This is the third article in the Oil Analysis 101 series and focuses on detecting and monitoring water content. While there are typically only one or two methods commonly used for measuring most oil properties, there are many methods that can be used for detecting the water-in-oil concentrations. Each method is important because it can be effective in different situations. In this article, we will discuss which methods are available for determining the moisture content of a used oil sample and discuss their strengths, weaknesses and limitations.

Water is perhaps the most harmful of all contaminants with the exception of solid particles. While the presence of water is often overlooked as the primary root cause of machine problems, excess moisture contamination can lead to premature oil degradation, increased corrosion and increased wear.

Visual Crackle Test
The simplest way to determine the presence of water in oil is to use the Visual Crackle test. While this is an effective test for identifying free and emulsified water down to say 500 ppm, its biggest limitation is that the test is nonquantitative and fairly subjective. False positives are possible with entrained volatile solvents and gases. Nevertheless, as a screening tool in the lab and the field, the crackle test will always have a role to play where a quick yes or no answer is required for free and emulsified water.

FTIR Analysis
FTIR can be an effective method for screening samples containing in excess of 1,000 ppm of water, provided a correct new oil baseline is available for spectral subtraction. However, due to its limited precision and comparatively high detection limits, FTIR is not adequate in many situations where precise water concentrations below 1,000 ppm or 0.1 percent are required.

Dean and Stark Method
The classic method for determining water-in-oil is the Dean and Stark distillation method (ASTM D95). This test method is fairly cumbersome and requires a comparatively large sample to ensure accuracy, which is why it is rarely used in production-style oil analysis labs today. The method involves the direct codistillation of the oil sample. As the oil is heated, any water present vaporizes. The water vapors are then condensed and collected in a graduated collection tube, such that the volume of water produced by distillation can be measured as a function of the total volume of oil used.

Dean and Stark Distillation Apparatus (ASTM D95)

Karl Fischer Moisture
The Karl Fischer Moisture test is the method of choice when accuracy and precision are required in determining the amount of free, dissolved and emulsified water in an oil sample. However, even within the scope of Karl Fischer testing, there are several methodologies that are used.

All Karl Fischer procedures work in essentially the same way. The oil sample is titrated with a standard Karl Fischer reagent until an end-point is reached. The difference in test methods is based on the amount of sample used for the test and the method used to determine the titration end-point.

The most frequently used Karl Fischer method follows ASTM D1744 and involves volumetric titration of the sample, using a potentiometric cell to determine the end-point. While this method is reliable and precise, there can be reproducibility problems at low water concentrations (200 ppm or less). In addition, the test can be subject to interferences from sulfurous additives (for instance, AW and EP-type additives) and ferric salts which may be present due to wear debris. Both of these react with the Karl Fischer reagent as if they were water and can give a false positive, resulting in an overstating of the water concentration. In fact, a new, clean, dry AW or EP oil may give a reading of as much as 200 to 300 ppm, due to the reaction of the additives, rather than because of excess moisture.

More recently, labs have been switching to a coulometric titration method described in ASTM D6304. This method is more reliable than D1744 at low water concentrations and is less prone to interference effects, although again, AW and EP additized oils can show as much as 100 ppm of water as a result of the effects of the sulfurous additives.

The most reliable method is ASTM D6304, complete with codistillation. With the codistillation method, the oil sample is heated under a vacuum so that any water present in the sample evaporates. The water vapors are condensed and dissolved into toluene, which is then titrated using the D6304 procedure. Because the additives and other interfering contaminants that may be present in a used oil sample remain dissolved or suspended in the oil, the condensed water in the toluene is free from interference effects and is a true count of water present in the sample.

Another less commonly used method is ASTM D1533, which is used for determining water concentrations down to 10 ppm or less in transformer oils using a coulometric Karl Fischer reagent.

Calcium Hydride Test Kits
One of the simplest and most convenient ways to determine water concentrations in the field is by using a calcium hydride test kit. This method employs the known reaction of water with solid calcium hydride to produce hydrogen gas. Because the reaction occurs stoiciometrically, the amount of hydrogen gas liberated is directly proportional to the amount of water present in the sample. Therefore, the water content of the sample can be determined by measuring the rise in pressure in a sealed container due to the liberation of hydrogen gas as any water in the sample reacts with the calcium hydride. Used correctly, these test kits are reported to be accurate down to 50 ppm free or emulsified water.

Saturation Meters
When the amount of water present in an oil sample is below the saturation point, saturation (dew-point) meters can be used to indirectly quantify water content. The saturation point of an oil is simply the point at which the oil contains as much water in the dissolved state as possible, at a given temperature. At this point, the oil is saturated or has a relative humidity of 100 percent. Most saturation meters use a thin film capacitive device, whose capacitance changes depending on the relative humidity of the fluid in which it is submerged. Saturation meters have proven to be accurate and reliable at determining the percent saturation of used oils.

The biggest drawback with saturation meters is the fact that the saturation point is strongly dependent on temperature as well as the presence (or absence) of polar species, including additives, contaminants and wear particles. In addition, with water levels in excess of the saturation point, typically 200 to 600 ppm for most industrial oils, saturation meters are unable to quantify water content accurately. Despite these limitations, saturation meters can be a useful trending tool to determine moisture onsite, provided they are used frequently and routinely.

Monitoring and controlling water levels in any lubricating system is important. Whether it is a large diesel engine, a steam turbine, a hydraulic system or an electrical transformer, water can have a significant impact on equipment reliability and longevity. Regular water monitoring, whether it be a simple onsite crackle test or a lab-based Karl Fischer moisture test should become a standard condition-monitoring tool. But remember, like all tests, the methods used to detect water in oil have strengths and weakness, so be sure to select the one that meets your needs and desired detection limits.

Deeter Foundry, located in Lincoln, Neb., produces gray iron castings used in manhole frames and covers, storm sewer inlet frames, grates and curbs, trench grating and tree grates. The foundry has enjoyed the benefits of using desiccant breathers on its machines for more than two years.

The foundry began using desiccant breathers for two reasons. First, during the summers, water contamination increased in the hydraulic reservoirs. Second, the foundry found it more difficult to maintain target ISO cleanliness codes throughout the plant.

It has always been the theory of the author that machines are like humans and should be treated as such. With this approach, the Deeter Foundry team recognized that like people, equipment must also breathe. During normal operation of the hydraulic units, the oil levels in the reservoirs rise and fall, much like the human lungs when breathing. Moisture from the air accumulates in the reservoir when the machine takes in, or “breathes in” humid air. The dirt, which comes from the clay and sand used for molding, combined with humidity and the heat generated from pouring molten gray iron, created a less than ideal environment for contaminant-sensitive hydraulic components. Deeter Foundry wanted to achieve two goals: to lower the water concentrations and reduce the amount of silicon (dirt) in the hydraulic fluids.

In the beginning, they reviewed different fill caps, breathers and vents. Nothing filtered the air well enough. To combat the water problem in the oil, a superabsorbent filter was used to remove the water from the oil. To reduce the water concentration in their hydraulic units, the author used a water gel filter. This type of filter has media in it which removes water. He consulted a filter manufacturer, providing information on each of the hydraulic units, such as size of unit, ppm of each unit, and the base oil sample. With this information, the filter manufacturer put Deeter on a program to change out the water gel filters. Upon discovering that using spin-on oil filters worked as breathers, they were able to maintain the oil ISO cleanliness code and kept water ppm within the target range. However, the spin-on oil filters were expensive. The additional cost of the superabsorbent filters made maintaining the cleanliness code an expensive proposition. This is when desiccant breathers became a reasonable option.

Desiccant breathers use filter media to remove particles greater than three microns, and a silica-gel desiccant to remove moisture from the air entering the hydraulic oil reservoir and contaminating the fluid. This approach enabled Deeter to achieve and maintain its target moisture and dirt levels through six months of use, and without the use of the superabsorbent oil filter element. Based on this success, the foundry upgraded other systems to incorporate desiccant breathers.

The teams started by installing desiccant breathers on the large gearboxes. Within 90 days, oil analysis reports showed a decrease in silicon levels. The ISO cleanliness levels were set at 17/15/13 - levels which could not be achieved previously. After installing the breathers, the teams saw a reduction in silicon in the first oil sample taken. Not all machines were immediately converted to desiccant breathers because at the time, size options were limited. Desiccant breather manufacturers now offer several different sizes. Today, Deeter Foundry has desiccant breathers on many types of applications, including air compressor separator exhaust, fan bearings (outside), gearboxes, bulk hydraulic oil totes, lube storage racks and all the hydraulic units.

Some may ask, “Why use desiccant breathers?” My response is “Why not?” A desiccant breather removes both moisture and dirt from the air the machine breathes. This is true with equipment of all sizes and most locations. Breathers are sized according to the required cubic feet per minute (cfm) of air exchange for each machine application. A filter distributor can help answer these questions. Another commonly asked question is “How do I know my breather is still working?” The desiccant beads in the breathers change color as they become saturated with moisture, indicating that the unit is spent.

For the true skeptic, a trial run on a piece of equipment with trendable contaminant (moisture and particles) is recommended. This should prove or disprove the desiccant breather performance and effectiveness. The Deeter Foundry plant has more than 50 desiccant breathers installed on a wide variety of equipment. Desiccant breathers are now a part of the yearly maintenance budget.

While it was a change in thought and concept, Deeter Foundry has found desiccant breathers to be a vital part of the maintenance and reliability optimization process. The plant realizes the benefits of desiccant filters every day. Many of the obstacles encountered in the beginning have been addressed. Such changes are not possible without the support of senior management and more importantly, the buy-in from your technicians. Good documentation and a continuing education can spell success for any program.

It is almost certain that some amount of water is present in hydraulic and lubrication systems. Because of its destructive potential, hydraulic and lubrication systems are best operated with no free or emulsified water present. Water normally enters a system through external influences; the most common sources are moisture from the surrounding air entering through reservoir openings and breathers, condensation, “splash” from process water, system wash down water and contaminated new oil. Water contamination accelerates the aging process resulting in oxidation, hydrolysis, additive depletion, reduced lubricant film strength, corrosion and damaged components. Most of these expensive problems can be avoided by monitoring and controlling the operating fluid’s water content.

Figure 1. Example of a Hydraulic Oil Saturation Curve

Monitoring Percent Water Saturation Levels
A practical method for monitoring water in oil is to report water concentration as a percent of the saturation level. Water above the saturation point is defined as free or emulsified water and is more harmful than dissolved water (levels below the saturation point). Different oils are capable of dissolving varying amounts of water depending on their basestock and additive composition and, therefore, have varying water saturation curves. The curve in Figure 1 shows the relationship of water saturation level versus fluid temperature in a typical mineral-based hydraulic or lubricating oil. The curve shows that most lubricants are capable of holding more water, or have higher saturation levels, as the temperature increases.

A New Way to Monitor Saturation
The new HYDAC AS 2000 series Aqua Sensor is a stationary, microprocessor-based measurement unit designed to continuously monitor water saturation and temperature in hydraulic and lubrication systems. The saturation level indicates the percentage of water dissolved in the oil relative to the maximum possible amount of water that can be dissolved in the oil at a specific temperature. A reading of zero percent would indicate oil is free of water, while a reading of 100 percent would indicate oil that is completely saturated.

Hydac AS2000 Aqua Sensor

Consider the example of a plant having an oil with a saturation curve similar to the graph in Figure 1, where the ambient temperature is 68°F and the oil operating temperature is 104°F. The saturation level curve shows the saturation level to be 600 parts per million (ppm) at 104°F but only 200 ppm at 68°F. It is important for the user to know when his operating fluid reaches its ambient temperature saturation limit so he can avoid the introduction of free water into his system during shutdown hours; therefore, the user at the plant would want to know when his oil is 33 percent saturated at 104°F.

If the saturation characteristics of the oil are known, ppm can be calculated by multiplying the percent saturation reading at a given temperature by the known ppm saturation limit at that temperature. The HYDAC AS 2000 reports saturation level and temperature continuously to the integrated display and built-in alarm relays. This information can be captured via PLC or PC.

Water, water, everywhere . . . Water is ever present in the environment. Unless you live in an arid region, it is a fundamental fact of life. Water co-exists in oil in essentially the same way it co-exists in the atmosphere. It starts off in the dissolved phase - dispersed molecule-by-molecule throughout the oil. Just like water present in the air, it cannot be seen in oil, which may appear clear and bright. However, once the saturation point is exceeded, water is typically present in the emulsified phase creating a milkiness or fog in the oil, just like moist air on a cool day. When sufficient water exists, or when the oil has adequate demulsibility, free water will collect. Because water is typically heavier than oil, it settles below the oil, at the bottom of sumps and reservoirs.

The point at which an oil contains the maximum amount of dissolved water is termed the saturation point. The saturation point is dependent on the oil’s temperature, age and additive composition. The higher the temperature, the higher the saturation point and hence more water held in solution, in the dissolved phase. This is the same as being able to dissolve more sugar in hot water, than in cold water. Similarly, the older the oil, the higher the level of water that can be dissolved. This is due to polar by-products of oxidation in the oil, which act as “hooks” holding on to the water molecules and keeping them in solution. Likewise, highly additized oils, like crankcase oils, have a higher saturation point than lightly additized oils like turbine oils, because the additives - many of which are polar - also hold the water in solution.

The Effects of Water
Why is water considered an evil? Water will affect the oil’s base stock, encouraging oxidation, viscosity increase and foaming.

Water can also affect the additive package through water washing and hydrolysis, leading to acids and additive depletion. Water encourages rust and corrosion and will cause increased wear as a result of aeration, changes in viscosity resulting in film strength failure, hydrogen blistering and embrittlement, and vaporous cavitation. Finally, water is a generator of other contaminants in the oil such as waxes, suspensions, carbon and oxide insolubles and even micro-organisms.

Click Here to See Table 1. Comparison of Water-Removing Technologies

Water Prevention and Removal Strategies
Water ingression is either insidious as a result of atmospheric humidity levels or immediate as in water jet washing or sudden seal failure. Whatever the source, immediate attention is required to remove it. If significant water ingress has occurred over a prolonged period, detailed oil analysis, such as rust and corrosion inhibition characteristics, remaining useful life measurements, demulsibility and foam suppression and tendency may also be necessary to determine the oil’s suitability for further use. Merely replacing the oil will not cure the ingress source. Root cause corrective measures are necessary to resolve or limit water ingression.

