UG-42

[Vattappilly]

Can anyone enlighten me about UG-42 rules?

For a 50 psi vessel,

On almost all cases, I find that we can do openings per Fig-UG-42 (a). I mean it makes you to do some extra steps such as UG-42 (a) conditions 1 & 2 and supplemental rules, 1-7 (a) (c), But we can do it without increasing the shell or the nozzle thicknesses.

UG-42 (c) (Fig –UG-42 (b)) looks like a showstopper as it expects the whole compensation to come out of the shell.

What is the philosophy behind these rules?

 

[tmdixon]

When you have two or more openings that are close together as described in UG-42(b) and (c) then the limits of reinforcement for each of the nozzles is overlapping, so you cannot use that shell material in your reinforcement alculations.

 

[johnnymist2003]

Vattappilly,

I cannot comment on the philosophy behind the rules of UG-42(c), save to say that the rules of the Code have been formulated over many years, contibuted to by many individuals with vast amounts of knowledge and experience. It would be best to assume that the Code rules, as written, will provide the safest margin against failure that is available. Not to heed them would constitute breaking the law in terms of the requirements of most, if not all, statutary bodies. Having said that, maybe this will help...UG-42(c) provides an alternative to the rules of UG-42 (a) & (b). UG-42 (c) would be likened to a "shortcut" so that the designer does not need to do the calculations to UG-42 (a) & (b). However, in the instance of two or more openings spaced less than 1 1/3 their avereage diameter, it is mandatory to use UG-42(c). For UG-40(c), you are quite correct, the nozzle necks shall not be considered in the available area calculation, thus all the reinforcement must come from the shell (IMHO). The limits of reinforcement for openings spaced less than 1 1/3 their average diameter overlap to such a degree that the available reinforcement in the shell between the openings would be negligible. For UG-42(c) the limits of reinforcement available in the shell shall be based on the dimensions of the assumed opening (the one encompassing the group of openings), and would presumably be quite large. This would compensate for ignoring the reinforcing area available in the nozzle necks of the actual openings.
John