Flanges - API vs. ASME/ANSI

Comparing API and ASME/ANSI flanges

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The difference between ASME/ANSI and API flanges is the fabrication material and the higher rated API operating pressure.

ASME/ANSI flanges are common in industrial process systems handling water, steam, air and gas. API flanges are manufactured for high strength operating refinery systems with products such as oil and explosive gases.

The flange standards API 6A and ASME/ANSI B16.5 are similar dimensionally - but the API 6A flanges are rated for higher pressures as shown in the table below:

API vs. ASME/ANSI Flanges
Flange Pressure Class Rating (psi) Nominal Size Range
(inches)
ASME/ANSI B16.5 API 6A ASME/ANSI B16.5 API 6A1)
Weld neck 600 2000 1/2 - 24 113/16 - 11
900 3000
1500 5000
Blind and Threaded 600 2000 113/16 - 211/4
900 3000 113/16 - 203/4
1500 5000 113/16 - 11

1) In the old API standard, flanges ranged from 11/2 to 10(20) inches.

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Related Topics

  • Codes and Standards - Piping codes and standards - ASME, ANSI, ASTM, AGA, API, AWWA, BS, ISO, DIN and more..
  • Dimensions - Sizes and dimensions of pipes and tubes, and their fittings - inside and outside diameter, weight and more

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