used.