First off, is this a Code requirement? For some reason I don't recall this as a requirement.
Second - if this is not a code requirement it is a good practice to do because it provides additional load carrying capacity, and in my opinion increases resistance to failure from fatigue crack propagation in service.
The code only requires a fillet weld for the joint between the repad OD surface and the nozzle. However, I have seen fatigue crack propagation off the toe of this fillet weld into a nozzle, and have seen cracking that started from the nozzle/shell weld underneath the repad. This resulted in a leak thru the tell tale hole. I always require full penetration tie in between the repad and nozzle, with an external fillet weld, in lieu of only a fillet weld.
