Full definition
Oil analysis is a crucial predictive maintenance technique that involves examining lubricating oil samples from machinery to identify potential issues before they lead to catastrophic failures. This method focuses on three primary areas: wear metals, contamination, and oil condition. Wear metals, such as iron, copper, chromium, aluminum, and lead, are detected through spectrometric analysis and particle counting, following the ISO 4406 standard. The presence of these metals indicates wear and tear of components, providing insights into the health of the machinery. For instance, elevated levels of copper might suggest bearing wear, while high iron levels could indicate gear wear. By monitoring these particles, operators can effectively assess the operational state of machinery and schedule maintenance accordingly.
Contamination is another critical aspect of oil analysis. It encompasses various factors such as water content, dirt, fuel dilution, and coolant contamination. Water contamination is typically measured using Karl Fischer titration, with a maximum acceptable level of 200 ppm for most systems. Dirt and silica can be assessed by analyzing silicon content. Fuel dilution and coolant contamination are also assessed to ensure the integrity of the lubricant. For example, the presence of glycol in the oil could indicate coolant leaks, which may lead to overheating and subsequent component failure if not addressed.
The condition of the oil itself is evaluated through changes in viscosity, Total Acid Number (TAN), and Total Base Number (TBN). Viscosity changes are determined using ASTM D445, while TAN and TBN indicate the state of the oil’s additives and its oxidative stability. An increase in TAN suggests oxidation and a breakdown of the oil, while a decrease in TBN indicates depletion of the additive package. Techniques like FTIR spectroscopy are employed to measure oxidation and nitration levels. By trending these oil analysis results over time, maintenance teams can identify developing problems 2-6 months before they lead to failures, allowing for planned interventions rather than emergency repairs. This proactive approach significantly reduces the risk of costly downtime and repair expenses.
Proper sampling is crucial for accurate oil analysis. Samples should be taken from a turbulent flow point rather than the drain to avoid sediment disturbance. Additionally, samples should be collected at the operating temperature and in clean sample bottles to prevent contamination. Consistent sampling intervals also help in establishing reliable trends. Standards such as ISO 4406 for particle counting, ASTM D6224 for in-service monitoring, and ASTM D7647 for trending provide a framework for effective oil analysis. The typical cost for oil analysis ranges from $15 to $40 per sample, which is minor compared to the potential loss incurred from a single bearing failure, which can exceed $50,000 including downtime.