Basic measures to address water ingression include the use of desiccating breathers, improved seal technology and training maintenance and operations personnel to avoid direct contact with wash down water on shaft seals and breathers.

Measures to minimize water ingress should start in the oil store. Drums and tanks should be sheltered from the environment. Even indoors, this means they should be sheltered against process water sprays, fire sprinkler tests and general cleaning sprays. Open barrels should also be protected with desiccant-style filters, particularly in humid storage areas, to prevent water build up and oil degradation.

A number of methods or technologies, from inexpensive gravity separation to complex vacuum dehydration, exist to remove water. Which technology is most effective will depend on the target dryness level required, the volume of water that must be removed, the base oil (mineral, synthetic, etc.) and the required flow and processing rate. The following is an outline of technologies that can remove water from oil, together with their relative advantages and disadvantages.

Gravity Separation
As already mentioned, free water in the system will settle to the bottom of the tank (assuming the specific gravity of water is greater than the lubricant). The time it takes the water to separate will depend on the system’s temperature, as well as the additive formulation, age of the oil and the base oil type. Some oils are designed to hold water in suspension rather than to allow it to separate out, making gravity separation a less-than-effective strategy.

In basic systems, opening the drain valve and allowing the water to drain off may be sufficient. The effectiveness of this action, however, will depend upon how long the system was allowed to stand prior to draining the water, whether the temperature was low enough to lower the saturation point dramatically and the oil’s demulsibility characteristics. Lowering the saturation point helps ensure that as much of the water as possible will exist in the free state. In larger volume systems, a separate settling tank may be employed to allow the oil to cool and demulsify prior to water removal (Figure 1).

Figure 1. Settling Tanks for Moisture and Solids Separation

The major downside to this method is that it removes only free water, so elements of emulsified and dissolved water will remain. The upside is the low cost of water removal.

Centrifuge - Spin Your Oil Clean
The principle of the centrifuge (Figure 2) is to separate the oil’s heavier elements by spinning the oil to create high G-forces - often in the tens of thousands of Gs.

Figure 2. Centrifugal Separation

The greater the difference in specific gravity between the contaminant and the oil, the more effective the process. For this reason, centrifuges often work better on low specific gravity and low viscosity oils, like turbine oils, rather than heavier gear type oils. In a centrifuge, both free and emulsified water will be removed; this will depend to some extent on the type of additive package, as some water will be held in suspension in the oil. Just like gravity separation, the lower the oil’s temperature, the more effective the removal process will be, because much of the water will exist in the emulsified and free states.

As a tool, a centrifuge is relatively expensive. However, given that it is also a means of removing other heavier contaminants and has a comparatively high throughput compared to other technologies, centrifugal separators are relatively cost effective.

The downside of centrifuges is that only emulsified and free water will be removed - although this can be partially overcome by keeping temperatures low.

Absorption Removal
Typically, most filter media will absorb a small amount of moisture from the oil, resulting in swelling of the media. This is particularly true for cellulose-based media. In fact, examination of used filters will often indicate if the presence of water is a concern. Some filter cartridges with an additional wrap consisting of polymer and desiccants are available. These filters are specifically designed to remove water by absorption and remove both emulsified and free water, as well as solids. However, the elements typically have a limited volume capacity and are best fitted to a portable filter cart for minor water ingression problems. In fact, when a small gearbox is being fitted with an expansion chamber type breather, it is worthwhile to filter the gearbox with a water-removing element to remove any trace elements of moisture that may condense out on surfaces within the unit when it cools.

The main disadvantage of absorption removal is that it has a limited capability for water removal per element. The positive aspect is not just its ability to trap solids, but also that it is a relatively cost-effective means of dealing with small systems that require polishing to remove moisture.

Vacuum the Oil Dry
The vacuum dehydration process (Figure 3) lowers the partial pressure, which assists in removing the water from the oil. Just like boiling water on top of Mount Everest, lowering the pressure allows water (and other volatile materials) to boil at a much lower pressure.

Figure 3. Vacuum Dehydrator

At the typical pressures used by most vacuum dehydrators (25" to 28" of mercury), water boils at 120°F to 130°F. By heating the oil, typically to 150°F to 160°F, water is vaporized inside the dehydrator, without causing excessive oil degradation due to thermal and oxidative stress. In most dehydrators, the air is warmed and dried prior to being passed over the oil, encouraging the water to transfer from the oil into the air. To maximize the process, the oil is thinned to obtain the greatest amount of surface area exposure possible. This is achieved by allowing the oil to pass over a number of surfaces internally in the vacuum chamber, or by creating an umbrella spray within the chamber through which the dry air passes.

The real benefit of this process is its ability to remove dissolved water and other low-boiling liquid impurities such as fuels and solvents. The removal of dissolved water makes it ideal for systems requiring low target levels of moisture. It is particularly useful in environments where large volumes of oil are at risk from the process or system, such as in steam turbines or paper mills. In fact, for lightly additized oils such as turbine oils and transformer oils, a vacuum dehydrator can remove as much as 80 percent to 90 percent of dissolved water, achieving water levels as low as a few ppm.

The main disadvantage of vacuum dehydrators is their cost and comparatively low flow rate. Because of the cost, many companies chose to rent dehydrators on an “as-needed” basis rather than purchase them.

The main advantage of vacuum dehydrators is that they offer the ability to remove moisture to very low levels. The greater the volume of oil and water, and the lower the target moisture level, the more cost-effective vacuum separation becomes.

Dehydration by Air Stripping
An alternative technology to vacuum dehydration is dehydration by air stripping (Figure 4), a process that removes water as well as gaseous contaminants in the oil. Not only does it remove free and emulsified water, but also dissolved water down to less than 100 ppm.

Figure 4. Air Stripping Dehydrator

Because of its ability to degas, it is also suitable for removing hydrocarbons in seal oil systems. Air stripping works by drawing air or nitrogen gas into a stream of heated oil, which mixes in and absorbs the water and gasses within the oil. The oil/air is then expanded to release the air or nitrogen, which takes the impurities with it. Generally, the water removed will be of a reasonable quality, sufficient to allow it to be drained off in the normal network without special disposal requirements. The exhaust air and gasses are also controlled to minimize the oil vapor released.

Just like vacuum dehydrators, cost is an issue with air stripping. However, its advantage is that it costs less to maintain than a typical vacuum dehydrator because it has fewer moving parts. The fact that it can also remove other gaseous impurities, as well as dissolved water, makes air stripping technology an effective alternative to vacuum dehydration.

Heat the Oil Dry
Some applications are self-cleansing because they run at elevated temperatures and consequently, water is evaporated. The combustion engine is a perfect example of a self-cleaning application. However, some settling tanks (see gravity separation) may also include heating elements to assist with water removal below the saturation point. Whether it is best practice to deliberately heat the oil briefly to drive off moisture to maintain oil health is open to debate. Allowing the water to remain in the oil is usually far more damaging than briefly heating the oil. Therefore, heater units are available as portable water removal systems. In static systems, like reservoirs, it is important to ensure that the power density of such elements remains below 5W/in² to minimize thermal stress to the oil.

The downside to heating oil is that it must be controlled, particularly with mineral oils, to avoid harm. However, the relative cost is less than the centrifugal or vacuum separation technologies, making this an effective water removing tool in certain circumstances. The decision about which main water removal technology is best will predominantly be based on the volume of oil and the water to be treated. The decision will be further impacted by the need to reach a target moisture level. If target moisture levels are well below the saturation limit, then more complex and expensive methods will be required as necessary if large quanitites of free and emulsified water are to be removed.

By now, most lubrication professionals are keenly aware of the reliability gains associated with contamination control. Those who have traveled down this road know that clean and dry lubricants often come at a price (filters aren’t cheap). However, best practice may have nothing to do with removing contaminants or changing the oil. Actually, it may have nothing to do with the oil at all. Instead, it’s a practice of stabilizing the cleanliness and dryness in the headspace environment - the air above the oil in tanks, reservoirs and lubrication compartments.

“Wear metals, in turn, catalyze oxidation, which when dirt ingresses through tank headspace openings and enters the oil, this dirt abrades surfaces and leads to wear metals. This in turn accelerates the formation of oxide insolubles, leading to surface deposits and varnish.”

Why is this important? First, a high percentage of the particles and moisture that ingress into lubricating oils and hydraulic fluids must pass through the headspace. Therefore, the practice of excluding contaminants from entering the headspace, by default, excludes contaminants from entering the oil. This can be accomplished by one of three methods:

1. Channeling incoming ambient air through filters (breathers) that remove water and dirt.
2. Using a bladder or similar device to prevent an exchange of headspace air with ambient air.
3. Maintaining positive headspace pressure by using instrument air or oil mist which eliminates the need to inhale contaminated ambient air.

Water removal is the second reason why stabilizing the headspace environment is important. With rare exception, a dry head space translates to dry oil - they go hand-in-hand. This is because wet is attracted to dry in the same way hot is attracted to cold. Basically, a dry headspace forms a desiccant blanket above the oil and, like a sponge, draws water out of the oil. The lower the relative humidity of the air in the headspace, the faster and more efficient the process of mass transfer of water out of the oil becomes.

We all know that there are other contaminants besides water and dirt, such as air, sludge and heat. However, many lubrication professionals may be unaware of the impact dirt and water can have on the build-up of these other contaminants over time. For instance, when emulsified water is allowed to co-exist in the oil, a common consequence is entrained air. Emulsified water has a tendency to impair the quality of oil to rapidly release entrained air. When air fails to detrain, a tertiary consequence is oil oxidation and adiabatic thermal failure, among others. Likewise, when dirt ingresses through tank headspace openings and enters the oil, this dirt abrades surfaces and leads to wear metals. This in turn accelerates the formation of oxide insolubles, leading to surface deposits and varnish. The list of secondary and tertiary consequences of dirt and water contamination is almost endless. Therefore, when you ask the “repetitive why” in your search for the cause of oil or machine failure, you might find the root cause to be poor headspace management - now no longer a secret.

Background
P&H MinePro Services Predictive Diagnostic teams provide condition-monitoring programs to mobile mining equipment throughout North and South America. The services include on-site oil analysis, vibration analysis, infrared thermography, passive ultrasonics and off-line motor testing.

One of the most noticeable improvements resulting from the diagnostic team’s program was increased oil cleanliness, which is important in the aggressive mining environment. The following case study discusses a water contamination issue and some surprising results from the oil lab.

The Problem
The transmission in question is one of two planetary swing transmissions on a 2800XPA electric mining shovel (Figure 3) at an open pit copper mine in New Mexico.

Click Here to See Figure 3.

This was the second monthly testing of this transmission. In June 1997, an oil change was recommended due to an improper grade of lubricant being used.

In July 1997, increases in the indexes of iron from the CSI Oilview on-site oil analysis equipment 5100 and 51 FW were noted with some concern.

Vibration analysis showed no problems with the transmission and no changes from testing the previous month. An oil change was recommended, and information regarding maintenance actions performed between the June and July visits was requested. The oil sample was sent to an outside oil lab for a more detailed analysis.

A Possible Cause
Discussion with maintenance personnel indicated that an oil change had recently been performed following the previous recommendation. An oil sample was drawn from lube trucks from both of the mines. Oilview testing indicated possible water contamination. A visual crackle test verified the presence of water contamination in the lube trucks.

The mine indicated that the source of the water was probably the wash rack, where the lube trucks are regularly washed off using a high-pressure washer. In the past, the trucks were washed with the tank vents open, allowing water into the lube tank. The oil in this transmission was changed and the lubrication staff was informed of the importance of keeping water out of the lube tanks.

The outside oil lab results came back from the July 1997 transmission sample confirming the water contamination (Table 2).

Diagnostic Message
The lab also provided the following comments: “Suggest immediate inspection of this unit, including resampling to verify results and check for sources of contamination, water ingress into system and wear. Wear debris analysis revealed several abrasive particles (cutting wear ribbons and needles of steel origin) and these should be considered abnormal in nature.”

With these results, the staff determined that the high ferrous and contaminant levels were caused by increased boundary wear due to water contamination.

Click here to see figure 2.

The Root Cause
Because of the known problem with water contamination, a visual crackle test was performed on each oil sample at the mine during subsequent diagnostic visits. There continued to be a problem with water contamination.

Lubrication personnel were blamed for the problem. P&H checked for other sources of contamination, beginning with sampling a newly delivered bulk storage tank. The results indicated high moisture levels and a contamination source.

P&H approached the lube vendor regarding the condition of the new lubricant and offered to help determine the source of the water. After some investigation, it was found that when the empty storage containers were returned to the oil supplier, they were steam-cleaned prior to refilling. A new employee was responsible for the cleaning. Apparently after cleaning the tank, the drain valve was closed without ensuring the tank was fully drained and dry. When the tanks were refilled, in some instances there was more than two inches of water standing in the bottom.

The vendor changed its cleaning procedure and the mine started random testing of its incoming lube. There has not been an issue of water contamination since.

References

1. Lukas, M. and Anderson, D. Rotrode Filter Spectroscopy, Does It Have a Place in the Commercial or Military Oil Analysis Laboratory? Spectro Incorporated, Littleton, Mass.
2. Lukas, M. and Anderson, D. Analytical Tools to Detect and Quantify Large Wear Particles in Used Lubricating Oil. Spectro Incorporated, Littleton, Mass.

Editor’s Note
This article was originally published as OilView Newsletter #6, available at www.compsys.com.

Water contamination in hydraulic systems can devastate an organization’s reliability objectives. Fortunately, with a diligent effort, water contamination can be effectively controlled by setting goal-based target dryness levels, achieving the targets through effective exclusion and removal of water and periodic monitoring to ensure that target levels are maintained. The critical first step is to establish target levels that reflect the organization’s reliability goals and take into account the mechanical sensitivity of the hydraulic system in question.

Rust and corrosion are the most obvious effects of water contamination. However, water also lies at the root of vaporous cavitation, hydrogen-induced embrittlement and blistering (Figure 1) and fatigue wear in rolling contacts.

Figure 1. Hydrogen-induced Embrittlement and
Blistering Caused by Water Contamination

Water’s destructive path extends beyond the machine to the lubricant itself. Water promotes base oil oxidation and hydrolysis, additive degradation and washing, microbial growth and formation of suspended ice crystals in cold application.

