Oil contamination may be defined as any foreign material found in the lubricant which is not added by design. Usually, contaminants are not beneficial, and may be detrimental, to the performance of the oil and/or the operating machinery. Contamination is a significant root cause of machine and lubricant degradation and failure. Often overlooked as a source of failure because its impact is usually slow and imperceptible, contamination is both a significant threat to reliability and quality efforts, and an opportunity because improvements are very attainable1. Research on an array of fluid dependent machinery such as bearings and rotating equipment, hydraulic systems, gearboxes, and diesel engines, clearly supports that often machine reliability is a function of contamination control.

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When a lubricant degrades, it forms reaction products that become insoluble and corrosive. So too, the original properties of lubricity and dispersancy can become impaired as the lubricant ages and additives deplete. Much has been published about the risks associated with overextended oil drains and the buildup of carbon insolubles from combustion blow-by.

However, surprisingly little has been said about the impact of fine abrasives in a lube oil as it relates to fuel economy over the engine’s life. One can imagine numerous scenarios in which solid abrasives suspended in the oil could diminish optimum energy performance.

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The monitoring of particle contamination in lubricating fluids is a critical indicator of incipient and impending failures. Recent research, under both laboratory and field conditions of the contaminant sensitivity of bearings, reveals a well defined cause and effect relationship between contaminant levels and relative machine life.

This paper discusses the contaminant sensitivity of bearings as well as turbines, diesel engines, gear systems, and hydraulic systems. Also discussed is the benefit of applying contaminant monitoring to both proactive and predictive maintenance programs. Proactive maintenance is the process of monitoring root causes (pre-degradation conditions) as opposed to predictive maintenance which focuses on impending failure conditions.

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In recent years, I’ve been part of numerous investigations relating to expensive machine failures preceded by oil samples that registered high particle counts. Each time I asked the asset owner, my client, why the aberrant particle trends were not investigated further. In most cases the response was that they didn’t think it merited the extra effort or they didn’t know how to probe further for more information.

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With the widespread use of plant-level particle counters, maintenance organizations are becoming more sophisticated and skilled in the management and control of oil cleanliness. This has led to the discovery of a host of new tactics and practices that involve combining the particle counter with other important onsite oil analysis tools and methods.

Contamination can be defined as any unwanted substance or energy that enters or contacts the oil. Contaminants can appear in many forms, and can be highly destructive to the oil, its additives and machine surfaces. It is often overlooked as a source of failure because its impact is usually slow and imperceptible yet, given time, the damage is analogous to eating up the machine from the inside out. While it is not practical to attempt to eradicate contamination from in-service lubricants, control of contaminant levels within acceptable limits can be accomplished and is vitally important.

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The inclusion of particle counting in the periodic analysis of hydraulic and lubricating fluids has provided an important new advancement to machine diagnostics. With particle counting, machinery users can monitor the principal cause of failure, not just the symptoms, or results, of failure. The benefit, when particle levels are controlled, is extended machine life and reduced failure frequency. This is the objective of the growing practice of proactive maintenance.

Along with this important trend has come the practical questioning of particle counter accuracy. It is estimated that by the year 2000, as many as 50 million particle counts will be performed on fluid samples each year. Hence, a failure to do particle counting with reasonable accuracy could effectively undermine user confidence and erode this incredible rate of growth.

While calibration techniques are available for most types of particle counters, the frequency and proper use of these techniques is not well understood. Likewise, it can be questioned whether the type of fluid and test particles (calibration fluid) used in calibration of particle counters is sufficiently close to field oils and field contaminants. Additionally, accuracy is also influenced by bottle cleanliness, fluid agitation, deaeration, dilution, dilution fluid cleanliness, and operator error.

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In condition monitoring, any property that is important to machine reliability and life extension should be a property that is measured, assuming it is technically and economically feasible. Of course, this is the point of considerable consternation by the oil labs when it comes to crankcase oils.

How does one perform practical particle counts on opaque fluids, achieving precision and cost efficiency at the same time? Before we examine the specific challenges of particle count methodologies, let’s review the various ways to assess the presence of destructive particles (other than soot) in used motor oils.

