UFC 3-240-13FN
25 May 2005
loose, porous structure may be left behind. This residual material can be effectively
removed from the equipment either mechanically or by washing with high-pressure
water.
9-2.2.3
Phosphate Deposits. The removal of phosphate deposits can usually be
accomplished by using hydrochloric acid; however, phosphate deposits have a
tendency to dissolve rather slowly. To minimize the total cleaning time, a temperature of
49 to 60 C (120 to 140 F) is usually necessary to remove a predominantly phosphate
scale.
9-2.2.4
Metallic Oxides. Most metallic oxides found in deposits can be removed
with hydrochloric acid. The rate of dissolution is a function of temperature and solution
velocity. If copper oxides are present on steel surfaces, special precautions are needed
to prevent copper metal plate-out on the steel.
9-2.2.5
Silica and Sulfate Scale. Heavy silica and sulfate scale is almost
impossible to remove with hydrochloric acid. Special chemicals and procedures are
required to remove this scale.
9-2.2.6
Hydrochloric Acid Limitations. Hydrochloric acid is not used to clean
stainless steel because the chloride ion in the acid solution may cause pitting or stress
corrosion cracking. Hydrochloric acid is not used for removing scale from galvanized
steel surfaces since the galvanizing will corrode. Aluminum is not cleaned using
hydrochloric acid.
9-2.3
Sulfamic Acid. Sulfamic acid is an odorless, white, crystalline solid
organic acid that is readily soluble in water. An inhibited sulfamic acid compound, in a
dry powder form, is available under Military Specification MIL-B-24155, Boiler Scale
Removing Compound. A 5 to 20% solution (2 to 9 kilograms to approximately 38 liters of
water [5 to 20 pounds to approximately 10 gallons of water]) is used for removing scale
from metal surfaces. The following information pertaining to sulfamic acid should be
considered:
Carbonate deposits are dissolved in sulfamic acid in a similar manner as
in hydrochloric acid. All the common sulfamate salts (including calcium)
are very soluble in water.
The dry powder form of sulfamic acid is safer to handle than a liquid
solution of hydrochloric acid; however, aqueous solutions of sulfamic acid
are much slower in action and require heating to remove scale. The
sulfamic acid solution is heated to a temperature in the range of 54 to 71
o
C (130 to 160 oF) to obtain the same fast cleaning time that is achieved
by using hydrochloric acid at room temperature. Sulfamic acid is more
effective on sulfate scale than hydrochloric acid.
Inhibited sulfamic acid, used at temperatures up to 43 oC (110 oF), will not
corrode galvanized steel. Its use is recommended for removing scale in
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