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By Lana Robin
The philosophy of oil analysis as a predictive maintenance technology has drastically changed over the past few years. We've moved far beyond simply looking at the dipstick or through a site glass to determine the oil's ability to keep performing. As technologies continue to increase and equipment reliability issues become more progressive, oil analysis also has advanced in its techniques.
Advanced lubricant techniques are now being used to determine the lubricant's condition, as well as to monitor the condition of the equipment.
An effective lubricant analysis program increases the reliability and availability of equipment while reducing the costs associated with labor, repairs and downtime. It is important to evaluate and select a program that best fits the needs of your company. Carefully selecting a test package that is consistent with the goals of the program ensures that you are performing the appropriate tests on the type of equipment being used.
Analytical techniques performed on oil samples can be classified in two categories, used oil analysis and wear particle analysis. Used oil analysis determines the condition of the lubricant itself, determines the quality of the lubricant and checks its suitability for continued use. Wear particle analysis determines the mechanical condition of machine components that are lubricated. Through wear particle analysis, you can identify the composition of the solid material present and evaluate particle type, size, concentration, distribution and morphology.
Problems detected in an oil analysis program include wear, contamination and degradation. The following represent the most common oil analysis techniques and their importance:
Solids content determines soot (in diesel engines), sludge, varnish and gross particulate contamination. Upward changes in the level of solids may indicate environmental or wear debris. It is especially useful in systems with poor or unsophisticated filtration.
Water content determines the presence of water in the sample. Water compromises the lubricating properties of oil, promotes component corrosion and indicates malfunctioning lubricating components. Increased water concentrations indicate possible condensation (possibly prior to adding a new lubricant), coolant leaks or process leaks around seals.
Viscosity is the most important physical property of oil. Therefore, viscosity determination is a critical component of an effective analysis program. Viscosity measurements monitor the resistance to flow at a specific temperature. A decrease in viscosity may indicate contamination with a solvent, fuel or an oil of lower viscosity. An increase may indicate lube oxidation or contamination with a thicker lubricant.
Particle counting tracks ranges of particles found in the sample. However, particle counting does not differentiate the composition of material present. Excessive particulate contamination is a major cause of failure in hydraulic pumps, motors, valves, pressure regulators and fluid controls. Results are typically reported in certain size ranges per milliliter or per 100 milliliters of sample.
The results can be directly correlated to a common classification issued by the International Standards Organization (ISO). An ISO code is based on the concentration of particles in a specific size range.
Direct reading (DR) ferrography monitors and trends the relative concentration of ferrous wear particles and determines a ratio of large to small ferrous particles to provide insight into the wear rate of the lubricated component.
This method can be used as a primary tracking and trending tool, especially in systems with a high ratio of particles. DR ferrography may also be used in cases in which particle count results are invalid, such as when the lubricant is opaque or contaminated with water.
Total acid number is a measurement of the amount of acidic agents present in the sample and indicates lube oxidation or contamination. Monitor systems in which an extended drain interval is contemplated or the potential exists for acidic contamination for an increase in acidic contaminants.
Total base number monitors the acid neutralizing reserve of the lubricant. This component is critical to the analysis of internal combustion engine lubricants. A decrease in the total base number indicates a corresponding decrease in the lubricant's acid-fighting ability.
Infrared analysis monitors the chemical composition of oil on the basis of IR response at certain key wavelengths. Contaminants such as glycol, fuel and water are detected in units such as emergency diesel crankcases. Lubricant degradation products, such as oxidation and nitration, are monitored and trended.
Analytical ferrography is a technology that uses microscopic analysis to identify the composition of the material present. This technology differentiates the type of material contained within the sample and aids in determining the wearing component from which it was generated.
This test method determines characteristics of a machine by evaluating the particle type, size, concentration, distribution and morphology. It will assist you in determining the source and resolution of the problem.
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