Figure 1-36.Acid cleaning by fill-and-soak method.
solution. In multiple-drum boilers, divide the charge and
put equal amounts in each of the lower drums.
2. Fill the boiler with hot feedwater to the level of the
bottom of the steam drum. Turn the steam into the boiler
through the usual boiling out connections, or bottom blow,
and allow the boiler to fill gradually to the top of the gauge
3. Steam pressure in the boiler should be kept
between 5 and 10 pounds. The boiling out should continue
for 48 hours. Immediately after boiling out, give a series of
bottom blows to remove the bulk of the sludge. The boiler
should be cooled, washed out immediately, and given the
usual mechanical cleaning.
You may not always want to use the above method
for boiling out.
The steps for a second satisfactory
method for boiling out are as follows:
1. Clean out all loose scale and any scale adhering to
the boiler that can be removed manually.
2. Place about 15 pounds of caustic soda or soda ash
and 10 pounds of metaphosphate for each 100-boiler
horsepower (hp) of the boiler.
3. Seal the boiler openings but OPEN ALL VENTS.
Fill the boiler about three-quarters full with water.
4. Start the burner and raise the temperature of the
water in the boiler to about 200°F. Maintain this
temperature for about 24 to 48 hours. Add makeup
water as required during this period to fill the boiler to
the base of the safety valve.
5. Analyze the boiler water during the boiling out
period and add enough caustic soda and metaphosphate to
maintain the following concentrations:
Causticity as ppm OH 300 to 500
Phosphate as ppm PO3 100 to 150
6. Open the boiler at the end of the boiling-out period
and clean out the sludge and loose scale. Pay particular
attention to removing scale and sludge from water legs in
7. Flush the boiler thoroughly.
8. If a lot of corrosion is exposed when the scale is
removed, notify your superior so a boiler inspection can be
When the boiler is operated, any residual scale may
cause faulty operation. The boiler should be taken out of
service at frequent intervals to remove sludge formed
from disintegrated scale. As soon as personnel can work
in the boilers, wire brush the drums and ends of all tubes.