(d) Remove the tube bundle from the cooler and carefully inspect the
internals of the unit for the following conditions.
(1) Corrosion to tubes, tube sheets, and baffles: Corrosion and
electrolysis (galvanic corrosion) may appear very similar, but they are
different and occur because of the presence of entirely different elements.
Since carbon dioxide and oxygen are the main causes of corrosion, any
operating method that reduces the content of carbon dioxide and/or oxygen will
reduce corrosive effects. One method to control CO2,and 02 levels in the
coolant is to reduce coolant losses wherever possible. This reduces the entry
of additional free CO2 and 02 present in most makeup water. Different
pretreatments of makeup water may be required such as: lime soda softening,
hot lime zeolite softening, acid cycle softening, and salt splitting. All
types reduce the quantity of CO2. Internally, corrosion of piping can be
controlled by the use of corrosion inhibitors.For more information, refer to
NAVFAC MO-225, Industrial Water Treatment.
(2) Electrolysis of tubes, tube sheets, and baffles: Electrolysis
is an electrochemical corrosion associated with the current caused by
dissimilar metals in an electrolyte (coolant). It resembles erosion in
appearance, but the loss of material is due to the exposure of two metals of
different compositions (such as steel and bronze or steel and aluminum) to an
electrolyte (coolant). Two methods used for controlling the effects of
electrolysis are electronic cathodic systems and sacrificial anode placement
within the system (such as zinc compound plugs).
(3) Erosion to tubes, tube sheets, and baffles: Erosion may be
evident at material edges, tube ends, and baffles, due to excessive flow rates
and coolant impurities. Evidence of erosion is rounded edges or depressions
in material surfaces at locations where the flow changes direction or rate.
(4) Leaking tubes: Any leaks in the cooler between the tubes
carrying coolant and the tubes carrying compressed air is detrimental to the
system. If a leak is found during a disassembly inspection it should be
repaired before reassembly. In many instances when the water pressure is
greater than the air pressure, the first indication of a leak is the sudden
increase of moisture at the separator or receiver. If the air pressure is
higher than the water pressure, air then enters the coolant system resulting
in higher temperatures.
(5) Plugged tubes: If tubes become plugged, it is an indication of
an imbalance in the coolant-equipment relationship and conditioning of the
coolant should be considered. Plugged tubes, depending on the number, usually
result in higher system temperatures. Most plugged tubes can be cleaned
without causing damage to the tube. Consult the manufacturer's instructions
(6) Scale deposits: Scale deposits are an indication of an
imbalance between the coolant-equipment relationship. Conditioning of the
coolant should be considered. Scale results in higher system temperatures.
Refer to the manufacturer's instructions for correctional procedures.