Hello Mak

PV Elite does not have a provision for external corrosion allowance on nozzles and reinforcement pads. I suggest you add the external corrosion allowance to the internal corrosion allowance for the nozzle, and reduce the thickness of the reinforcement pad by the external corrosion allowance. You may also have to adjust the outside welds for the external corrosion allowance.

This will give you a conservative result.