Resources | Technical Documents

Lubricants can be categorised in many different ways. One of the most common classifications is by the constituent base oil: mineral, synthetic or vegetable. Mineral oil, which is derived from crude oil, can be produced to provide a range of qualities associated with the oil’s refining process. Natural esters, derived from 100% renewable vegetable oils, are superior to mineral oil for use in distribution and power-generation transformers of all voltage classes, both new and retrofilled. In this Technical Bulletin, Corné Dames discusses the different condition monitoring options for the analysis of transformer component performance where natural esters are used as lubricants in transformers, to determine the degree of contamination by mineral oils and other substances.

Anyone reading this technical bulletin will be familiar with the condition monitoring technique of oil analysis. A small sample of oil is drawn from a lubricated piece of machinery and analysed for the presence of wear debris and contaminants, as well as an assessment of the health of the oil itself. So far, so good, the oil (or grease) can be subject to a whole battery of physical and chemical tests which, in turn, can provide upward of 50 (in the case of a fully comprehensive analysis) different parameters that need to be assessed in order to determine the health of the machine, the health of the oil and the levels of contamination.

This Technical Bulletin discusses a variety of turbine sample tests - how they are conducted, and what information they provide. The test results enable the best remedial action to be taken for the component in question, in turn boosting the reliability of the turbine by maintaining the oil - which is often a large financial investment - in peak operating condition.

The month end or management report contains a wealth of very valuable and useful information. It comprises a statistical distillation of the previous month’s samples and compares these data to the previous twelve months. Analyses include a variety of parameters that will give the customer a good idea of how effective their oil analysis programme is and where the problem areas lie in terms of what the problems are, what components are affected and how severe the problems are.

What do the results mean? This is a very common question asked of the diagnosticians at WearCheck. The answer to this is to read the diagnosis because this is the distillation of all the inputs that the company receives. What the diagnostics department does every day as a service to customers, diagnosing sample results, comes easily when there are years of experience at hand and the diagnostic processes are designed in-house to streamline what could be a difficult, highly complex and time-consuming job. This diagnostic process is underpinned with many very sophisticated software systems that have all been specified by the department and written in-house. These processes run in the background and ensure that the diagnosis is made timeously, accurately and efficiently. This bulletin will shed some light on how the diagnostics department takes the multitude of information attached to each sample and uses it to supply the customer with a meaningful diagnosis.

Questions on limits on oil analysis parameters, such as wear levels, additive levels and viscosity are high on the list of those that the WearCheck diagnosticians field most often. “When is the iron too high?”, “how much viscosity increase is acceptable?” and so on and so forth. Unfortunately, there are not always hard and fast answers to these questions; in fact there are seldom such answers.

The accuracy of analysis of an oil sample is greatly influenced by two aspects of the whole procedure the customer controls: how the sample is taken and the information accompanying the sample. The latter has been dealt with in previous technical bulletins. The taking of an oil sample is where the whole analytical process begins. All the sophisticated oil analysis tools, techniques and diagnostic processes are meaningless if the oil sample fails to represent the actual condition of the oil in service in the machine.

The effect of temperature on engine lubricating oil is an important consideration to take into account when operating a large fleet of vehicles. Except for electrically powered units, all vehicles are powered by a combustion engine of some description, be it fuelled by gas, petrol or diesel.

In a recent meeting we were discussing what the topic for the next technical bulletin should be. After writing technical bulletins for fifteen years it suddenly dawned on me that we have never written a bulletin outlining the benefits of performing used oil analysis. I have written brochures and I can find at least two dozen PowerPoint presentations that address this question but the material has never ended up in this format. So, without further ado, what are the benefits of a well-run oil analysis programme?

Wearcheck provides its customers with a wide range of tests that cover most problems encountered in most types of equipment in most types of environments and applications. There are obviously a range of tests that some of our clients would like us to do but are cost prohibitive. Laboratory equipment, like earthmoving equipment, is expensive and we too have a weak Rand working against us. It is very difficult to justify spending a million Rand on a laboratory instrument if we are only going to use it for a few tests per month, and customers would not be prepared to pay a couple of thousand per sample in order to make the equipment pay for itself. Having said that, every effort is made to outsource tests that we cannot do.

Before looking at the effective management of oil analysis programmes it is salutary to look first at the reason why these programmes sometimes do not work. The service provider is frequently blamed for the failure of a doomed oil analysis programme when the fault almost always lies with the end user. This is generally not as a result of poor management but a lack of education and understanding.

There is a common misconception that ‘oil is just oil’ and this simply is not the case. Consider the many types of machines that need lubrication and that these machines can operate in many different environments doing many different jobs. There are also dozens of different oil suppliers who can supply thousands of different oils based on viscosity and additive chemistry which dictate their function. This is why there is such a variety of oils in the market place. This technical bulletin will look at the different classes of oils (liquid lubricants) and why they are different.

In the last Technical Bulletin we looked at the four tests which every sample receives. We now take a look at tests specific to various sample test classes, and extra tests which are triggered in extraordinary circumstances.

Air intake system check; Air cleaner element holed or not sealing correctly; Incorrect size air cleaner element for type of housing.

Abnormal Wear/Debris Checks; Check magnetic drain plug for particles and examine; Check magnetic screens.

Two of the most common questions Wearcheck"s diagnosticians are asked are: "What tests do you do?" and "How do I interpret the results?" The first question is easy to answer, the second not quite so. In addition to their formal academic instruction, all Wearcheck diagnosticians undergo a six month internal training programme before they get their wings. During this time they diagnose twenty-five to thirty thousand samples, each of which is vetted by a qualified diagnostician before being accepted. The reasons for this are that the tests are so inter-related and mutually dependent that interpretation of the results is not always straightforward. Knowing this it is easy to appreciate the impossibility of putting the whole process of diagnosis into a few lines.

The concept of on-site analysis (OSA) - a company setting up a small laboratory on its premises where it performs its own oil analysis instead of contracting it out to a specialised external oil analysis laboratory - has been around for many years. The sort of organisations that have opted for OSA are usually large operations in out of the way places such as mines where transporting oil samples is difficult and time-consuming, or where security considerations create problems such as on diamond mines.

Wearcheck technical staff are always happy to answer queries from customers to help them get the most from their oil analysis programme. For the benefit of all Wearcheck customers, we have put together the most commonly asked questions and feature them, along with the answers, in this technical bulletin.

The effectiveness of an oil analysis program is significantly affected by how well maintenance staff understand the program and by the quality of their input to WearCheck. This bulletin gives an insight into the different factors which can influence the effectiveness of oil analysis and so help companies get the best results from their program.

According to Webster’s dictionary tribology is "the study of lubrication", and comes from the Greek tribein, which means "to rub". When two components in a lubricated system rub, wear particles are generated. Contrary to what you might think, wear particles do not come in all sizes and shapes. There are, in fact, only a handful of distinct types of wear particles, and these particles occur in only specific size ranges. The most common wear particle in a lubricated system is the normal rubbing wear particle.

Used oil analysis is comparable to a medical analysis with a blood test. Like blood, lubricating oil contains a good deal of information about the envelope in which it circulates. Wear of metallic parts, for example, produces a lot of minute particles, which are carried by the lubricant. These small metal particles can give information about the machine elements that are wearing, and can be detected by various methods, for example, Atomic Emission Spectrometry. Determination of larger particles can be done using optical or electronic microscopy, or ferrography.