The approach of detecting and analyzing sludge and varnish problems in machinery is not the same as used oil analysis. In many instances this is because the evidence is not always in the oil. The sludge and varnish should be analyzed directly, using a completely different set of tests and evaluation parameters. Still, used oil analysis plays an important diagnostic role to help reveal candidate causes as well as to rule-out others.

The conditions that commonly lead to sludge and varnish problems vary, which complicates the process of identifying the root cause analytically. There are at least 25 unique lubricant degradation mechanisms leading to sludge or varnish formation.

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With few exceptions, the chemical and physical stability of lubricants are threatened by even the slightest amount of suspended water. Water can promote a host of chemical reactions (hydrolysis) with compounds and atomic species including oil additives, base stock and suspended contaminants. In combination with oxygen, heat, and metal catalysts, water is known to promote the oxidation and the formation of free radicals and peroxide compounds. Oxidation inhibitors are sacrificed by both neutralizing peroxides and breaking oxidation chain reactions to form stable compounds.

Other oxidation inhibitors are known to form hydrogen sulfide and sulfonic acids when reacting with water. Experiments have shown the protection provided by zinc dialkyldithio phosphate (ZDDP), a common antiwear additive and antioxidant, to be destroyed by as little as one drop of water in a gallon of oil, with oil temperature above l 80°F.

Water is also known to attack rust inhibitors, viscosity improvers, and the oil’s base stock. The effects are undesirable by-products such as varnish, sludge, organic and inorganic acids, surface deposits and lubricant thickening (polymerization). Large amounts of emulsified water can lower viscosity, thereby reducing a lubricant’s load carrying ability. When water is combined with metal catalysts such as iron or copper, accelerated stressing of the oil can occur. This results in base stock oxidation and the forming of free radicals (which continue the oxidation process), hydroperoxides, and acids (see figure 2).

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Moisture is generally referred to as a chemical contaminant when suspended in lubricating oils. Its destructive effects in bearings can reach or exceed that of particle contamination, depending on conditions. Like particles, control must be exercised to minimize water accumulation and damage to bearing surfaces. Once water enters a machine with bearings (i.e., an engine, turbine, or gear box) it may move through several chemical and physical states. Water will often enter an oil in one of the five following ways.

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Historically, water contaminated oil has been said to exist in two states:

• Dissolved water (bound molecularly in the matrix of the oil)
• Free water (not molecularly bound)

In the last 30 years or so, most of the literature, including Noria’s publications, refer to water as having three states. Free water has been redefined as being water that, by force of gravity, will phase out of the oil. This means it will separate below (most common) or above the oil phase depending on oil density.

The new third state is emulsified water. Water that is held tightly in micro-globules in the oil is no longer referred to as free water. Instead, it has been more accurately referred to as emulsified water, or a “micro-emulsion”.

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It takes only a small amount of water (less than 500 ppm) to substantially shorten the service life of rolling element bearings. There is a vast amount of research that supports this. Being a career-long crusader of clean and dry oil, I will certainly not argue the contrary. In fact, water’s destructive effects on bearings can easily reach or exceed that of particle contamination, depending on the conditions.

My theme for this column, therefore, is not about whether water imparts harm but rather how it does. Knowing how water attacks and causes damage helps in setting important dryness targets and also aids failure investigations post mortem. Further, when water contamination is unavoidable, understanding these water-induced failure modes can be valuable in the optimum selection of lubricants, bearings and seals for defensive purposes.

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In recent years, there has been an unusually large number of reported cases associated with varnish and sludge formation in turbine-generator and compressor applications using Group II turbine oil formulations. Explanations for these problems have varied but typically include Group I/Group II incompatibility, additive instability, bulk oil oxidation, adiabatic compressive heating, electrostatic discharge, among others. This paper reviews these failure pathways and discusses actual case history including root cause analysis. Analytical methods for the sludge/varnish and the degraded oll are also reviewed.

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Most oil-related problems in machinery lead to wear or corrosion. However, there is one very serious problem – the presence of sludge and varnish – that may cause neither. Instead, these substances plug flow passages and cause valve sticking. Sludge and varnish can occur even In the most well maintained machines. Surprisingly, they may also appear when oils are not particularly old or contaminated. And they can occur in even though most thermally robust synthetic hydraulic fluids. While there a:re many well-known reasons why oils will throw sludge, there are an equal number that are unknown or misunderstood.

First, what is the distinction between varnish and sludge? Both can form directly or through n sequence of intermediate steps. For simplify lion, we will define varnish as tough, adherent oxide or carbonaceous material that coats internal machine surfaces. Heat and/or time will cure varnish to a hard, brittle consistency. On the other hand, sludge, which is sometimes a precursor to varnish, is soft and sticky in form. Sludge can move around a system until it finally comes to rest at sump bottoms, troughs, strainers, filters, and narrow fluid passages. Other common names for varnish and sludge include deposits, lacquer, tars, pigments, gums, and resins.

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Most of us are well aware of the enormous damage water can exact on a machine and its lubricants. However, the magnitude of this potential destruction seems to depend directly on five enabling factors. These factors are listed below and are further diagramed in Figure 1.