Water enters the hydraulic system at points where the system interfaces with its environment. Condensation is common in moisture-rich environments - particularly where the machine is frequently started and stopped. New oil is often contaminated with water due to poor handling practices. Cooler leaks, exposure to rain and direct water spray also result in contaminant ingestion.

Setting Moisture Contamination Targets
The first step in moisture contamination control is to establish appropriate target moisture content levels. The decision should be driven primarily by mechanical sensitivity and economics. The benefits associated with controlling moisture contamination should sufficiently outweigh the costs to provide a reasonable return on investment.

Research on rolling element bearings, which operate primarily under elastohydrodynamic lubrication, suggests that halving the fluid moisture level increases the life of the bearing by roughly half-again over the normal life when all other variables remain constant. In other words, a bearing with a normal life of 1,000 hours at 500 ppm water would last about 1,500 hours by reducing the oil’s moisture level to about 250 ppm. Likewise, reducing water contamination to about 125 ppm would increase the same bearing’s life to about 2,300 hours of service (Figure 2).

Figure 2. Rolling-Element Bearing Life vs.
Water Contamination Level

Other research on journal bearings, which operate under hydrodynamic lubrication, suggests that halving the average water contamination level reduces wear rate by about 20 percent (Figure 3). For example, reducing the moisture level from 500 ppm to 250 ppm in a plain bearing would increase the component’s life from 1,000 hours to 1,200 hours, on average. Likewise, decreasing moisture from 500 ppm to 125 ppm would yield an increase in component life from 1,000 hours to almost 1,500 hours (Figure 3).

Figure 3. Journal Bearing Wear Rate vs.
Water Contamination Level

Hydraulic systems operate under both hydrodynamic and elastohydrodynamic lubrication regimes, and are also typically at risk for cavitation-related wear. Research at the Nippon Mining Co., Ltd. in Japan revealed a substantial increase in hydraulic pump wear with the addition of just 500 ppm of water. Two oils were tested in 22 gpm vane pumps at 112 bar of pressure. Wear generation more than doubled for oil X, and increased by orders of magnitude when oil Y was used (Table 1).

Table 1. Increased Pump Wear in
the Presence of Water is Evident

Water increases wear under both hydrodynamic and elastohydrodynamic lubrication regimes. Due to variations in hydraulic system design, fluid type and operating conditions (such as pressure), the relationship between water contamination levels and wear rates would likewise vary for the systems. It seems reasonable to deduce however that the effect of halving water contamination levels could reduce wear rates by 20 to 50 percent for pumps and other hydraulic components subject to triboligcal wear. Given that mechanical reliability is related to moisture contamination levels, the question for the technologists becomes how much reliability do you want to buy through moisture contamination control?

A good starting point for assigning moisture target levels is the equipment supplier’s manual, if such a recommendation is available. You should then adjust this recommended level according to the following factors:

• Safety Requirements - If a failure or repair of a failure places people at risk, or if your organization’s safety assurance requirements are stricter than normal for a class of equipment, the moisture target should be adjusted downward.
• Reliability Goals - If production losses caused by a hydraulic system failure are unusually high, or the expected duration of lost productivity caused by a failure is abnormally high, adjust your target down.
• Application Severity - If your machine is operating at the outer limit of its design capability, adjust the target moisture level down.
• Environment Severity - If the risk of moisture contaminant ingestion is higher than normal, adjust the target down.
• Repair Costs - Systems with expensive or hard-to-get parts, or those that are difficult to repair due to lack of access or maintainability, require tighter-than-average moisture control.

One systematic approach for developing target cleanliness levels for moisture has its roots in reliability-centered maintenance (RCM). Start by evaluating the machine’s mission criticality using the reliability penalty factor (RPF) calculator (Figure 4).

Click Here to See Figure 4. Reliability Penalty Factor

The RPF method rates the machine as a function of mission criticality, cost to repair and effectiveness of any early warning systems, like oil analysis, that are used to detect failures. While the RPF is systematic and it produces a number as output, it is not truly quantitative. Tools like the RPF calculator are most accurate when they reflect the consensus of a representative group of organizational stakeholders. So employ a Delphi-type method to produce RPF scores that represent the collective opinions and experience of the stakeholder group.

Click Here to See Table 2. Hydraulic Target Dryness

Once the RPF score is defined, refer to Table 2 to arrive at a recommended target moisture level. The recommendations are experience-based and have proven useful for plant-level engineers. This target level should serve as a starting point. Adjust these levels according to field conditions.

If 200 ppm is easily achieved, it might be reasonable to push the limit down to 100 ppm and so on. Conversely, if achieving 200 ppm seems unrealistic given available technology, adjust the goal upward accordingly. Ideally, the water contamination should be kept below the oil’s saturation point. Economics should drive your moisture contamination control efforts. Discontinue efforts when further control becomes economically unviable.

Water contamination adversely affects the health of hydraulic machines and fluids. Its control is central to reliability, dependability and low cost of equipment ownership. Water contamination control requires the establishment of a sensible goal-based target level, contaminant exclusion and removal initiatives to achieve the target. Getting the target moisture level set is the critical first step. It drives all other water contamination control decisions.

References

1. Schatzberg, P. and I. Felsen. “Effects of Water and Oxygen During Rolling Contact Lubrication.” Wear, Vol. 12. 1968.
2. Rowe, C. “Lubricated Wear.” CRC Handbook of Lubrication: Theory and Practice of Tribology, Volume II. Ed. E. Booser, 1984.
3. Fitch, E. Proactive Maintenance for Mechanical Systems. Stillwater, OK: FES, Inc., 1992.
4. Rothwell, N. and M. Tillmin. The Corrosion Monitoring Handbook. Kingham, Oxford, UK: Coxmoor Publishing, 2000.
5. Smolenski, D. and S. Schwartz. “Automotive Engine Oil Condition Monitoring.” CRC Handbook of Lubrication: Theory and Practice of Tribology, Volume III. Ed. E. Booser, 1994.
6. Fitch, E. Fluid Contamination Control. Stillwater, OK: FES, Inc., 1988.
7. Bloch, H. “Criteria for Water Removal from Mechanical Drive Steam Turbine Lube Oils.” Lubrication Engineering, December 1980.
8. Beercheck, R. “How Dirt and Water Slash Bearing Life.” Machine Design Magazine, July 1978.
9. Schatzberg, P. and I. Felsen. “Effects of Water and Oxygen During Rolling Contact Lubrication.” Wear, Vol. 12. 1968.
10. Fitch, J. and S. Jaggernauth. “Moisture … The Second Most Destructive Contaminant and its Effects on Bearing Life.” P/PM Technology, December 1994.
11. Fitch E. An Encyclopedia of Contamination Control. Stillwater, OK: FES, Inc., 1980.
12. Troyer, D. “Advanced Strategies for the Monitoring and Control of Water Contamination in Oil Hydraulic Fluids.” Hydraulic Failure Analysis: Fluids, Components and System Effects. ASTM STP 1339, G. Totten, D. Wills, and D. Feldmann, Editors. American Society for Testing and Materials: West Conshohocken, Penn., 2000.
13. Troyer, D. “Estimating Values in the Absence of Real Data - Deploying the Delphi Method.” Practicing Oil Analysis magazine, January 2002.

Water contamination is a cause for major concern in a large number of applications. In some industries and environments, water is a far more damaging contaminant than solid particles and is often overlooked as a primary cause of component failure. For certain applications, even a small amount of water may have damaging effects on production or equipment.

Water can exist in three states or phases. Dissolved water is characterized by individual water molecules dispersed throughout the oil. Similar to humidity in the air, dissolved water cannot be seen in the oil. If too much water is present in the oil, the dispersed water molecules begin to saturate; this is similar to the formation of fog. When this occurs, the water is considered emulsified. Free water is formed when the addition of water leads to a phase separation of both liquid components producing a layer of water.

Several methods are available to determine the water contamination level in fluids. A Karl Fischer (KF) coulometric titrator is one of the most accurate methods. Unlike other techniques, it can trace low levels of free, emulsified and dissolved (which cannot be detected with other methods such as a crackle test). When used correctly, the test is capable of measuring water levels as low as 1 ppm or 0.0001 percent.

Coulometric vs. Volumetric
Titration is a chemical analysis that determines the content of a substance, such as water, by adding a reagent of known concentration in carefully measured amounts until a chemical reaction is complete. There are two types of Karl Fischer titrators: volumetric and coulometric titrators. The main difference between the two is that with the volumetric method, the titrant is added directly to the sample by a burette. Conversely, with the coulometric method, the titrant is generated electrochemically in the titration cell. The coulometric method measures water levels much lower than the volumetric method.

Titration Chemistry Fundamentals
The following reaction scheme has been proposed for the Karl Fischer titration:

ROH represents an alcohol like methanol or ethanol.

In the coulometric method, the titration cell consists of two parts: an anodic and a cathodic compartment. Figure 1 shows both compartments separated by a ceramic diaphragm. The anodic compartment contains the anolyte solution which includes sulfur dioxide (SO₂), iodide (I^–) and imidazole needed in the chemical reaction. Methanol or ethanol (ROH) is usually used as a solvent.

Figure 1. Titration Cell (Courtesy of Mettler-Toledo)

In coulometric Karl Ficher titration, iodine (I₂) is generated electrochemically from iodide (I^–). When iodine (I₂) comes in contact with the water in the sample, water is titrated according to the above mentioned reaction scheme (equations No. 1 and No. 2). Once all of the water available has reacted, the reaction is complete. The amount of water in the sample is calculated by measuring the current needed for the electrochemical generation of iodine (I₂) from iodide (I^–) according to the following reaction (equation No. 3):

Coulometric Titrator Features
There are several features to consider when selecting a Karl Fischer coulometric titrator. Table 1 lists a number of manufacturers that offer Karl Fischer coulometric titrators. Each manufacturer offers different features.

Sensitivity to Humidity
Humidity is probably the largest source of error during the titration. Special precautions should be taken during setup and testing, especially in coastal or tropical regions. The air conditioning system should be equipped with a moisture condenser. Also, a Karl Fischer titrator should not be installed near an air conditioner vent.

The titration cells are enclosed to help ensure that water does not enter from the atmosphere; however, a very small amount of water almost always makes it into the titration cell. The amount of water that enters over a period of time is known as the drift. Many manufacturers will give specifications on drift values and maximum allowable air humidity.

Sensitivity to pH
The chemical reaction is sensitive to the solution’s acidity or alkalinity. The optimum pH range of the sample solution for efficient Karl Fischer titration is between pH 5.5 and 8. When the pH is greater than 8.5, the reaction rate increases due to chemical side reactions. This results in a more sluggish endpoint and higher iodine consumption, which will affect results. Buffering agents are available for acidic or basic samples to keep an ideal pH between 5.5 and 8.

Diaphragm vs. Diaphragmless Titration
The diaphragm separates the anodic and cathodic compartments. Its purpose is to prevent the electrochemically generated iodine from reversing back to iodide at the cathode instead of reacting with the water. The diaphragmless titrator uses a different geometric construction to prevent the generated iodine from reversing back to iodide (Figure 2). As hydrogen gas is generated in the cathodic compartment, it creates a layer of gas bubbles on the surface of the cathode. This layer of gas prevents the iodine from being reduced at the cathode. However, it is still possible for small amounts of iodine to be reversed to iodide when reaching the cathode.

Figure 2. Diaphrapm and Diaphragmless Configurations
(Courtesy of Mettler-Toledo)

Diaphragmless titration is advantageous because there is no diaphragm to become contaminated; it is easier to clean; and a lower drift can be used (this relates to how quickly the reaction completes).

A diaphragmless cell is accurate enough for many applications. However, check with your Karl Fischer Titrator supplier to verify whether your applications require a diaphragm.

Codistillation Method
Some samples may release water slowly or have side reactions with the reagents. In this case, the ASTM D6304 with codistillation is a more reliable technique and will mitigate the chances of this occurring. With this method, the oil sample is heated under a vacuum so that any water in the sample will evaporate. Water vapors are condensed and dissolved in toluene.

This is then titrated using the ASTM D6304 procedure. Because additives and other interfering contaminants that may be present in a used oil sample remain dissolved or suspended in the oil, the condensed water in the toluene is free from interference effects and is a true count of water in the sample. Many companies offer optional drying ovens for this purpose.

Programmable or Built-in Methods
The Karl Fischer coulometric titrator method can be adjusted depending on the application and accuracy needed. Adjustment requires some understanding of the titrator’s working and controlling principles. To help ensure accurate adjustment, many titrators have methods built-in that can be used for more common applications. This more user-friendly method makes it possible for a person who doesn’t have a lot of experience to use the instrument.

For special applications, a particular method may not be built-in. In this case, many titrators allow the user to program a method. Once all of the settings are in place, that specific method can be selected each time the application is needed, and the titrator will run on its own.

The number of built-in and programmable methods vary among instruments. It is useful to determine approximately how many applications are available, and to become familiar with each application’s specialties.

Built-in Pumps
It is important that the reagents do not become contaminated. Some coulometric titrators come with a built-in pump that can fill and drain reagents. This helps eliminate reagent contamination and reduces the number of steps required for the procedure.

Titration Speeds
Titration speeds vary for each unit. While speed may be important, the faster the unit titrates, the less accurate it will be. For samples with low levels of water (less than 50 µg), the titration should take place slowly. It is also best to titrate the sample slowly if the water level accuracy is critical. If high levels of water (greater than 1,000 µg per sample) are being measured, the titration can be quicker.

Memory Storage Capacity
Most units come with a connection for a computer or printer and some have built-in printers. Each unit has a different memory storing capacity. If it will not be attached to a personal computer, then its memory storage capacity may be an important consideration.

References

1. ASTM D6304: Standard Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer Titration.
2. (2003, July-August). Water - Oil Analysis 101. Practicing Oil Analysis.
3. (2001, July-August). Water - The Forgotten Contaminant. Practicing Oil Analysis.
4. Mettler-Toledo Applications Brochure 32, Fundamentals of the Coulometric Karl Fischer Titration with Selected Applications. Mettler-Toledo Inc. Retrieved August 1, 2003 from www.mt.com.

Sidebar 1
Karl Fischer Method Made Easy Through Auto Sampling Titration
Automated titration is an accessory offered by some Karl Fischer manufacturers that allows the user to perform multiple titrations without stopping to prepare a sample. It is combined with either a coulometric or volumetric Karl Fischer titrator to determine the amount of water in the sample efficiently and unmonitored, allowing the analyst to focus on other important jobs while it runs.

