ANSI or ASME? Getting the Standard Name Right

In the field people say "ANSI flange" and "ASME flange" interchangeably. Both point to the same part, but the organisations differ, and the confusion occasionally causes ordering errors.

Two organisations, one standard

• ASME (American Society of Mechanical Engineers) is the engineering body that writes the standard. B16.5, B16.47 and B16.9 are all ASME documents.

• ANSI (American National Standards Institute) does not write standards; it accredits and recognises them as national standards. Because ASME B16.5 was approved by ANSI, it was long referred to as "ANSI B16.5".

So ANSI B16.5 and ASME B16.5 are the same document. The correct designation today is ASME B16.5.

Why the confusion persists

• Older drawings and specifications use the ANSI designation
• "ANSI 150#" became habit in the market
• Some manufacturers keep the old wording in catalogues and markings

This is not an error, but new specifications should use ASME.

What really must not be confused

The problem is not ANSI versus ASME but mixing up standard families:

What to write on an enquiry

Instead of "ANSI 150# flange", write "ASME B16.5, Class 150, RF, WN, ASTM A105". Standard, class, type, face and material together remove any ambiguity.

See our flange page and DIN/EN versus ANSI/ASME.

FAQ

Are ANSI and ASME flanges different?
No, they refer to the same standard. ASME writes it and ANSI recognises it as a national standard.

Which designation should I use?
ASME B16.5 is preferred in new specifications and enquiries.

Are old drawings marked ANSI invalid?
No. They denote the same standard and the dimension tables have not changed.