Types of Flanges

flange is a method of connecting pipes, valves, pumps and other equipment to form a piping system. It also provides easy access for cleaning, inspection or modification. Flanges are usually welded or screwed. Flanged joints are made by bolting together two flanges with a gasket between them to provide a seal.

Type of flanges

Types of Flanges

  1. Welded neck flange
  2. Slip-on flange
  3. Screwed flange
  4. Lap joint flange
  5. Blind flange

1. Welded neck flange: 

It is used for high temperature, high-pressure operation or where there is wide fluctuation in pressure and temperature. These flanges are useful for handling costly, hazardous, flammable, explosive fluids because failure or leakage of a flange joint can prove disastrous for the plant. The various dimensions to be specified for a welded neck flange are:
welded neck flange

  • (a) The outside diameter of the flange.
  • (B) Minimum flange thickness.
  • (c) The outside diameter of the raised face.
  • (D) The diameter of the hub at the base.
  • (E) The diameter of hub at point of welding.
  • (F) Length through the hub.
  • (G) The diameter of hole.
  • (H) The diameter of the bolts.
  • (I) Bolt circle diameter.
  • (J) No. of holes.

2. Slip-on flange: 

It is widely used because of ease of alignment in welding. Its cost is also less. The flange is useful for moderate service process operations where temperature, pressure changes, vibrations, shocks are not severe. Its strength is around 70% as that of the welded neck flange and its fatigue life is nearly 1/3 as compared to a welded neck flange

slip on flange

3.Screwed flange: 

The screwed flange can be connected to threaded pipes without welding. It is not useful for operations that involve bending or thermal cycles, because there is always the possibility of leakage through the threaded joint. It can be used with high alloy steel for high-pressure operations satisfactorily because welding of high alloy steel is difficult.
screwed flange

4. Lap joint flange: 

Lap joint flange is usually used with a lap-joint & hub. These are useful where temperature, pressure changes, vibrations, and shocks are not severe. These flanges are not useful where severe bending stresses exist. These flanges have only about 10% of the fatigue life as compared to welded neck flange. For these flanges, bolt holes can be easily aligned and this simplifies the installation of large diameter vessels. These flanges are useful for operations where the vessel is frequently opened up for cleaning and inspection.
lapped flange

5. Blind flanges:

Blind flanges are very commonly used for the pressure vessel openings e.g. hand holes and inspection parts. These are also used at the ends of pipes and valves. These flanges are capable of handling high bending stresses but do not have to absorb stresses due to thermal expansion. These flanges are used for heat exchangers. A blind flange is a flat plate. It is simply supported at the gasket load reaction line. It is loaded by a gasket seating load and a combination of gasket seating load, and uniform pressure load.

Blind flange

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