- Buyer's Guide
Lost revenue due to equipment downtime is often a direct result of some type of contamination, whether from dirt, water, an incorrect lubricant or a combination of these. Oil analysis testing can identify these contaminants, but unless you are aware of the issues that can arise from them, it can be difficult to take the appropriate actions. This article will review the most common contamination types, the oil analysis tests most likely to indicate them, normal test results when these contaminants are present, and recommended actions for correcting each problem.
Abrasives are the top problem-inducing contaminants because they tend to cause the most damage. They are more likely to be hard contaminants and be in sizes that are well within your clearance ranges. The most prevalent forms of abrasives are dust or dirt and product or process contamination. If there is a process that includes any level of particulate, it is possible for this particulate to get into the lubricating system and cause damage no matter how soft the particle is.
Degradation from abrasive contamination comes primarily in the form of equipment wear, but another less widespread lubricant degradation problem can also occur. Abrasive wear or cutting wear is usually found in systems with a sliding motion load somewhere in the unit. Commonly with thrust bearings or other softer metal bearings, the abrasive can wedge into the soft metal and gouge the harder steel surface. This is not to say that you can’t have copper-alloy cutting wear. The metal produced depends on the contact surfaces in the path of the abrasive contamination and the hardness of the contaminant.
Systems with rolling actions such as rolling-element bearings, gear teeth, etc., are more likely to have pitting from abrasive contamination. As particulates roll through the load zone, the extreme pressure exerted on the contact point between the races and the rolling elements can pit the surfaces, forming cracks and initiating fatigue wear and spalling.
While lubricant degradation usually comes from another source, you may see some lost lubricant life from abrasive contamination. When a unit is wearing, the metal released by the abrasives can become a catalyst, and these particles increase the available surface area on which lubricants can form degradation byproducts.
Identifying abrasive contamination and wear is generally done through metals testing. If oil analysis is performed, what you typically will see with plain abrasive/dirt contamination is an elevation of the metals that are in direct contact with the abrasives. In gears, this will tend to be high iron levels with low alloy metals (chrome, nickel, manganese, etc.) and an increase in silicon and possibly aluminum if there is enough contamination.
Particle counting is another common test used to monitor contamination. However, keep in mind that a particle count is not selective in the particulate it is counting. Additional testing will be needed to determine the type of contaminant (water, air, dirt, fibers, metals, etc.).
Typical recommendations will include repairing the ingression point and filtering the lubricant, which are not always feasible. The protection of the equipment should be the analyst’s first and foremost concern when making recommendations. If filtration is not an option, changing the lubricant may be suggested. This is not as optimal as filtration, but when you have contamination, it is likely that the new lubricant will be much cleaner than the lubricant in the sump and can in effect dilute the problem contaminant, reducing the abrasive wear.
Some type of exception testing may also be recommended. This will depend on whether there is obvious wear in the system. Analytical ferrography or filter patch analysis can help determine the extent of the damage and if you need to take immediate action.
Water is the second most common contaminant that can cause equipment problems. There are three forms of water: dissolved, emulsified and free.
Dissolved water is usually benign except in extreme cases that require exceptionally low moisture levels. This form of water generally enters the lubricant via humidity or a similar process. The lubricant simply absorbs the water up to the saturation point and does not exhibit any signs of water contamination such as clouding.
Emulsified water is the most damaging form of water contamination. It occurs when the amount of water is beyond the saturation point and has likely entered the lubricating stream. A mixing action in the equipment may have emulsified the water, or it may be a function of a lubricant additive. Regardless, the initial identifier of this type of water contamination is that the lubricant is usually cloudy. This cloudiness comes from the water becoming small droplets within the oil. Emulsified water is the most damaging because it is free flowing with all of the lubricant and will be in the load zone.
