Flanges - API vs. ASME/ANSI

Comparing API and ASME/ANSI flanges

Although the dimensions of ASME and API flanges sometimes are compatible for bolting - 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 are similar dimensionally - but the API 6A flanges are rated for higher pressures as indicated 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 1 1/2 to 10(20) inches.

Search the Engineering ToolBox

Engineering ToolBox - SketchUp Edition - Online 3D modeling!

3D Engineering ToolBox - draw and model technical applications

Engineering ToolBox - SketchUp Edition - enabled for use with the amazing, fun and free SketchUp

Translate the Engineering ToolBox
About the EngineeringToolbox