Technical guide
Flange pressure rating: complete guide to PN and ANSI Class
Published 25 March 2026 · 7 min read
When selecting industrial flanges, one of the fundamental parameters is the pressure rating. But what does it actually mean? And what's the difference between the European system (PN) and American (ANSI Class)?
What is PN (Nominal Pressure)?
PN stands for Pressure Nominale (Nominal Pressure) — a dimensionless number indicating the maximum allowable pressure in bar at 20°C.
Example: a PN16 flange can withstand 16 bar at 20°C. But note: this value decreases as temperature rises!
The PN system is defined by standard EN 1092-1 and is the standard in Europe.
What is ANSI Class?
The American system, defined by ASME B16.5 (and B16.47 for large diameters), uses Class instead of PN. Classes: 150, 300, 600, 900, 1500, 2500.
The number does not directly represent a pressure in bar or psi. It's an index linked to ASME tables that define allowable pressure based on material and temperature.
Why PN and Class are NOT equivalent
This is a common source of confusion. The two systems have different philosophies:
| Aspect | PN (EN) | Class (ASME) |
|---|---|---|
| Reference temp | 20°C | Varies by material |
| Derating | Simplified coefficient | Detailed tables per material |
| Bolt pattern | Different from ANSI | Different from EN |
⚠️ Warning
PN16 and Class 150 flanges are NOT interchangeable! The bolt patterns (number, diameter, PCD) are different. Mating them requires adapters or special drilling.
PN – ANSI Class correspondence table
This table provides approximate pressure equivalence. It does NOT mean the flanges are physically interchangeable!
| PN | Bar at 20°C | ANSI Class ~ equivalent |
|---|---|---|
| PN16 | 16 | Class 150 (≈20 bar) |
| PN40 | 40 | Class 300 (≈51 bar) |
| PN100 | 100 | Class 600 (≈102 bar) |
| PN160 | 160 | Class 900 (≈153 bar) |
| PN250 | 250 | Class 1500 (≈255 bar) |
How pressure varies with temperature
This is the crucial point. Allowable pressure decreases as temperature rises because metal loses strength.
Example for Class 150 in carbon steel (ASTM A105):
| Temp | Max pressure (bar) | % of 38°C |
|---|---|---|
| 38°C (100°F) | 19.6 | 100% |
| 150°C | 15.8 | 81% |
| 200°C | 13.8 | 70% |
| 300°C | 10.2 | 52% |
This means a Class 150 flange on a steam system at 200°C can only withstand ~14 bar, not 20 bar!
Key takeaways
- PN indicates pressure at 20°C
- ANSI Class requires specific tables for each temperature and material
- The two systems are NOT physically interchangeable
- Allowable pressure decreases with temperature
For complete tables and conversions, visit our Technical Tables page. For flange selection assistance, contact us.