You're changing a connection on an existing system and you need to identify a flange. It may be ANSI Class 150, it may be AWWA Class D or it may be a DIN standard. Nearly all flanges are now stamped with identifying numbers on the side but you cannot find any markings on your flange, so what do you do?
There are at least a dozen standards for pipe flanges. Nearly all are unique with very little interchangeability. The standard could be based on an ASME, ASTM, ANSI, API, MSS, AWWA, DIN, standard recognized industry guidelines or it may be based on specific application guidelines.
Fortunately there is a way to identify your flange. With the following information a qualified supplier should be able to identify the correct standard.
These first three are critical and may be enough to identify your flange.
Diameter of Bolt Circle (Centerline to centerline across the flange. This may require un-bolting the flange)
Number of Bolt Holes
Diameter of Bolt Hole or Bolt
Additional information you will need is listed below.
Type of Material
Flange Facing or type of Gasket used
Outside Diameter of Flange
Thickness of Flange