Quantcast CHAPTER 2. CONTROL AND MAINTENANCE

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TB 55-1900-207-24
CHAPTER 2. CONTROL AND MAINTENANCE
SECTION I. CONTROL
2-1. Prevention of Scale.
a. Only fresh water will be used in closed cooling systems. Sea water (raw water) will not be used in any closed
cooling system. Water from the ship's potable water system or direct from shore fresh water connection may be used
when condensate, distilled, or mineral-free water is not available.  Where means are available, fresh water being
introduced into the cooling system should be softened prior to use in order to remove the scale forming elements. This
can be accomplished by using sodium tetraphosphate, technical (Specification O-S-635).
b. As softened water is not always readily available, it is necessary to soften the water inside the cooling system by
chemical means. The conditioning chemicals used in treatment of cooling water tend to hold the scale-forming elements
in suspension and to convert the sludge-forming elements into a relatively harmless solution, which can be removed by
periodic cleaning of the cooling system.
2-2. Scale and Corrosion Control. Treatment of cooling water to prevent formation of scale and corrosion include:
a. Mechanical filtration to remove dirt and foreign matter.
b. Water softening procedures to prevent mineral deposit buildup.
c. Addition of antifreeze extender to prevent rust and corrosion and control pH value.
2-3. Specific Control Measures. The factors contributing to and accelerating harmful conditions in the cooling system
are controlled as follows:
a. Dirt and solid matter are removed by straining and filtering the untreated cooling water prior to use.
b. Carbonic acid and other acidity is controlled by the addition of antifreeze extender additive (MILA-53009) which
contains sodium borate (borax). pH values below 6.5 indicate acid activity and possible corrosion. pH values above 9.5
indicate high alkalinity conditions which favor deposition of scale and may cause damage to brass fittings, aluminum,
solder, and pump packing/seal. The borax keeps the pH of the cooling water stabilized around 9.2 in the summer. This
value corresponds to a low alkalinity condition. In winter when military anti-freeze, MILA-46153, is used in the cooling
system, the pH value will range from 7.5 to 8.0. The antifreeze extender additive is compatible with military antifreeze
only and is used to reinhibit used MILA-46153 in order that it can be used for up to two additional years.
c. The concentration of oxygen is reduced by sodium chromate which acts as an oxygen scavenger. This chemical
also inhibits the corrosion and pitting of cylinder liners. It reacts with iron and oxygen to form a protective coating on the
metal surface.
d. Scale forming elements are held in suspension by the sodium salts in sodium tetraphosphate. This process is
called water-softening.
e. Non-ferrous metals are protected from corrosion by the sodium mercaptobenzothiazole (NaMBT) contained in
the antifreeze extender additive.
2-4. Treatment Chemicals.
a. Antifreeze extender additive conforming to Military Specification MIL-A-53009 contains borax, NaMBT, and
potassium silicate. The borax acts as an alkalizer and buffering agent. NaMBT prevents copper and brass corrosion and
provides additional buffering action. The potassium silicate prevents aluminum corrosion.
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