Hello leehc

To get a better handle on the problem, it would be good to send me the file at: support@coade.com.

PD 5500 is very conservative. One of the major problems is the fact that the pressure stress which is the hoop stress multiplied by the stress concentration factor (scf) is added to the membrane componen differently from the way it is done in WRC107. In effect, this pressure stress gets added twice. Also, you will notice that in WRC107 there are a number of blanks in their table, and PD5500 fills in all the blanks.

To see which load is causing the major problem,you could try and see what happens when the pressure is reduced to zero. Also, the circumferential moment can cause a problem.

In Annex W of PD 5500, there is a sample calculation of a nozzle with a re-pad installed in a cylindrical shell, and you will see there how the stress components are added.