Pressure numbers (PN) vs. flange class designations.
Piping Class Ratings based on the ASME B16.5 - Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24 Metric/Inch Standard - class and the corresponding ISO 7005 PN (Pression Nominal*) ratings:
|Flange Pressure Nominal (PN)||20||50||68||110||150||260||420|
* "Pression Nominal" is the French equivalent of Pressure Nominal
"Pression Nominal" is the rating designator followed by a designation number indicating the approximate pressure rating in bars.
- 1 bar = 1x105 Pa (N/m2) = 0.1 N/mm2 = 10,197 kp/m2 = 10.20 m H2O = 0.98692 atm = 14.5038 psi (lbf/in2)
PN ratings do not provide a proportional relationship between different PN numbers, whereas class numbers do. Class numbers are therefore recommended before PN ratings.
Note! The piping rating must follow the pressure-temperature rating of the weakest pressure containing item in the system.