API and ASME/ANSI flanges - comparing dimensions and pressure ratings
Although the dimensions of ASME and API flanges may sometimes be compatible for bolting - using the same bolt circle and the same number of bolts - they do not share the same pressure rating system.
- ASME rates the pressure of a class based on the material of construction and the design temperature
- API specifies allowable materials and gives it a specific pressure rating
The difference between ASME/ANSI and API is the fabrication material and a higher rated API operating pressure.
ASME/ANSI flanges are commonly used 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 have the same dimensions - but the API 6A flanges are rated for higher pressures as indicated below:
|API vs. ASME/ANSI Flanges with the same Dimensions|
|Flange||Pressure Class Rating (psi)||Nominal Size Range |
|ASME/ANSI B16.5||API 6A||ASME/ANSI B16.5||API 6A1)|
|Weld neck||600||2000||1/2 - 24||113/16 - 11|
|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 1 1/2 to 10(20) inches.