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OPERATION AND MAINTENANCE OF AUXILIARY BOILERS

The wide variation in design of auxiliary boilers and their auxiliaries, accessories, and controls makes it impractical for this chapter to include specific operating and maintenance instructions for all types of boilers.

All personnel charged with the operation of an auxiliary boiler should be thoroughly familiar with the boiler, its controls, and all safety precautions. Operating instructions can be found in the appropriate manufacturer’s technical manual. All boiler operators must be concerned with two hazardous conditions that could occur in a boiler when the automatic control system malfunctions: (1) low water level or (2) excess fuel in the combustion space (which tends to turn the boiler into a bomb). Operator and maintenance personnel must NEVER bypass or defeat any of the safety controls and devices used on auxiliary boilers. Maintenance requirements for auxiliary boilers are contained in your ship’s PMS Manual.

Testing the Boiler Water

You must be able to determine the actual condition of the water used in auxiliary boilers. You can make this determination by chemically testing the water. The tests you may be required to perform are for alkalinity, phosphate, chloride content, and conductivity. We will briefly discuss each of these tests.

TESTING FOR ALKALINITY.-Alkalinity is a property that water acquires from certain chemical impurities. The allowable limits for alkalinity authorized by NAVSEA are 0.10 to 0.50 epm.

There are two methods of testing for alkalinity. The phenolphthalein test is used to test water samples from steaming boilers and to test water samples from idle boilers which have been steamed. The methyl-purple test is used to test water from freshly filled boilers which have NOT been steamed. If a boiler has been idle for a long time, it is best to use both tests.

TESTING FOR PHOSPHATE.-Phosphate is a chemical that is added to boiler water to aid in making suspended solids of the scale-forming impurities in the boiler water. The chemical action of suspending impurities helps to prevent boiler waterside scale formations that may interfere with the circulation of the boiler water and the effectiveness of the heat transfer surfaces. The phosphate test will indicate the amount of phosphate dissolved in the boiler water. The allowable limits for phosphate treatment of water in auxiliary boilers, as authorized by NAVSEA, are between 50 and 100 ppm.

TESTING FOR CHLORIDE CONTENT.- The term chloride content really refers to the concentration of the chloride ion, rather than the concentration of any one sea salt. Because the concentration of chloride ions is relatively constant in seawater, the chloride content may be used as a measure of the amount of solid matter in boiler water that is caused by contamination, either from poor quality output from distilling plants or from leakage into feedwater storage tanks located below the ship’s waterline. The result of the chloride test is used as one indication of the need for blowdown of the boiler to prevent excessive contamination of the water. The allowable limit for chloride content authorized by NAVSEA is 1.0 epm.

TESTING FOR CONDUCTIVITY.-Con-ductivity, a measure of how well a substance can pass an electric current, is measured in micro-mhos per centimeter (µmho/cm). The reason you should be concerned about conductivity is that conductivity is directly related to corrosion. An increase in boiler water conductivity is an indication that boiler metal may be corroding. Pure water is the ideal boiler water, because pure water has a high resistance and low conductivity. The rate of metal corrosion is low in pure water. As suspended and dissolved solids (impurities), such as the chlorides and sulphates of sodium, calcium, and magnesium, form in the water, they add ions to the water. IONS are charged particles that provide a path for current to travel. As the level of impurities rises, the level of ions also rises and the conductivity of the boiler water increases. This condition will accelerate corrosion. Therefore, by measuring for conductivity of the boiler water, you can determine the purity of the water and whether or not corrosion is taking place. The allowable limit for conductivity, as authorized by NAVSEA, is 600 µmhos/cm.

Making boiler water tests is a rather complicated job which requires a great deal of care and attention on your part. A water test result that is based on careless or inaccurate test procedures is not only useless but also may be dangerously misleading. You will not be able to obtain any useful information about the condition of the boiler water unless you perform each test with accuracy.

Since you must complete the prescribed certification course to conduct boiler water/feed-water tests, we will not cover the test procedures in this chapter. You can find the testing procedures in the Naval Ships’ Technical Manual, Chapter 220, Volume 2, “Boiler Water/Feedwater Test and Treatment.”



 


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