A flange is a forged or cast steel ring designed to mechanically connect sections of pipe or joint pipe to a pressure vessel, pump, valve, or any other piece of equipment.

Types of pipe flanges: 

Standard types of flanges

The type of flange used for a piping application depends primarily on the strength required for the flanged joint. Flanges are used, as an alternative to welded connections, to facilitate maintenance (a flanged joint can be dismantled quickly and conveniently).

Welding neck flange

A weld neck flange ("WN") features a long tapered hub that can be welded to a pipe. This flange is normally used in high pressure and high/low temperatures, which require an unrestricted flow of the fluid carried by the piping system.

The absence of pressure drops prevents effects such as turbulence and erosion/corrosion of metals near the flanged joints. Super duplex flanges manufacturer allows a distribution of mechanical stresses between the pipe and the flange weld neck and facilitates the execution of radiographic inspections to detect possible leaks and welding defects.

The size of the flange (NPS and pipe schedule) must match the size of the connecting pipe. A weld neck flange is connected to a pipe by a single full penetration V-shaped butt weld.

Long welding neck

Long weld neck flanges ("LWN") are similar to weld neck flanges, except that the neck (tapered hub) is extended and acts as a boring extension. Long weld neck flanges are usually vessels, columns or barrels. These flange types are also available in the heavy barrel (HB) and equal barrel (E) types.

Slip on flange

A slip-on flange is connected to pipe or fittings by two fillet welds, one performed inside and one outside the flange cavity. The bore size of a slip-on flange is larger than the outside diameter of the connecting pipe, as the pipe must slip inside the flange to be connected by making a fillet weld.

Slip-on flanges are also referred to as "hub flanges" and are easy to recognize due to their slim, compact shape. Dimensions and weights of ASTM A182 F22 slip-on flanges can be found.

Welding neck vs. slip on flange

Flanged joints made with slip-on flanges are more brittle than connections made with weld neck flanges.  A weld neck flange features a tapered hub, absent in a flange socket weld, which evenly distributes mechanical stress between the pipe and the flange. A weld neck joint has one weld area instead of two (socket weld flange). Another advantage of a weld neck flange is that it can be connected to both pipes and fittings, while socket weld flanges only fit pipes.

Threaded flange

Threaded flanges are joined to pipes by screwing the pipe (which has a male thread, usually NPT per ASTM A182 F11) onto the flange with no seam welds. Threaded flanges are available in sizes up to 4 inches and multiple pressure ratings. However, they are mostly used on small piping in low-temperature applications such as water and air utilities.

Threaded flanges are also a requirement in explosive areas, such as petrol stations and plants, as making welded connections in such environments would be dangerous. For more information, you can contact with Alloy Steel Flanges manufacturers in india.