Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGconditions. These steam leaks will waste morefuel than could be saved by a few minutes ofsuperheat operation.The no-control, integral superheater boilercreates a different types of problem. The superheatertubes must be protected from the heat ofthe furnace in the interval during which firesare lighted but the rate of steam generation isstill insufficient to ensure a safe flow throughthe superheater. During operation, there is noproblem since all steam passes through thesuperheater and leaves the boiler at superheattemperature. After the boiler is on the line andfurnishing steam, there will be sufficient flowbecause all steam passes through the superheater.It is sometimes necessary to light off and putadditional boilers on the line, when a ship isunderway. With no-control superheat boilers, thesteps are much the same as for putting the firstboiler or boilers onthe line. With superheat controlboilers, additional precautions must betaken.When the steam lines are carrying superheatedsteam, it would be dangerous to admitsaturated steam to the lines. It is not usuallypossible to establish enough steam flow to lightoff the superheaters of the incoming boilers,until they are on the line. It is permissible tobring in the incoming boilers, without theirsuperheaters in operation, if the superheateroutlet temerature of the steaming boilers islowered to 600° F. Lowering of the superheattemperature on the steaming boilers should bestarted in time so that the cutting- in temperaturecan be reached before the incoming boilersare up to operating pressure. Except in anemergency, the temperature of the superheatersshould NOT be lowered or raised at a fasterrate than 50° F every 5 minutes.A number of other items must be checked orinspected at frequent intervals when a ship isunderway. Engineeroom personnel must be constantlyalert for abnormal pressures, temperatures,sound and vibrations.The first indication of bearing trouble isusually a rise in temperature. There is no objectionto a bearing running warm as long asthe temperature is not high enough to causedamage to the bearing. Any RAPID rise intemperature, or any increase over the normaloperating temperature, is probably a sign oftrouble. The first things to check are thequantity of lube oil and the quality of lube oil.If possible, the amount of oil going to the overheatedbearing should be increased and the flowof cooling water through the lube oil cooler should344be increased. If these measures do not reduce thebearing temperature, the unit must be stopped orslowed.A sight-flow indicator is fitted in the lube oilline of each main engine bearing and each reductiongear bearing. When the plant is in operation,each sight-flow indicator should alwaysshow a steady flow of lube oil.The rotor position indicator for each turbinemust be checked every hour and the readingmust be logged. Any abnormal reading must beinvestigated at once.Once of the first indications of engineroomtrouble is an abnormal reading on a thermometeror pressure gage. All gages should be checkedfrequently.The oil level in the main engine sump mustbe checked every hour and logged in the mainengine operating record. In addition, otherchecks should be made in between the requiredhourly checks. A rise in the oil level may meanthat water is entering the lube oil system or thatthe system is gaining oil in an abnormal manner.A drop in the oil level of the main engine sumpmay indicate a leak in the lube oil system orincorrect operation of the lube oil purifier.The water level in each operating deaeratingfeed tank should be kept between the minimumand the maximum allowable levels. If the waterlevel goes above the maximum, the tank nolonger deaerates the water. If the water level isbelow the minimum, a sudden demand for feedwater may empty the deaerating feed tank andcause cumulative casualties to the feed boosterpump, the main feed pump, and the boilers.A salinity indicator is located at or near thethrottle board in each engineroom so that engineroompersonnel can detect the entrance of saltwater into the condensate system. The salinityindicator must be checked constantly. Even avery small amount of salt in the condensatesystem will very rapidly contaminate a steamingboiler. Any abnormal reading of the salinityindicator must be investigated immediately andthe source of contamination must be found andcorrected.PLANT MAINTENANCEThe maintenance of maximum operationalreliability and efficiency of steam propulsionplants requires a carefully planned and executedprogram of inspections and preventive maintenance,in addition to strict adherence to prescribedoperating instructions and safety precautions.If proper maintenance procedures arefollowed, abnormal conditions may be prevented.