24 July 2003
including Change 1, Jan 2004 and Change 2, March 2005
D-3.2 For a short storage period, condensate or feedwater containing approximately
100 to 200 ppm of sodium sulfite may be used. If the superheater is drainable, it can
also be filled with the same treated water by overflow from the boiler.
D-3.3 If the superheater is not drainable, refer to the plant operating manual or
request assistance from your cognizant EFD.
Alternative Wet Lay-Up Methods. The boiler may be stored with water at a
normal operating level in the drum and nitrogen maintained at greater than atmospheric
pressure in all vapor spaces. To prevent in-leakage of air, it is necessary to supply
nitrogen at the vents before the boiler pressure falls to zero as the boiler is coming off
line. If boiler pressure falls to zero, the boiler should be fired to reestablish pressure
and the superheater and reheater thoroughly vented to remove air before nitrogen is
admitted. All partly filled steam drums and superheater and reheater headers should be
connected in parallel to the nitrogen supply. If nitrogen is supplied only to the steam
drum, nitrogen pressure should be greater than the hydrostatic head of the longest
vertical column of condensate that could be produced in the superheater. Rather than
maintain the water in the boiler at normal operating level with a nitrogen cap, it is
sometimes preferable to drain the boiler completely, applying nitrogen continuously
during the draining operation and maintaining a pressure of nitrogen greater than
atmospheric throughout the draining and subsequent storage.