Rule of thumb · applies

PN 16 is not always 16 bar – nominal pressure, temperature and material

PN 16 does not mean: always 16 bar.

This rule of thumb does not replace the design calculation or the applicable standard.

Category: robust rule
Standards referenced: DIN EN 1092-1:2018-12 Annex G (Tables G.5, G.18), EN 1333

Rule of thumb

PN is a designation of the connection geometry; the allowable pressure depends on material and temperature.

Where does the rule come from?

PN 16 and "16 bar" sit so close together that equating them is almost unavoidable in daily work – and for water at room temperature it is even true. The rule is born where temperature comes in: the nominal pressure refers to 20 °C, and anyone applying the 16 bar to steam at 200 °C has missed the temperature reservation.

What is technically correct?

PN (pression nominale, EN 1333) designates the pressure rating of a component series: all DN 100 PN 16 flanges share the same connection dimensions – outside diameter, bolt circle, number of holes. How much pressure a particular flange withstands is given by the pressure-temperature rating of its material group. For group 3E0 (P245GH/P250GH, the usual steel welding neck flange) PN 16 allows 16.0 bar at room temperature, 14.8 bar at 100 °C, 13.3 bar at 200 °C, 11.0 bar at 300 °C and 9.5 bar at 400 °C. For 1.4301 (group 11E0) the figures are 16.0 – 14.5 – 11.9 – 10.2 bar at the same temperatures; 1.4571 (15E0) holds up longer: 16.0 – 16.0 – 14.9 – 13.3 bar. Same connection, three different curves.

The nominal pressure is therefore an upper limit at room temperature and, beyond that, only a name.

Where does the rule end?

It applies to the flange. The gasket (material, temperature limit), the bolts (strength class) and the mating flange may limit the joint earlier – a flanged joint is as strong as its weakest member.
Valves and fittings follow their own rules (EN 12516 for valves, pressure capacity to EN 10253 for fittings), even though "PN" appears there too.
Below 20 °C the allowable pressure does not rise above PN; at low temperatures toughness requirements are added.
PN cannot be converted into class (see the sister rule).

What does the standard say?

EN 1333 defines PN as an alphanumeric designation without unit that is related to bar. EN 1092-1 gives the pressure-temperature ratings in Annex G, one table per PN rating with one row per material group (G.5 for PN 16, non-austenitic; G.18 for PN 16, austenitic). Linear interpolation between values is permitted; values in the creep range are printed in italics in the standard.

DIN/EN versus ASME/ASTM

The same principle on both sides: PN plus Annex G here, class plus Section 2 there. PN 16 and Class 150 are often equated; both allow similar pressures at 200 °C in carbon steel (13.3 versus 13.8 bar) but not at room temperature (16.0 versus 19.6 bar) – and the flanges do not mate.

Worked example

Welding neck flange type 11, DN 100 PN 16, P250GH, for pipe 114.3 (core range, in stock): 16 bar up to room temperature, 13.3 bar at 200 °C, 11.0 bar at 300 °C. For a saturated-steam line at 12 bar (about 190 °C) PN 16 is sufficient – just, with 13.4 bar allowable. For 16 bar at 200 °C it is not; there PN 25 (group 3E0: 20.8 bar at 200 °C) is the right rating. That is exactly the calculation skipped by anyone who reads PN 16 as "16 bar".

Checked today

Traffic light: applies (class A). The rule is correct without restriction; PN 16 is 16 bar at room temperature and less above.

Frequently asked questions

How many bar does a PN 16 flange withstand at 200 °C?

For steel P250GH (group 3E0) 13.3 bar, for 1.4301 11.9 bar, for 1.4571 14.9 bar – according to EN 1092-1, Annex G.

Does the PN value apply at 20 °C?

Yes. The nominal pressure is the upper limit at room temperature; the allowable pressure falls as temperature rises.

May I mix PN 16 and Class 150?

No – the connection dimensions differ. The correspondence is a purchasing convention for the pressure rating, not a rule for assembly.

All rules of thumb