Tagged: oil tests

Interpreting the Oil Analysis Report in Practice

Now, we will actually read a report to help put all of these into practice.

Here is a sample report from Eurofins for a turbine oil. In this report, the various types of tests are classified according to wear metals, additives, and contaminants, as shown in Figure 2.

According to the report, samples have been collected over a period of time. This helps with the trending of the data, so we can spot when the values start varying from the “normal levels”. The reference values are also provided in the first column to help users determine whether these values fall within tolerance limits or not.

Interpreting the Oil Analysis Report in Practice

Figure 2: Sample Turbine Oil Analysis Report

Typically, the lab will provide some type of traffic light system where:

Red – indicates there may be an abnormal reading or the oil should be changed immediately, as certain values have surpassed the critical limits.
Amber – shows that the values are approaching the warning limits, but there is still some time to investigate and fix the problem.
Green – tells us that all values are within the tolerance limits and the oil is performing normally.

For this report, they also include additional tests as shown in Figure 3.

Figure 3: Additional Tests for Turbine Oils

For turbine oils, understanding the demulsibility of the oil is important, as this is the oil’s ability to separate from water, or rather, not to form an emulsion. Excessive water in the oil can lead to rust or even a washout of the additives.

The Foam test is also administered to detect the oil’s ability to release air from the oil, ensuring that the air doesn’t get trapped. If air is trapped, it can lead to microdieseling and cavitation on the inside of the equipment.

RPVOT – Rotating Pressure Vessel Oxidation test is also performed, as it indicates the expected oxidation of the oil. MPC (Membrane Patch Colorimetry) and Ultracentrifuge detect the potential of the oil to form varnish, and the RULER® values give the actual quantity of antioxidants present. These values are all critical for monitoring the health of the turbine oil, as it is very susceptible to oxidation and the formation of varnish.

In essence, reading the oil analysis report involves understanding what the tests are meant to measure, knowing your equipment and its operating conditions, and having a history of your equipment. These factors all contribute to trending the data to ensure that there are no surprises with unplanned downtime due to wear or oil degradation.

References

Eurofins. (2025, September 06). Annual Turbine Analysis. Retrieved from Eurofins Testoil: https://testoil.com/services/turbine-oil-analysis/annual-turbine-analysis/

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Oil Properties / Used Oil Analysis

How to Interpret Your Oil Analysis Results

Have you ever received your bloodwork results from your doctor, only to be more confused than ever? With all the long names and numbers just sitting on the piece of paper, Google (or ChatGPT) becomes your best friend to help interpret what they mean. However, even with these tools of reason, there is usually a disclaimer that states, “Please consult your doctor for a more accurate interpretation”.

Numbers alone don’t tell the whole story – context is what makes oil analysis meaningful.

One of the reasons for constantly looping your doctor back into the mix is that they have your history, they know how your body responds to certain things, and values which may get flagged because they are outside of the limits may be waived away by your doctor because it is normal for your body based on your history and DNA.

The same applies to oil analysis. Depending on the application and operating environment, certain conditions may be met that can be interpreted as unusual. Still, if you’re familiar with your system, you will understand the reason behind the numbers.

How to Interpret Your Oil Analysis Results

Figure 1: DIN 515519 table showing viscosity limits

Viscosity

As mentioned earlier, viscosity is the most important characteristic of a lubricant. If it is too thick for the application, this can lead to efficiency loss, increased heating, and a slowdown of the system. Essentially, a significant amount of work needs to be done on the oil to make it compatible with the application.

On the other hand, if it is too thin, then we run the risk of improper lubrication. Therefore, we increase the chances of wear occurring in the applications.

Viscosity is usually measured at either 40°C (for industrial applications) or 100°C (for engine applications). However, most labs put a ±5% tolerance limit for many oils. But why use such a random figure? The DIN 51519 table is used to determine ISO viscosity, with each value within a 10% range, as shown in Figure 1.

When you see an ISO VG 100 oil, the chances are that the actual viscosity of that oil varies between 90-110cSt. Therefore, if we start seeing our results vary by around 5% or trend towards the outer limits of any viscosity class, we know that something is going on with our oil.

Presence of Wear Metals

Wear metals prove that some type of wear is occurring. However, depending on their quantity, they can also provide some more insights into what is actually wearing away and whether it is normal wear or abnormal wear. Wear is reported in parts per million (ppm) or as a percentage. Here’s how to convert those percentages to ppm:

100% = 1,000,000ppm

1% = 10,000ppm

0.1% = 1,000ppm

The most common wear metals tested include Aluminum, Iron, Chromium, Copper, Lead, and Tin. Depending on the application, there are varying levels at which these will be flagged.

