the oil may be added in i.e. a high insolubles content as that causes a depletion of the detergent additive.


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 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. The study of lubrication and wear in machinery is called tribology. Strictly, tribology is the science and engineering of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear. Tribology is a branch of mechanical engineering and materials science. LOA can be divided into three categories:


• analysis of oil properties including those of the base oil and its additives.


• analysis of contaminants.


• analysis of wear debris from machinery.


Oil sampling is a procedure for collecting a volume of fluid from lubricated machinery for the purpose of oil analysis and it is important to ensure that procedures are used to minimize disturbance of the sample during and after the sampling process. The samples are typically drawn into a small, clean bottle which is sealed and sent to a laboratory for analysis. A key factor in the success of the analysis was the development of the spectrograph, an instrument which replaced several wet chemical methods for detecting and measuring individual chemical elements such as iron or copper.


In addition to monitoring 46 | The Report • March 2017 • Issue 79


oil contamination and wear metals, modern usage of LOA includes the analysis of the additives in oils to determine if an extended drain interval may be used. Maintenance costs can be reduced using LOA to determine the remaining useful life of additives in the oil. By comparing the LOA results of new and used oil, a tribologist can determine when the oil must be replaced. Careful analysis might even allow the oil to be sweetened to its original additive levels by either adding fresh oil or replenishing additives that have been depleted.


The analysis usually comprises four standard tests:


1. a spectral examination, 2. an insolubles test, 3. a viscosity test, 4. a flash point test.


In the spectral examination, a portion of the oil sample is taken and passed through a machine called a spectrometer which analyses the oil and yields data that show the various metals and additives that are present. This gives a direct measure of how much wear is taking place in the engine and show the parts of the engine from whence the various particles come.


The insolubles test measures the amount of abrasive solids that a present in the oil. The solids are formed by oil oxidation which takes place when the oil is in the presence of oxygen and heat. The insolubles blow past the piston rings causing wear damage. The test shows how well the oil filter is performing and to what extent the oil has oxidised.


The viscosity test measures the actual grade or thickness of the oil sample. Whatever the original grade of the oil, it should lie within a specific range of viscosity and if the sample falls outside that range the oil will probably have been


contaminated by overheat, fuel, moisture or coolant.


The flash point test measures the temperature at which the vapours from the oil ignite. As with viscosity the oil whatever its grade should ignite at a specific known temperature.


at or above that temperature then the oil is not contaminated.


If the vapours ignite If,


however, they ignite at a lower temperature then the oil is probably contaminated, most likely with fuel oil.


These standards can be performed on any sample of oil, whether it is engine oil, transmission oil, an oil based additive, steering gear fluid, hydraulic oil, biodiesel or any other type of oil. The marine surveyor should know that there are other more specialised tests.


To confirm the results of the ferrous spectroscopy test, two other tests are commonly performed to analyse wear debris.


These are: • particle counting, • analytical microscopy.


Particle counting is actually a test for particle contaminant levels and not specifically wear debris. It does not distinguish between wear and dirt particles but, if it can be determined that nonferrous contamination has remained stable, then an increase in the particle count must be attributable to wear. A magnet can be used to modify the particle count to count ferrous debris only. There are various ways of doing that but essentially a magnet holds back the ferrous debris while the nonferrous debris is flushed from the sample after which a ferrous debris particle count is performed. Such particle counts are invariably reported according to ISO 4406:99. Other standards do exist but they are not as commonly used. ISO 4406:99 yields a three digit solid contamination code. The method of particle counting is not as


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