Types and Applications of Flanges

Slip-On Flange

The Flange is slipped over the Pipe and then welded both inside and outside to provide sufficient strength and prevent leakage. This Flange is used in preference to Weld Necks by many users because of its lower cost and the fact that less accuracy is required when cutting pipe to length.

Blind Flanges

This is a Flange without a bore and is used to shut off a Piping system or vessel opening. It also permits easy access to vessels or Piping systems for inspection purposes. Blind Flanges can be supplied with or without Hubs at the manufacturers option.

Weld-Neck Flanges

This is designed to be joned to a Piping system by Bun Welding. It is relatively expensive because of its long neck, but is preferred for High Stress applications. The Neck, or Hub, transmits stresses to the Pioe, reducing stress concentrations at the base of the Flange. The gradual transition of thickness from the base of the Hub to the wall thickness at the Bun Weld, provides important reinforcement of the Flange. The bore of the Flange matches the bore of the Pipe, reducing turbulence and erosion.

Threaded Flanges

This is similar to a Slip-On Flange in outline, but the bore is threaded, thus enabling assembly without welding. This obviously limits its applications to relatively low pressure Piping systems. The Flange may be welded around the joint after assembly, but this is not considered a satisfactory method of increasing its applications.

Socket Weld Flanges

This is similar to a Slip-On Flange in outline, but the bore is counter-bored to accept Pipe. The diameter of the remaining bore is the same as the inside diameter of the Pipe. The Flange is attached to the Pipe by a Fillet Weld around the Hub of the Flange. An optional interval weld may be applied in High stress applications. Ifs biggest use is in High Pressure Systems such as Hydraulic and Steam Lines.

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Flange : Definition

A Flange is a forged or cast ring of Steel designed to connect sections of Pipe or join Pipe to a pressure vessel, valve, pump or any other integral Flanged assembly.
Flanges are joined to each other by bolting and joined to the Piping system by welding or threading.

The basic tyries of Flanges are Slip On. Blind, Weld Neck. Threaded. Socket Weld. Lap Joint and Orifice,

Flanges are designed to the following pressure ratings: 150 lb. 300 lb., 400 lb., 600 lb.. 900 lb., 1500 lb. and 2500 lb.



The most common facings machined on Flanges are:
(a) Raised face, for 150 lb. and 300 lb., ‘ for 400 lb. and heavier.
(b) Flat Face, for 150 lb. and 300 lb. only, other may be Flat face on request.
(c) Ring Type Joint, may be applied to all pressure ratings

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Fitting : Defenition

A pipe fitting is defined as a part, used in a piping system to change direction or function, which is mechanically joined to the system. Probably the simplest way to achieve this end would be to bend the pipe in the direction required, but this process will stretch and thin the outer wall whilst tnickening and wrinkling the inner wall. This results in flow resistance and accelerated wall erosion.

A second method sometimes used is a mitred joint, where pipes are cut to the correct angle and welded together to achieve the desired change. Whilst the cross-section area and wall thickness are maintained a great deal of efficiency is lost due to friction and turbulence resulting from the severe changes in direction; for example a single-mitred bend offers about six times the resistance of a swept elbow.


For these reasons swept fittings are preferred on most piping systems, particularly where internal pressure, flow and corrosion are major considerations.

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