25 May 2005
used instrument of this type is a linear polarization corrosion instrument that provides
instantaneous corrosion measurement and is often used for troubleshooting.
Heat Transfer Corrosion Test Equipment. Heat transfer corrosion test
equipment is used to determine the corrosion rate under heat transfer conditions. This
type of equipment can more accurately determine corrosion in chillers.
INTERPRETATION OF RESULTS FROM WATER TESTS. Adequate
chemical treatment of water systems requires that specific levels of specific chemicals
be maintained in the water to provide the system with protection from corrosion and
deposits. This requirement applies to both cooling and boiler water systems. When an
analytical test indicates that the concentration of a given chemical is not within the
required limits, the testing process must be evaluated to determine whether sampling
and testing were performed properly and the test result is valid. As part of an adequate
QA/QC program, test methods, including the chemical reagents, must be checked on a
routine basis. Consider these guidelines when evaluating test results:
When the (valid) test results indicate a treatment level that is too low, the
chemical addition program should be evaluated and the appropriate
adjustment made; this normally means increasing the chemical feed rate
by 10% or less. If adjustments to the treatment program do not correct the
situation, then the entire water system may need to be evaluated to
determine the nature of the problem. You can obtain assistance through
the military offices suggested in paragraph 1-1.10.2.
When the (valid) test results indicate that a given level of treatment
chemical is too high, the chemical addition program should be evaluated.
Exercise caution when reducing chemical feed rates to adjust the level of
a treatment chemical that exceeds the required limits. The chemical feed
rate should not be reduced more than 5 to 10% at any one time.
When the test results indicate that the level of hardness in the water is
higher than the required level, the makeup water treatment system should
be investigated and problems identified, including other possible incoming
sources of water hardness into the system.
Alkalinity Test Relationships
Sources of Alkalinity. The three basic sources of alkalinity in water result
from the bicarbonate ion (HCO3-), the carbonate ion (CO3-), and the hydroxyl ion (OH-).
The amount of each of these ions in water can be determined by titration with an acid to
specific pH levels (end points) using phenolphthalein (P alkalinity) or methyl orange (M
alkalinity) indicators to their particular titration end-points. The relationship between pH
and the various types of alkalinity is shown in Figure 6-4.