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Need to drill 3 thread holes on a blind flange 2
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B16.5 permits a single concentric opening in the blind flange without affecting the pressure-temperature rating. However, the maximum size opening is restricted; if a larger size opening is used then a hubbed flange is required. See Table 6 in B16.5 (Table 7 in earlier Editions).
Modifying the blind flange by placing multiple openings would seem to be a modification such that it no longer qualifies as a standard pressure component and the standard pressure-temperature ratings would no longer be applicable. Design/analysis of the modified blind flange would fall under the applicable design code (piping code, boiler and pressure vessel code, etc).
Modifying the blind flange by placing multiple openings would seem to be a modification such that it no longer qualifies as a standard pressure component and the standard pressure-temperature ratings would no longer be applicable. Design/analysis of the modified blind flange would fall under the applicable design code (piping code, boiler and pressure vessel code, etc).
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moltenmetal
Chemical
TomBarsh has given the "correct" answer. If you want the "practical" answer, here it is: assuming that the connections to these new holes are of a nature that do not transfer significant moments to the flange, and the total area of the three holes is no larger than the area of the single hole permitted in an ordinary blind flange per B16.5, you're OK in practical terms. The openings must be spaced properly to permit the attachment welds (if those are necessary) to be done properly.
If the total area exceeds that permitted for a single hole in a blind flange, you need a hubbed blind (good luck finding one!) and you probably should do an Appendix 2 calculation per ASME VIII-1. The blind flange (in fact even the hubbed blind) will probably fail per Appendix 2 because ASME B16.5 flanges are over-bolted, but you will need to add thickness (i.e. to make a custom flange) or increase the flange class if you go the Appendix 2 route.
If the total area exceeds that permitted for a single hole in a blind flange, you need a hubbed blind (good luck finding one!) and you probably should do an Appendix 2 calculation per ASME VIII-1. The blind flange (in fact even the hubbed blind) will probably fail per Appendix 2 because ASME B16.5 flanges are over-bolted, but you will need to add thickness (i.e. to make a custom flange) or increase the flange class if you go the Appendix 2 route.
where are the 3 holes? Are you drilling threaded holes into the OD of the flange for lift eyes?
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