Pressure nominal. The number roughly equals the allowable pressure in bar at room temperature for the reference material, with derating at higher temperatures. PN 6, 10, 16, 25 and 40 are the common steps. PN and ASME class flanges differ in bolt circles and bolt counts in most sizes, so a PN 16 valve will not simply bolt into a Class 150 line.
Valves came in PN 16 and the plant is ANSI 150, bolt holes are off by a few millimeters, we can't use them.
Also heard as
- nominal pressure
- PN rating
Related terms
Pressure class
The standardized rating step, such as 150, 300 or 600, that sets a valve or flange's allowable pressure at each temperature.
WOG
Water, oil, gas: a cold working pressure rating stamped on small threaded valves, such as 600 WOG.
Raised face
A flange facing where the gasket surface stands slightly proud of the bolt circle area, concentrating gasket load.