Table 1 provides an example of various applications and their respective limitations. These will vary based on your OEM and environment, but can be used as a general guideline. All numbers in Table 1 are in ppm.

Table 1: Wear metal limits for various applications

AN/BN and the Presence of Contaminants

Contaminants are any foreign material in the system. Sometimes, lab tests may not be able to detect contaminants in a system because they are not specifically designed to identify that particular contaminant.

In these cases, users would need to specify what additional contaminants the lab should look for, or perform a broader FTIR (Fourier Transform Infrared) analysis to identify all the components in the oil and then determine which of them are contaminants.

The most common contaminants tested include Silicon, Water, and Fuel. Although AN/BN (Acid Number and Base Number) may not be considered a contaminant, it helps quantify the acid in your system, which shouldn’t be there; therefore, in some ways, it can be viewed as a contaminant. However, it is primarily a physical property and is listed separately.

Acid and base numbers act like an early warning system for oil health.

Table 2: Tolerance limits for some contaminants

For diesel engines, BN is measured as having high base numbers, which will decline over time as acids accumulate. If the BN value declines to around 50% of its original value, then we have an issue with the acids increasing too quickly in the oils. On the other hand, AN is used for all other industrial oils (gears, hydraulics, etc.). There are varying limits for AN depending on the application, as shown in Table 2.

Silicon usually indicates the presence of sand, which is highly abrasive. This can accelerate wear in any equipment by essentially turning the oil into sandpaper and wearing away the insides of the equipment. Some of its limits are shown in Table 2.

Water in any form is highly destructive to all assets. However, some systems can tolerate a bit more water than others. This can be due to the nature of the oils (good demulsibility) or the nature of the systems, where heat is involved to help remove the water. Water in the system can lead to an increase in viscosity and disrupt the oil layer.

As such, the lubricant will not be able to form a full film to protect the asset. Water can also create an emulsion in the oil or lead to corrosivity issues. Table 2 gives some examples of limits for various systems.

Fuel contamination is an issue for most diesel engines. The presence of fuel in your oil can lead to a lower viscosity (hence the oil can no longer protect the components) and an increase in the flash/fire point of the oil, which can be particularly dangerous. We have some limits noted in Table 2.

Presence of Additives

It is more challenging to place these tests in a one-size-fits-all table, as oil formulations are consistently changing. The best way to interpret these additives would be to compare them against the initial values for the finished lubricant.

For your oil analysis program, always have a representative sample of the new oil so that comparisons can be made against it as the oil ages in the system. Additionally, the presence of additives in your report when they shouldn’t be there is also a sign of contamination, likely with another type of oil.

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Oil Properties / Used Oil Analysis

Why Different Oils Require Different Tests

Oil analysis reports often wear an invisible cloak, and only if we have a wizard capable of revealing what the numbers mean, they will more than likely end up in a drawer or file on the computer. There are many similarities between oil analysis and blood tests, as they both serve similar functions.

They both test fluids, quantify the results according to different categories, and provide envelope limits within which these values should exist. If the values fall outside these limits (either below or above), we need to take action to prevent failure of the critical asset (or human organ accordingly).

An oil analysis report is less about numbers and more about the story they reveal.

In this article, we will focus on understanding the basics of reading an oil analysis report, interpreting the results, and developing action items based on the information collected. We will take a closer look at reports on turbines (rotating equipment), gear, hydraulics, and engine oils, and what this all really means for your equipment.

Why Different Oils Require Different Tests

Before we dive into the report, we need to establish that not all oils are the same! As such, different oils are required for various types of applications. Therefore, each type of oil will require slightly different tests to determine whether it is performing optimally or not. However, there are a few tests that remain the same for all oils.

The most critical characteristic of an oil is its viscosity. As such, all oils are typically tested to determine whether their viscosity meets the requirements. Another function of the oil is to prevent wear. Thus, most oils are tested for the presence of wear particles, as this can help the user identify if any wear is occurring in the asset.

Oils should be kept clean; therefore, tests are performed to determine the presence of any contaminants, and these are carried out on most oils. Similarly, additives help oils perform their functions; hence, their presence or absence should be quantified to determine if they are indeed achieving their functions for all oils.

Tests for viscosity, the presence of wear metals, contaminants, and additives are the standard sets of tests that should be performed on any oil. There are more detailed tests that examine the specifics of various types of applications, but we will delve into these later in the article.

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