Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/655822
18 | March - April 2016 | www.machinerylubrication.com OIL ANALYSIS form results in accelerated wear, increased friction and high operating temperatures. If left unchecked, water can lead to premature component failure. The Karl Fischer coulometric moisture test is the most common method used to analyze water levels in oil. When reviewing these test results, remember that low levels of water are typically the result of condensa- tion, while higher levels can indicate a source of water ingress. In most systems, water should not exceed 500 parts per million. Common sources of water include external contamination (breathers, seals and reservoir covers), internal leaks (heat exchangers or water jackets) and condensation. Determining Oil Condition: Acid Number Acid number (AN) is an indicator of oil condition. It is useful in monitoring acid buildup. Oil oxidation causes acidic byproducts to form. High acid levels can indicate excessive oil oxidation or additive depletion and can lead to corrosion of internal components. Acid number testing uses titration to detect the formation of acidic byproducts in oil. This test involves diluting the oil sample and adding incremental amounts of an alka- line solution until a neutral end point is achieved. Since the test measures the concentration of acids in the oil, the effects of dilution often negate the effectiveness of acid number testing. Similarly, some oils containing anti-wear or extreme-pressure additives that are mildly acidic can also provide false high or low readings due to additive depletion. Acid number values should be considered in concert with other factors such as additive health and water content. Gauging Particle Counts The concentration of wear particles in oil is a key indicator of potential component problems. Therefore, oil analysis must be capable of measuring a wide range of wear and contaminant particles. Some types of wear produce particles that are extremely small. Other types of wear generate larger particles that can be visually observed in the oil. Particles of any size have the propensity to cause serious damage if allowed to enter the lubricating oil. Particle count analysis is conducted on a representative sample of the fluid in a system. The particle count test provides the quantity and particle size of the various solid contaminants in the fluid. The actual particle count and subsequent ISO cleanli- ness code are compared to the target code for the system. If the actual cleanliness level of a system is worse than the desired target, corrective action is recommended. Particle counts generally are reported in six size ranges: greater than 4 microns, greater than 6 microns, greater than 14 microns, greater than 25 microns, greater than 50 microns and greater than 100 microns. By measuring and reporting these values, you can gain an understanding of the solid particles in the oil. Monitoring these values also can help confirm the presence of large wear particles that cannot be seen through other test methods. However, particle counting simply indicates the pres - ence of particles and does not reveal the type of particles present. ISO Cleanliness Code The ISO cleanliness code is utilized to help determine solid contamination levels in both new and used oils. The current ISO standard for reporting cleanliness is ISO 4406:99. In accordance with this standard, the values used from the particle count data are related to the greater than 4, greater than 6 and greater than 14 micron levels. The raw data at these micron levels are compared to a standard table and then translated to a code value. It is important to understand the concept behind the ISO code table. The maximum value of each level is approxi - mately two times the value of the preceding level. This means the minimum value of each level is also nearly double the minimum value of the preceding level. This is accom- plished by using the ISO code, which is a value that is an exponent of two, dividing that result by 100 and then rounding. Analytical Ferrography Analytical ferrography is among the most powerful diagnostic tools in oil analysis today. When implemented correctly, it can be an excellent tool for identifying an active wear problem. However, it also has limitations. Analytical ferrography is frequently excluded from oil analysis programs because of its comparatively high price and a general misun - derstanding of its value. The results of an analytical ferrography test typically include a photomicrograph of the found debris along with specific descriptions of the particles and their suspected cause. Particles are categorized based on size, shape and metallurgy. Conclusions can be made regarding the wear rate and health of the component from which the sample was drawn. The analyst relies on composition and shape to determine the characteristics of the particles. Due to the subjective nature of this test, it is best to trust the analyst's interpretation regarding any action to be taken. This test is qualitative, which means it relies on the skill and knowledge of the ferrographic analyst. While most lubrication professionals rely on oil analysis to help safeguard their equipment from unplanned downtime, an inability to dissect and comprehend a problematic report often yields inappro- priate action when abnormal results appear. Your lab can only provide you with the machine condition data. It is up to you to take action. ISO 4406 CHART Range Number of Particles per 100 ml Number More than Up to and including 24 8,000,000 16,000,000 23 4,000,000 8,000,000 22 2,000,000 4,000,000 21 1,000,000 2,000,000 20 500,000 1,000,000 19 250,000 500,000 18 130,000 250,000 17 64,000 130,000 16 32,000 64,000 15 16,000 32,000 14 8,000 16,000 13 4,000 8,000 12 2,000 4,000 11 1,000 2,000 10 500 1,000 9 250 500 8 130 250 7 64 130 6 32 64