Industrial Valve Pressure Ratings Explained: A Complete Guide

In industrial piping systems, valve pressure rating is one of the most important parameters for ensuring safety, reliability, and compliance with international standards. Choosing the correct pressure class directly impacts valve performance, service life, and overall plant safety.

This article provides a comprehensive explanation of valve pressure ratings, including common classification systems, pressure–temperature relationships, and practical selection guidelines.

1. What Is Valve Pressure Rating?

The pressure rating of a valve defines the maximum allowable pressure that the valve can safely withstand at a specific temperature.

• It ensures the valve body and internal components can operate without leakage, deformation, or failure.

• Pressure ratings are always linked to temperature, as higher temperatures reduce the strength of materials.

• Different standards organizations (ASME, API, ISO, DIN, etc.) have their own classification systems.

2. Common Valve Pressure Rating Systems

(1) ASME Pressure Class (Class Rating)

• Expressed as Class 150, 300, 600, 900, 1500, 2500.

• Widely used in oil & gas, petrochemical, and power industries.

• The number (e.g., Class 150) does not directly equal maximum pressure in psi/bar—it depends on material and temperature.

(2) PN Rating (Nominal Pressure – DIN/EN Standard)

• Expressed as PN10, PN16, PN25, PN40, PN100, etc.

• Common in Europe and industries following EN standards.

• Number indicates allowable bar of pressure at reference temperature (20°C).

  • Example: PN16 = 16 bar (at 20°C).

(3) API Ratings

• API 6D / API 6A valves (for pipeline and wellhead service) often use pressure classes aligned with ASME.

• Also includes PSL (Product Specification Level) for oil & gas critical service valves.

(4) JIS Pressure Ratings (Japanese Standards)

• Expressed as 10K, 16K, 20K, where “K” indicates kg/cm² (≈ bar).

• Common in Asia-Pacific region.

3. Pressure–Temperature Relationship

Valve pressure ratings are not fixed values—they vary with temperature:

• At room temperature, a Class 150 carbon steel valve may withstand around 19 bar (275 psi).

• At 400°C, the same valve’s pressure limit may drop by 40–50%.

• This is because material strength decreases as temperature rises.

👉 That’s why manufacturers provide Pressure–Temperature Charts to define exact limits for each material grade (e.g., carbon steel, stainless steel, alloy steel).

4. How to Read a Valve Pressure Rating

• Class 150 (ASME) ≈ 285 psi (19 bar) at 38°C for carbon steel.

• Class 300 (ASME) ≈ 740 psi (51 bar) at 38°C.

• PN16 = 16 bar at 20°C, but drops with higher temperatures.

• Always check both standard and material specification before final selection.

5. Typical Applications by Pressure Class

• Class 150 / PN16–PN25 → Low-pressure water, HVAC, general industrial pipelines.

• Class 300 / PN40 → Medium-pressure steam, chemical process lines.

• Class 600 / PN100 → Oil & gas transmission, refinery pipelines.

• Class 900–2500 / PN160–PN420 → High-pressure steam, power plants, offshore platforms.

6. Common Misunderstandings

❌ Myth 1: Class 150 means 150 psi.

• Wrong. ASME Class rating is not equal to psi—it varies by material and temperature.

❌ Myth 2: PN rating is the same at all temperatures.

• Wrong. PN is defined at 20°C, but actual allowable pressure decreases as temperature rises.

❌ Myth 3: All valve materials have the same pressure rating in Class 300.

• Wrong. Stainless steel, carbon steel, and alloy steel differ in strength at elevated temperatures.

7. Guidelines for Selecting Valve Pressure Rating

✅ Always check design pressure and design temperature of the pipeline.
✅ Refer to ASME B16.34, EN 1092-1, or API 6D pressure–temperature charts.
✅ Choose higher pressure classes when:

• Fluids are toxic, flammable, or critical service.

• Temperature fluctuates frequently.

• There is a risk of pressure surges (water hammer, compressor start-up).
  ✅ Consult valve manufacturers for material selection (e.g., carbon steel vs stainless steel vs alloy).

8. Conclusion

Understanding valve pressure ratings is essential for safe and efficient pipeline design.

• ASME Class ratings (150–2500) are widely used in oil & gas and power industries.

• PN ratings (PN10–PN400) are common in European standards.

• Pressure limits always depend on temperature and material properties.

By carefully analyzing your process conditions, you can select the right pressure class, avoid safety risks, and extend valve service life.