Proceedings Of The Marine

SUM 2016

Proceedings magazine is a communication tool for the Coast Guard's Marine Safety & Security Council. Each quarterly magazine focuses on a specific theme of interest to the marine industry.

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74 Proceedings Summer 2016 www.uscg.mil/proceedings A nswers Engineering 1. A. prior to conducting the insulation resistance check only Incorrect answer. While any accumulated electrostatic/capacitive charge stored must be removed prior to conducting the insulation resistance check, this is not the only time this discharge is performed. B. while performing the insulation resistance check only Incorrect answer. While performing the insulation resistance check, the machine windings and frame will accumulate an electrostatic/capacitive charge that must be removed after the comple- tion of the check. C. after conducting the insulation resistance check only Incorrect answer. While any accumulated electrostatic/capacitive charge stored must be removed after conducting the insulation resistance check, this is not the only time this discharge is performed. D. prior to and after con- ducting the insulation resistance check Correct answer. For reasons of safety and the prevention of erroneous megohmmeter readings, any accumulated electrostatic/capacitive charge stored must be removed both prior to and after conducting the insulation resistance check. 2. Note: To properly seal the shaft while performing lubrication and cooling functions, the correct number of properly installed packing rings of the correct type must be properly taken up to achieve the designed leak-off rate. A. Replace all of the packing. Incorrect answer. Replacing an insufficient number of correct packing rings with an equal num- ber of correct packing rings will yield the same result: a bottomed-out gland with excessive leakage. B Replace with larger cross-sectional turns of packing. Incorrect answer. Replacing an insufficient number of correct packing rings with an equal num- ber of packing rings with larger cross-sectional dimensions will only substitute one problem for another: inadequate lubrication and cooling accompanied by insufficient leak-off. C. Replace soft packing with packing turns that are covered with lead wrap. Incorrect answer. Replacing an insufficient number of correct packing rings with an equal num- ber of soft packing rings with lead wrap will also substitute one problem for another: inadequate lubrication and cooling accompanied by scoring of the pump shaft. D. Continue to add more turns of packing. Correct answer. Adding more rings of the correct packing to augment an insufficient number of correct packing rings will properly seal the shaft while performing the necessary lubrication and cooling functions as long as the gland is taken up properly to achieve the designed leak-off rate. 3. Note: On V-type medium-speed diesel engines, typically only one bank of cylinders is fitted with air starting valves. A. operation is under higher compression Incorrect answer. Compression pressures are essentially the same for all cylinders, whether or not they are fitted with air starting valves. B. fuel is admitted only to these cylinders during cranking Incorrect answer. During cranking, fuel is admitted to all cylinders in the sequence of their fir- ing order. C. compression is released during starting by opening the exhaust valve Incorrect answer. During cranking, compression is not released by any means. The exhaust valves open toward the end of the power stroke, as they would normally when the engine is in operation. D. cylinders are not chilled by the expansion of the starting air Correct answer. Even though the compression pressures are essentially the same for all cylin- ders — whether or not fitted with air starting valves — those cylinders fitted with air starting valves would tend to have a lower final compression temperature due to the chilling effect of starting air. Therefore, those cylinders not fitted with air starting valves would tend to fire first. 4. Note: Corrosion within boilers may occur on the boiler firesides or watersides. Hydrogen sulfide and sulfur dioxide are troublesome corrosive substances that impact boiler firesides. Oxygen and carbon dioxide, on the other hand, are troublesome corrosive substances that impact boiler watersides. A. hydrogen sulfide Incorrect answer. Hydrogen sulfide, a byproduct of fuel containing sulfur, is a troublesome corrosive substance present in boiler flue gas impacting boiler firesides corrosion patterns. B. sulfur dioxide Incorrect answer. Hydrogen sulfide, a byproduct of fuel containing sulfur, is a troublesome corrosive substance present in boiler flue gas impacting boiler firesides corrosion patterns. C. carbon dioxide Correct answer. Carbon dioxide, a result of faulty deaeration and/or inadequate chemical treatment, is a troublesome corrosive substance which forms carbonic acid, which can lead to carbon dioxide attack of boiler watersides and condensate systems. D. ammonia Incorrect answer. Hydrazine is used as an oxygen scavenger that volatizes into ammonia in helping to maintain condensate and boiler water at the correct levels of alkalinity for corrosion control.

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