How Does it Work?
The samples are placed in the rotating tray and sealed. Once the instrument starts, the first sample is moved into a temperature-controlled oven. Then, the sample is pierced so that as the water is converted into a vapor, it is transferred into either a coulometric or volumetric titrator which will determine the water content of the sample. By controlling the temperature, only the water evaporates while the remaining sample stays in the sample bottle. Once all of the water is removed and measured, the sample bottle is put back into its original position on the tray, and the tray rotates to the next sample to be performed.

Advantages

• Multiple samples can be analyzed at once without stopping to prepare each sample.
• There is no contamination in the oven or the titration cell because the remaining liquid or solid sample remains in the sample bottle.
• There’s no need to worry about any side reactions that may occur between the sample and the titrating reagents.
• Much less reagent is used in the process.

The Mettler-Toledo DL39
Coulometer with Stromboli and Optional Air Pump

The Metrohm 774 KF Oven
Sample Processor with 756
Karl Fischer Coulometer

Water contamination in lubricating oil accelerates the natural oxidation that normally takes place in the oil. Even when additives are used to retard the natural process, the presence of water will degrade the effectiveness of certain additives potentially leading to tight emulsions and the formation of sediment in the oil. In addition, water in lubricating oil increases the risk of microbial attack and contributes to further loss of oil performance and thereby to corrosion of the components in the various oil systems.

In modern diesel engines, frictional surfaces are exposed to heavy loads, which place tough demands on lubricant condition and performance. The Gertsen & Olufsen AS Survey Water Monitor (SWM) is a unique system that provides a way to monitor water contamination in real-time, alerting equipment owners to take immediate corrective action, if or when necessary. The system is suitable for use on all types of oil-lubricated machinery, including engines, turbines, gearboxes, compressors and hydraulic systems.

The working principle of the SWM system is based on the difference in boiling points of water and oil. In short, a continuous flow of oil is by-passed through an evaporator where the oil is heated sufficiently to vaporize any water. Subsequently, the water is condensed and measured by passing it through a sealed orifice calibrated to produce drops of a fixed size. Each drop from the orifice causes an electrical impulse, which by way of the relay box is fed to a computer with results displayed locally.

When a fixed water concentration limit (decided by the operator or engine manufacturer) is breached, an alarm will sound.

The measured value is converted into a current signal, 0 to 20 mA or 4 to 20 mA, representing 0 percent to 5 percent water content. The SWM system is recommended for installation on new engines and as a valuable safety add-on for existing engines and various oil systems.

The newest version of the instrument provides a water content measurement as low as 0.03 percent (lower limit of sensitivity), which represents literally one single drop of water in a measured volume of oil. The SWM constantly updates the readings, giving a real-time characterization of the oil’s moisture level.

In the past, the unit was used primarily on four-stroke fast- running engines, including engines of some of the biggest cruise ships in the world. In addition, a number of SWM systems have been supplied to international ship owners of large tankers and container vessels. However, these systems are now being used to monitor the separators on two-stroke engines as a redundant safety measure, ensuring that the lubricating oil is free of significant water content at all times.

Although the SWM was initially intended for use in lubricating oil systems, it has proven that it can be used in a variety of applications, including fuel oil systems and hydraulic oil systems. One of the latest applications is measuring water in oil on thruster oil systems and Azipod systems (podded propulsion units for large marine vessels).

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:

Click Here to See Figure 1.

1. Sensitivity of the machine and lubricant to water. Some machine types and components have unique sensitivity to water-induced damage, such as corrosion, cavitation, hydrogen embrittlement, silt lock, elastohydrodynamics (EHD), etc. Likewise, certain lubricants (both base oils and additives) are more prone than others to degradation in the presence of water. The degradation or depletion modes include hydrolysis, oxidation, water washing and others.

2. How long water stays in the oil. The longer water exists in a suspended state in the oil, the higher the risk it poses to the machine and the lubricant. The longevity of water in the oil is influenced by factors such as turbulence, emulsification, the rate of water ingression and the rate of water removal, including evaporation, dehydration and settling.

3. Amount of oil/water interfacial surface area. If water and oil are allowed to become emulsified, high surface area between the oil and water results. This occurs when larger droplets of water are crushed into numerous microglobules of water, which can increase the interfacial surface area by more than one million times. When surface area multiplies so do chemical reaction sites between the water, additives, base oils and other contaminants.

4. Mobility of the water within the machine. Water is less likely to crush into microglobules unless it is mobile and able to be carried into turbulent and mechanically dynamic zones within the machine. Once emulsions are allowed to form and stabilize, the risk water poses to the lubricant and machine is significantly magnified. One could say that the movement of the oil gives “legs” to the water, spreading its destructive potential. The water is then able to go wherever the oil goes, including reliability-sensitive zones within the machine.

5. Heat. Heat provides the activation energy necessary to initiate chemical reactions (corrosion, oxidation, hydrolysis, etc.) and hinder effective lubrication (film strength) in highly loaded frictional machine surfaces.

Figure 1 illustrates the principal conditions that enable the five factors to potentially inflict damage from water contamination. For instance, how long water stays in the oil is influenced ultimately by more than 16 other conditions. Not all of these conditions are likely to occur at any one time, but then again, only a few are actually required. Perhaps the best thing to do, using the diagram, is to perform an inventory of the applicable influencing conditions to rate your machine’s tendency for water-induced failure.

Controlling Water’s Grip
It is frequently said that water is the most destructive when it is emulsified in the oil - perhaps its most prevalent state of coexistence. As previously stated, an emulsion not only engages the oil and its additives via high interfacial surface area but also aids its mobility in the flowing fluid to load-bearing and metallurgically sensitive surfaces. If the water wasn’t emulsified (trapped in the oil) it couldn’t be so easily transported.

Let’s take a closer look at how this happens. To have stable oil/water emulsions you need not only a mixture of oil and water but also emulsifying agents, also known as water handles. This is illustrated in Figure 2. In fact, there is convincing evidence that these water handles are perhaps the core enabler of most water-related problems. Without these handles, water - being heavier than the oil - has nothing to prevent it from settling out of the way.

As a practical matter, whatever is in the oil that is “water-loving” will effectively serve the function of being a water handle. Most water handles are polar soluble suspensions within the oil. For certain oils, these polar handles are primarily polar additives such as detergents and dispersants. In such cases, they can’t be avoided - they are a part of the oil’s formulation. In other cases, they are both uninvited and unwanted guests. These include oxides, surfactants and many common solid and dissolved suspended contaminants.

Seeing the Water Hazard
Eventually water will enter your lubricants. The damage it inflicts will largely depend on how long it stays and the surface area it attains in contact with the oil (enabled by water handles).

A good start at controlling the risk is to monitor both root causes and symptoms of the risk. This includes monitoring not only the amount of water in the oil, but also its state of coexistence (dissolved, emulsified or free). Next, assess the oil’s population of water handles. Perhaps the best way this can be done is to use the demulsibility test (ASTM D1401). Start with new oil to get a baseline, then assess the condition of in-service lubricants. Some oil analysis labs have began using D1401 for routine oil analysis of turbine oils, hydraulic fluids and paper machine oils.

Any significant failure of demulsibility should be investigated. Don’t simply change the oil and go on down the road. Knowing where the handles came from will give you a better idea of how control their recurrence.

Finally, go back to the basics and take stock of where water comes from, then develop a workable plan to control its ingression. Plainly stated, proactive maintenance is always the best machine reliability strategy whether you are trying to control dirt, heat, misalignment or water contamination.

Moisture is considered a chemical contaminant when suspended or mixed with lubricating oils. It presents a combination of chemical and physical problems for the lubricant and machinery, respectively. The potential problems, states of existence and methods for measuring moisture are discussed here.

Effects of Water on Equipment and Lubricants
The effects of water are insidious. Failure due to water contamination may be catastrophic, but it may not be immediate. Many failures blamed on lubricants are truly caused by excess water. The following are some of the effects of water on equipment:

• Shorter component life due to rust and corrosion

• Water etching/erosion and vaporous cavitation

• Hydrogen embrittlement

• Oxidation of bearing babbitt

• Wear caused by loss of oil film or hard water deposits

Rust and Corrosion
Water attacks iron and steel surfaces to produce iron oxides. Water teams up with acid in the oil and corrodes ferrous and nonferrous metals. Rust particles are abrasive. Abrasion exposes fresh metal which corrodes more easily in the presence of water and acid.

Water Etching
Water etching can be found on bearing surfaces and raceways. It is primarily caused by generation of hydrogen sulfide and sulfuric acid from water-induced lubricant degradation.

Erosion
Erosion occurs when free water flashes onto hot metal surfaces and causes pitting.

Vaporous Cavitation
If the vapor pressure of water is reached in the low-pressure regions of a machine, such as the suction line of a pump or the pre-load region of a journal bearing, the vapor bubbles expand. Should the vapor bubble be subsequently exposed to sudden high pressure, such as in a pump or the load zone of a journal bearing, the water vapor bubbles quickly contract (implode) and simultaneously condense back to the liquid phase. The water droplet impacts a small area of the machine’s surface with great force in the form of a needle-like micro-jet, which causes localized surface fatigue and erosion. Water contamination also increases the oil’s ability to entrain air, thus increasing gaseous cavitation.

Hydrogen Embrittlement
Hydrogen embrittlement occurs when water invades microscopic cracks in metal surfaces. Under extreme pressure, water decomposes into its components and releases hydrogen. This explosive force forces the cracks to become wider and deeper, leading to spalling.

Film Strength Loss
Rolling element bearings and the pitch line of a gear tooth are protected because oil viscosity increases as pressure increases. Water does not possess this property. Its viscosity remains constant (or drops slightly) as pressure increases. As a result, water contamination increases the likelihood of contact fatigue (spalling failure).

The effects on lubricating oil can be equally harmful:

• Water accelerates oxidation of the oil

• Depletes oxidation inhibitors and demulsifiers

• May cause some additives to precipitate

• Causes ZDDP antiwear additive to destabilize over 180°F

• Competes with polar additives for metal surfaces

Maximum Recommended Water Concentrations
Oil, unless it is dried, contains some dissolved water. Figure 1 shows the amount of dissolved water that can be found in ISO 220 paper machine oil and ISO 32 turbine lubricant before it turns cloudy.

Figure 1. Dissolved Water as a Function of Temperature
in Paper Machine Oil and Turbine Oil

Table 1 helps determine the relative life of mechanical equipment versus the amount of water in the lubricant. To use the chart, estimate the current moisture level in the system along the y-axis, move toward the right to the target moisture level. The top of the chart gives the estimate of how much the life of the oil is extended. For example, by reducing moisture from 2,500 ppm to 156 ppm, machine life is extended by a factor of 5.

Tests for Water in Oil
The guidelines in Table 1 help only if it is known how much water is in the oil. There are several qualitative and quantitative tests to determine water content. The easiest one to perform is a simple visual test. An ISO 68 turbine lubricant was observed at room temperature with controlled amounts of water. Table 2 shows the results of the test.

Bear in mind that several factors can affect the cloudy or hazy appearance of the oil. First, as the oil sits, it will clear up and the oil may become supersaturated. Second, dye and dark-color oil can mask cloudiness.

Visual Crackle Test
A test that can be performed on-site is the crackle test. It is a quick control test that is performed by heating the oil in a small metal pan using a Bunsen burner or hot plate. It is heated rapidly to 100°C and the technician listens carefully for the number of pops or crackles. It is not run on hazy oil unless there is a doubt as to whether the haziness is caused by water or some other substance.

Noria has copyrighted the following technique for running a visual crackle test. Here are the instructions from the Web site at www.practicingoilanalysis.com.¹

• Maintain surface temperature on a hot plate of 300°F (135°C).

• Violently agitate oil sample (such as in a paint shaker) to achieve homogenous suspension of water in oil.

• Using a clean dropper, place a drop of oil on the hot plate.

If no crackling or vapor bubbles are produced after a few seconds, no free or emulsified water is present.

If very small bubbles (0.5 mm) are produced but disappear quickly, approximately 0.05 percent to 0.1 percent water is present.

If bubbles approximately 2 mm are produced, gather to center of oil spot, enlarge to about 4 mm, then disappear, approximately 0.1 percent to 0.2 percent water is present.

For moisture levels above 0.2 percent, bubbles may start out about 2 to 3 mm then grow to 4 mm, with the process repeating once or twice. For even higher moisture levels, violent bubbling and audible crackling may result.

The method is not quantitative. Hot plate temperatures above 300°F induce rapid scintillation that may be undetectable. The method does not measure the presence of chemically dissolved water. Different base stocks, viscosities and additives will exhibit varying results. Certain synthetics, such as esters, may not produce scintillation. Refrigerants and other low boiling-point suspensions may affect results. False positives are possible with entrained volatile solvents and gases.

Wearing protective eyewear and long sleeves is suggested, and the test should be performed in a well-ventilated area.

Calcium Hydride Test
A convenient way to determine water concentration in the field is by using a calcium hydride test kit (Figure 2). Water reacts with solid calcium hydride to produce hydrogen gas, which is directly proportional to the amount of water present in the sample. The water content of the sample is measured by the increase in pressure in a sealed container. These test kits are reported to be accurate down to 50 ppm free or emulsified water.

Figure 2. Calcium Hydride Test Kit

All of the water must come into contact with the calcium hydride. Viscous oils physically prevent water from mixing with calcium hydride whereas polar additives chemically attract water molecules to hold the water in solution.

On-line Sensors
There are several on-line sensors that measure water while equipment is operating (Figure 3).

Figure 3. On-line Impedance-type
Moisture Sensor

Some sensors measure the temperature and relative water saturation of petroleum and synthetic fluids and fuels. A probe senses water at a representative point of the system. The devices change capacitance as water concentration increases and decreases. Results are read as percent water saturation. Another technology monitors the humidity in the sump or reservoir headspace (Figure 4). Relative humidity of the headspace air has been found to correlate to lubricant moisture levels.

Figure 4. On-line Headspace
Moisture Sensor

By monitoring water content below the saturation level, these units allow action to be taken prior to the formation of free water, thus preventing problems such as additive depletion, oil oxidation, corrosion and reduced lubricating film thickness.

