Short answer
PN and Class are designations used in different flange classification systems; Class 150 does not directly mean 150 psi. The permissible pressure is determined from the relevant standard table together with material and temperature.
Technical explanation
EN 1092-1 covers steel flanges designated by PN; ASME B16.5 covers the corresponding flanges and fittings designated by Class. Dimensions, faces and bolt patterns may differ between the two families. Converting one class into the other by unit conversion does not create mechanical equivalence. Nominal diameter alone does not define the hole pattern or the sealing face either. The pressure-temperature table must be read from the licensed standard and for the actual material group.
Topic-specific checkpoints
| Item | Description |
|---|---|
| Class | PN or Class; a classification, not a unit |
| Size | DN/NPS and actual connection dimensions |
| Material/temperature | Conditions of the permissible pressure |
| Face | Compatibility with the gasket and mating flange |
How is it assessed in practice?
In a flanged hose order, write DN/NPS, PN/Class, the standard, material, face type and mating flange information together. Do not decide based only on the outside diameter of the old part. If the connection is to join two different standards, do not assemble by enlarging holes or by forcing without an engineering assessment. In a quotation comparison, do not use the Class number like a label converted to a bar value. Gaskets and bolts must also be verified as part of the selected flange system.
Original editorial recommendation; not a clause of a standard.
Frequently asked questions
Is the limit of a Class 150 flange 150 psi?
This direct equation is not correct. The permissible value is determined by the relevant material and temperature table.
Source coverage
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S090
DIN EN 1092-1:2018-12 / EN 1092-1:2018 DIN Media · accessed 2026-10-19 Public metadata: PN-designated steel flanges, pressure-temperature ratings; no tables imported
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S093
ASME B16.5 Pipe Flanges and Flanged Fittings ASME · accessed 2026-10-19 Public description: class-designated flanges, materials and pressure-temperature ratings; no normative tables imported