come from grease cups which are used on some
water pumps to lubricate bearings. If the cups are
turned down too much or too often, grease is
forced into the circulating water. A hole in the
element of an oil cooler permits oil to flow into
the cooling system. Any source of oil or grease
should be located and repairs made as soon as
Corrosion or erosion of the element in a heat
exchanger, as well as operation at excessive
pressure, may cause LEAKS. These leaks can
develop either in the element or in the casing.
Leakage from the cooler casing can usually be
detected by inspection. Element leaks, however,
are more difficult to detect. Any noticeable decline
or rise in the freshwater tank level, with the
temperature remaining normal, usually indicates
A hole made by corrosion in a cooler element
indicates that corrosion probably exists
throughout the element, and a thorough inspec-
tion should be made. Corrosion can be prevented
to a large extent by using the prescribed freshwater
treatment, inspecting as necessary and venting the
cooler to remove entrapped air.
Holes due to erosion are usually caused by
particles of grit (sand, dirt, etc., resulting
usually from operation in shallow water) striking
an element at high velocity. Grit is for the most
part so fine that it passes easily through the
strainer. If the strainer is defective, even the larger
particles of grit may enter the cooler.
Erosion by water at high velocity may also
result in holes in a cooler element. This occurs
when water flow has to be increased above the
rated capacity in order to maintain a desired
freshwater temperature. Whenever it is found
necessary to greatly increase the water flow, the
cooler should be cleaned.
If the designed maximum operating pressure
(indicated on the exchanger name plate) is ex-
ceeded, leaks are apt to result. Excessive pressure
is likely to occur in conjunction with clogging,
because additional pressure is necessary to force
a given quantity of water through a clogged
MAINTENANCE AND REPAIR
Because of the difference in their construction,
methods of cleaning both types of heat exchangers
(radiator and tubular) differ in some respects.
Radiator-type heat exchangers are cleaned by
chemical means because mechanical cleaning is
not satisfactory for this type heat exchanger.
Chemical cleaning of radiator-type units is
discussed in Engineman 3 & 2, NAVEDTRA
10541 (current edition). Tubular heat exchangers,
on the other hand, are cleaned by mechanical
In both types of heat exchangers, loose foreign
matter such as seaweed, sand, and dirt may be
removed by blowing steam through the element
in a direction opposite to the normal flow of
water. When an element is badly clogged, care
must be exercised not to admit steam at a pressure
exceeding the maximum specified for the element.
If a film of oil or grease is evident, the element
should be cleaned like an oil cooler element.
Leakage from the CASING of a radiator-type
heat exchanger may be caused by a damaged
gasket. If so, the heat exchanger should be re-
moved from the piping in order that flange faces
may be tightened evenly after a new gasket is
installed. If there is any reason to suspect that
there are leaks in a heat exchanger element, the
best method for locating them is by an air test.
This test may be accomplished as follows:
1. Remove the element from the casing.
2. Block off the discharge side of the element.
3. Attach a pressure gage to the inlet line of
4. Supply low-pressure air to the inlet side of
the element. Remember: Air pressure must
NEVER exceed design pressure for the
5. Immerse the element in a tank of water.
6. Check for bubbles.
An element of a heat exchanger may also be
tested hydrostatically by filling the element with
water under pressure and checking for leaks.
Emergency repair of leaks in the element of
a radiator-type heat exchanger can be made as
shown in figure 3-13. When emergency repairs to
the radiator-type heat exchanger are necessary,
they may be made with the use of soft solder and
a small torch or soldering iron. Extreme care must
be taken to prevent the surrounding area from
being overheated, thus causing the existing solder
to melt. Small radiator-type heat exchangers
ENGINEMAN 1 & C