FEPipe has a "low tank nozzle" template to do an FEA stress check on the Tank/nozzle interface.

Justify the loads by this "rigorous calc" (a much sharper pencil) than the antiquated API method. Again check the local stress by calculation. A good stress engineer typically is light years ahead of most vendors in this regard. The vendors just follow the GENERAL cookbook CODE guidelines.

Calculate, Calculate, Calc...