One of the most frequent errors in international industrial procurement is treating PN and Class as direct one-to-one equivalents. They are different pressure-designation systems that work with different standards, materials, temperature limits and flange dimensions. A valve can be described as "high pressure" and still be incompatible with your piping.
What does PN mean?
PN is a nominal pressure designation commonly used with European and international metric standards. You may see PN10, PN16, PN25, PN40 and higher designations. It is normally used alongside DN nominal size and the relevant flange or valve standard.
PN is a designation, not a universal statement that every material can continuously operate at that exact pressure under every temperature. Temperature and material must always be checked against the applicable standard and manufacturer data.
What does Class mean?
Class, often informally called ANSI Class, is commonly used in ASME-based piping systems. Typical designations include Class 150, 300, 600, 900, 1500 and 2500. The permitted pressure depends on the material group and temperature, so Class 150 does not mean a flat 150 psi rating in all conditions.
Why the systems cannot be converted casually
The two systems differ in more than pressure. Flange drilling, outside diameter, thickness, facing, bolts and face-to-face dimensions can vary. A nominally similar pressure range does not prove that two flanges will bolt together or seal correctly.
| In an RFQ, confirm | Why it matters |
|---|---|
| DN or NPS size | Establishes nominal bore system |
| PN or ASME Class | Defines the project pressure designation |
| Flange standard | Confirms dimensions and drilling |
| Facing | RF, FF, RTJ or another specified facing must match |
| Material and temperature | Determines permitted operating envelope |
| End connection | Prevents a mismatch between valve and piping |
Best practice for buyers
Copy the exact designation from the line list, isometric drawing or existing valve tag. For example, "DN100, PN16, EN flange" is more actionable than "4-inch 16 bar valve." Likewise, "NPS 4, Class 300, ASME B16.5 RF" communicates the flange basis more clearly.
If you are replacing an installed valve, include photos of the nameplate and flange, key dimensions, medium, operating temperature and any project standard. A supplier should flag an incomplete or contradictory specification instead of silently substituting a similar-looking product.
A note on the term "ANSI"
Buyers frequently say "ANSI flange," but current project documents often reference ASME standards for dimensions and pressure-temperature ratings. Use the exact standard named in your project documentation rather than relying on informal terminology.
Need a compatibility check?
Send your data sheet, flange standard, material and design conditions to StarSprink before ordering. We can help verify the sourcing specification with candidate manufacturers and provide drawings or inspection records as required.
Need a compatibility check? Browse industrial products or send StarSprink your inquiry.
FAQ
Can a PN16 valve replace a Class 150 valve?
Only after a qualified review of the applicable standards, dimensions, material and design conditions. Never approve a substitution from a simplified conversion table alone.
What should I send a supplier to avoid a flange mismatch?
Provide nominal size, pressure system, flange standard, facing, material, temperature and a drawing or photograph whenever possible.