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Condition monitoring can be easily performed by following a few simple principles. Among these principles include monitoring two sets of conditions:

1. The operating and environmental conditions that precede failure, and
2. Early-stage failure symptoms

Several models are presented that show the benefits of monitoring machine conditions, as well as the consequences of ignoring them . Also discussed is the integration of both proactive and predictive maintenance techniques to extend machine life.

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This isn’t your usual article on how important clean oil is to lubricant health and machine reliability. Yes, we are going to talk about particle contamination, but we’re going to take a much closer look at the destructive traits of this nearly invisible material that cohabitates with our lubricants.

As it turns out, there is a lot more to particles than their size and count. This column will peer into the intricacies of the physical and chemical properties that make up and characterize solid particle contamination.

I’ll begin by discussing 10 particle characteristics that should be important to lubricant analysts and lubrication professionals. Each of these characteristics or traits influences the health of lubricated machinery. While the name of the trait may be familiar, the damage it causes may not be.

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Do you know about silt lock? This common condition causes motion impediment failure in certain machines. While this type of failure usually doesn’t involve wear or permanent internal damage to the machine, it is sudden and abrupt. Silt lock is the result of solid contamination and is amplified by other conditions that must be controlled where possible. It is most often associated with hydraulic systems and produces seizure or jamming of components.

Because of its lack of warning or predictability, silt lock is responsible for some of the most devastating and destructive catastrophes in mechanical machinery. These include mechanical casualties, prolonged production losses and even loss of human life.

Silt lock has been found to be the root cause of countless failures related to aircraft, spacecraft, passenger cars, elevators, turbine generators, tower cranes, etc.

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Particles. Think about it. Tribological studies on wear-related machine failure rank particle-induced abrasion as the No. 1 cause of wear. This is often referred to as three-body abrasion, where particles become interposed between two surfaces in relative motion, leading to damage (cutting) of both surfaces. Particles contribute to an assortment of other types of wear and failure too, including surface fatigue, silting and erosion.

With this in mind, it is only natural that monitoring the size and concentration of particles in lubricating oil would be of keen interest to the astute reliability professional. It’s no wonder the particle counter is a leading oil analysis instrument and is high on the list of favored instruments in the condition-monitoring field in general.

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The definition of a contaminant is any foreign “something” that enters a lubricant during formulation, packaging, transport, storage or service. Contaminants compromise the lubricant’s integrity, performance and service life as well as impart harm to the machine. No lubricant is indemnified from their effects or can safely co-exist with contaminants. So too, there are no lubricants or machines that can realistically be defined as contaminant-free.

The hazards brought on by various types of contaminants have been covered extensively in the pages of Machinery Lubrication magazine. We’ve shown how the damage can progress slowly or attack suddenly and destructively. Either way, contaminants are a serious lubricant disease that merit vigilant attention by lubricant analysts and reliability professionals.

Solid contaminants (also known as particles) come in wide-ranging sizes, shapes, hardness and composition. Often missed in the discussion on particle contamination are the ghost riders that lurk in your oil. These contaminants, which go unnoticed by maintenance staff and unmeasured and unreported by oil analysis labs, need to be exposed and understood. Their destructive capacity is immense, and since conventional filters cannot address them, we must look to other solutions, such as separation technologies.

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Do you really know how your lubricants become contaminated? Have you taken an inventory of the sources of contamination and the primary points of entry? If not, you are in the majority as sadly, few organizations go to the trouble of performing a contaminant ingression study.

For many machines, the exclusion of contamination is the only way to control contamination. This is because these machines either have no filter or the filter in use is coarse, providing no practical protection in the particle size range of critical oil films.

When particles are not removed by filtration or by settling, a lubricant’s contaminant level equals the machine’s service hours multiplied by the number of particles ingressed per hour (ingression rate). For machines exposed to high ambient dust, particle counts can exceed recommended levels in just a few hours. After days of exposure, an oil can turn into more of a honing compound than a lubricating medium.

