There are many different flange standards to be found worldwide. To allow easy functionality and inter-changeability, these are designed to have standard dimensions. Common world standards include ASA/ANSI/ASME (USA), PN/DIN (European), BS10 (British/Australian), and JIS/KS (Japanese/Korean).
Compact of flanges
Traditional flanges such as ANSI, DIN and BS all rely on a dynamic joint which, when bending forces and tensile loads are applied, become loose and weak. The gap created by the raised face introduces corrosion problems particularly to the bolting aspect, which is a particular issue in critical environments as the design actually depends on the large bolt forces to maintain gasket integrity.
Source: China Flange Manufacturer - Yaang Pipe Industry Co., Limited (www.yaang.com)