PRINCIPLES OF NAVAL ENGINEERING 



38.140 

 Figure 10-29. — Evidence of carryover in 

 superheater tube. 



the carryover of large slugs of water, is partic- 

 ularly dangerous because it can do such severe 

 damage to machinery. For example, priming can 

 actually rip turbine blades from their wheels. 

 One cause of carryover is foaming of the 

 boiler water. Foaming occurs when the water 

 contains too much dissolved or suspended solid 

 matter. The solids tend to stabilize the bubbles 

 and cause them to pile up instead of bursting. 

 If a great deal of solid matter is present in the 

 boiler water, a considerable amount of foam 



will pile up. Under these conditions, carryover 

 is almost sure to occur. 



In order to counteract the effects of the im- 

 purities in boiler water, it is necessary to have 

 a precise knowledge of the actual condition of 

 the water. This knowledge is obtained by fre- 

 quent tests of the boiler water and of the feed 

 water. Boiler water tests include chloride tests, 

 hardness tests, alkalinity tests, pH tests, phos- 

 phate tests, and electrical conductivity tests 

 which indicate the dissolved solid content of the 

 boiler water. 8 Feed water is tested routinely 

 for chloride, hardness, and dissolved oxygen; 

 alkalinity, pH, phosphate, and electrical conduc- 

 tivity tests are not normally made on feed water. 

 The frequency of boiler water and feed water 

 tests is specified by the Naval Ship Systems 

 Command. Also, the allowable limits of con- 

 tamination are specified by the Naval Ship Sys- 

 tems Command. In general, the requirements 

 for purity of boiler water become more stringent 

 with increasing boiler pressure. 



Water tests aboard ship are made by the oil 

 and water king (usually a Boilerman), although 

 certain aspects of the preparation and handling 

 of the chemicals may require the supervision 

 of an officer. The tests require some knowledge 

 of chemistry and a high degree of precision in 

 preparing, using, and measuring the chemicals. 

 Therefore, only personnel holding a current 

 certification resulting from successful comple- 

 tion of a NavShips boiler water/feed water test 

 and treatment training course may test and 

 treat boiler water and feed water on propulsion 

 boilers. 



Some of the water tests made aboard ship 

 give a direct indication of just what contaminat- 

 ing substance is present, and in just what amount 

 it is present. In other cases, it is more im- 

 portant to know what effects the contaminating 

 substances have upon the water than it is to 

 know what the substances are or exactly how 

 much of each is present. Therefore, some water 

 tests are designed to measure properties the 

 water acquires because of the presence of vari- 

 ous impurities. 



The term chloride content really refers to 

 the concentration of the chloride ion, rather 

 than to the concentration of any one sea salt. 



Note, however, that no one ship makes all of these 

 tests of boiler water. The types of boiler water tests 

 required on any particular ship depend upon the method 

 of boiler water treatment authorized for that ship. 



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