API TR 6AF2

The original design criteria and pressure ratings that form the basis of all present API flanges dimensions are based, developed in the late 1920s and 1930s, did not address external loading capabilities. The flange designs were based on surface stress calculations, which were appropriate for uniform-axis symmetric loading conditions as used for bolt loading and pressure.

Determining the limiting conditions of flanges beyond that of pressure rating, where external loading is considered, requires knowledge of stresses as they are distributed through the thickness. Methods of calculating these stresses have been developed through the use of finite element programs, and have been applied in this technical report.

Compliance with the API 6A criteria requires stress linearization calculations based on the methodology established by ASME Pressure Vessel Code, Section VIII, Division 2. These criteria are defined in terms of stress distributions through the thickness and necessitate a more accurate means of calculating component stresses as provided by finite element analysis. The present work establishes a better understanding of the stress distribution in these flanges under the effect of the combined actions of pressure, bending moment, tension, and the original bolt make up of the flange. The flange capacities which meet the design stress criteria of API 6A are determined.