UFC 3-240-13FN
25 May 2005
increased. These procedures are recommended for wet layup of a boiler without
draining or cleaning:
1. Approximately 4 hours before the boiler is to be shut down, add sufficient
sodium hydroxide (caustic) to increase the hydroxyl alkalinity (causticity) to
10 to 20% higher than the upper limit given in Tables 3-19 and 3-20 for the
pressure of the boiler to be laid up.
2. Add sufficient sodium sulfite to increase the sulfite residual to 200 ppm (as
SO3).
3. Extinguish the fire to the boiler.
4. Add water to completely fill the entire boiler until the water runs out of the
vent (safety) valve or air cock.
5. When the boiler is completely cool, add more water to ensure it is full.
6. Maintain a pressure of 35 to 69 kilopascals (5 to 10 pounds per square
inch gauge) during layup and maintain the levels of alkalinity and sulfite.
7. Check the boiler frequently to make sure no water has leaked out.
8. Analyze the boiler water at least once per month to make sure the
chemical residuals are being maintained.
3-5.4.2
boilers that have been emptied for cleaning or repair before wet layup:
1. Drain the boiler completely and remove scale or deposits.
2. Remove connections to other active boilers, feedwater, and steam
systems.
3. Fill the boiler with water (deaerated water if available) and add enough
sodium hydroxide (caustic) to give a hydroxyl level of about 200 ppm (as
OH).
4. Add sodium sulfite to give a sulfite residual of 200 ppm (as SO3).
5. Circulate chemicals in the boiler by careful boiling for 2 hours. Be sure to
fill the boiler to replace any losses during this treatment.
6. Extinguish the fire to the boiler.
7. Add water to completely fill the entire boiler until the water runs out of the
vent (safety) valve or air cock.
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