There are many different designs for boilers and so there will never be "standard" allowable nozzle loadings. The only thing you can do is to ask the OEM to provide the allowable nozzle loadings for various inlet and outlet headers. My experience with this has not been good. The typical response to such a request is for the OEM to propose an analysis at a huge expense. Sometimes though, you get lucky and someone in the OEM's engineering department will look in the archives and find (and send you) the header drawings that were provided with the boiler (for installation purposes) and these drawings will sometimes have the allowable loadings (and the calculated cold-to-hot expansion movements) for the piping "by others". Sometimes, but it happens rarely. More rare (twice in my 46 years in the business) is the response from the OEM telling you that their header construction is so robust that your pipe will yield under loading before the loadings will challange the structural integrity of their boiler ("they just don't build 'em that way any more" - but at one time they tried to).
The structural analysis of the headers and their supporting boiler structure is likely the only way to develop "maximum allowable loadings". It is important to NOT look at the local header connection exclusively because often the limiting construction detail is some distance from the connection. We have all been through this and there is no easy way to get the information needed to perform the analyses correctly.
I would like to second John Breen's comments about the lack of boiler OEM cooperation on this issue. After all, he is in the business of selling essentially the same boilers over and over and gets this question repeatedly
The stress analyst's simple legitimate requests for information from the boiler OEM are looked upon by the MBAs as an opportunity to make money, not as cooperation between professionals.
I also have been involved with developing "more accurate" CAESAR-II piping models by incorporating the headers (ASME Section I)and supports. In my opinion, this is one method to prove to management that the loads you have developed are more legitimate. Of course, this assumes that you have boiler drawings on time and that everyone is cooperating....
Here is another link where this issue was discussed..
Also, here are standard loadings used by GDF Production (NEDERLAND B.V.)for shell and tube heat exchangers.
These are preliminary loads, to be used by th HX supplier in his design and by the stress analyst in his stress evaluation of the system and pipe support placement..
We occasionally run into similar issues. One problem is that the allowable load depends on the direction of the load and depends on the combinations of other loads and other conditions, so it's not always meaningful to just specify some number. If the piping person comes up with a nozzle load without considering the stiffness or deflection (ie, deflection from other non-pipe loads) of the nozzle, then the requested load is liable not to be too meaningful either.
