Why do you not indicate any "limit values" in your laboratory reports?

Year of publication: 2012


We have been using OELCHECK lubricant analyses for several years now and couldn’t manage without them. But why do you not indicate any “limit values” in your laboratory reports, in particular for wear metals? You only give the values for the current sample and previous investigations. If limit values were also provided, we could draw conclusions on the condition of the oil or the machine even faster ourselves and with greater accuracy.


OELCHECK answers:

The suggestion to provide the limit, threshold and warning values for wear metals or even for lubricant additives was a hot topic in our last customer survey. But unfortunately we cannot grant this wish as limit values, which are independent of time, do not reflect application-specific scenarios. In conclusion, every machine, with its own operational conditions, needs to be considered on an individual basis. For this, not only do we have to take into account the machine type, the actual lubricant used, its maintenance and the amount to be filled – above all its operating time as well as environmental conditions influence threshold limit consideration.

In the case of complex systems, this is often even more complicated. This is because some manufacturers purchase components from alternate suppliers which may have the same features but are made from different materials. Also, if partial-flow filters have been installed, large amounts of oil have been refilled or additives have been added retrospectively, fixed limit values are no longer helpful. Limit values with corresponding limitations are published only in a handful of cases by machine and engine manufacturers. Therefore, with the help of our own database, which contains over two million samples, we decided to make the complex topic more transparent for our diagnosis engineers. Meanwhile, for assessing the examined samples, we use internal wear threshold values for over 150,000 different machines. In the event of a deviation or change in a single component of a device, we create a new database. For this specifi c machine type, however, we won’t have threshold values until we have conducted at least 50 analyses for the same or a similar type of machine.

Because even though such detailed knowledge on limits for wear metals may be available, it is not sufficient for assessing an actual sample.This is where our know-how comes into play because all values must also be considered together as a whole. A diagnosis that is based solely on comparing laboratory data that has just been established with limit values can quickly become misleading. Values will look different if they are assessed after 20, 200, 2,000 or 20,000 hours.

In order to rule out the time-related risk, for example, we do not publish threshold values as a matter of principle.

How complex the contexts can be overall is illustrated in the following examples:

Not all elements and metals detected in a sample necessarily suggest wear. Some (e.g. copper) can also be additives that are found in lubricants. First of all, a comparison of the used oil values with the additives from the fresh oil, together with the IR spectrum, gives an indication of additive decomposition. Perhaps just a single active component from the whole additive package changed by forming a new type of bond with wear particles.

It is essential that even the threshold limits typical for impurities for silicon and water are examined. For example, if silicon is detected in the oil, it usually means that the oil has been contaminated with dust. Silicone is also specifically added as an anti-foaming additive to almost all oils. In new or overhauled engines, silicon can be a component of silicone-containing assembly pastes or sealants. Additionally, it is an alloy component of aluminium and therefore possibly a wear element in full-aluminium engines. How can a threshold value, which needs to be generally applicable, be created as a benchmark here if all these possible contexts are not taken into account?

Too much water in the oil can, for example, promote corrosion, cavitation or oil oxidation. Even mineral-oil-based fresh oil has 50 to 500 ppm water, depending on oil type or production plant to various extents and with varying relative humidity. Depending on their intended purpose, oils also deliberately possess demulsifying or emulsifying characteristics. The level at which water content becomes risky depends on the oil type, its performance requirements and its operating time.

Limit values, which you may get from the OEM or lubricant manufacturer, are only useful to a certain degree in our diagnoses. If at all, they display the values from different perspectives. What is most important to the manufacturer in this case is the warranty, for the oil manufacturer it’s the oil service life that’s important, and a lubricant laboratory like OELCHECK mainly considers the values from a condition monitoring perspective. Warning and threshold limits also play a role but you achieve a consistently positive effect, primarily, with our trend analyses. If we analyse an oil, which is used in a machine, on a regular basis and over a long period of time, we can quickly and accurately detect the tiniest of deviations and specifically warn you before any dangerous levels are exceeded