For many, used oil analysis is the bedrock of a successful equipment maintenance strategy. Jarmo Vihersalo, industrial marketing adviser at ExxonMobil, explains what makes it so important.
What is used oil analysis? It’s best described as a blood test for machinery, providing insights into the condition and performance of the equipment and the lubricant being used. This information can help users detect potential problems – such as oil contamination, deposit build-up and wear – often before they become an issue, helping improve equipment reliability and reduce costs.
Gaining the right insights from oil analysis depends on knowing what signals to look for in the results. Since launching its Mobil Serv lubricant analysis platform in 2016, ExxonMobil has processed more than a million samples. Based on its experience, here are four key areas to focus on:
1. A single test does not always tell the full story
Receiving an alert for a single test is not necessarily indicative of an equipment performance issue. Instead, it’s important to look at all test results for the same sample together to decide what might be happening. For example, a common test for gas engines is acid number (AN). In samples ExxonMobil processed, AN figures resulted in alerts more than 5% of the time.
But the AN result alone does not provide insight into how the gas engine is performing. Operators need to consider the significance and relevance of the test when making maintenance decisions. In relative importance, consider oxidation, nitration, viscosity, wear metals and base number (BN) results to truly understand if the lubricant is still performing well. Relying solely on the AN result may lead to the wrong interpretation. This is why consistent monitoring of the complete analysis results trend is an effective method to understand what is happening inside the equipment.
2. Consider the trend, not the absolute test limit
A single alert doesn’t necessarily mean the lubricant is underperforming. In some cases, test limits may not always indicate a cause for concern or may not account for equipment design. Operators must look at the trend over time to understand true performance. A consistent alert over multiple sampling periods, for example, would certainly be cause for closer inspection.
For example, the test for copper wear metal appeared consistently as a top alert in diesel engine samples tested by ExxonMobil. However, some engines have undergone significant design and component changes in recent years. The testing programme must therefore adapt to changes that may affect the limits applied to properly confirm the actual engine condition, and as a result, a single copper alert may not indicate a performance issue. Instead, operators should monitor the trend to see if the copper wear increases over time.
3. Sometimes lubricant formulation can influence test results
When evaluating used oil analysis results, it’s important to consider the lubricant formulation as well as the metallurgy of the equipment. In some cases, components in the formulation can cause alerts for certain tests. For example, some hydraulic oils are formulated with zinc-based additives. These lubricants may cause metal wear test results – including copper tests – to seem abnormally high. In those instances, operators should take a closer look to discover whether copper is actually entering the system or whether components in the lubricant formulation may in fact be triggering the alert.
4. When dealing with water, perform the right test
Water contamination is a major challenge for several industrial applications, including compressors, steam turbines and paper machines, so this potential contaminant deserves its own test.
There are two types of tests that are typically used to measure water contamination in industrial applications – Karl Fischer and hot plate tests. The hot plate test only signifies whether water is present, but it does not provide insight into how much. The Karl Fischer test gives a quantifiable measure, providing far more insight into whether or not the lubricant is suffering from too much water contamination. Therefore operators should consider the hot plate as a conditional test to decide whether the more in-depth Karl Fisher analysis should be conducted to determine the actual level of contamination.
For example, more than 25% of compressor samples tested by ExxonMobil came back with hot plate alerts, but the Karl Fischer test showed alerts around 5% of the time. The implication is that water isn’t yet an issue for most of the equipment tested, and relying on the hot plate test alone may not provide an accurate picture.
In summary, to properly evaluate used oil analysis results, it is critical to work with a lubrication partner that has the right experience to provide application-specific insights and guidance.
To learn more, visit mobilserv.mobil.com or contact your local ExxonMobil representative.