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What ExxonMobil learned from analysing oil samples

Any good maintenance strategy should consider using used oil analysis (UOA), so operators can make informed decisions about when to make costly interventions such as oil changes and learn about any issues in the machinery, such as excessive wear or water contamination.

To help operators analyse their oils, Mobil launched its Mobil Serv Lubricant Analysis programme in 2016. This relieved Mobil’s customers of the need for in-house analysis equipment by allowing them to send samples to Mobil in pre-labelled bottles. By using a smartphone app to scan both the code on the bottle and the machine, the need for manual labelling is removed, helping to speed up the process.

Since the programme’s introduction, Mobil has analysed a million oil samples from equipment such as gas engines (over 100,000 samples), hydraulic systems (over 100,000 samples), diesel engines (over 243,000 samples) and many more. Not surprisingly, this, combined with the company’s previous experiences with oil analysis, has given it some key insights into interpreting UOA results.

A lubricant’s formula can affect a test’s results

It may be often overlooked, but some lubricants may include elements that help trigger alerts on oil analysis. As an example, it’s possible that a hydraulic oil may contain some zinc-based additives. Clearly they are there for a reason, but they may also make the tests for metal wear, including copper, give inflated results. In such cases, the machinery needs to be considered in this context. Question whether it really is machine wear or lubricant ingredients, and if needed, take a closer look to get to the bottom of it.

One result is not always sufficient

It may be tempting to heed an alert from a single test, but this is not always telling the whole story. Looking at all the test results for a single sample will be more useful in determining how your equipment is performing.

For example, Mobil said that of the samples it processed from gas engines, more than 5% led to an alert for the acid number (AN). Considering this alone, though, could well lead to an incorrect interpretation. If you instead also consider the results for factors like oxidation, wear metals, nitration, base number, and viscosity, you will gain a better overall understanding of how an oil is really performing within a piece of equipment. This in turn enables you to make better maintenance decisions.

Trends are also important

An alert may be a cause for concern, but sometimes they can occur because the limit does not consider the design of a certain piece of equipment. In such cases, it may be worth looking at the trend over time rather than the individual alerts. For example, if the copper wear is increasing over subsequent tests, it’s more likely to indicate an issue.

Water needs the right test

There are two tests for water contamination: The Hot Plate test, which only indicates the presence of water, and the Karl-Fischer test, which quantifies the amount of water.

Should the Hot Plate test indicate water, a second Karl-Fischer test may be warranted to establish if the lubricant is actually suffering because of it.

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