Question:

How does COMPRESS determine the UG-99 stress ratio for flanges designed to Appendix 2? I get a value different from what is reported in the Hydrotest Report.

Answer:

According to UG-99(a)(2)(b), the MAWP is multiplied by "the lowest ratio (for the materials of which the vessel is constructed) of the stress value S for the test temperature on the vessel to the stress value S for the design temperature (see UG-21)." For flanges, the values for S also include the bolt material. This is often overlooked.

(See http://www.codeware.com/support/faq/1033.html for discussion of testing for standard ASME B16.5/B16.47 flanges)