What’s the Difference Between PN and MPa?

When dealing with piping systems and valve selection, understanding PN (Nominal Pressure) and MPa (Megapascal) is essential. Although both relate to pressure, they serve very different purposes in engineering and procurement. Misunderstanding these terms can lead to incorrect valve selection—and costly safety risks.

In this article, we’ll break down the key differences between PN and MPa and show you how to choose the right valve based on accurate pressure ratings.

1. What is PN (Nominal Pressure)?

PN stands for "Pressure Nominale" or Nominal Pressure, primarily used in European standards like DIN, EN, and GB/T.

• Definition: PN indicates the pressure rating of valves, flanges, and fittings at 20°C (room temperature).

• Example: A PN16 flange is rated to handle 16 bar at 20°C, which equals 1.6 MPa.

• Important Note: PN is not a fixed pressure value—it’s a rating level. The actual allowable pressure decreases as temperature increases.

Common PN Levels:

PN6, PN10, PN16, PN25, PN40, PN63, PN100, etc.

2. What is MPa (Megapascal)?

MPa is a standard unit of pressure in the International System (SI), used globally in engineering calculations.

• 1 MPa = 1,000,000 Pa = 10 bar ≈ 145 psi

• MPa expresses actual pressure values—such as design pressure, test pressure, or working pressure.

• MPa is temperature-independent and suitable for all types of mechanical calculations and reports.

3. PN vs MPa: Key Differences

Category	PN (Nominal Pressure)	MPa (Megapascal)
Type	Pressure class / rating	Pressure unit
Meaning	Max allowable pressure at 20°C	Actual pressure value
Standard Use	Valve & flange ratings (EU standards)	Global engineering use
Temperature Relation	Decreases with temperature	Not affected
Conversion (approx.)	1 PN ≈ 0.1 MPa	1 MPa = 10 bar

4. Real-World Example: How to Choose the Right Valve

Scenario:
A piping system is designed to operate at 2.5 MPa and 100°C.

Common Mistake:

Choosing a PN25 valve, assuming it equals 2.5 MPa.

The Truth:

• At 100°C, a PN25 valve may only handle ~1.8 MPa due to material limitations.

• 2.5 MPa > 1.8 MPa → PN25 is insufficient.

Correct Action:

Choose a higher-rated valve—such as PN40, which ensures safety and compliance.

5. Common Misconceptions

❌ PN16 = 16 MPa?
Wrong. PN16 = 16 bar = 1.6 MPa.

❌ Temperature doesn’t affect PN?
Wrong. Higher temperatures reduce a valve’s pressure capacity—always check the temperature-pressure chart.

❌ PN and Class ratings are interchangeable?
Wrong. European PN ratings and American ASME Class ratings follow different systems:

Always check conversion charts before selecting valves.

6. Additional Pressure Standards

• ASME (U.S. Standard): Uses "Class" designations like Class 150, Class 300.

• JIS (Japan): Uses “K” ratings (e.g., 10K ≈ PN10, 20K ≈ PN20).

• GB/T (China): Adopts similar PN system as EN/DIN.

7. Summary: Choose the Right Valve, Avoid Downtime

• PN = Nominal pressure rating at room temperature.

• MPa = Exact pressure unit for calculations.

• Rule of thumb: PN16 ≈ 1.6 MPa (but check temperature correction).

To ensure safety and long-term reliability, select valves not only based on pressure but also temperature, material compatibility, and international standards.

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At COVNA, we manufacture a full range of PN-rated and ASME Class-rated valves—including ball valves, butterfly valves, gate valves, and globe valves.

✔ Certified materials
✔ Precise engineering
✔ Pressure-temperature charts provided
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Contact us today for a free consultation and quote. Choose the right valve from a manufacturer that understands pressure—and your needs.