There are many different types of flanges found worldwide.  Most common include ASA, ANSI, and ASME (USA) PN/DIN (European), BS10 (British/Australian), and JIS/KS (Japanese/Korean).  These can be interchangeable as most local standards have been aligned to ISO standards.  However, some local standards are different.  For example an ANSI/ASME 150 flange will not mate with an ANSI/ASME 300.  

These pressure classes have different pressure and temperature ratings for different materials.  The ANSI/ASME pressure classes for Flat-Face flanges are 125# and 250#.  The classes for ring-joint, tongue & groove and raised-face flanges are 150#, 300#, 600#, 900#, 1500# and 2500#.  

The flange faces are also made to standard dimensions and are typically flat faced, raised face, tongue and groove, or ring joint.  

Flange designs are available as weld neck, slip-on, lap joint, socket weld, threaded and blind.  

Pipe flanges that are made to standards written by ASME B16.5 or ASME B16.47 are made from forged materials and machined surfaces.  B16.5 refers to nominal pipe sizes from ½” to 24”.  B16.47 covers NPS from 26” – 60”.  

The Pressure classes do not correspond to maximum pressures in psi.  Instead, the maximum pressure is dependent upon the material of the flange and the temperature.  For example, the maximum pressure for a Class 150 flange is 285 psi and for a Class 300 is 740 psi.  

Flanges always require bolt and nut sets and are generally specified by the standards.  

Flanges are typically manufactured from carbon steel for piping applications.  However, there are many industry standard flanges that in some circumstances require different materials of construction.

Visual examples of the various types of flanges:

 Image result for images of types of flanges