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Pipe Class Ratings vs. Pressure Numbers (PN)

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:

Pipe Class Ratings vs. Pressure Numbers (PN)
Flange Class 150 300 400 600 900 1500 2500
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.

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