If the nozzle geometry does not satisfy the API 650 requirement, then do we have any other method to evaluate the nozzle loads?

Any thought will be appriciated.

As I said, let the vendor to qualify the loads. Give him some reasonable loads.

Regards,

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...