Hi marionetking

In my opinion, doing FEA is not really necessary. If you inscribe a circle inside the square outline of the pad, that should be sufficient. The wall of a storage tank has a very large diameter to thickness ratio making it very flexible. The riser if well supported should not be too much of a load on the shell, and the thermal movements should be accommodated by the fairly flexible shell. Just do a simple API 650 analysis with the round pad I suggested above.

That is my opinion.