PN ratings: the European system
PN numbers are defined by EN 1333 and correlate to the maximum allowable gauge pressure in bar at 20°C for a specific material group. PN6, PN10, PN16, PN25, PN40, PN63, PN100 and PN160 are the standard series. The PN number is a dimensionless reference — PN16 does not literally mean 16 bar everywhere, because the allowable pressure decreases as temperature rises.
For example, a ductile iron valve rated PN16 is rated to 16 bar at 20°C. At 120°C the same valve may be limited to 12 bar or less, depending on the material de-rating curve. Always check the pressure-temperature table for the specific material when operating above ambient.
EN 1092-1 defines the flange dimensions for each PN rating. The flange dimensions at PN16 differ from PN25, so changing the pressure class requires changing the flanges on both the valve and the mating pipe spools.
ANSI/ASME Class: the American system
The ASME Class system (Class 150, 300, 600, 900, 1500, 2500) defines pressure-temperature ratings per material group in ASME B16.34. Class 150 in carbon steel (Group 1.1) is rated to 19.6 bar (285 psi) at ambient temperature — not 150 bar or 150 psi. The class number is an index, not a pressure value.
Class ratings step up roughly as follows: Class 300 allows approximately 2.6× the Class 150 allowable pressure; Class 600 allows approximately 5.2×. The ratio is not exact because it depends on material and temperature.
ASME B16.5 defines flange dimensions for each class. Class 150 and Class 300 flanges are dimensionally different and not interchangeable, even at the same pipe size.
JIS K ratings: the Japanese marine system
Japanese Industrial Standard flange ratings use the K designation: JIS 5K, 10K, 16K, 20K, 30K, 40K and 63K. The K number corresponds approximately to the maximum working pressure in kgf/cm² (kilograms-force per square centimetre) at normal temperature — so JIS 10K is approximately 10 kgf/cm², which equals approximately 0.98 MPa (about 9.8 bar).
JIS valves are specified on Japanese-built ships and on vessels with Japanese class notation. JIS 5K and JIS 10K are the most common marine ratings, corresponding approximately to PN5 and PN10 in working pressure, but with different flange dimensions.
Approximate crossover values
The table below gives approximate equivalent pressures across the three systems at ambient temperature for common materials. These are indicative — always verify against the appropriate standard and material de-rating table.
| PN (EN) | ANSI/ASME Class | JIS K | Approx. pressure (bar, 20°C) |
|---|---|---|---|
| PN6 | — | JIS 5K | ~6 |
| PN10 | Class 150 (partial) | JIS 10K | ~10 |
| PN16 | Class 150 | JIS 16K | ~16–19 |
| PN25 | — | JIS 20K | ~25 |
| PN40 | Class 300 (partial) | JIS 30K | ~40–51 |
| PN63 | Class 600 (partial) | — | ~63–103 |
| PN100 | Class 600 | — | ~100–103 |
Which system to specify
The choice of pressure rating system is driven by the applicable piping standard and the origin of the equipment. European projects using EN piping should specify PN and EN 1092-1 flanges throughout. Projects using ASME piping specify Class and ASME B16.5. Marine projects specify JIS K where the vessel uses Japanese flanging.
Mixing rating systems on the same project is possible but requires care at the interface. Transition flanges must be custom-made to match the OD, bolt circle and thickness of both standards at the junction point. This is a source of specification errors and should be resolved explicitly in the design documentation rather than left to the valve or pipe supplier to interpret.