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• To avoid biological contamination and minimize the risk of Legionella, initiate the
biocide treatment program at start-up and continue on a regular basis thereafter in
accordance with the treatment supplier’s instructions.
• Bleed/blowdown or chemical treatment used for corrosion and scale control alone is
not adequate for control of biological contamination.
• Introduce solid or granular biocides through a chemical “pot” feeder installed in
parallel with the system circulating pump. Diluted liquid biocides may be added
directly to the cold water basin.
• If ozone water treatment is used, at no point should concentrations exceed 0.5 ppm to
avoid corrosion.
Chemical Treatment Requirements
Chemical treatment programs must meet the following requirements:
• The chemicals must be compatible with the unit materials of construction as well as
other materials used in the system (pipe, heat exchanger, etc.).
• Chemical scale and corrosion inhibitors, particularly acid (if used), should be
introduced into the circulating water through automatic feeders. This should be done
at a point in the system where total mixing and dilution occur before reaching the
evaporative cooling equipment. The preferred injection point for chemical scale and
corrosion inhibitors is on the discharge side of the system circulating pump(s). These
chemicals should not be batch-fed directly into the unit’s cold water basin or water
distribution system, as this can severely damage areas directly contacted.
• When chlorine is added to the system, free residual chlorine should not exceed 1 ppm,
except during start-up if biological shock treatment is utilized during treatment. Refer
to “Start-Up” on
page 5
for limits. Exceeding this limit may accelerate corrosion.
Passivation
• Passivation is the formation of a protective, passive, carbonate layer on galvanized
steel surfaces.
• To provide maximum protection from corrosion on newly installed units take special
measures to passivate galvanized steel surfaces.
• To ensure proper passivation of the galvanized steel, keep the pH of the circulating
water between 7.0 to 8.2 for four to eight weeks after start-up, or until new zinc
surfaces turn dull gray in color.
• If white rust forms on galvanized steel surfaces after the pH is returned to normal
service levels, it may be necessary to repeat the passivation process.
NOTE:
Stainless steel cold water
basins and basins protected by
the TriArmor
®
Corrosion Protection
System or thermosetting hybrid
polymer do not require passivation.
However, if the upper structure is
galvanized steel, passivation is
required on the galvanized area.