A range of factors must be taken into account when evaluating an oil analysis: type of lubricant, usage time and operating conditions are just as significant as maintenance, servicing and the typical design features of a machine or lubricated components. However, factual knowledge of these factors is in itself often not sufficient. If you really want to make the oil talk, having background knowledge of the systems and machines, production processes and lubricants, and knowing how the oil and machines interact is essential.

Here‘s an example of this: The customer states that 2,000 litres of hydraulic oil HLPD 68 has been in use in a forming press for around two years (5,000 operating hours). The experienced tribologists adds that the forming press is used to manufacture plastic parts (query), the HLPD contains the additive zinc (fresh oil database) and is used at temperatures of max. 60°C (machine manufacturer).

The experienced OELCHECK tribologists have a fundamental knowledge of mechanical engineering and chemicals. They are also familiar with the production processes of almost all industries. As experienced tribologists, they have extensive practical application experience with all types of lubricants. What‘s more, they specialise in specific fields. This means that they know how a lubricant reacts under certain conditions, or what it could be contaminated with, and they know how different factors relate to one another.

Each sample that arrives in the OELCHECK laboratory in a prepaid „all-inclusive“ analysis kit first of all undergoes a series of tests. The test procedures that will determine the values in the laboratory are selected according to the colour of the cap and the information relating to the system the sample came from. Our laboratories are equipped with state-of-the-art analysis devices. We have optimised many of the testing devices together with the device manufacturers and adapted them to the specific requirements of testing aged, sometimes highly viscous or pasty lubricants, both used and still in use. An experienced team of chemists and laboratory technicians maintain and operate the extensive range of analysis equipment and determine over 30 individual values from up to 2,000 lubricant samples every day.

Only once all of the tests for a sample have been carried out in the laboratory and the values have been transferred from the individual laboratory device memory to the central LIMS (Laboratory Information Management System) is the order „Next please!“ given. This means that, for every sample, all of the laboratory values, infrared spectra, photos, titration curves and device diagrams are logged in the LIMS. The experienced tribologists can access all of the values and information at the touch of a button. For each individual sample, a tribologist takes time to follow the predefined steps of the analysis process.

First of all, the experienced tribologist gets an idea of which oil, from which customer and which system he is dealing with. To do this, he checks the sample information form on the screen, which was scanned when the sample was unpacked, and checks the information provided by the customer for completeness and plausibility, among other things. Then he asks the first key question: why did the customer send the sample in?

Routine check
In most cases a routine check, for trend monitoring if possible, should be carried out. The customer wants to know if the oil can remain in use and if wear or contaminants indicate a problem. Checks are made to establish whether unexpected changes have taken place or whether the values from the sample follow the expected trend.

Problem check
The customer has noticed abnormalities when applying the lubricant, or has specific questions like: What causes clouding or other visual changes in the lubricant? Why is the oil foaming? Why are filter service lives so much shorter? Has the oil really been changed by the service? Is the right oil even being used? What causes damage or are there signs of damage? Fresh oil testing, oil changeover testing or start-up testing are often also required.

Once the reason for the oil analysis has been established, the experienced tribologist knows what he needs to look out for during the analysis. With this in mind, he first of all considers the fresh oil values, then the limit and warning values compiled in-house for the relevant system.

Fresh oil values and oil changes compared
The values that are characteristic of the fresh oil are considered for every sample. In addition to the additive elements present, particular attention is given to the IR index, IR spectrum and viscosity. For this purpose, the reference values of over 8,000 fresh oils are available in the OELCHECK database. If the wrong oil has been poured in, then this is exactly where the first indications of that will become visible. The examination of how closely the fresh oil values correspond to those of the used oil sample are taken into account for the diagnosis, particularly where there are noticeable deviations. Where there are questions regarding the inspection of fresh oils or oil changes that have been carried out, comparing with fresh oil values is essential.

Limit and warning values
Defining limit values for wear and contaminants is the biggest challenge in assessing the analysis values of used lubricants. Generally applicable limit values are only available from machine/lubricant manufacturers or their associations in a small number of cases. But which value counts as too high or unexpectedly low? Which value is still tolerable for the time being and at what point will it become critical? Is it even possible to have fixed limits for wear that is directly linked to the service life of the lubricant? The more analysis results with different usage times for a particular type of machine or engine there are available, the better the limit values for wear based on usage time that can be generated. When reviewing the laboratory results, the experienced OELCHECK tribologists use limit values that have been calculated based on many thousands of analyses. In the company‘s internal database, which is growing daily, there are now, after 25 years, over 2 million records of a wide range of machines, lubricants and applications available. In order to assess the values for wear metals, it is important to know where the elements might come from and in which combination and concentration they could potentially cause problems. Elements which in one application indicate wear could in another case be a component of oil additives or even contaminants. A number of individual values are taken into account when diagnosing a sample. However these must never be viewed in isolation, but in terms of how they relate to one another.

Here‘s an example: the viscosity of an engine oil is higher than expected. This could be the result of oil oxidation, nitration, soot ingress or even cooling water ingress. But it is also possible that the viscosity class stated is simply incorrect, or that there is fuel in the oil which is disguising the result. The abnormally high viscosity value can therefore only be interpreted in relation to other individual values.

