come from grease cups which are used on somewater pumps to lubricate bearings. If the cups areturned down too much or too often, grease isforced into the circulating water. A hole in theelement of an oil cooler permits oil to flow intothe cooling system. Any source of oil or greaseshould be located and repairs made as soon aspossible.Corrosion or erosion of the element in a heatexchanger, as well as operation at excessivepressure, may cause LEAKS. These leaks candevelop either in the element or in the casing.Leakage from the cooler casing can usually bedetected by inspection. Element leaks, however,are more difficult to detect. Any noticeable declineor rise in the freshwater tank level, with thetemperature remaining normal, usually indicatesleakage.A hole made by corrosion in a cooler elementindicates that corrosion probably existsthroughout the element, and a thorough inspec-tion should be made. Corrosion can be preventedto a large extent by using the prescribed freshwatertreatment, inspecting as necessary and venting thecooler to remove entrapped air.Holes due to erosion are usually caused byparticles of grit (sand, dirt, etc., resultingusually from operation in shallow water) strikingan element at high velocity. Grit is for the mostpart so fine that it passes easily through thestrainer. If the strainer is defective, even the largerparticles of grit may enter the cooler.Erosion by water at high velocity may alsoresult in holes in a cooler element. This occurswhen water flow has to be increased above therated capacity in order to maintain a desiredfreshwater temperature. Whenever it is foundnecessary to greatly increase the water flow, thecooler should be cleaned.If the designed maximum operating pressure(indicated on the exchanger name plate) is ex-ceeded, leaks are apt to result. Excessive pressureis likely to occur in conjunction with clogging,because additional pressure is necessary to forcea given quantity of water through a cloggedelement.MAINTENANCE AND REPAIRBecause 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 bychemical means because mechanical cleaning isnot satisfactory for this type heat exchanger.Chemical cleaning of radiator-type units isdiscussed in Engineman 3 & 2, NAVEDTRA10541 (current edition). Tubular heat exchangers,on the other hand, are cleaned by mechanicalmeans.In both types of heat exchangers, loose foreignmatter such as seaweed, sand, and dirt may beremoved by blowing steam through the elementin a direction opposite to the normal flow ofwater. When an element is badly clogged, caremust be exercised not to admit steam at a pressureexceeding the maximum specified for the element.If a film of oil or grease is evident, the elementshould be cleaned like an oil cooler element.Leakage from the CASING of a radiator-typeheat exchanger may be caused by a damagedgasket. If so, the heat exchanger should be re-moved from the piping in order that flange facesmay be tightened evenly after a new gasket isinstalled. If there is any reason to suspect thatthere are leaks in a heat exchanger element, thebest 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 ofthe element.4. Supply low-pressure air to the inlet side ofthe element. Remember: Air pressure mustNEVER exceed design pressure for theelement.5. Immerse the element in a tank of water.6. Check for bubbles.An element of a heat exchanger may also betested hydrostatically by filling the element withwater under pressure and checking for leaks.Emergency repair of leaks in the element ofa radiator-type heat exchanger can be made asshown in figure 3-13. When emergency repairs tothe radiator-type heat exchanger are necessary,they may be made with the use of soft solder anda small torch or soldering iron. Extreme care mustbe taken to prevent the surrounding area frombeing overheated, thus causing the existing solderto melt. Small radiator-type heat exchangersENGINEMAN 1 & C3-14
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