Temperature changes affect saturation. An oil with 200 ppm water may be suitable for use at an operating temperature of 180°F, but if the equipment cools down to 60°F, saturated water can be released as potentially damaging free water. Testing the oil in-service and correcting for temperature allows operators to discover and correct water problems before they reach the stage where water drops out.

One drawback of saturation meters is that temperature, additives, contaminants and wear particles affect saturation point. In addition, saturation meters are unable to quantify water content accurately when water is above the saturation point, typically 200 to 600 ppm for industrial oils. Despite these limitations, saturation meters can be a useful trending tool to determine moisture, provided they are used frequently and routinely.

Another sensor technology is based on the absorption of infrared light (Figure 5).

Figure 5. Single-channel Infrared
Moisture Sensor

One channel measures the amount of water in the oil while the other is a reference channel. The infrared absorption is determined from the difference between these two channels at the target spectral band for water. This absorption, using a calibration curve, is used to estimate the amount of water in the oil sample as traditionally presented in ppm or percent. According the manufacturer, it will read concentrations to two percent water.

Quantitative tests for water include Karl Fischer, water by distillation and FTIR. Karl Fischer (Figure 6) is accurate from 1 ppm to 100 percent and is relatively quick and inexpensive. The oil sample is titrated with a standard Karl Fischer reagent until an end-point is reached. The difference in test methods is based on the amount of sample used for the test and the method used to determine the titration end-point.

Figure 6. Coulometric Karl Fischer
Titration Analyzer

ASTM D1744, a volumetric method, is reliable and precise, but there can be reproducibility problems at low water concentrations (200 ppm or less). Soaps, salts from wear debris and sulfur-based additives react with the Karl Fischer and can give a false positive. In fact, a new, clean, dry antiwear (AW) or extreme pressure (EP) oil may give a reading of as much as 200 to 300 ppm.

ASTM D6304, a coulometric titration method (Figure 6), is more reliable than D1744 at low water concentrations and is less prone to interference effects, although again, AW and EP additized oils can show as much as 100 ppm of water.

The most reliable method is ASTM D6304. The oil sample is heated under a vacuum so that any water present in the sample evaporates. Water vapors are condensed and dissolved into toluene, which is then titrated. Because the additives and other interfering contaminants remain in the oil, the condensed water in the toluene is a true indication of water present in the sample.

Water by Distillation
Water by distillation measures the amount of water boiled off in a special still (Figure 7).

	Figure 7. Distillation Method for Determining Moisture Levels
Figure 7. Distillation Method for Determining Moisture Levels

The classic method for determining water-in-oil is the Dean and Stark distillation method (ASTM D95). This test method is fairly cumbersome and requires a comparatively large sample to ensure accuracy, which is why it is rarely used in production-style oil analysis labs today.

As the oil is heated, any water present vaporizes. The water vapors are then condensed and collected in a graduated collection tube, such that the volume of water produced by distillation can be measured as a function of the total volume of oil used. It can detect between 500 ppm and 25 percent water.

Fourier Transform Infrared
FTIR can be an effective method for screening samples containing in excess of 1,000 ppm of water, provided a correct new oil baseline is available for spectral subtraction. However, due to its limited precision and comparatively high detection limits, FTIR is not adequate in many situations where precise water concentrations below 1,000 ppm or 0.1 percent are required.

Control of Water Sources
Now that the amount of water in the oil has been determined, how does one control it?

First, control the source of water contamination. Following are common sources of water into lubricating oil and suggestions on how to control them:

• Manage new oil properly.

• Use desiccant breathers or other tank headspace protection.

• Avoid shafts, fill ports and breathers when washing down machines.

• Avoid high-pressure sprays around seals if possible.

• Maintain steam and heating/cooling water system seals.

• Periodically inspect rotary steam joints for leaks; replace seals and/or correct alignment as appropriate; install flinger flanges to direct steam away from labyrinth seals.

• Repair heat exchanger leaks.

• Prevent washdown water from entering vents and reservoir covers.

• Properly install and seal covers and hatches.

• Watch for condensation caused by cold water lines located close to a hot reservoir.

• Gutter water to divert flow away from reservoir hatches.

• Install secondary seals or V-rings on critical systems.

• Use and maintain high-quality shaft and wiper seals.

• Prevent contamination from conden-sation by using a bladder-type breather on vents.

• Install desiccant air breathers on vents

• Prevent water from entering new oil by storing drums indoors. If they must be stored outdoors, keep them in a shed or under a tarp, or store them on their sides.

• Install a vapor extractor or fan to remove humidity from large reservoirs.

• Periodically drain water from low points in system.

Moisture can be an insidious problem for the equipment operator. With general precautions to prevent contamination, and an appropriate understanding of the methods for and a plan to detect the presence of moisture in mechanical systems, the deleterious effects of moisture can be avoided. Coupled with an effective moisture removal approach, lubricant and machine life may be extended appreciably, providing the equipment operator with one more lever to use in the pursuit of reliability.

Editor’s Note:
This article was originally published in the Lubrication Excellence 2005 Conference Proceedings, Noria Corporation.

Reference
Troyer, D. “The Visual Crackle - A New Twist to an Old Technique.” Practicing Oil Analysis magazine, September-October 1998.

It’s doubtful that anyone working in less than pristine surroundings would be surprised to learn particle contaminants cause lubricant and hydraulic system deterioration. What may be surprising though is that many experts consider moisture accumulation in lubricating oils a chemical contaminant, which can be even more destructive than particle contamination.

As with particle control, maintenance personnel must take care to minimize entry of moisture to curtail damage within hydraulic systems, turbines or gearboxes to prevent downtime, the expense of labor and having to replace oil and damaged parts.

One of the most cost-effective ways to prevent contaminants from entering machinery is by using a breather. Numerous kinds are available, including oil coalescing, expansion chamber/bladder, desiccant and hybrids. Finding the right breather for an application is a good first maintenance consideration when attempting to extend a system’s life. Recently, many original equipment manufacturers (OEMs) have chosen to supply desiccant breathers on their products to accomplish such a task.

Removing Moisture Extends Oil and Equipment Life
Every manufacturing industry creates its own unique environment, resulting in contamination peculiar to that industry, which in turn, requires appropriately designed breathers. Desiccant breathers are particularly useful in environments that contain high dust and humidity levels.

There are a number of ways that contaminants can enter equipment, including poor oil top-up and sampling methods, improper handling practices, inadequate or poorly maintained seals and the lack of breather filters. The abrasive effects that particles have on hydraulic pumps, turbines or gearboxes are obvious. The effects water has on moving parts are much less understood.

Solid, Liquid and Gas
Water can exist in oil in three states: dissolved, emulsified and free. Individual water molecules dispersed throughout oil are considered to be dissolved. New lubricating oil can retain dissolved water at levels between 200 ppm to 600 ppm, and new motor oils can retain three times this amount before any evidence of moisture is evident. The older the oil, the more water it can hold. At some point the oil becomes saturated and the individual water molecules begin to coalesce, creating microdroplets and a cloudy appearance. As the amount of emulsified water in the oil increases, a layer of free water is produced, which settles to the bottom of tanks and sumps.

Once water has mixed with oil, chemical reactions occur between the water, base oil and various additives, including extreme pressure and wear resistance agents, oxidation and rust inhibitors, and viscosity improvers. The chemical reaction is called hydrolysis. Water can accelerate the oil’s aging rate tenfold. These chemical reactions result in varnish, sludge, organic and inorganic acids, surface deposits and polymerization (a thickening of the lubricant). As little as one percent contamination can reduce bearing life by as much as 90 percent. Additionally, vaporous cavitation, the implosion of water vapor within pressurized systems, can produce honeycomb pitting on mechanical surfaces.

How Desiccant Breathers Work
Even though the basic concept for desiccant breathers has been the same for more than 20 years, they have evolved into numerous products that can handle a multitude of applications.

Comprised of a hygroscopic agent—silica gel that can attract and retain up to 40 percent of its weight in water—and a synthetic filter media, desiccant breathers are an important element in an effective preventive maintenance program. They are designed to prevent moisture and particulate contaminants from entering fluid reservoirs as pressures occur through thermal expansion and contraction of the fluid, and through level changes caused by filling and emptying of reservoirs.

With the addition of carbon (to the silica gel), desiccant breathers can capture oil mist and evenly disperse incoming air to ensure efficient use of the synthetic filter in combination with the silica gel. As the air passes through the synthetic filter, ideally it will retain all particulate matter down to three microns, and 70 percent or more of particulate matter down to 0.5 micron. Moisture is absorbed as air passes through the silica gel. A second filter can give added protection, as clean, dry air continues to flow through the breather vent. The air then passes again back through the silica gel, partially regenerating it and extending the life of the breather.

By capturing the oil mist, the breather drastically reduces pollution in the work environment. If the breather is designed with more vent holes to allow variable airflow patterns, the filtration media and the desiccant’s drying properties will be increased. This simple design allows the desiccant breather to be more efficient and reduces the amount of desiccant gel that each breather must contain. In applications where there are minimal volume changes and the environment is damp and dirty, the newer expansion-type breathers can control the breathing and permit expansion and contraction of the airspace. Knowing when to change desiccant breathers is obvious because manufacturers have added dyes to the silica gel that changes colors as the gel becomes saturated.

When choosing the size of a desiccant breather, consider the amount of air exchanged (the required cubic feet per minute) for each application. Airflow capacity must match or surpass the tank’s fill and drawdown rate. As the flow rates increase, so should the size of the desiccant breather. It’s recommended to consult with the breather manufacturer when trying to determine the correct size for an application.

Additionally, consideration for the operating environment is important when choosing which breather housing (steel or plastic) to select. While plastic housing can be sufficient for many industrial settings, steel housings are appropriate in hot, dirty environments.

A few suggested applications for desiccant breather filters include:

• stationary and mobile hydraulic systems

• switch gears

• gearboxes

• turbines

• feed pumps

• agriculture equipment

• oil cooled transformers

• diesel fuel storage tanks

Desiccant breathers are powerful preventive maintenance tools that can protect industrial and commercial equipment, yet they are only as good as the entire contamination control and maintenance practices used with them. Proper sampling techniques, the use of the system filters, application of the correct seals, and the appropriate lubricant storage and disposal systems all come into play along with desiccant breathers, in preventing lubricant contamination. Used together, these solutions can maximize machine and lubricant life while minimizing capital and operating expenses, ensuring the greatest return on investment.

Dust and water in bearings lead to early-life destruction. Therefore, protection methods against ingress are needed. This article introduces several protection methods and reviews shaft seal designs suited to contaminated conditions.

Machine Environment
Dusty surroundings are one of the most difficult environments for bearings. In equipment handling powders or in processes generating dust, the protection of bearings against contamination by fine particles requires special consideration.

Wet environments are even more difficult for bearings. Moisture in a bearing, whether it is water or a chemical, sits at the bottom of the race and emulsifies (mixes) with the oil. The roller runs through and displaces the mixture, creating conditions for rolling element to race contact and their destruction. Instead of hydrodynamic gliding through the loading cycle, the element rubs or scrapes against the surface. Eventually the surface interaction leads to failure of the race or roller.

Bearing Housings
Bearings are contained within a housing from which a shaft extends. The shaft entry into the housing offers opportunity for dust and moisture to enter the bearing. The shaft seal acts to close the gap between the housing and shaft. Choosing the appropriate shaft seal and seal configuration to protect against dust and moisture ingress is critical to bearing life.

Figure 1. Shaft Bearing Housing Seals

Bearing housing seals for dusty environments are traditionally labyrinth or contact type (Figure 1). The labyrinth-type requires a straight shaft running true. Rubbing seals are the more common and allow for some flexing of the shaft. To prevent dust ingress when setting a lip seal into place, ensure the sealing lip faces outward.

Lip and Labyrinth Seals
The lip seal, while selected mainly for sealing the shaft to housing gap, is typically an unsatisfactory sealing device. Over time, the rubber used to make the lip is attacked by various oxidation catalysts, including oxygen, heat, wear metals and chemicals. It then degrades, cracks, hardens or deforms, and the lip causes fretting corrosion of the shaft (the gouge seen under the lip when it slides off the shaft). Moisture on the shaft capillaries is drawn past the lip, and water sprayed directly at the lip seal blows past the seal and into the bearing. Lip seals are rarely replaced in installed equipment although, as the seal is a perishable component, it should be routinely replaced.

If you have equipment with lip seals, and you want reliable long-life operation, you must replace the lip seal before it fails. To decide the replacement frequency, estimate the mean time (the middle time of the range of times for seal lives) between the seal failures on each particular type of equipment in the operation and schedule a replacement preventive maintenance work order to replace them at 70 to 80 percent of those mean time spans.

The labyrinth seal has a better reputation for shaft sealing than the lip seal if used with grease flush. The gaps between the two parts of the labyrinth must be sealed to keep out dust and water.

To improve bearing life for both labyrinth and lip shaft seals, use an automatic lubricator. Only a small quantity is necessary when slowly flushed into the bearing cavity to force dust and moisture away from the elements.

Grease flushing is not practical for oil-filled equipment. A better option is to replace shaft seals at a predetermined frequency just prior to failure.

Because of the inconvenience and high cost involved in caring for conventional shaft seals, there has been much development work to extend seal lifecycles. New designs and configurations are continually being developed and improved.

In situations of high dust contamination there may be a need to redesign the shaft seal arrangement for better dust protection than what is provided in standard housings. Some ideas which can reduce dust ingress into bearing housings include the following:

1. Parallel seal configuration. Bearing housings can usually be purchased with combination seals as standard equipment.

2. Design spring-loaded shaft-wiping devices to prevent dust ingress. The spring pushes the soft seal against both the shaft and the equipment wall to create a barrier. Figure 2 shows a conceptual design sketch. The assembly is installed in its own housing.
   

3. Stand the bearing off the equipment to create a gap between the end of the equipment and the bearing housing, and install a stuffing box and packing at the housing interface. This approach usually leads to scoring on the shaft in materials-handling equipment; therefore, it is best to install a surface-hardened, replaceable sleeve for the packing to run against.

4. Put in a felt seal wipe between the housing and the wall of the equipment to rub the shaft clean. This can be changed to a stuffing box and a packed gland if desired. It is best to install a hardened, removable sleeve on the shaft because the packing will eventually score the shaft.

5. Install a grease barrier chamber between two seals. This barrier is separate from the bearing housing and acts as the primary seal for the bearing. Grease pumped into the chamber will flush out past the seals. Provide an auto-lube set with slow discharge for continuous purging.