The individual trend
For wear metals, limit values have only limited significance, particularly for very long oil usage times. If results from previous tests are available, a continual comparison is made of how the values have developed over time for the oil charge of the machine. This means that the different operating and environmental conditions can be considered individually. Detailed prognoses can therefore be made for continued low-wear operation of the machine or the extension of an oil change interval. The following example shows just how crucial this can be: an industrial gear oil CLP 220 is monitored at six-month intervals using trend analyses. There are now five oil analyses saved in the database. The copper value was always between 2 and 3 mg/kg in all five of the previous analyses. The limit value for copper for the gears being analysed is set by OELCHECK at 15 mg/kg. In the sixth analysis, the copper value suddenly reaches an unexpected 9 mg/kg. – No problem though, since the defined limit value of 15 mg/kg is still far from being reached? No, watch out! The increased copper value could indicate the early stages of a wear process in a copper-containing component, like a roller bearing with brass cage. The tribologist advises in his diagnosis that the gear oil be analysed again after three months at the latest so that countermeasures can be implemented promptly or the cause can be established by other methods.

Once the experienced tribologist has examined the individual values in relation to the limit values, he produces a diagnose statement which can be easily understood by non-experts. It includes a summarised evaluation of each of the three aspects wear, contaminants and oil condition.

Wear

Higher wear values or significant variations from one sample to the next are an early indication of wear and therefore of a reduced remaining service life of the components, or even of developing damage. If abnormal wear values are detected, then the components from which they may originate must be examined more closely:

• On which components could the abrasion from which the wear particles originated have formed? Are there perhaps even two or more elements with increased values that could point to particular alloys and therefore specific components?
• Is the cause of the increased wear values obvious from the analysis? Has the wear been formed by abrasive contaminants, water, insufficient lubricity of the oil or by chemical reactions in ageing oil?
• Unlike mechanical wear in the form of particles, which form because of fatigue or from hard contaminants, chemical-abrasive wear dissolved in oil is caused by reaction products with water or acidic oil components.

Contaminants

Contaminants affect the service life of the lubricant and the wear behaviour of the components. Warning values for contaminants apply independently of the service life, oil type or oil quantity. The lubricant analysis must identify contaminants at an early stage and comment on them. Often only an early oil/filter change or improved oil maintenance measures can prevent negative consequences. Water and dust are among the most common contaminants. Residues from manufacturing processes, release agents, assembly aids or entry of other lubricants are also often the cause of contamination. As with the wear values, background knowledge and insight are essential when analysing contaminants. Individual numerical values alone can otherwise quickly lead to confusion.

Here‘s another example: silicon (Si), for example, can get into the lubricant in the form of dust. However, it could also be an anti-foaming additive from the fresh oil or residues from assembly greases/ pastes that contain silicon. It is also possible that silicon has been released from seals made from silicone rubber.

Oil condition

The condition of the oil provides information in terms of if and how much longer the oil can remain in use. Every application has its own „ageing scenario“:

• Motor oils age differently from gear oils, circulating oils and hydraulic fluids, not least because of higher oil temperatures and contamination by soot and sulphurous fuel.
• Mineral oils, bio-oils and synthetic oils also display different ageing behaviour.
• An oil ages differently in continuous operation compared to stop-and-go operation.
• Oils also age differently in systems which are structurally identical but which operate in different environmental conditions.
• Maintenance and servicing of the system and oil also have a huge effect on oil ageing.

When the oil condition is being analysed, particular consideration is given to the values for the viscosity, oxidation, nitration, sulfation and often also the acid number (AN, NN - neutralisation number) and base number (BN), as well as the change in the additive elements. The IR spectrum and IR index recently defined by OELCHECK (see OELCHECKER Winter 2015) play a fundamental role here. Often only limit values that are difficult to apply generally can be defined for the oil condition. The experienced tribologist must have a detailed knowledge of a wide range of lubricants, their characteristics and typical reactions in different applications to be able to give an accurate statement. Here too it is a case of making typical patterns of change clear rather than simply „ticking off“ individual values in isolation.

After the standard procedure of examining and analysing limit and warning values, taking into account the oil type, usage time and application site, come the specifics:

The individual diagnose statement contained in every OELCHECK laboratory report is produced.

The experienced tribologist comments on wear, any contaminants and changes in the oil condition. He then gives a recommendation for further action. This could be a recommendation to maintain the oil better, to change the oil or to continue using the oil without any corrective measures. It is also stated when the next sample should be analysed in order to monitor a trend. Once the basic commentary has been given, specific questions from customers, like „Why is my oil foaming?“ are answered. Particular care is taken here to ensure that the complete text of the recommendation is easily comprehensible to a non-expert.

The diagnosis symbol

Finally, the experienced tribologist assigns a green, yellow or red diagnosis symbol as a way of summarising his diagnosis. These symbols have the following meanings:

• The values analysed are within the normal range. Further use of the oil is possible without any corrective action.
• Some values are outside the normal range but are not critical. Further use of the oil is possible. The recommended corrective measures must be implemented or shortened analysis intervals observed.
• At least one value, which has been commented on separately, is in the critical range. The recommended corrective measures must be implemented.

The symbols, which are based on the globally recognised traffic light colours, are intended to give non-experts and those who have to manage a large number of reports on a daily basis a quick understanding of the analysis results. On the web portal at www.lab.report, the analysis results can also be sorted easily according to the symbols and the critical results dealt with first. Only once the experienced tribologist has provided an individual statement and released the PDF laboratory report with the evaluation symbol, he gives the order „Next please!“ again.