The difference between ASME/ANSI and API flanges

 

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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