PN Pressure Class Selector (PN 10, PN 16, PN 25, PN 40)

What is PN?

PN is a designation for the pressure class of pipework components such as flanges, valves and fittings. A flange marked PN 16 is, roughly speaking, designed for 16 bar at ambient temperature. Under EN 1333 the PN number is dimensionless and does not by itself represent a measurable value: the exact allowable pressure is read from the product standard's table for the material and temperature.

The PN series

The values in the EN 1333 series are PN 2.5, 6, 10, 16, 25, 40, 63, 100, 160, 250, 320 and 400. PN 10 and PN 16 are common in building services and water lines, PN 25 and PN 40 in steam and process lines.

Why temperature matters

Materials lose strength as they heat up, so the same PN class carries less pressure at high temperature. The calculator takes this derating as a ratio: divide the pressure read from the standard's table at design temperature by the PN number. The condition is simple: PN × ratio ≥ design pressure.

Example

A line with an operating pressure of 12 bar needs PN 16 at ambient temperature, with 75 percent utilisation. If the same line runs hot and the table gives a ratio of 70 percent, PN 16 carries only 11.2 bar: PN 25 is chosen, which carries 17.5 bar.

Limits

This is a preliminary selection. The pressure and temperature table is not in the tool, so you enter the ratio. ASME Class and PN are not one to one equivalents. Gaskets, bolting, fluid category and test pressure are assessed separately.