“Within 14 days after welding, all products of
zirconium Grade R60705 shall be heat-treated
at 1000 °F–1100 °F (538 °C–593 °C) for a minimum
of 1 hr for thicknesses up to 1 in. (25.4
mm) plus ½ hr for each additional inch of thickness.
Above 800 °F (427 °C), cooling shall be
done in a closed furnace or cooling chamber at
a rate not greater than 500 °F/hr (260 °C/hr)
divided by the maximum metal thickness of the
shell or head plate in inches but in no case more
than 500 °F/hr. From 800 °F, the vessel may be
cooled in still air.”