25 May 2005
3. Maintain a pH of 7.5 to 8.9. Adjust with dilute hydrochloric or caustic as
4. If copper is present, maintain a minimum of 10 ppm of tolyltriazole.
5. Test monthly for proper pH and treatment levels.
Treatment and Control of Microbiological Growth. Treatment and
control of microbiological growth is a concern in chilled or closed cooling water systems.
It is a particular concern if a nitrite-based corrosion inhibitor is used. Nitrite can serve as
a nutrient for some bacteria. Microbiocide selection must be compatible with the
corrosion inhibitor program and the pH levels in the system water. Glutaraldehyde and
isothiazolone are commonly used in chilled water systems. Oxidizing biocides should
not be used since they are not compatible with nitrite water treatment.
Identifying Water Leaks. The best way to check for leaks in a closed
water system is to periodically read and record the water usage displayed by a totalizing
water meter installed in the makeup water line or to use an inert, fluorescent material
indicate a leak. The florescent material can also be used to help pinpoint leaks or do
leak studies. If the system does not have a water meter, the existence of leaks can be
checked by testing the inhibitor concentration in the circulating water. The inhibitor
concentration should be measured once per month using molybdate, polysilicate, or
azole, but not nitrite. Do not depend upon the nitrite test; nitrite can be lost due to
bacteria action. If nitrite is measured and its concentration has decreased while the
values for both parameters decrease, there is a leak in the system. Borate
concentration would be the best indicator of leak detection. When the inhibitor
concentration has dropped to 98% of the original value, about 2% of the system water
will have been lost. If the lapsed time for this 2% loss is less than 4 months, the
system's loss of water is excessive and any leaks should be found and eliminated.
Another convenient indication of water loss is the measurement over time of a drop in
conductivity. If the system water conductivity equals that of the makeup, the treatment
chemical is totally absent. Inert florescent material can be added to the system and
used to help pinpoint leaks, or do leak studies. Loss of the fluorescent material can be
monitored in real time; such loss indicates a leak.
NOTE: A 2% loss over 4 months equals 0.5% loss per month. The accuracy of this test
is limited, so if the loss for any month exceeds 1%, the test should be repeated. If
retesting confirms the water loss, the leaks should be found and eliminated.
a) The initial recommended molybdate concentration in chilled water systems
is 125 ppm. After 4 months, the concentration is 123 ppm. Is the water
Loss = ([initial final]/initial) x 100