6. Replace the grease barrier chamber with an air purge (pressurized chamber).

7. Install a shaft-wiping rubber shroud covering the bearing or the dust-emitting opening. The potential for overheating the bearing in a fully enclosed shroud limits its use to slowmoving bearings only.

8. Purge grease through shaft seals or through a 15 mm hole (relief port) drilled in the housing. The hole must be on the side of the bearing opposite from the grease nipple, at the bottom of the bearing housing when in service and between the bearing and seal.

9. Mechanical seals can be fitted to the shaft with the stationary seal sitting against the machine and the rotating seal mounted back along the shaft. Combinations of other seals and wipers can also be used in conjunction with the mechanical seal. Mount the auxiliary seals so that they encounter the dust/water first, and keep the mechanical seal as the last line of protection.

10. In high-dust environments use a mechanical seal that has hard seal faces because the dust will score and scratch a soft seal face. An example is silicon carbide against silicon carbide.

11. Spray-on flexible and elastic plastic coatings such as soft polyurethanes and ethylcellulose to cover the housing and a short length of the protruding shaft. The length of coating over the shaft acts like a long wiping shaft seal. Because of its length and continuous unbroken surface, it takes dust and moisture a long time to work their way up the shaft and into the housing.

The housing plastic coating does not prevent heat transfer because the coating is at the same temperature as the housing and still radiates and convects heat away.

Some conceptual examples of alternate shaft seal designs for dusty situations are shown in Figure 3.

Assembly
Bearing assembly must be spotlessly clean. If contamination occurs when the housing and element are joined, no amount of external protection will stop the bearing from premature failure. When assembling bearings into housings, take the following steps to ensure cleanliness:

1. Wash your hands.

2. Ensure there is no dust or powder in the air.

3. Clear the work bench and wipe it clean.

4. To prevent creating dust, ensure that there is no grinding or sweeping nearby during assembly.

5. Use only fresh, clean grease (to the extent that you can control) to pack the housing.

6. Clean components and remove all old grease, grime and solid buildup.

Breathers
A breather releases hot air out of a confined space and allows the air to return when the space cools. Enclosed bearings get hot during operation and cool to ambient temperature when not in use. The air drawn back into the space should be clean of dust and moisture. A poorly screened and filtered breather on a bearing housing or bearing housing enclosure allows ingress of moisture and dust into the bearings, causing premature life failure.

An inadequate breather should be replaced with a low-micron air filter that removes dust particles that are two micron and larger. Protect the breather or filter from water spray and damp conditions (for example, ban “hosing down” if possible) with a shroud or by using an extension tube going into a clean, safe environment. Make sure the breather extension tube cannot be crushed closed.

Editor’s Note:
Reprinted with permission of Mike Sondalini from Lifetime Reliability Solutions, www.lifetime-reliability.com. Related information is available from Feed Forward Publications at www.feedforward.com.au.

Lube oil cleanliness is necessary for the reliable operation of machinery components such as bearings, gears and hydraulics. Failure to adhere to cleanliness standards can result in sluggish operation, excessive wear and premature failure. This article provides a brief overview of appropriate oil filtration practices and guidelines.

Typical Contaminants
While oil contamination takes many forms, the following three classifications cover the majority of industrial problems:

1. Dirt - Dust and solid contaminants creep in from the surrounding atmosphere. Contaminants could include metal chips from machining, rust and wear products from seals, bearings and gears, core sand from castings, weld spatter from welding, paint flakes from painted surfaces and soot from diesel engines.

2. Water - The most troublesome sources are often condensation, cooler leaks, gland leakage and seal leakage.

3. Sludge - This forms primarily as a result of oxidation of the oil itself, especially at high temperatures. Accumulation of fine particles may also fill clearance spaces by silting, resulting in erratic operation and sticking of hydraulic system valves and variable flow pumps.

Different filtration specifications are required for each of these contaminants. With particulates, the maximum particle size should be kept below the minimum thickness of the fluid film. Table 1 gives typical ranges of film thickness requirements for industrial system components.

With water, any free moisture may promote both rust and sludge by reacting with oil additives and metal surfaces. The critical limit of free water in the lubricant is the amount that causes the fluid film to fail in the load zone.

Filter Performance Factors
Before selecting an appropriate filter, the following must be examined:

• Demands Imposed by Machinery Components - oil viscosity at the operating temperature, oil feed rate and permissible pressure drop.

• Expected Size, Type and Level of Contaminants - the ingression and formation rate of environmental dust, metal chips, fly ash, wear particles, water, and/or other contaminants.

Many oil filtration units involve small cartridges with flow capacities up to three to five gallons per minute (gpm). To increase the allowable flow rates, a system of smaller cartridges is arranged into a filtration unit. The following factors provide guidelines for selecting these filter units and possible alternatives.

Table 1. Typical Minimum Fluid Film Thickness

Particle Size. Film thickness data in Table 1 represents the approximate filtration levels that would sustain the optimal protection from particles. Smaller particles will freely pass through the load zone, but wear accelerates as their size approaches or exceeds the minimum film thickness. In ball and rolling element bearings where elastohydrodynamic lubrication prevails, larger abrasive contaminants tend to cause surface damage in the form of microspalls accompanied by shortened fatigue life.

Figure 1. Increase in Journal Bearing Wear as Particle Size Exceeds the Minimum Film Thickness (Broeder and Heijnkemp)

Table 2. Typical Filtration in Circulating Oil Systems

In general, a filter selected with a nominal rating to match these requirements will remove the majority of larger particles. It must be kept in mind, however, that too fine of a filter may be undesirable because of the possibility of clogging, which requires frequent maintenance. Also, because of the large pressure drop across a filter, the power losses could become excessive.

Despite this particle size criterion, little damage is expected with soft contaminants such as fragments of cloth, paper, plastics and other particles with less than approximately one-third the hardness of the lubricated surfaces. Isolated hard particles such as weld beads or metal chips can also be accommodated without significant damage by embedding in the soft babbitt lining of an oil-film bearing. This occurs only if particles fully embed themselves into the liner. However, an abrasive contaminant can plow through the lining and bridge itself across the gap between the shaft and the bushing. In addition to scoring the shaft, there is the possibility of high local temperatures leading to scuffing and bearing failure.

Wear can be accelerated by a machine rotating at reduced speeds which reduces the lubricant film thickness. For instance, during normal operating speeds, fine fly ash will pass freely through machinery bearings in a coal burning electric power station without causing damage. However, when the rotational speed drops to five to 10 rpm, the bearings in a steam turbine are susceptible to excessive wear due to reduced film thickness and the associated reduction in the clearance for the contaminants. The same situation may be encountered in sleeve or ball bearings of a fan during slow-speed windmilling. Research also shows that in hydrodynamic bearings there is a possibility for high frictional loss and temperature rise with large concentration of small particles.

Typical filter ratings for industrial circulating oil systems are provided in Table 2.

Filter Flow Characteristics. Cartridge elements in an oil filter chamber should match the oil flow, pressure drop limitation and contaminant level. Surface filters (Figure 2) are the first choice for limited amounts of solid contaminants in gas and steam turbines, compressors and electric motors. These are mainly pleated paper filters that collect contaminants on their surface while allowing high flow rates with little pressure drop.

Figure 2. Pleated Paper-type Filter Cartridges (Courtesy Pall Corp.) 

Depth-type filters should be considered for applications involving heavy levels of contamination, such as steel and paper mills. In these applications, surface filters would quickly lose their flow capacity. Depth-type filters, on the other hand, are capable of removing particles throughout the depth of the filter material. Examples of these filters include cotton-waste packing, wound yarn, wire wool, fiberglass, cellulose and granular materials such as diatomaceous earth and activated alumina powder.

Wall thickness provides the depth-type filter cartridge with its large dirt-removal capacity. With wound yarn, for instance, the winding forms a myriad of storage cells for solid contaminants with only minimum flow resistance. As dirty oil feeds though the outer periphery of each cartridge, contaminants are removed and retained in smaller storage cells next to the central supporting core. Dirt collection then progresses outward into cells of increasing size until the filter is loaded with dirt and must be replaced.

Adsorbent Filters. Using the surface-active properties of Fuller's earth, charcoal or activated alumina, absorbent filters remove polar materials such as water and oil oxidation products while serving as depth-type filters to remove solid contaminants from the oil. Activated alumina filters extend the life of phosphate ester fire-resistant hydraulic fluids by removing initial degradation products. Too much water, however, destroys the effectiveness of absorbent filters as well as removes various polar type additives from the oil to degrade lubricant performance in turbine, paper-mill, hydraulic and other industrial applications.

Supplementary Oil Cleaning
A dirt load of 100 ppm in an oil is about the highest a depth filter can handle effectively. For higher concentrations of contaminants preliminary settling, centrifuging and/or a self-cleaning stage is needed.

Settling. Preliminary settling in the system reservoir typically provides optimum first stage oil purification. Larger particles and water settle to the reservoir floor, and most entrained air will be released at the surface when providing ample "dwell" periods. For turbines, compressors and electric motors with low levels of contamination, about five to 10 minutes dwell time is needed. The settling time is about 30 minutes for lubricants heavily contaminated by water, metal scale and particle fines in steel and paper mill equipment.

To supplement settling, an off-line loop from the base of the reservoir (Figure 3) is often the best location for contaminant removal.

(Click Image to Enlarge)

Figure 3. Filtration in a Typical Lubrication System (adopted from Parkhurst)

Water Removal. Removing large quantities of free water is outside the capability of typical oil filters. For these applications, the use of settling or centrifugal separation drops the free water content in the oil to approximately 20 ppm above the saturation level. Coalescing filter cartridges, absorbent type filters and vacuum chambers can also be used. More expensive gas sparging with air or nitrogen can be used to strip off dissolved and emulsified water without endangering loss of oil additives.

Free water, commonly in the form of relatively large droplets, is inexpensively removed from oil by settling, centrifuging or coalescing. The maximum water concentration in circulating oil systems should be held to the saturation level of about 300 ppm depending on temperature and lubricant formulation. A lower level of around 100 ppm will minimize any long-term component damage. With 10 percent of the oil flow in the system being circulated through a bypass loop, approximately 0.1 to 0.3 gallons of water removal is commonly available per filter cartridge.¹

Magnetic Filters. Commercial units with capacities up to 200 gpm use permanent magnets to remove iron and steel particles from oil in steel mill or metalworking operations and also from wear on machine elements. The magnetic filter is generally built into the oil piping for industrial gear sets, hydraulic units and turbine-gear drives with periodic disassembly and cleaning scheduled.

Bypass, Full-flow and Duplex Arrangements
Bypass filters were originally used in cars, steam turbines and a variety of industrial machines. With a small bypass stream of oil being continually filtered, wear from particle damage was minimized. Bypass filters allow finer filtration with a smaller pressure drop. A bypass stream ranges from the 10 percent of the total flow rate (once common in automobiles, diesel engines and steel mills) to as little as two to five percent for steam turbines. Duplex filters in the bypass stream allowed periodic cleaning during operation by removing only one of the two parallel units at a time.

Full-flow filters have since become more popular than bypass filters. The full-flow filters provide only filtered oil throughout a machine. This minimizes the opportunity for damage to bearings, gears and other system components by large contaminant particles that would have missed the bypass filter. Duplex arrangement with two alternate filter units, such as those shown in Figure 4, allows the replacement of one of the full-flow filters when it becomes loaded with contaminant particles. For safety against lubricant starvation, a bypass valve will actuate when an overloaded filter element becomes plugged. Otherwise, the system would fail to deliver adequate oil feed.

Figure 4. Representative Filter Housings and Cartridges. Duplex Arrangement Allows Replacement of Contaminated Cartridges without Shutdown. (Courtesy Pall Corp.)

References:

1. Filtration Technology. Parker Hannifin Corp, Bulletin 0247-B1, 1997. (Available from Noria.)

2. L. Leugner. The Practical Handbook of Machinery Lubrication. Maintenance Tech. Inc. (Available from Noria.)

3. J.J. Broeder and, J.W. Heijnkemp. "Abrasive Wear of Journal Bearings by Particles in the Oil (Apparatus, Experiments and Observation)." proceedings of Mechanical Engineers, London, V. 180, p. 35-40, 1965-66.

4. J.K. Duchowski. "Examination of Journal Bearing Filtration Requirements." Lubrication Engineering, September 1998. p. 18-28.

5. H. Amirkhanian. "Advances in Centrifugal Filtration." Machinery Lubrication, July-August 2004. p. 34-36.

6. Y. El-Ibiary. "Extending Bearing Life and Performance." Machinery Lubrication, July-August 2004. p. 46-47.

7. H.J. Parkhurst. "Filter Element Service Life Evaluation and Optimization in Paper Machine Lubrication Systems." Lubrication Engineering, October 1994. p. 760-764.

8. M.M. Khonsari and E.R. Booser. Applied Tribology-Bearing Design and Lubrication, John Wiley & Sons, 2001.

9. M.M. Khonsari and E.R. Booser. "Effect of Contamination on the Performance of Hydrodynamic Bearings." Journal of Engineering Tribology, Proceedings of the IMechE, Part J, August 2006. p. 419-428.

Water covers 70 percent of the Earth's surface, with the majority located in oceans, lakes and rivers. Water is necessary for life. Before the Industrial Revolution, water was the primary production force in manufacturing, transportation and agriculture industries, from water wheels to beasts of burden. Of course, this is no longer the case as industry currently relies on high-performance machinery. Most of these machines use oil for lubrication, heat removal and power transmission. Modern essential oil-wetted systems include hydraulics, steam and gas turbines, engines, motors, gearboxes and electrical transformers.

As essential as water is for biological life, it can be devastating for machine life. Along with particles from dirt and wear, water is one of the two most harmful contaminants. Water problems range from corrosion to oil degradation and from plugging gels to flourishing microbial colonies. Minimizing water contamination maximizes performance, fuel efficiency, productivity and machine life.

Water Problems
Below is a list of problems caused and/or aggravated by water.

Corrosion: It is a significant problem with free water in oil. It also produces abrasive oxides, such as iron rust that abrade surfaces, block clearances and break off to damage moving parts.

Loss of Film Strength: When water contaminates the film it displaces the oil. Water cannot keep the surfaces apart, resulting in high friction, adhesive wear and even seizure.

