High water content is possibly an exception. On some plants it would be removed simply by centrifuging the oil, but such a process is not usually available on smaller installations and, if excess water is found, the diagnostic and maintenance engineer should at least suggest that the oil should be changed. For detergent oils, a third reason for changing the oil may be added in i.e. a high insolubles content as that causes a depletion of the detergent additive.
Oil samples should be taken and analysed annually and at least three samples should be taken at each investigation; one either side of the filter and a minimum of one from the machine’s sump.
Lubricating oil analysis (LOA) is the laboratory analysis of a lubricant’s properties, suspended contaminants and wear debris. It is a quick non-destructive method of gauging the health of an engine by taking a close, specialised look at what is in the oil and should be performed as part of a routine preventative maintenance scheme to provide meaningful and accurate information on the lubricant and machine condition. By tracking oil analysis sample results over the life of a particular machine, trends can be established which can help eliminate costly repairs and down time.
The diagnostic or maintenance engineer should be aware, however, that receiving a warning from a single sample is not necessarily indicative of a machine performance issue and he should know that it’s extremely important to examine all test results from a given sample in order to be able to decide what is happening. An acid number (AN) test, for example, may give off a warning but, by itself, that does not provide any meaning full insight into how the machine under test may be performing. The engineer needs to consider the relevance of the test when making any maintenance decision and, in relative importance, he should also consider viscosity, oxidation, nitration, the presence of wear metals and the base number (BN) in order to truly understand whether or not the lubricant is performing as well as it should. Reliance on one factor such as the acid number may well lead to erroneous results. It does not mean that the lubricant is underperforming. Consistent monitoring of the complete analysis results trend over time are, therefore, essential and become an effective tool to enable him to understand what is happening inside the machine. As another example, when a series of particular compression ignition engines were tested over a long period, a consistent warning was found on copper wear metal.
Investigation showed, however, that a number
of the engines had undergone significant design and component changes.
It was agreed, therefore,
that the testing programme had to adapt to changes that affected the limits applied in order properly confirm the actual engine condition. That showed that a single copper waning did not necessarily indicate a performance issue and that the trend over time needed to be considered to see if the copper wear figures increased in the studied period.
When the diagnostic or maintenance engineer is analysing the results of a used oil sample, as well as the metallurgy of the machine’s components, he should also consider the chemical formulation of the lubricant itself. Occasionally, the lubricant’s own components may give warning signs for certain tests. For example, some oils are formulated with zinc based additives which may indicate that metal wear test results including copper tests to seem abnormally high. If such a result appears, then the analyst and engineers should make a more detailed study to see whether the copper is actually entering the lubrication system or whether components in the oil are the direct cause of the warning.
Perhaps the worst major challenge for a number of industrial machines is the presence of water. As a result,
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