AmbEng17:
It would seem that you would do well to get yourself some good PV Design textbooks or a good PV Design Handbook, and study them for answers to these kinds of questions. You should also study some good books on Engineering Mechanics and Strength of Materials. You should not be designing PV’s, for construction, and asking these kinds of basic questions. It appears that your software is much smarter on this subject than you are, and that’s a dangerous way to design and build PV’s. What are the various loads on the legs, gravity and lateral, etc? What happens to the legs, what loads are added to the legs, when the vessel expands or contracts due to working pressures? Do the legs move laterally at their base plates, at the foundation when they are loaded?
I think if you had written to Codeware Technical Support they might have told you that the local stresses in the cylindrical shell where the leg attaches should be considered in the design of the shell. It is possible that these local stresses (analyzed by something like WRC bulletin 537) could limit the maximum pressure that the shell could sustain.
