Flanges are flat rings around the end of pipes which mate with an equivalent flange from another pipe, the two being held together by bolts usually passed through holes drilled through the flanges. A deformable gasket, usually elastomeric, placed between raised faces on the mating flanges provides the seal. Flanges are designed to a large number of specifications that differ because of dimensional variations in pipes sizes and pressure requirements, and because of independent standards development. In the US, flanges are either threaded or welded onto the pipe. In the European market flanges are usually welded onto the pipe. In the US, flanges are available in a standard 125 lb bolt pattern as well as a 250 lb (and heavier) bolt pattern (steel bolt pattern). Both are usually rated at . A flanged joint is rigid and can bear both tension and compression as well as a limited degree of shear and bending. It also can be dismantled after assembly.  Due to the rigid nature of the joint and the risk of excessive bending moment being imposed, it is advised that flanged pipework not be buried.
Current flange standards used in the water industry are ANSI B16.1 in the US, EN 1092 in Europe, and AS/NZS 4087 in Australia and New Zealand.