Oil analysis methods and lubrication monitoring

Don’t let machine friction drive profit and power loss.

By Amin Almasi, Rotating Machinery Consultant

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An oil analysis and lubrication monitoring program should addresses a wide variety of effects and should involve contamination control methods and established oil cleanliness procedures. Friction, lubrication oil, wear, and wear particles are interactive and cannot be separated.

The friction within machineries directly translates into power loss. Lubrication oil costs constitute significant parts of machinery operation costs in any plant. The wear is one of the primary characteristics defining the end of life for plant machinery and leads to costs of maintenance, replacement, and production outage. An effective oil analysis and lubrication oil monitoring program can increase efficiencies of machineries and reduce the operating costs. The value of this program can only be realized if it can be collected and analyzed in a timely and organized manner. The oil analysis can reveal important information about the condition of machinery, oils, and contaminations in the oils.

In order to reduce the operating costs of any plant, the focus should be on its machineries. It’s necessary to improve machinery availability and reduce the operational and maintenance costs associated with them. The reliability and availability of operating machinery depend largely on the protective properties of their lubrication oil. The machinery industry currently uses lubrication oil analysis for monitoring machineries, particularly lubrication oil performance, bearing wear, and gear system operation.

One of the purposes of lubrication oil condition monitoring is to determine whether the lubrication oil has deteriorated to such a degree that it no longer fulfills its functions. However, this is not the only purpose. Different lubrication oil condition monitoring techniques can be used to monitor lubrication oil wetted components and detect their degradation rates and possible developing damage. Many moving components are actually lubrication oil wetted parts such as bearings, gear units, or piston/cylinder in reciprocating machines. Viscosity and dielectric constant could be used as the performance parameters to identify the degradation of lubrication oils. Particles, as the result of wear of wetted machinery components, could also be detected and classified to identify the wear rates and health situations of such components.

Water and impurities

The oil contamination analysis can reveal deterioration or breakdown of the oil, contamination of the system with water or particulate debris, and wear of the lubricated machinery.

Water or impurities in the lubrication oil can clearly be seen at the visual inspection of samples. Water can be seen either in the form of emulsification or as a distinct water layer. The general cleanliness level of the lubrication oil may also be determined by a visual test of samples. Once filtered, the debris should be visually examined prior to microscopic examination. The presence of water within the lubrication oil can also be detected from the filter paper used for oil analysis. This is seen in the form of light circular areas on the filter paper. Water also sometimes oxidizes the ferrous material, and the presence of rust could indicate the ingress of water. Water affects the viscosity of the lubrication oil, considerably reducing the effect of the lubrication oil and increasing wear rates.

Frequently gear units become contaminated with mineral particles such as silica, coal, and shale. These produce fine abrasive wear particles normally only observed under the microscope. The unchecked presence of mineral particles, specifically quartzite with its high hardness, should be avoided in the lubrication oil system. The mineral particles in suspension act as a grinding medium and can produce excessive bearing wear, which leads to loss of shaft location and further accelerates the wearing process.

Wear debris analysis

Wear debris analysis is a technique for analyzing the debris, or particles, present in lubrication oil that could indicate wear, particularly mechanical wear. This method provides microscopic examination and analysis of debris/particles found in a lubrication oil. These particles consist of metallic and nonmetallic matters. The metallic particles usually indicate a wear condition that separates different sizes and shapes of metallic dust from components like bearings, gears, and generally any components that can be wetted by lubrication oil. Nonmetallic particles may consist of dirt, sand, or corroded metallic particle. Analytical ferrography is one of the methods used in wear debris analysis; it’s among the most powerful diagnostic tools for condition monitoring.

When implemented correctly, the wear debris analysis provides very useful information on machinery under operation. It’s not still in common use for all machineries because of its comparatively high price and a general misunderstanding of its value. Wear debris analysis can also help with improving lubrication oil filtration efficiency and frequency for the lubrication oil cleaning and changeover. Machinery performance may be improved through proper filtration of oil. Clean oil lubrication is always more effective.

The wear debris analysis procedure in its comprehensive form is lengthy and requires the skill of trained analysts and experts. As such, there are significant costs for a comprehensive wear-debris-analysis procedure. However, most machinery experts agree that the benefits significantly outweigh the costs and elect to automatically incorporate such a method when abnormal wear is encountered.

The most important aspect of wear debris analysis is its capability to identify developing damages and malfunctions in their initial stages. This is the main reason why such an expensive and complicated condition monitoring method should be used instead of or in addition to simpler and cheaper condition monitoring tools such as online vibration monitoring.

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