External or internal ridge, or rim which provides strength
A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength (as the flange of an iron beam such as an I-beam or a T-beam); for easy attachment/transfer of contact force with another object (as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera); or for stabilizing and guiding the movements of a machine or its parts (as the inside flange of a rail car or tram wheel, which keep the wheels from running off the rails). Flanges are often attached using bolts in the pattern of a bolt circle.
Flanges play a pivotal role in piping systems by allowing easy access for maintenance, inspection, and modification. They provide a means to connect or disconnect pipes and equipment without the need for welding, which simplifies installation and reduces downtime during repairs or upgrades. Additionally, flanges facilitate the alignment of pipes, ensuring a proper fit and minimizing stress on the system.