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:
- Spectrometric analysis is the technology that is most commonly used for trending the concentrations of wear metals such as iron, lead, tin and copper. This technology also detects certain contamination. Coolant contamination can be detected by monitoring the concentrations of elements such as sodium and boron, and dirt contamination can be detected by monitoring the concentration of silicon.
- Since this technology does not detect abnormal particles, it is not an efficient way of predicting machine condition. The main focus of this technology is to trend the accumulation of small particles of wear metals and elemental constituents of additives and to identify possible introduction of contaminants.
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.
Lana Robin is Marketing Manager in the Oil Division at PdMA Corp., Tampa, Florida. Photos courtesy of PdMA. Additional information about PdMA and its services can be obtained by visiting its Web site at www.pdma.com.
Issues to consider
A properly implemented oil analysis program provides significant benefits to the operations of any plant. When implementing an oil analysis program, consider the following issues to receive the best value from your investment:
- When selecting a laboratory for oil analysis, look for one with a quality assurance program. A laboratory with a good quality assurance program can ensure accurate, dependable results in every report. Make sure that the laboratory can provide you with all of your testing requirements in a timely manner.
- Provide the laboratory with as much information as possible about equipment, including lubricant types and maintenance practices. The more information you can provide the laboratory, the more information it will be able to provide you in the report through in-depth interpretations of the data.
- Proper sampling techniques are critical in attaining consistent and accurate lubricant analysis. Improper use of sampling equipment results in contamination. Store sampling equipment in a clean, dry area. Discard disposable sampling equipment after each use. On any given machine, try to use the same sampling technique and obtain the sample from the same relative location in the reservoir. Variations in the oil can sometimes be seen at different locations in the reservoir.
- Place labels on the samples immediately after sampling to prevent possible confusion on reservoir identification. Mislabeled samples could cause a false alarm. The data obtained on the mislabeled sample could show distinct changes in the lubricant's properties. Although the data obtained from laboratory testing on the mislabeled sample would be accurate, the history it would be compared with would be incorrect. Sample quality has an enormous impact on how well your oil analysis program works for you.
- Knowledge of lubricants, their applications and machinery is essential in obtaining the greatest value from your oil analysis program. It is critical that you select the proper tests for the type of equipment and lubricant being tested. Most hydraulic and turbine oil systems have limits on particulate and moisture contamination. Test engine samples for coolant and fuel contamination.
- It's also important to select a proper sample frequency. Sample critical equipment on a more frequent basis and include more extensive testing.
- Once a report has been received from the laboratory, it is important to review it in a timely manner. Be certain that you thoroughly understand the data interpretations and recommended actions provided by the laboratory. It's also important to act quickly on any report findings.
Implementing a routine oil analysis program with analyses consistent with the goals of the program can significantly reduce maintenance costs and improve machine reliability. The analytical costs of a properly implemented program should be covered by the extension of the lubricant change interval. Increased reliability, availability and the prevention of unexpected failures and downtime are added benefits.