Free water is somewhat less damaging than emulsified water but is still problematic. Some lubricants will not hold water in suspension past the saturation point, so it falls to the bottom of the sump. Among the problems resulting from this type of contamination include allowing water to become part of the lubricating stream, impacting the lubricant’s ability to shed water (demulsibility) and letting it emulsify, initiating biological contamination that will further degrade the oil, and plugging the filter. There is also the possibility of a safety hazard if free water is allowed to continue to enter the sump and overflow it.
With water contamination, there is just as much if not more damage to the lubricant as there is to the equipment. The main source of equipment degradation will be rust. Any time you have a degraded lubricant with water contamination, there is the possibility of rust on nearly any iron/steel surface. Rust is very hard (harder than steel) and creates abrasive particles in addition to the existing water problem.
Another problem with water contamination involves hydrogen embrittlement. In this phenomenon, water is cracked into oxygen and hydrogen, and the hydrogen is absorbed into metal surfaces. This creates a harder but more brittle surface that is unable to flex as needed for rolling elements to work properly. This results in cracking of the rolling surfaces and spalling.
In regards to lubricant degradation, the primary issue is having water in the equipment’s load zone. Water in a load zone is incapable of supporting a load, so the load continuously collapses onto a much thinner lubricant film. This allows significant surface-to-surface contact, which leads to wear.
Water contamination will also cause premature aging of the lubricant. It is estimated that water in a lubricant can reduce the lubricant’s lifespan by one-tenth. In addition, water in a lubricant sump can produce sludge. This is primarily a factor of simple premature aging of the lubricant but should be considered because it can give rise to a number of other issues such as thickening of the lubricant’s viscosity, preventing splash lubrication or plugging a filter.
Water usually does not enter a lubricating system by itself. External machine surfaces tend to be dirty, and the water will suspend this dirt and then enter the system with it. This not only causes water damage to the lubricant but also abrasive damage to the equipment.
In many cases, water contamination can be identified onsite with a visual test, as emulsified water in oil will become milky. However, air entrainment is another potential issue with cloudy oil, so you should go beyond just a visual test.
The hot-plate crackle test can also be used to check for water onsite as well as at most commercial laboratories. You can perform a go/no-go test by simply raising the hot-plate temperature to 320 degrees F and seeing if the sample sizzles like bacon when you put it on the surface. Of course, this should be done with caution, since hot liquid can spatter if there is a lot of water. Other methods are also available, but the hot plate provides a good initial detection for general-purpose analysis.
Water contamination can often be identified with a visual test. The hot-plate crackle test can also be used to check for water contamination.
For a more exact measurement or to detect water at very low levels, have a Karl Fischer water test done. There are multiple variations of this test, including coulometric and volumetric, but they all have similar capabilities. Check to see which is being performed and if it will meet your needs. Coulometric tends to be more accurate at lower levels, while volumetric is usually better at higher levels. Certain additives, such as those that contain sulfur, can interfere with this type of test and should be taken into account.
Typical oil analysis recommendations include correcting the source of water. This should be done before any further action is taken. In some applications, water must be removed continually, and the water ingression cannot be prevented.
The next most common recommendation is to change the lubricant. This may be suggested in conjunction with other water-removal options (water drain-off, dehydration, centrifuge, etc.), depending on the lab’s knowledge of the sump size and the site’s capabilities.
Incorrect lubricant problems come in a myriad of forms. The most common include using a mineral oil in a glycol-based lubricant sump, missing additives/wrong additives and the wrong viscosity.
With a mineral oil in a glycol-based sump, you tend to see increased viscosity and sludge formation due to the chemical reaction between the hydrocarbon and glycol products. Once this chemical reaction begins, you may notice excessive wear, as the lubricant viscosity is excessively high. Since the two lubricants do not typically mix, you may also observe elevated wear because the load-zone lubricant film will not be a single lubricant and could have a reduced load-carrying capability. Significantly reduced lubricant life is also likely to result.
Because of the increased viscosity and sludge formation, you may have slow-flowing or even plugged filters. Acid formation as a degradation byproduct can also increase and attack the lubricated surfaces.
