Minimum distance with reinforcing pad

[jnog]

When designing pressure vessel following ASME VIII, I have a reinforcing pad for a nozzle very close to the knuckle region of the thorispherical head. I suppose there is requirement on minimum distance between them but I don't find anything in the code. Could you help me ?
Thank you.

 

[DSB123]

jnog,
Have a look in PD5500. There is a sketch which shows the proximity of re-pads to knuckle regions.

 

[jte]

jnog-

You didn't state whether the nozzle is in the head or shell. In any case it's ok. Specifically, for a nozzle in a shell, see Interpretations Volume 25 for Int VIII-89-83:

Question: A pressure vessel with an inside shell diameter of 42 in. has a 28 in. diameter circular opening into which a nozzle will be inserted. This opening is located such that the limits of reinforcement measured parallel to the vessel wall will extend to the dished portion of the head. Do UG-40(a) and (b) permit the limits of reinforcement to extend to the dished portion of the head?


Reply: Yes.



jt

 

[jnog]

The nozzle is in the head. Maybe could I decrease the pad diameter and increase his thickness, to keep the same area ?

 

[jte]

jnog-

Have you already ordered the head? Sounds to me that the easiest way to deal with this will be to just order a thicker head and use a thicker nozzle neck and increase the fillet weld size. Forming a repad for this would more or less require you to order a second, slightly larger head, cutting out the pad section and then hoping that it fits up well over the head. In any case, it is VIII-1 legal as far as I know. But in this case the integral reinforcement option that I mentioned above will be better from a reliability perspective as well as easier to fabricate. If you go with a thicker repad, make sure that it is not too much thicker than the corroded thickness of the head - say no more than 1.5* the corroded thickness.

jt

 

[PVinspector]

jte,

That is a strangely worded question/interpretation. Jnog is asking about the knuckle, not the dish, but if I understand the question in the interpretation the opening is not in the head, but the reinforcing region is. So, it would have to cross the knuckle to get to the dish, unless it is a dished only head, which is rare except when welded to a bolting flange.

I agree though, it is acceptable either way.