There are many different pipe flanges standards to be found worldwide. In order to allow easy functionality and inter-changeability, these are designed to have standardized dimensions. Common world standards include ASA/ANSI (USA), PN/DIN (European), BS10 (British/Australian), and JIS/KS (Japanese/Korean).

       In most cases these are not interchangeable. That is to say, an ANSI pipe flanges will not mate against  JIS flanges. In addition, many of the flanges in each standard are divided into "pressure classes", allowing flanges to be capable of taking different pressure ratings. Again these are not generally interchangeable. These pressure classes also have differing pressure and temperature ratings for different materials. Unique pressure classes for piping can also be developed for a process plant or power generating station; these may be specific to the corporation, engineering procurement and construction (EPC) contractor, or the process plant owner.

       The flange is an external, internal ridge, or rim (lip). There four kinds of flanges:

  1. For strength, as the flange of an iron beam such as an I-beam or a T-beam;
  2. For attachment to another object, as the flange on the end of a pipe, steam cylinder, etc.
  3. On the lens mount of a camera;
  4. For a flange of a rail car or tram wheel.