Viscosity testing and metals analysis are the primary methods used to identify a mineral oil in a glycol-based sump. Information about the lubricant in use will be required by the analyst to properly interpret the results.
If a mineral/glycol contamination issue is discovered, the likely recommendation would be to flush the sump. There is no other filtration option for a lubricant contaminated in this manner, so the contamination must be physically removed.
Another recommendation might be to review the relubrication practices, since this type of contamination usually is the result of misidentification of the lubricant(s) in question.
Please note that while the latest glycols derived from butylene are far more compatible with mineral oils than those using propylene and ethylene, the analysis of these new glycols is still evolving. This should be taken into consideration when evaluating oil analysis data from a glycol-based lubricant system.
Missing or wrong additives can lead to many potential problems. It is common to see a missing extreme-pressure (EP) or anti-wear (AW) additive in gear, bearing and hydraulic applications. If you are missing one of these additives and the equipment requires it, excessive rubbing wear and severe sliding wear could occur, depending on the tolerances and workload. These additives physically separate the loaded surfaces when the lubricant viscosity is insufficient, and without them you will be contacting these loaded surfaces.
If a lubricant with a detergency additive is put into a system designed to shed water, the detergency additive will ruin this shedding property of the lubricant. Generally, the only solution is to remove and completely replace the lubricant or risk having water ingression cause significant bearing wear. This problem is most common when dealing with large turbine sumps that have been contaminated with diesel engine oil. Consider that as little as a quart of diesel engine oil can destroy the demulsibility of 2,000 gallons of turbine oil.
This sample also had mildly elevated silicon levels.
If a system with yellow metal (copper alloys) has a manufacturer’s recommendation to not use an EP additive, this is usually because the EP additive would be highly corrosive to the yellow metals when the additive reaches activation temperatures. In these instances, a metals test should be conducted to reveal the problem. This test can detect additives and allow you to see changes in the additive levels. Oxidation or nitration tests may also be helpful.
In addition, you may be able to identify an incorrect additive with an infrared spectrum comparison/overlay. With this test, two lubricants can be overlaid on a single graph to determine if there are any chemical signature differences in the infrared signal. This is not a typical test and should be viewed as an exception test in most cases.
For these types of issues, the common recommendations will include using exception testing (analytical ferrography, etc.), which can reveal the extent of surface degradation if there are wear problems. Another recommendation would be to check the manufacturer’s specifications as well as the operating temperatures and how they relate to the lubricant selection.
The more widespread issue with an incorrect lubricant involves using the wrong viscosity. If the viscosity is too high, you may see increased wear in gear systems due to reduced or no splashing ability (if the system requires splash lubrication). In hydraulics, a high viscosity can lead to slow performance and low filtration rates. In nearly all low-viscosity situations, the result will be elevated wear. This is because the fluid film is not thick enough to prevent surface-to-surface contact during operation.
To detect a viscosity problem, perform a viscosity test. Also, consider conducting a baseline test on the new lubricant, as viscosities can change from batch to batch, and a lubricant top-up using a similar lubricant with a different viscosity may not be readily apparent. In addition, you may be able to identify this issue with metals testing, since additive levels will commonly fluctuate along with a viscosity change, even within the same product line.
The recommendations for viscosity problems can be fairly involved. This is because along with the possibility of having put a lubricant with the wrong viscosity into a machine, there may have also been an operating change that has affected the machine and caused the issue. For example, if the ambient temperature has increased, the viscosity may now be too low for the operating temperature, and wear may start to occur.
Outside of this possibility, the most common recommendation will be to change the oil in the sump. If the sump size is significant, it may be suggested to sweeten the oil or drain off a portion and replace it with fresh lubricant to improve the viscosity.
Please keep in mind that these are only a small portion of the problems that may arise and that laboratory testing capabilities are an ever-changing field. New technologies and improved methods are constantly becoming available. If you have a specific issue that requires testing, contact your oil analysis lab and be sure to get the best, most effective testing you can find.