What Is the Difference Between ANSI and PN Flanges?

If you’re specifying piping components for international projects, you’ve probably asked: what is the difference between ANSI and PN flanges? 

Understanding this can help avoid mismatched parts, project delays, and installation headaches.

Different Systems, Different Measures

To understand the difference between an ANSI flange and a PN flange, you first need to look at the measurement systems behind them. Each follows a different set of global standards—and those differences affect everything from pressure ratings to bolt alignment. 

• ANSI flanges (also called ASME) use an imperial-based pressure class system (e.g., Class 150, 300, 600), defined in ASME B16.5/B16.47. These classes are not direct pressure values in psi, though commonly associated with them.
• PN flanges come from the metric DIN/EN system (e.g., PN10, PN16, PN25), where PN indicates nominal pressure in bars (such as 10 bar for PN10).

Size and Compatibility Issues

ANSI and PN flanges are not interchangeable. Flange bolt patterns, thicknesses, and diameters differ across these standards. Even so, some cross-referencing tables exist:

Despite these mappings, they should never be directly mixed on the same piping system.

Choosing the Right Flange Standard

Use ANSI flanges when:

• Projects adhere to ASME or API standards
• Materials are in imperial units (inches, psi)
• Your pipeline specs reference Class 150, 300, or higher

Use PN flanges when:

• Working with European or ISO-based specs
• Measuring pressure in bar and dimensions in metric
• Projects call for PN16, PN25, etc., commonly in water and chemical plants

Impact on Procurement and Installation

Mixing flange standards can lead to misaligned bolt holes, sealing failures, and safety issues. 

For seamless supply chains, it’s wise to stick with one system—either ANSI or PN—and ensure all components, including stainless steel or other ASME-compliant options, match that standard. 

It’s also smart to verify that flanges like those from Longan Flange meet your chosen system specs, whether you’re sourcing stainless steel flanges or ASME flange types.

What is the difference between ANSI and PN flanges? Final Take

What is the difference between ANSI and PN flanges?

It boils down to standards:

• ANSI = imperial, class‑based; 
• PN = metric, bar‑based. 

They differ in dimensions, bolt layouts, and ratings. Staying consistent with the correct system ensures compatibility, reduces risk, and simplifies procurement.Need help aligning flange standards with your project specs? Longan Flange can guide you to the right ANSI or PN-compliant solutions, making sure your systems fit and perform. Contact us today!