The dictionary defines flanges as “a protruding rim, edge, rib, or collar, as on a wheel or a pipe shaft, used to strengthen an object, hold it in place, or attach it to another object.” Essentially, it's a disc-shaped ring of steel that is casted or forged to connect or join either a pipe to a pressure vessel or sections of a pipe together. Fixed through the process of either threading or welding, it works as a heavy-duty connector. Flanges are of different types, shapes and sizes, based on their applications, of which the main kinds have been discussed below.
Hubbed or Slip-on Flanges: as per the name, these flanges have a bigger inner rim as compared to the diameter of the pipe, so that they can slide into the pipe and fit securely. Even though this kind of flange is less in thickness as opposed its counterparts, it's still stronger, highly dependable and economical. When slipped into and welded, it provides optimum protection from leakages.
Threaded Flange: Though the design of the threaded flange is similar to the slip-on flange, the only added feature to it is that it has tapered threads within the inner rim so as to work into pipes that have external threads to it. These flanges are generally used in areas where welding cannot be used due to highly combustible environments. Its use is also limited to low pressure piping systems because locking in both the flange and the pipe through the threads does not enable sufficient load capacity.
Loose or Lap Joint Flange: This kind of flange is essentially used to combat issues that arise with bolt holes alignment. They are used along with stub end fittings, which are welded on to the pipe. The lap joint flange then slides over the pipe and rotates round the stub. Since they do not come into contact with the gas or fluid, they can be reused. It also finds place in sections which require dismantling for replacement and inspections.
Weld Neck Flange: This particular flange is comparatively expensive to manufacture and is generally welded to the base of pipes of high pressure vessels. In terms of design it has a tapered hub on one side of the inner rim allowing for reduction in stress concentration and maximization of flexibility and strength. It also reduces erosion and turbulence within the pipe in high pressure conditions. See image below:
Blind Flange: These generally find place at the end of pipe systems to aid sealing them. Due to their design, they allow for easy working and around pipes. They also help preventing flow of gases and fluids with intense speed therefore making it easier to conduct pressure tests.
Besides the above, there are various other kinds of flanges like the bulk head flange, socket weld flange, orifice flange, groove and tongue flange and the spectacle flange. While flanges are built to provide secure joints and prevent leakages, forged flanges are even sturdier and potent due to the process they are manufactured.