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Machinery Lubrication Magazine

When you throw a rock in a lake, it goes down – fast. Wear particles are heavier than rocks of the same size, often four to five times heavier. Of course, the heavier the object, the faster it falls. Oil is viscous, and this resistance can slow down the rate objects fall, but it doesn’t come close to stopping them.

The rate at which objects fall in viscous fluids is described by Stokes’ law. In sum, (1) the larger the object, (2) the heavier the object (density), (3) the thinner the fluid (lower viscosity), (4) the lower the density of the fluid (oil has extremely low density), the faster the object falls. Conversely, small, low-density objects in highly viscous fluids settle more slowly.

In oil analysis, this is critical because you want to know about the particles in your oil – all of the particles, including those that can damage machines and those that reveal damage has already occurred and is continuing to occur. Not much in oil analysis is more important than this.

This article will address two common oil analysis-related problems that sadly are often dismissed by both users and laboratories. These problems are sampling oil from machines at rest (oil not circulating) and failing to properly resuspend particles just prior to analysis.

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The practice of transferring suspended particles to the surface of a membrane for analysis has been around for decades. It is perhaps the earliest method for inspecting solid contaminants and wear debris in a used sample of oil. It is of no surprise that these methods have enduring use today. In fact, some are the basis of recently adopted standardized methods by ASTM and ISO.

While membrane-based procedures for preparing particles for analysis can be time consuming and messy (usually involving the use of glassware and solvents), the benefits can be substantial compared to alternative methods. The main advantage is the ability to both quantitatively and qualitatively describe particle contamination, depending on the method used. As in the case of microscopic particle counting, you see what you’re counting and can confirm visually what appears to be a particle. You can also characterize particle type (e.g., dirt, wear debris, rust, fibers, etc.).

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Without the lens of a microscope, bacteria and viruses might only be recognized as painful symptoms of sickness and disease by those who are infected. Just as technology is an important enabler in human pathology, it also serves in the detection and diagnosis of a host of machine health issues, including the invasion of lubricant contamination.

However, for most machinery maintainers, the threat posed by fluid contamination runs contrary to human intuition. Just like a viral infection, in lubrication, it’s what we can’t see that hurts us most. The naked eye is generally blind to the destructive potential of most types of contaminants. In fact, none of our “unaided” human senses can be relied upon to detect and recognize significant concentrations of contamination.

When I first entered the oil analysis field in the 1980s, portable and user-level oil analysis technology was years ahead of its time. This is not so today. Contaminant monitoring instruments have advanced rapidly in the past two decades as has the awareness of its importance. What was previously only the domain of analytical chemists is now an essential maintenance tool available to field technicians and condition monitoring specialists. Thankfully, the “now generation” is largely a population of sophisticated consumer electronics users who also have an insatiable appetite for instant information.

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This past year Practicing Oil Analysis featured many end-user case studies documenting cost savings from oil analysis. Surprisingly, the majority of these studies describe the partnering of oil analysis with contamination control*. In this issue is yet another case study, by Weyerhaeuser, deploying this same strategic combination. It is unlikely that these are random events but rather a well-defined pattern. If so, exactly what is this lesson and what is its meaning to machine reliability?

To some it might seem a little like an old tune. After all, hasn’t filtration been around nearly as long as lubrication? And, what’s new that hasn’t already been thoroughly explored and widely applied? For one, when it comes to cleanliness, knowing is definitely not doing. Many maintenance professionals know oil should be clean but the use of filtration and contamination control lacks rigor and discipline. Why?

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Equipment maintenance costs represent an unclaimed gold mine of savings opportunities. Yet deep maintenance cost reductions have evaded the efforts of even the most diligent and sophisticated operations. Why? Because there has been a general lack of emphasis on maintenance that corrects root causes, as opposed to responding to the symptoms or results of failure.

A shift in maintenance philosophy is needed, one that targets life extension and avoids the onset of component degradation.

The philosophy must not be reactive but proactive. A true proactive maintenance program must stabilize healthy, non-degrading, non-decaying, operating conditions by always being ahead of the first indication of failure.

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