What Does PN Mean in Piping Engineering? History, Uses, Standards & Examples
PN in piping stands for “Pressure Nominal” (often shown as “Nominal Pressure”). It’s a simple number that classifies the pressure-bearing capability of piping components—flanges, valves, fittings—under standardized conditions. Examples include PN10, PN16, PN25, PN40, PN100, etc.
While the PN number is close to the allowable pressure in bar at 20 °C, it’s still a nominal rating: the real allowable pressure depends on material, temperature, and the relevant standard’s pressure-temperature tables.
PN—Clear Definition
PN (Pressure Nominal) is a designation system in European and international standards to categorize the pressure capability of piping components. The number following “PN” (e.g., 16 in PN16) is approximately the allowable pressure in bar at 20 °C for a reference material group. Because real systems run at different temperatures and use different materials, standards provide derating curves/tables to determine the exact allowable pressure at your operating temperature.
A Short History of PN
- Origins (mid-20th century): PN originated in European standardization—most notably in German DIN standards (e.g., DIN 2401), where “PN” was adopted from the French term Pression Nominale.
- Harmonization in Europe: With the creation of the European Committee for Standardization (CEN), legacy DIN/BS/NF systems were aligned into EN standards (for flanges, see EN 1092 series).
- Global alignment: The International Organization for Standardization (ISO) published ISO 7005 for flanges, reinforcing PN designations globally. Today PN is widely used for water, district energy, HVAC, and many process applications across Europe, Asia, Africa, and beyond.
Key Standards That Use PN
- EN 1092 (Flanges):
- EN 1092-1: Steel flanges
- EN 1092-2: Cast iron flanges
- EN 1092-3: Copper alloy flanges
- EN 1092-4: Aluminium alloy flanges
- ISO 7005 (Flanges): International series that mirrors the PN designation.
- EN/ISO valve & fitting standards (e.g., EN 558 for face-to-face, EN 1092 bolt patterns) also label products with PN.
- EN 13480 (Metallic Industrial Piping) and the EU PED (Pressure Equipment Directive) reference PN components in compliance frameworks.
DN vs PN (Don’t Mix Them Up)
DN is Diameter Nominal—a size label for the pipe bore (e.g., DN50 ≈ 2″). PN is Pressure Nominal—a strength/pressure label (e.g., PN16). You need both to fully specify a part, e.g., Flange DN50 PN16 EN 1092-1.
Typical PN Ratings & Approximate Pressures (20 °C)
Rule of thumb: the PN number is roughly the pressure in bar at 20 °C for a reference material. Real allowable pressure changes with temperature and material—always check the standard’s pressure-temperature tables.
| PN | Approx. bar @ 20 °C | Approx. psi @ 68 °F | Typical Use Examples |
|---|---|---|---|
| PN6 | 6 | 87 | Low-pressure water, gravity networks |
| PN10 | 10 | 145 | Municipal water, irrigation |
| PN16 | 16 | 232 | HVAC/chilled/hot water, fire mains |
| PN25 | 25 | 363 | Higher-pressure water, utility steam |
| PN40 | 40 | 580 | Refining/chemical services, steam |
| PN63 | 63 | 913 | High-pressure gas/liquids |
| PN100 | 100 | 1450 | Instrumentation manifolds, test services |
| PN160 | 160 | 2320 | Specialty high-pressure systems |
| PN250 | 250 | 3625 | Oil & gas HP services |
| PN320 | 320 | 4640 | Very high-pressure applications |
| PN400 | 400 | 5800 | Extreme duty packages |
Note: 1 bar ≈ 14.5038 psi. Always consult the specific standard for temperature derating.
PN vs. ASME “Class” Ratings (Important Differences)
In North America, pressure capability is often specified by ASME B16.5/B16.47 “Class” (e.g., Class 150, 300, 600, …) rather than PN. These systems are not identical—bolt patterns, dimensions, and pressure-temperature ratings differ. Do not mix PN and ASME Class components unless a standard or manufacturer explicitly allows it.
| ASME Class | Very Rough PN “ballpark” at ~20 °C* | Comment |
|---|---|---|
| Class 150 | ~PN20 | ~19–20 bar at 38 °C for CS per B16.5 tables |
| Class 300 | ~PN50 | ~50 bar ballpark at low temp |
| Class 600 | ~PN110 | Ballpark only |
| Class 900 | ~PN150 | Ballpark only |
| Class 1500 | ~PN260 | Ballpark only |
| Class 2500 | ~PN420 | Ballpark only |
*These are rough comparisons for quick orientation—never use this table for design or procurement. Always follow the relevant standard’s charts.
Where & Why PN Is Used
- Municipal water & wastewater: PN10–PN16 for transmission and distribution.
- HVAC & district energy: PN16–PN25 for chilled/hot water, district heating.
- Fire protection mains: PN16 commonly specified in many regions.
- Industrial utilities (air, steam): PN16–PN40 depending on temperature and medium.
- Refining & chemicals: PN25–PN40 for many process lines; higher PN for critical services.
- Oil & gas: PN40–PN250+ in high-pressure applications.
How to Select the Right PN (Step-by-Step)
- Know your MAWP (maximum allowable working pressure) and design temperature.
- Identify the medium (water, steam, air, hydrocarbons, corrosives) and the code (EN 13480, PED category, etc.).
- Choose material (carbon steel, stainless, cast iron, copper alloy, etc.).
- Use the standard’s pressure-temperature tables (e.g., EN 1092-1) to find allowable pressure at your temperature for your material group.
- Select PN so allowable ≥ MAWP, with reasonable margin for transients and aging.
- Check compatibility across all components (flanges, bolts, gaskets, valves) for the same PN and facing.
Example: If your line needs 12 bar at 60 °C water service in carbon steel, PN10 is likely too low after derating; PN16 is the typical choice (verify in the pressure-temperature table for your standard and material group).
Real-World Marking Examples
Valve body marking: DN50 PN16 EN 12266 (tested per EN 12266; rated PN16) Flange drawing note: Flange EN 1092-1, Type 11, DN100, PN16, RF Gasket spec: EN 1514-1, DN80, PN40, Spiral Wound, Graphite filler Pipe class line: CS, DN150, PN25, 3LPE, EN 10220
Frequently Asked Questions
What does PN stand for?
Pressure Nominal—a standardized pressure rating label for piping components.
Who created PN and why?
PN grew out of European standardization (early DIN practice, later harmonized by EN standards and the international ISO 7005 series). It gave engineers a simple, consistent way to specify pressure capability across different materials and product types.
Is the PN number equal to pressure in bar?
Approximately at 20 °C for reference material groups—but actual allowable pressure depends on temperature and material. Always check the standard’s tables.
Can I mix PN and ASME Class parts?
Generally no. Dimensions (bolt patterns, facing) and ratings differ. Only mix if a standard or the manufacturer explicitly certifies interchangeability.
What’s the difference between DN and PN?
DN is size (Diameter Nominal). PN is pressure rating (Pressure Nominal). You need both to specify a component.
What are common PN levels?
PN6, PN10, PN16, PN25, PN40, PN63, PN100, PN160, PN250, PN320, PN400—availability varies by size and material.
Conclusion
PN is the universal “pressure shorthand” for European and many global piping systems. Understanding how PN ties to material, temperature, and the correct standard lets you pick components that are safe, economical, and compliant. For most water and HVAC services you’ll see PN10–PN25; for steam and process lines PN25–PN40; and for special duty much higher PNs. Always verify with the applicable standard before finalizing your selection.
Disclaimer: This guide is for educational purposes. Always consult the latest edition of the applicable standards and your project specifications.