1. RECOMMENDED PROCEDURES
FOR
LAYING UP BOILERS
A. Pre-operation Period. When the boiler is ready for the hydrostatic test, proceed as follows:
1. Fill the superheater with condensate or demineralized water containing 10 ppm (10
cm3/m3) of ammonia and 20 ppm (200 cmi/mi) of hydrazine. The pH value of the
solution should be approximately 10.0. The condensate is added at the superheater
outlet to overflow into the boiler drum.
2. When the condensate overflows from the superheater into the boiler drum, the
addition of condensate at the superheater can be stopped and the unit filled as
described in step3.
3. Fill the boiler through the normal. filling connections with hydrazine treated water.
Close boiler drains and open boiler vents as during normal filling procedures.
4. At the conclusion of the hydrostatic test, with the boiler and superheater filled to
overflowing, pressurize the unit to 3-5 psi (21-35 kPa) gage with nitrogen.
a. Where freezing is a problem, the water in the drainable circuits can be displaced
with nitrogen and then the unit is laid up under nitrogen pressure. Auxiliary
heat is then applied to keep the non:drainable superheater elements above
freezing.
b. With drainable superheaters allsurfaces can belaid up under nitrogen pressure.
5. Boilers without stop valves in the main steam line should have the outlet isolated by
meansof a blank flange, or equivalent, so that a small positive pressure can be applied.
8. Post Boil-Out Period. Ifthe operation of the boiler isdelayed after boiling out or acid cleaning
it should be filled as follows:
Introduce condensate containing about 10 ppm (10 cm3/m3) of ammonia and 200 ppm (200
cm3/m3) of hydrazine to the boiler and superheater and pressurize the unit with nitrogen.
C. Short Outage Period. No draining. If the boiler isshut down for a period of three to four days,
and the boiler pressure will drop to atmospheric pressure:
Introduce nitrogen through the boiler drum vent or at a superheater drain valve when the
steam pressure drops below5 psi (35 kPa). Maintain a total pressure of 5 psi (35 kPa) due to
nitrogen.
D. Long Outage. Boiler not opened for repair work. Where the boiler is removed from service
for a prolonged shutdown, asa seasonal outage of a month or longer:
1. Fillthe superheater, adding the condensate to the outlet of the non-drainable sections
until overflowing into the boiler. Then proceed with filling the boiler with a
condensate containing 10 ppm(10 cm3/m3) of ammonia and 200 ppm (200 cm3/m3) of
hydrazine.

2. The treated condensate can be displaced with nitrogen or
the entire unit can be laid up wet under nitrogen pressure
depending upon the temperature of the surrounding
area. Maintain a nitrogen pressure of 3-5 psi (21-35 kPa)
gage. If the main steam line is not equipped with a stop
valve, steps should be taken to blank off the line so that
the boiler can be pressurized.
2. If freezing weather conditions arise during the outage
means must be provided to keep the elements above
freezing temperature.
NOTES: The use of hydrazine (N2H4) has been found acceptable as a reducing
agent.
Nitrogen purging is important in the complete
elimination of oxygen.
When the unit is to be put. in service, it will be
necessary to bring the water levelto normal
and open the drum and superheater vents
before lighting off. To conserve nitrogen supply
used in pressurizing the unit, shut off the supply
before opening the vents.