API Flanges

High pressure oilfield application service

A standard developed for the American Petroleum Institute, the API 6A specification shares many characteristics with ANSI/ASME flanges. They are dimensionally similar, however their minimal design requirements for operating pressure begin in the 2000# class, which is derived from the ASME/ANSI 600# class. Certain jobs require the use of pressure classes as high as the 6BX 25000#, though this is much less common than the typical 6B range of 5000# and below. All API flanges require ring type joint facings with the proper gaskets for optimal integrity of their application. This higher-pressure base requirement is due to their overwhelmingly popular use in petrochemical / oilfield applications of a volatile nature. Upstream assemblies with API flanges consist of wellheads, drilling equipment, and much more. The downstream sectors of refinery and processing also require these flanges for the development of crude oil into products for the everyday consumer.


API Ring Type Joint Flange

^^^ ( a ring groove is a standard requirement for API flange faces ) ^^^


*API stands for “American Petroleum Institute” and more information can be found on their website: https://www.api.org/


Looking For Dimensional Data? Check out our API Flange Slide Rule!





API vs. ASME/ANSI flanges

Compatibility between pressure classes and size


API and ASME/ANSI flanges are not necessarily interchangeable, however some of the RTJ styles from ASME B16.5 do match up dimensionally with existing API flanges. API 6A flanges in 5000# class and below are often made from A105 carbon steel with a 45K minimum yield strength, whereas the API 6BX flanges of 10000# class and above require a steel with an even higher yield strength. The most common of those is AISI 4130 with a 75K yield.

You are more likely to find ASME/ANSI flanges in general pipeline assembly work and vessel service, whereas API flanges are often found in oilfield equipment as originally intended. B16.5 flanges will typically deal with materials such as air and high flow liquids, whereas API will handle primarily unrefined crude oil, refined petrochemicals, and high energy gases.

The flanges per standards API 6A and ASME/ANSI B16.5 which share dimensions are listed below: