COMPRESS provides an option to design flanges per ASME Section VIII Division 1, Appendix 2, "Rules for bolted flange connections with ring type gaskets."

O-rings are considered to be a "self-energizing" type of gasket. The gasket seal is maintained without any amount of compressive force applied to the gasket. See Table 2-5.1, "self-energizing types" for gasket factors 'm' and 'y' for this type of gasket. Note that no corresponding flange facing sketch is indicated for this type of gasket.

Appendix 2 further stipulates special rules for self-energizing gaskets. These rules are implemented by COMPRESS when both the Gasket Factor 'm' and Gasket Factor 'y' are entered as 0. Appendix 2-5(c)(3)(a) specifically defines the hydrostatic end load Hp and gasket force diameter G for self-energizing gaskets. Thus when both 'm' and 'y' are entered as 0, COMPRESS will apply dimension G as to the outside diameter of the gasket and Hp = 0.

Because the Appendix defines the total joint-contact surface compression load, Hp, the flange facing selection does not affect the flange calculations. Consequently, the specific flange facing selected in COMPRESS is immaterial to the analysis of the flange.

Thus to model a flange with an O-ring gasket in COMPRESS: Select the Appendix 2 flange design option and enter gasket factors 'm' and 'y' as 0. It does not matter which flange facing sketch is selected because the rules from Appendix 2-5(c)(3)(a) will override the flange facing.

Note that facing sketch (6) in Table 2-5.2 is indicated in Table 2-5.1 as for ring-joint gaskets. This type of gasket is generally a relatively soft metal and is often used for specialized applications involving rough service (pipelines, refineries, etc). It is not indicated in Table 2-5.1 as intended for use with calculations for self-energizing gaskets, such as O-rings. Please refer to the first entry in Table 2-5.1, which is for self-energizing gaskets such as O-rings, for which no facing sketch is indicated.