Oil Oxidation: Water accelerates oil oxidation. Negative consequences include excessive viscosity, acidity and insoluble resins.

Additive Depletion: When additives migrate into free water, the concentration of some additives falls below effective levels.

Hydrolysis: In the presence of water, ester-based additives and synthetic fluids (such as phosphate esters and polyol esters) decompose into alcohols and acids.

Reduced Fatigue Life: Dissolved water enters microcracks in rolling contacts, dissociates into hydrogen gas and weakens steel by hydrogen embrittlement.

Microbial Growth: Negative consequences include rancid foul odors, human health problems, biomass slimes, foaming and acidic oil.

Gels: Some additives interact with water to form gels. These gels foul flow passages, reduce heat rejection and plug filters.

Transformers: Even minute amounts of water contamination will reduce the life and efficiency of a transformer.

Contamination Control
For minimum protection, it is recommended to keep water below the saturation level, generally 200 to 500 ppm for many oils and 10 ppm for transformer oils. For optimum protection it is recommended to maintain water levels at or below 30 percent saturation, generally 75 to 150 ppm for most machines and 3 ppm for transformers. Maintaining water levels at or below 30 percent saturation alleviates the problems related to water as well as provides a safety margin against accidental spikes of contamination.

Donaldson has developed a new method for preventing the ingression of humid air. It is based on thin film technology and the fact that warm air leaving a reservoir (exhalation) has lower relative humidity than cool air entering a reservoir (inhalation).

Figure 1. Inhalation

Figure 2. Exhalation

The T.R.A.P.™ (Thermally Reactive Advanced Protection) is manufactured by coating the walls of a porous network with a thin film of water-absorbing chemicals called a deliquescent salt. The resulting high surface area of absorbent provides rapid removal of water vapor from air while maintaining size and weight. Unlike desiccant breathers, the open porous structure presents minimal air flow restriction, so fluid flow into and out of the reservoir is not impeded. In addition, the proprietary absorbents are not sensitive to oil mists entrained in the air leaving the reservoir.

The breather unit includes a pleated 3 µm filter to protect against the ingression of hard abrasive contaminant particles that contribute to the wear of mechanical components. It is manufactured from materials that can be safely disposed of or recycled.

As illustrated in Figure 1, during "inhalation" cold humid air entering the system is drawn over the large absorbent surface area inside the breather. The high humidity drives water into the absorbent and the majority of water vapor is removed. This dry air maintains the water concentration below 30 percent saturation. Once inside the system, the air contacts the warm fluid and metal surfaces which increases air temperature and further reduces the air's relative humidity.

During exhalation (Figure 2), warm, dry air passes over the same absorbent. The low humidity air pulls water out of the thin films of absorbent. The rehumidified air exits the unit and is emitted into the surroundings.

The difference between the desiccant breathers and deliquescent breathers is the deliquescent's ability to release moisture back in to the air at standard temperatures. For a desiccant breather to release moisture the temperature need to be in excess of 360°F. The ability of the deliquescent to release moisture at standard temperatures gives the unit the ability to last longer.

The deliquescent breather is either absorbing or releasing moisture, depending upon the humidity of the air. This difference in relative humidity - high during inhalation and low during exhalation - is the force that drives the process. It is also aided by the temperature change to increase the difference between the low and high humidity air. The heating of the air in the headspace creates an air that is dryer than the air that went through the breather. The result is dry oil and regeneration of the absorbent during each cycle.

Water contamination causes major problems in oil-wetted machinery. Upon invading the system, its presence may be hidden from the outside eye. Preventing water ingression in an oil reservoir is the best cure for contamination. Desiccant breathers are successful at reducing the ingression of moisture, but they are limited by their low water-holding capacity and the need for frequent replacement. The self-regenerating breather, the T.R.A.P.™, effectively maintains the water concentration well below the saturation level of the oil. It is small, lightweight, and doesn't harm the oil.

References

1. Armstrong, R. and Hall, C. "The Corrosion of Metals in Contact with Ester Oils Containing Water at 60 and 150?C." Electrochimica Acta. p. 40, 9, 1135-1147. 1995.

2. ASTM D6304-04a. "Standard Test Method for Determination of Water in Petroleum Products, Lubricating Oils and Additives by Coulometric Karl Fischer Titration." March 2005.

3. Atkins, P. Physical Chemistry. 6th Ed. 1998.

4. Beercheck, R.C. "How Dirt and Water Slash Bearing Life." Machine Design. p. 50, 7, 68-73. 1978.

5. Cantley, R.E. "The Effect of Water in Lubricating Oil on Bearing Fatigue Life." ASLE Transactions. p. 20, 3, 244-248. 1977.

6. Clint, J., Fletcher, P. and Todorov, I. "Evaporation Rates of Water from Water-in-Oil Microemulsions." Phys. Chem. Chem. Phys. 1. p. 5005-5009. 1999.

7. Donaldson Company, Inc. "Hydraulic Filters and Accessories." Catalog HYD-100. 2006.

8. Emsley, A.M. "The Kinetics and Mechanisms of Degradation of Cellulosic Insulation in Power Transformers." Polymer Degradation and Stability. p. 44, 343-349. 1994.

9. Ferner, M. "An Investigation Into Used Engine Oil Condition." Lubes'N'Greases. p. 11, 8, 15-19. August 2005.

10. Fox, M., Picken, J. and Pawlak, Z. "The Effect of Water on the Acid-Base Properties of New and Used IC Engine Lubricating Oils." Tribology International. p. 23, 3, 183-187. 1990.

11. Gernon, M. and Hemming, B. "Modern Tools Ancient Art - Metalworking Fluids and BioSynergy." Lubes'N'Greases. p. 11, 5, 19-24. May 2005.

12. Gresham, R. "Hydraulics: The Reservoir." Tribology and Lubrication Technology. p. 61, 8, 18-19 August 2005.

13. Hill, E.C. and Genner, C. "Avoidance of Microbial Infection and Corrosion in Slow-Speed Diesel Engines by Improved Design of the Crankcase Oil System." Tribology International. April 1981.

14. Hovis, J. "What Causes Humidty?" Scientific American. p. 294, 1, 100. January 2006.

15. Jada, A. and Chaou, A. "Surface Properties of Petroleum Oil Polar Fraction as Investigated by Zetametry and Drift Spectroscopy." J. Petroleum Science and Engineering. p. 39, 287-296. 2003.

16. Kell, G.S. "Thermodynamic and Transport Properties of Fluid Water." Water: A Comprehensive Treatise. F. Franks, ed. Plenum Press, p. 363-412. 1972.

17. Naylor, T., Brown, L. and Powell, K. "Microbiological Investigations of Turbine Oil Spoilage." Tribology International. p. 182-184. August 1982.

18. Needelman, W. and LaVallee, G. "Forms of Water in Oil and Their Control." Noria Lubrication Excellence Conference. Columbus, Ohio. May 2006.

19. Rao, C.N.R. "Theory of Hydrogen Bonding in Water." Water: A Comprehensive Treatise. F. Franks, ed. Plenum Press, p. 93-114. 1972.

20. Seoud, O.A.E. "Acidities and Basicities in Reversed Micellar Systems." Reverse Micelles. P.L. Luisi and B.E. Straub, eds. Plenum Press, p. 81-94. 1984.

21. Smiechowski, M. and Lvovich, V. "Electrochemical Monitoring of Water-Surfactant Interactions in Industrial Lubricants." J. Electroanalytical Chemistry. p. 534, 171-180. 2002.

22. Stenius, P. "Micelles and Reversed Micelles: A Historical Overview." Reverse Micelles. P.L. Luisi and B.E. Straub, eds. Plenum Press, p. 1-20. 1984.

23. Stoll, P. "Limits of the Vacuum Processing of Insulating Oils in the Electrical Industry." Vacuum. p. 13, 267-270. 1962.

24. Troyer, D. "Looking Forward to Lubricant Oxidation?" Practicing Oil Analysis magazine. March 2004.

25. Wasserbauer, R. "Biocorrosion in Transformer Oils." Tribology International. p. 22, 1, 39-42. 1989.

26. Winslow, R., Kemmerer, W., Naman, T. and Jenneman, G. "Effects of Bacterial Contamination on Steam Turbine Oil Systems." Tribology and Lubrication Technology. p. 61, 3, 26-24. March 2005.

Mosaic is the merger of two global leaders in the fertilizer industry, IMC Global and Cargill Crop Nutrition. As one of the world's largest potash and phosphate mining and processing operations, Mosaic provides an expanding selection of products and services to enhance crop yield and livestock nutrition.

Figure 1. Test apparatus used for analysis

One of Mosaic's potash mining sites, the Belle Plaine plant in Regina, Saskatchewan, relies on two General Electric 20 MWe turbine generator sets for co-generated power and process steam, and three Westinghouse EL125 prime movers for process applications. A major consideration for any turbine operation is the development of a comprehensive preventive maintenance program to ensure long service life. A major destructive contaminant to a turbine's bearings and hydraulic system is water. Despite the measures in place to prevent water ingression into a turbine's lubrication system, water contamination is an inevitable phenomenon that should be carefully managed. Sources of water ingression include the high pressure steam driving the turbine, condensation of water vapor in the head space of a lubrication reservoir and failed bearing seals.

Figure 2. HMP228 transmitter installed on #4 turbine engine

Due to continuous moisture problems, the Mosaic technical services group initiated a research project in 2005 to actively identify moisture levels in the turbine's oil and hydraulic systems. To accomplish this goal, an online oil sensor to measure water concentration needed to be chosen and calibrated to their needs.

Figure 3. HMP228 probe is inserted directly into the line with ball valve assembly. The unit is installed in a bearing return oil drain adjacent to the high-pressure end turbine packing.

Mosaic chose Vaisala's HMP228 moisture in oil instrument to provide in-line, continuous measurement. The instrument displays the reading and provides an analog output signal and adjustable alarm relays. The HMP228 directly measures water activity (aw), which indicates a fluid's margin to saturation on a scale of zero to one; zero being completely dry and one being fully saturated. Before installation, Mosaic needed to characterize the performance of the instrument as a function of temperature and water concentration (in ppm(mass)) as a variable of aw output. A test apparatus was created consisting of a steel drum placed on a heating plate with an agitator to circulate the oil. The apparatus was created to evaluate how the sensor responsed to specific conditions and to calibrate the sensor to Mosaic's specific needs.

Three different test procedures were designed to evaluate the sensor performance.

• Test 1.Determine if the HMP228 transmitter will respond to the oils used in Mosaic's turbines at the Belle Plaine location.

• Test 2.Determine how temperature affects the water saturation level of the virgin turbine oil.

• Test 3.Determine how the HMP228 transmitter responds to water content changes in turbine oil.

As expected, the water activity readings decreased as the oil temperature increased.

As anticipated, the water activity readings increased linearly as the water content of the oil increased.

With the good results from the testing, Mosaic installed the HMP228 on both 20 MWe turbine generators. "Based on this positive result, our intent is to alarm at 0.60 water activity. Both temperature and water activity will be used to calculate ppm water in oil within plant DCS systems. The ppm water calculation can be compared to oil analysis results. Corrective actions will be taken beyond 0.65 aw and can include external scrubbing, corrections to gland condenser systems, and packing inspections," said a member of the Mosaic technical services group.

The installation, calibration and field testing of the HMP228 is a typical example of collaboration between functional groups within Mosaic and vendors who support Mosaic's objectives with technology for process improvement.

Special thanks goes to the Mosaic Technical Services Group for their technical expertise, cooperation and sharing of results and performance test data for this research study.

High water content of lubricating oils negatively impacts the operation and longevity of the oils and the mechanical equipment components being lubricated. Water increases the oxidation rate of oils, thus prematurely using up the oils’
oxidation inhibitors. Additionally, water has been known to cause certain oil additives to precipitate out, as well as to chemically attack some additives. Some of the modes by which water exists in lubricating oils can lead to catastrophic equipment failure. These include corrosion, erosion, etching and hydrogen embrittlement.

Water in oils can occur in dissolved, emulsified and free states. Visual indication is reliable for quantifying water content only in the free state, while the hot plate crackle test can be used to detect free and emulsified water. However, neither of these methods can detect dissolved water or reproducibly detect trace levels of emulsified water. Furthermore, neither visual indication nor the hot plate test can be used to reliably quantify the water present. Distillation methods, such as ASTM D95 and D4006 provide better quantitative data in the range of approximately 500 ppm to 25 percent, but require large sample sizes and involve long analysis times, typically 60 to 110 minutes.

Since its invention by German petroleum chemist Dr. Karl Fischer in 1935, Karl Fischer (KF) analysis has progressed from an esoteric laboratory procedure to a widely accepted instrumental method routinely used for water determination in the petrochemical industry. It is estimated that nearly 500,000 KF determinations are performed daily around the world. The method forms the basis of several commonly used ASTM standards for water determination in oils, including ASTM D1533, D1744, D4377, D4928 and D6304. The KF method does not suffer from the same issues and limitations associated with the other techniques described above, and a number of recent advances in titrator instrumentation and reagent formulations have further improved the accuracy and reproducibility of KF analyses.

ROH + SO₂ + RN → (RNH)·SO₃R

(RNH).SO₃R + 2 RN + I₂ + H₂O + → (RNH)·SO₄R + 2 (RNH)I

The end-point determination in KF titration occurs by means of bivoltametric indication. That is, while the iodine in the KF reagent is reacting with water, there is no free iodine present in the titration cell, and a high voltage is required to maintain the set polarization current at the double platinum pin indicator electrode. Once all the water has reacted with the iodine, trace quantities of free iodine appear in the titration cell, causing a drop in voltage necessary to keep the polarization current constant, which in turn signals the end-point of the titration.

The most widely used standard methods based on volumetric KF are ASTM D1533 (Method A), D1744 and D4377. Volumetric KF is most accurate in the range of 500 ppm to 100 percent water.

Figure 1. Key Components of a Modern Volumetric KF Titrator

Coulometric KF
In coulometric KF, the iodine needed by the KF reaction is not present in the KF reagent, but is instead generated electrochemically in situ from iodide at the anode of the generator electrode, a component of the coulometric titration cell (Figure 2). Corresponding reduction of hydride to hydrogen takes place at the cathode. In coulometry, the quantity of iodine generated corresponding to the amount of water present is calculated by the titrator on the basis of current (mA) and time (sec). Coulometric KF is considered an absolute method because time and current can both be accurately measured. The most widely used standard methods based on coulometric KF are ASTM D1533 (Method B), D4928 and D6304 (Method A). Coulometric KF is most accurate in the range of 1 ppm to 5 percent water.

