UFC 3-240-13FN
25 May 2005
to gray or reddish, depending on the composition of the scale. No scale should be
present. It is important to inspect heat exchanger tubes at least once per year.
Fouling-type deposits may look similar to scale deposits. Unlike scale, these
deposits usually adhere loosely to the tube surface. Biomass will appear slimy and feel
slippery, and will usually adhere loosely.
4-6.7.5
Chiller Performance. Degradation of chiller performance or chiller
efficiency may be a strong indication of scale or fouling problems in the chiller. If a
reduction in chiller capacity occurs while cooling water is being cooled efficiently and
within design parameters, then the chiller condenser section should be opened and
examined. The chiller evaporator section may not contain water material scale but may
be fouled with corrosion products. You should open and examine the chiller evaporator
if chilled water could possibly be inadequately treated.
4-6.7.6
Cooling Tower Surfaces. Cooling towers made of galvanized steel
should be examined for white rust or possible rusty surfaces that may indicate that the
galvanizing is no longer present on the metal surfaces and the steel is rusting. Cooling
towers constructed of wood should be examined for wood deterioration or decay.
4-7
COOLING WATER SYSTEM START-UP AND LAYUP
REQUIREMENTS. The startup of a new cooling water system requires special
consideration. Proper cooling water system layup is also important, especially for chiller
tube bundles or other heat exchange equipment. For a new cooling tower system, it is
important to make sure that the equipment that contacts the cooling water is clean and
properly protected from initial corrosion. Also, disinfection is needed to eliminate the
presence of microbiological organisms that can cause corrosion, deposits, and growth
of pathogenic organisms such as Legionella bacteria. Implementation of a proper layup
process is critical to prevent corrosion and microbiological growth during stagnant water
conditions.
4-7.1
Stand-by Conditions. The term "stand-by" is often applied to a chiller that
is in rotation with other chillers on-line. This stand-by period could be of varying
duration, from a few days to a few weeks. Rotating chillers frequently is important for
minimizing stagnant conditions that lead to under-deposit and MIC corrosion. It is good
practice to run the recirculation pumps through a stand-by chiller for at least 15 minutes
each day to minimize corrosion. A chiller that must be left on stand-by for an extended
period of weeks without recirculation should be laid up wet or dry according to
procedures described in paragraph 4-7.4.
4-7.2
Common Problems During Layup or Due to Improper Initial Start-up.
Common problems that occur during layup or due to improper initial start-up include
corrosion of tubes and transfer piping (sometimes to the point of failure), micro-
biological growth with potential for MIC corrosion, and growth of pathogenic
microorganisms.
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