Nozzle through Blind Flange

chaulklate,

Nozzles can be attached to a standard ASME/ANSI blind flange when the blind is designed as a bolted cover per UG-34. In COMPRESS the mating ASME/ANSI weld neck flange must be designed as an Appendix 2 flange. When this construction is followed a nozzle can be attached to the blind flange in COMPRESS.

This procedure is required because (1) The replacement area required to reinforce the nozzle opening is a function of the required thickness of the blind flange. This value is available only when the blind flange is analyzed as a bolted cover. Analyzing as a bolted cover per UG-34 requires that the edge moment come from the flange analysis. (2) The standard blind flange pressure-temperature ratings are based on the flange cover without holes.

Because COMPRESS will increase thicknesses as required in "design" mode the flange thicknesses may be increased over those of the standard flange. This is due to the different analyses and acceptance criteria of "standard" flanges and those designed by analysis. It is not at all uncommon for B16.47 flanges not to meet the allowable stress criteria of Appendix 2. In this case you may need to change the calculation mode to "rating". COMPRESS will determine the MAWP of the vessel based on the specified thicknesses.

Remember that this forum does not replace Codeware technical support. If you continue to have questions on this issue, write to support@codeware.com.

Tom Barsh
Codeware Technical Support

Thanks Tom. I will take a look at this in greater detail.

Here's a Tip: ASME B16.5 allows a single, central opening in a blind flange without affecting the pressure-temperture ratings. See Table 7. Typically these are limited to small openings, eg: 3.5" NPT in a 24" blind (I go from memory on the size).


Tom Barsh
Codeware Technical Support

I am aware and take full advantage of Table 7 when it applies. It works for some of my applications but not all. I will run some number as per you original reply and see what comes up. Thanks.

Table 7 specifically only addresses "threaded" openings.

Can you use the sizes in Table 7 to validate openings associated with full-penetration welded pipe connections?

Or does any "smooth" opening void the pressure/temperature ratings?

This discussion really belongs in forum292.

In the 2003 ed of B16.5 its Table 6, Reducing Threaded and Slip-On Flanges for Classes 150 Through 2500. This shows a nice cartoon of a flange with a slip on type reducing connection. A slip on type connection would have a larger hole in the flange and two fillet welds as compared to a full pen welded set on attachment. I really doubt any engineer could argue that the slip on approach provides a more robust connection than a full pen set on attachment. It would be nice, though, if B16.5 was a bit more clear on the subject.

jt

Yes - but the slip-on flange includes the extra hub that would not be present with a drilled blind.

OK, taking another look at Note 1 on Table 6, it's clear that a standard blind can be drilled (smooth or tapped)as long as the hole is less than that shown in the Table (ex. 24" blind can have up to a 3-1/2" hole) without invalidating the B16.5 ratings.

Thanks.

Yup, gotta read them notes!

jt