Explain briefly how shore analysts might test the oil.
State the type of information that would be expected.
Give possible reasons for an excess of
Iron
Copper
Antimony
Tin
Silica
Ans)
A) The shore analyst test the oil by the following procedures;
1. FLASH POINT: By Pensky martin apparatus. This method determines the flash point of the LO in a closed cup. This gives the lowest possible ignition point of the oil . The test portion is slowly heated at a constant rate, whilst continuous stirring is provided . A small flame is directed through an open shutter at regular temperature interval with simultaneous interruption of stirring. The flash point is the lowest temp at which the application of the test flame causes the vapour above the test portion to ignite.
2. BASE NUMBER: This method determines the alkaline properties of the oil by titration with perchloric acid. The sample is dissolved in an anhydrous mixture of chlorobenzene and glacial acid and titrated with a solution of perchioric acid in glacial acetic acid. The rate of neutralization of the mixture is indicated using an electrical potential bridge arrangement. Measurements of current are plotted against quantity of the titrating acid mixture. The graph indicates the alkaline reserve at the point where the graph plot inflect
3. KINEMATIC VISCOSITY: The measurement of viscosity is carried out by measuring the time taken for a controlled volume of flow under gravity through a fixed capillary. In order to produce an accurate result, the driving head and the temperature must be controlled. The time taken is directly related to the kinematics viscosity
4.DENSITY: A glass hydrometer is used to measure this. While the test is carried out the temperature should be maintained constant. It is also important that the hydrometer is allowed to reach the same temperature as the measured liquid.
5. INSOLUBLES: This method uses both toluene and pentane to find the level of insolubles. A sample of oil is mixed with pentane and centrifuged. The oil solution is decanted and the precipitate washed twice with pentane, dried, and weighed to give pentane insolubles and then for toluene insolubles , a separate sample of the oil is mixed with pentane and then centrifuged, the precipitate is washed twice with pentane , once with toluence alcohol solution and once with toluene. The insoluble material is then dried and weighed to give the toluene insolubles.
6. WATER CONTENT: In shore testing, water content is found by the distillation method. The oil mixture to be tested is heated under reflux with a water immiscible solvent which co-distils with the water in the sample .Condensed solvent and water are continuously separated by a trap, the water settling in the graduated section of the trap and the solvent returning to the still.
b) type of information expected from the above tests would be the following
1. the flash point of a standard LO is set ( 220 deg c for M E ). Any reduction would surely indicate fuel oil contamination.
2. The base number indicate the level of alkaline reserve. A sharp increase of this indicates contamination of crankcase oil by cylinder oil. Or may be due to leaky stuffing box and excess cylinder lubrication. For auxiliary engines, reduction in BN indicate levels of acid formation due to combustion .
3. If the used oil has lower viscosity it may be due to light fuel dilution like D.o. (leakage from nozzle cooling line etc in auxiliary engine)
4. The pentane insoluble gives the measure of all insolubles due to dirt, wear particles and carbonaceous products from combustion. Whereas toluene insolubles give dirt and inorganic particles and hence a flow of the quantity of combustion desired insolubles in the oil assessed. If the level of insolubles is rising, it indicates the efficiency of the oil cleaning plant are lower ( fine filters and centrifuges). More carbonaceous products indicate an occurrence of poor combustion characteristics.
5.
Any water in the lub oil affects the primary property of lubrication and hence load bearing capacity.
High water content may be indicative of leakages from the water cooled components.
Excess of iron: Excess wear and tear of liners, crank shafts timing gears, camshafts, piston heads, piston rings etc. Iron ore carriers may suffer from these due to the suction of iron ore particles through intake air fitters.
Copper,antimony, tin: due to excess wear and tear from top end bushes, crank pin and main bearings., these are main constituent of white metal overlay
Silica: Due to air- borne or dirt ingress. Also, if the fuel oil contained higher degree of catalytic cracking fines, (mainly alumina and silica), it may contaminate crankcase oil through leaking stuffing box.
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