Hi Machoguy

As far Api 610 is concern nozzle allowable has no relation with pressure rating like static equipment. Only different specific vendor may agree with higher allowable ( vendor specific).

Just to add one point in this discussion topic.
people consider different temperature profile for idle pump.

1)header to isolation valve average of (ambient + line temperature), since flow is stagnant then valve to pump nozzle ambient temperature.

2) header to isolation valve line temperature. valve to pump nozzle ambient temperature.

Forum member can put some light on the issue.

Regards

Habib