BAC PCT Series Operation & Maintenance Manual page 33

Chemical Treatment Programs Must Meet or Exceed the Following
Requirements:
1. The chemicals must be compatible with the unit materials of
construction as well as other materials used in the system (pipe,
heat exchanger, etc.).
2. Chemical scale and corrosion inhibitors, and particularly acid (if
used) should be introduced into the circulating water through
automatic feeders 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.
3. When chlorine is added to the system, free residual chlorine
should not exceed 1 ppm, except as noted in start-up and
shutdown section. Exceeding this limit may accelerate corrosion.
Passivation:
1. Passivation is the formation of a protective, passive, carbonate
layer on galvanised steel surfaces.
2. On the newly installed units, to provide maximum protection
from corrosion, take special measures to passivate galvanised
steel surfaces.
3. To ensure proper passivation of the galvanised 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
colour.
4. If white deposits form on galvanised steel surfaces after the
pH is returned to normal service levels, it may be necessary to
repeat the passivation process.
Corrosion and Scale Control
Corrosion and Scale Control
Passivation
M A R 1 0 8 - 2
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