What Is An Appendix-2 Flange?Posted on May 5, 2011 by dburr

What are Appendix-2 flanges? Firstly, the name stems from the fact that they are found in Appendix-2 of

ASME VIII-1.

Secondly, they are custom flanges. This allows the designer the flexibility to manipulate the different flange

variables, unlike flanges designed to ASME B16.5 and ASME B16.47, which fully describe materials,

dimensions and pressure ratings for flanges.

Design Options:

Style: Appendix-2 flanges can be designed in a number of configurations, such as slip-on, lap joint, and

weld neck, even for very large flanges.

Dimension: Aside from the flange configuration, some other variables that can be manipulated are the

bolt circle diameter, number and size of bolts, hub thickness and length, flange thickness and outer

diameter.

Shape: Appendix-2 flanges can be circular or non-circular. However, there does not appear to be any

provision for a non-circular bore in Appendix-2. Hence, only the flange’s outside edge can be of another

shape.

Split: Flanges designed to Appendix-2 can be split loose flanges, where the flange is split into two halves.

Further, an Appendix-2 split flange can be designed as a pair of concentric split rings, where the splits are

offset by 90°.

Limitations:

Gasket: For an Appendix-2 flange, the gasket must be completely contained within the bolt circle

diameter. This prevents the use of a full-face gasket on an Appendix-2 flange.

Contact: There must be no metal-to-metal contact outside of the bolt-circle diameter in an Appendix-2

flange. If there is any metal-to-metal contact the flange will most likely fall under Appendix-Y.

Loads: Appendix-2 calculations cover the hydrostatic end load, called the operating condition, and the

gasket seating condition only. Thus it is designed for pressure loads only. The effect of external piping loads

must be accounted for separately.

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