How can you compare ANSI Class and Nominal pressure?
The pressure rating defines the maximum allowable pressure that a flange can withstand at a given temperature. According to the ANSI/ASME B16.5 specification, there are the following seven flange pressure classes: Class 150#, Class 300#, Class 400#, Class 600#, Class 900#, Class 1500# and Class 2500#.
In the table shown, these ANSI flange pressure ratings are assigned to the nominal pressure. However, depending on the material and temperature, the respective operating pressures can be found in the corresponding pressure-temperature assignments.
The terms "pressure rating", "class", "#", "Lb" or "Lbs" are not firmly defined, they all refer to the pressure-temperature assignment of a flange.
| ANSI Class Rating | Nominal pressure in bar |
| Class #150 | 20 |
| Class #300 | 50 |
| Class #400 | 64 |
| Class #600 | 100 |
| Class #900 | 150 |
| Class #1500 | 250 |
| Class #2500 | 420 |