Figure 2. Key Components of a Modern Coulometric KF Titrator

For those oil samples which fail to adequately dissolve even when using KF reagents formulated with organic co-solvents, or those that are suspected of containing interfering compounds, an indirect KF analysis using an oil evaporator is recommended, as described below.

Figure 3. Oil Evaporator for Indirect KF Analysis of Oils

The procedure involves adding the oil sample to the solvent present in the evaporation chamber where it dissolves in the solvent, and in the process forms a binary azeotrope between the solvent and the sample's water content. The solvent/sample mixture is then heated to near the azeotropic point and kept at that temperature while a dry, inert carrier gas, such as nitrogen, is used to carry the azeotropic vapor into the titration cell of the KF titrator, where the water content is quantified. This method thus combines the best features of both KF titration and distillation techniques, such as ASTM D95, because the oil evaporator is simply a miniaturized Dean & Stark distillation apparatus. The distillation component of the indirect titration method ensures that the hard-to-dissolve oil samples, or those containing potentially interfering compounds, are not introduced to the titration cell, while the KF titration component of the method accurately quantifies the water content of the azeotropic vapor carried into the titration cell by the dry gas.

Additionally, because the oil evaporator contains a miniaturized distillation set-up, only small sample (0.1 to 2.5g) and solvent (10 to 15mL) quantities are required.

Table 1. Recommended Sample Sizes for KF Analysis

KF analysis is a versatile and robust analytical tool for water content analysis in oil samples, and can detect water in any of three states commonly found in oils. The technique also offers other substantial advantages over more conventional hot plate crackle test and distillation methods, and it has been incorporated into numerous ASTM standards. Volumetric or coulometric KF methods, utilizing either direct titration or the oil evaporator technique, can be used to quantify water in oil samples from trace amounts to 100 percent.

1. Slater, K. “Real-Time Monitoring of Water in Oil.” Lubrication Excellence 2005 Conference Proceedings. April 2005.
   
2. Duncanson, M. “Detecting and Controlling Water in Oil.” Practicing Oil Analysis magazine. September-October 2005.
   
   
3. Gebarin, S. “A Closer Look at Karl Fischer Coulometric Titration.” Practicing Oil Analysis magazine. March-April 2004.
   
   
4. Kunkel, S. and DeSandro, J. “Titration Method Improves Water Measurement.” Oil & Gas Journal. December 1986.
   
   
5. Rouessac, F. and Rouessac, A. Chemical Analysis: Modern Instrumental Methods and Techniques. (2000).
   
   
6. McClure, M. and Steffen, R. “Water Testing in Pharmaceutical Products.” Current Separations. August 2005.
   
   
7. Mettler-Toledo GmbH. Application brochure 26. Fundamentals of Volumetric Karl Fischer Titration. 1999.

Free and emulsified water can cause contamination in critical fluids, resulting in additive depletion, oxidization, bacterial growth, component wear and corrosion. Before signs of water contamination occur (cloudy appearance of the oil), it is also possible for bearings to lose up to 75 percent of their potential service life. Water causes damage even in its dissolved state, attacking the base stock, additive package and machine. Additionally, water carries organisms that can potentially disable critical hydraulic systems.

Above this saturation point, any additional water will sit in the oil as water droplets, or it will form an emulsion. This free water can be detrimental to systems, for instance:

• Free water can react with the oil's additive package, rendering the oil unsuitable for the application.

• Emulsion can reduce the film thickness in bearings and other moving parts, which accelerates wear.

• Free water can settle in machine sumps, pistons and filter housings, resulting in corrosion.

The Sensor
As maintenance costs increase and production capacity and equipment efficiency are maximized, remote online sensor technologies are being recognized as the new cost-effective form of analysis. The ANALEXrs range of online sensors are designed to provide plant engineers and maintenance managers with real time, continuously monitored testing and analysis data for critical plants and equipment. The ANALEXrs moisture sensor, which forms part of this range of online sensors, goes beyond the normal water screening tests to indicate the actual dryness of the oil. Providing percent relative humidity (RH) and temperature values, monitoring can now occur in real time. Personnel can ensure oil is always below the saturation point before free and emulsified water forms. The sensor monitors one of the root causes of the machine and lubricant failure, water.

The ANALEXrs moisture sensor measures the oil's percent relative humidity (RH), resulting from the dissolved water within the lubricant, using a combination of proven thin film capacitance sensors combined with smart algorithms to provide a temperature and percent RH value. Using internal processing power, the self-diagnostic sensor does not require handheld units to analyze or display results, which can be reported using standard displays or PCs. Whether verifying the health of a machine or an alert of changing moisture ingression rates, the moisture sensor provides instant information, which compliments existing laboratory programs.

It is suitable for use with diesel engines, gas turbines, gearboxes, compressors, generators and other lubricant-filled equipment. These sensors help to increase productivity, reduce costs and improve profitability.

ANALEXrs equipment can be fitted on any machine with a circulating lubricating system, and where atmospheric, process or coolant issues are a concern. Industries that benefit from the ANALEXrs equipment include:

• power generation (steam, nuclear and wind turbine)

• steel

• pulp and paper

• petrochemical

• transportation

• military

• marine

Moisture sensors from Kittiwake form part of a range of new online sensors for condition monitoring and maintenance experts. The ANALEXrs range of online sensors include total ferrous wear debris (PPM), particle content (ferrous and nonferrous) and oil condition (oil quality units).

Water in oil can cause quick and costly breakdowns. This type of fluid contamination can also result in problems such as additive depletion, oil oxidation, corrosion and accelerated component wear rates. Because water contamination can occur at any time, it is possible for bearings and other lubricated components to be seriously damaged without giving any obvious warning signs.

Online monitoring is a proven successful method for the prevention of water contamination in fluids. EESIFLO® has developed the EASZ-1 online moisture sensor, a water in oil analyzer that provides early warning signals when a problem is detected, therefore prompting corrective action to be taken immediately.

The unit can be used in online moisture monitoring and as a control instrument allowing separators and oil purifiers to be operated only when needed. One major benefit is the response time. In seconds, the unit will respond to a change in the capacitance of the oil monitored and is not affected or knocked out of service by saturation. It will continue to work in both high and low measurement ranges.

The moisture sensor takes advantage of this fact by employing high-speed analog-sensing electronics to accurately measure the K of any fluid passing through its dual cylinder cell. Knowing the K of the original fluid (oil or fuel), and the K of the second fluid (water), it is a simple matter to determine the oil/water ratio to accurate values.

A single-button calibration feature allows the user to calibrate the oil sensor for use on any fluid regardless of its age or current moisture content. This feature permits oil changes without extensive recalibration of the entire system.

One of the advantages of this moisture-sensing technology is its ability to measure total water in all three phases (dissolved, emulsified and free) in real-time, from 35 ppm to 65 percent.

The moisture sensor measures water contamination in a dissolved, emulsion or free water state. It can detect below 100 ppm with a resolution of +/- 35 ppm. The instrument is able to measure below and above saturation levels with a response time of only one second. This is advantageous to users who need to correlate actual moisture readings with laboratory results. In this sense, the sensor is more reliable than spot sampling or laboratory results simply because it is monitoring the total volume of oil 24 hours a day.

• Aviation hydraulics

• Reduction gears

• Diesel engines

• Paper mill lubricating systems

• Circulating gear oils

• Hydraulic systems

These are just a few examples of the applications that may utilize the online moisture sensor. Because it can calibrated to any type of oil, the electronics do not drift and the sensing elements are not destroyed by water.

Some contaminants are important to monitor and analyze because they are root causes of premature oil degradation and engine failure. Other contaminants are symptomatic of an active failure condition that requires a response other than just an oil change. For instance, seal damage leading to fuel dilution or glycol contamination cannot be remedied by performing an oil change or switching to a better quality lubricant. Such symptom-based contaminants are also root causes that enable new failures to occur. The value of oil analysis in detecting problems early goes without saying.

Any one of the contaminants described below is capable of causing premature or even sudden engine failure. I've left dirt contamination off the list because I covered particle-induced engine failures in a previous column. It is worth noting that problems are more pronounced when contamination combos exist, such as high soot load with glycol or high soot load with fuel dilution. There are numerous failure pathways and consequential sequence of events. Thousands of diesel engines fail prematurely each year aided by the presences of glycol, fuel, soot and water in the engine oil.

Glycol
Glycol enters diesel engine motor oils as a result of defective seals, blown head gaskets, cracked cylinder heads, corrosion damage and cavitation. One study found glycol in 8.6 percent of 100,000 diesel engine samples tested. A separate study of 11,000 long-haul trucks found severe levels of glycol in 1.5 percent of samples and minor amounts of glycol in 16 percent of samples. The following are some of the risks associated with glycol contamination:

• Just 0.4 percent coolant containing glycol in diesel engine oil is enough to coagulate soot and cause a dump-out condition leading to sludge, deposits, oil flow restrictions and filter blockage.

• According to one study, glycol contamination results in wear rates 10 times greater than water contamination alone.

• Glycol reacts with oil additives causing precipitation. For instance, an important antiwear additive in motor oils, zinc dialkyl dithiophosphate (ZDDP), will form reaction products and plug filters when oil is contaminated with glycol. This leads to loss of antiwear and antioxidant performance as well.

• Glycol has led to cold seizure of engines.

• Ethylene glycol oxidizes into corrosive acids, including the following: glycolic acid, oxalic acid, formic acid and carbonic acid. These acids cause a rapid drop in the oil's alkalinity (base number), resulting in an unprotected corrosive environment and base oil oxidation.

• Oil balls (abrasive spherical contaminants) form from the reaction of calcium sulfonate detergent additives (found in nearly all motor oils) and glycol contamination. These balls are a known cause of damage to crankcase bearings and other frictional surfaces within an engine.

• Glycol contamination substantially increases oil viscosity which impairs lubrication and oil cooling.

Fuel Dilution
Frequent starts of an engine, excessive idling and cold running conditions can lead to moderate fuel dilution problems. Severe dilution (excess of two percent) is associated with leakage, fuel injector problems and impaired combustion efficiency. These are symptomatic of serious conditions that cannot be corrected by an oil change. According to one reference, 0.36 percent of total fuel consumption ends up in the crankcase. Problems associated with fuel dilution include:

• Diesel fuel dilution in cold operating conditions can cause waxing. During startup, this can result in low oil pressure and starvation conditions.

• Diesel fuel carries unsaturated aromatic molecules into the motor oil which are pro-oxidants. This can result in a premature loss of base number (loss of corrosion protection) and oxidative thickening of the motor oil, causing deposits and mild starvation.

• Fuel dilution can drop the viscosity of a motor oil from say, a 15W40 to a 5W20. This collapses critical oil film thicknesses, resulting in premature combustion zone wear (piston, rings and liner) and crankcase bearing wear.

• Fuel dilution from defective injectors commonly causes wash-down of oil on cylinder liners which accelerates ring, piston and cylinder wear. It also causes high blow-by conditions and increased oil consumption (reverse blow-by).

• Severe fuel dilution dilutes the concentration of oil additives and hence, diluting their effectiveness.

• Fuel dilution by biodiesel may result in higher than normal problems compared to diesel refined by crude stock. These problems include oxidation stability, filter plugging issues, deposit formation and volatility resulting in crankcase accumulations.

Soot
Soot is a by-product of combustion and exists in all in-service diesel engine motor oils. It reaches the engine by various means of blow-by during engine operation. While the presence of soot is normal and expected for a given number of miles or hours of service on an engine oil, the concentration and state of soot may be abnormal, signaling a problem with the engine and/or a need for an oil change. Following are some issues related to soot contamination:

• Combustion efficiency is directly related to the soot generation rate. Poor ignition timing, restricted air filter and excessive ring clearance cause high soot load. Combustion problems are not solved by an oil change.

• New diesel engines designed for lower emissions have higher injection pressures. This corresponds to increased sensitivity to abrasive wear (for example, from soot) between rocker, shaft and rocker bearing and can lead to rocker arm seizure. New exhaust gas recirculation (EGR) units on diesel engines amplify the amount and abrasivity of soot production.

• Viscosity increases with soot load. However, high dispersancy associated with some modern engine oils may increase viscosity with soot even more. High viscosity corresponds to cold-start problems and risk of oil starvation.

• Soot and sludge in engines deposit or separate from the oil in the following areas, all presenting risks to engine reliability including rocker boxes, valve covers, oil pans and head deck.

• Deposits on engine surfaces interfere with combustion efficiency and fuel/oil economy.

• Soot polishes off protective antiwear soap films in boundary zones such as cam and cam-follower zones.

• Carbon jacking from the buildup of soot and sludge behind piston rings in grooves can cause rapid wear of rings and cylinder walls. This can cause broken or severely damaged rings during cold-start conditions.

Water
Water is one of the most destructive contaminants in most all lubricants. It attacks additives, induces base oil oxidation and interferes with oil film production. Low levels of water contamination are normal in engine oils. High levels of water ingression merit attention and are rarely correctable by performing an oil change. The following are some additional notes on water contamination:

• Long idling in wintertime causes water condensation in crankcase, which leads to loss of base number and corrosive attack on surfaces, oxidation of the oil, etc.

• Emulsified water can mop up dead additives, soot, oxidation products and sludge. When mobilized by flowing oil, these globular pools of sludge can knock out filters and restrict oil flow to bearings, pistons and the valve deck.

• Water sharply increases the corrosive potential of common acids found in motor oil.

Failure Development Period
The failure development period can vary considerably for these contaminants. Most sudden-death failures from moderate levels of contamination will usually have one or more aggravating factors (the combo effect). Conversely, massive concentrations of one or more of these contaminants can result in sudden-death failures unaided by an aggravating circumstance. There are dozens of other aggravating factors that can drastically shorten the failure development period as well. More typical is when a moderate problem goes unnoticed and develops over time. This can shorten engine life from say, 750,000 miles to 300,000 miles.

The cumulative effect of oil contamination on engine reliability, fuel economy, exhaust stream emissions and maintenance cost of a large fleet is massive. There are no motor oil additives that control the damage caused by these contaminants. Therefore, proactive maintenance and oil analysis are critical strategies to counteract risks.