Pipe flanges that are made to standards

　　Pipe flanges that are made to standards called out by ASME B16.5 or ASME B16.47 are typically made from forged materials and have machined surfaces. B16.5 refers to nominal pipe sizes (NPS) from ½" to 24". B16.47 covers NPSs from 26" to 60". Each specification further delineates flanges into pressure classes: 150, 300, 400, 600, 900, 1500 and 2500 for B16.5, and B16.47 delineates its flanges into pressure classes 75, 150, 300, 400, 600, 900. However these classes do not correspond to maximum pressures in psi. Instead, the maximum pressure depends on 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 Flange it is 740 psi (both are for ASTM A105 Carbon Steel and temperatures below 100F).