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Viscosity can go up, down or remain unchanged. The list of root causes that can alter a viscosity reading is quite extensive; hence the reason why viscosity has become such an information-rich measure of used oil condition. After all, when viscosity has not changed, you can rightly conclude that the many known viscosity-altering factors are probably not happening – a good thing for sure.

What’s not so good is when viscosity moves suddenly with no obvious explanation or warning. What does it mean and why did it occur? Let’s explore the many possible causes of low viscosity.

It’s safe to say that viscosity will not change without a forcing event or condition that incites the change. The oil analysis community is aware of the usual suspect conditions or events, but some remain undiscovered or at least are not fully understood. When it comes to an abrupt loss of viscosity or a downward viscosity movement.

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Water in a hydraulic system constitutes a serious form of oil contamination. However, water contamination is rarely recognized as such, hardly understood, and, until recently, considered difficult to combat. The damage caused by water is usually attributed to other causes. Water often interacts with other types of contamination. It causes both degradation of the hydraulic oil and damage to the hydraulic components, which reinforce each other. In the past, the filtration of hydraulic oil was solely aimed at removing solid particles. The hydraulic industry has therefore made great progress over the last twenty years in applying and maintaining well-designed filtration of solid particles from hydraulic oil. However, the recent introduction of water-removing filters seems destined to shift the focus in the management of hydraulic oil contamination.

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Here is the latest component for hydraulic system filtration and contamination control Water is a very serious contaminant in oil hydraulic systems. Yet, water contamination is rarely identified, poorly understood, and, until recently, considered very difficult to remove. In most cases, the damage done by water is blamed on other factors. Water often works together with other contaminants to produce a combined synergistic degradation of fluid and components.

In the past, hydraulic filtration processes were designed to separate solid contaminants from the hydraulic fluid and, over the last 20 years, the hydraulics industry has made great progress in implementing and maintaining well-conceived solid-contaminant filtration on hydraulic equipment. However, the recent introduction of water-removing filters appears destined to change the focus of fluid power contamination control.

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Water, once in an oil, is in constant search of a stable existence. Unlike oil, the water molecule is polar, which greatly limits its ability to dissolve; and many additives have polar extremities which can markedly increase water solubility. Water may cling to hydrophilic metal surfaces or form a thin film around polar solid contaminants such as silica particles. If a dry air boundary exists, water molecules may simply choose to migrate out of the oil to the far more absorbent air interface. This migration can be accelerated if air and oil mix, Such as in splash lubricated and oil mist systems or any system where a stable fluid foam may exist.

If water molecules are unable to find polar compounds on which to attach, the oil is said to be saturated. Any additional water will create a supersaturated condition causing free water to be suspended or settle at the bottom of the sump. This supersaturation can also occur as a result of lower oil temperature.

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Water, once in an oil, is in constant search of a stable existence. _Unlike oil, the water molecule is polar, which greatly limits its ability to dissolve; and many additives have polar extremities which can markedly increase water solubility. Water may cling to hydrophilic metal surfaces or form a thin film around polar solid contaminants such as silica particles. If a dry air boundary exists, water molecules may simply choose to migrate out of the oil to the far more absorbent air interface. This migration can be accelerated if air and oil mix, Such as in splash lubricated and oil mist systems or any system where a stable fluid foam may exist.

If water molecules are unable to find polar compounds on which to attach, the oil is said to be saturated. Any additional water will create a supersaturated condition causing free water to be suspended or settle at the bottom of the sump. This supersaturation can also occur as a result of lower oil temperature.

The post Moisture… the Second Most Destructive Lubricant Contaminant, and its Effects on Bearing Life appeared first on Tesibis.

Water in a hydraulic system constitutes a very serious form of oil contamination. Technically, water contamination is rarely recognized as such, poorly understood, and, until recently, considered difficult to combat. The damage caused by water is usually attributed to other causes. Water often interacts with other types of contamination. It causes both degradation of the hydraulic oil and damage to the hydraulic components, which reinforce each other. In the past, the filtration of hydraulic oil was solely aimed at removing solid particles. The hydraulic industry has therefore made great progress over the last twenty years in the application and maintenance of well-designed filtration systems for solid particles in hydraulic oil. However, the recent introduction of water-removing filters seems destined to shift the focus in the management of hydraulic oil contamination.

The post Filters can remove the water from hydraulic oil appeared first on Tesibis.

Water in a hydraulic system constitutes a very serious contaminant of the oil. Nevertheless, water contamination itself is rarely recognized, poorly understood, and until recently, considered difficult to combat. Sometimes, the damage caused by water is attributed to other types of contamination. Water often interacts with other contaminants, causing both degradation of the hydraulic oil and damage to the hydraulic components, with these effects reinforcing each other. Until now, hydraulic oil filtration has primarily focused on removing solid particles. The hydraulics industry has made significant progress in the application and maintenance of well-designed solid particle filtration systems over the past twenty years. However, the recent introduction of water-separating filters appears poised to shift the focus of oil contamination control.

The post Filters kunnen het water uit hydraulische olie verwijderen (Filters can remove the water from hydraulic oil) appeared first on Tesibis.