- Buyer's Guide
How much value do you get from a drop of oil? Consider not just the raw cost of the oil, but rather the total benefit that one drop of oil or grease provides over its anticipated life. For argument sake, let’s say that a drop has the potential to provide $1 of value before it needs changing. How much of that $1 value do you actually recoup? Ninety cents? Eighty cents? If you’re constantly adding new make-up oil due to leakage, changing oil too frequently, stressing the oil oxidatively through elevated operating temperatures or pumping grease until it comes out of the seals, you’re throwing away valuable lubricant and wasting money (Figure 1).
Figure 1. Hidden inefficiencies and Waste in an Oil Drop
So how can you extract every last cent of value from that drop of oil? The answer is a careful lubricant management and conservation program, encompassing a well-engineered, strategized approach to maximizing lubricant life.
Lubrication management starts by changing the organization’s view of lubricants and lubrication, beginning in the purchasing department. All too often, lubricants are treated as consumables, which must be purchased at the lowest cost. However, lubricants are in fact valuable assets that must be nurtured and cared for if the maximum in-service value is to be realized. This involves a cradle-to-grave approach, whereby the lubricant is stored, handled, dispensed and used appropriately at all stages to maximize its total life cycle value (Figure 2).
Figure 2. Life-cycle Management
and Monitoring of Lubricant Quality
Storage is perhaps the most important, yet most frequently overlooked area. All too often, lubricants are stored outside, or in dirty or dusty environments. Oil stored in this manor is prone to contamination ingress, which can result in premature degradation of both base oil and additives. Under these circumstances, the oil or grease may have lost a significant portion of its serviceable life before it is even put into service.
Similarly, it is important to deploy a first-in, first-out (FIFO) lubricant usage strategy, because many lubricants have a finite shelf life. This is particularly important if storage conditions are less than ideal. In many instances, oil and grease life can be reduced to a year or less if careful storage procedures are not followed.
Lubricant handling and dispensing are just as critical. Using inappropriate oil top-off containers can result in water and particle contamination, again shortening the life of the oil. Similarly, failure to correctly label lubricant handling and dispensing hardware can result in cross-contamination. While using the wrong oil or grease for a specific application can of course result in serious operational issue, even if the problem is recognized in time, any cross-contamination by default will almost certainly mean a premature oil change, including extensive flushing, to ensure the correct lubricant in use.
Tracking Lubricant Usage
The first step to establishing a solid lubrication management program is to develop a system that accounts for lubrication usage. This often reveals some rather surprising and overlooked costs. For example, a hydraulic system at a pulp mill was identified as a persistent leakage problem - considered by most at the mill to be a minor problem and merely “the cost of doing business.” When questions about the severity of the leak were asked, no one could answer the question as to how much make-up oil was being added. A check at mill stores revealed that more than 10 barrels of a specialized synthetic lubricant was being purchased on a monthly basis to support this “minor” leak. Based on these figures, the total cost of servicing this leak was estimated to be nearly $30,000 per year; however, it was not until an investigation into the amount of oil being used was initiated that anyone thought to question if constantly adding make-up oil was the fiscally responsible thing to do.
Tracking lubricant usage is an important first step in making necessary improvements, because it is a baseline by which subsequent improvements can be benchmarked. Measuring the amount of oil or grease used is a relatively simple task in today’s world of computerized inventory control. By tracking lubricant consumption, a metric or key performance indicator (KPI) can be introduced that provides maintenance, purchasing and management with a simple number to indicate compliance with stated lubricant consumption targets. One simple KPI is to calculate the plant-wide consumption ratio. The consumption ratio is simply the ratio of the total lubricant usage over a given time period, to the total volume of lubricant required by each component.
Consumption Ratio = Total Annual Lube Usage / Total Machine Volume
Perhaps more instructive is to calculate individual consumption ratios, either by lubricant type - for example, a specific grade of hydraulic fluid - or by component type. For example, tracking the amount of grease used to relubricate electric motor bearings can be used to determine the impact of new regreasing initiatives such as using ultrasonic monitoring to guide grease volumes. While tracking lubricant usage on a component-by-component basis may at face value appear onerous, this information is relatively easy to obtain and document with a well-implemented CMMS and lube routing software database, in conjunction with metering devices on all lubricant dispensing equipment. In fact, new environmental regulations such as ISO 14001, may make tracking lubricant consumption against disposal mandatory, further justifying the upfront cost of adding lube-metering devices.
The potential upside of lubricant usage KPIs is that changes in lubrication procedures and practices can be compared with specific consumption ratios to determine the overall effectiveness of any new initiative, allowing cost benefits to be calculated. For example, a series of hydraulic units may be deemed perennial “lubricant consumers.” Consider calculating the annual consumption ratio for these hydraulics systems and compare this against improvement initiatives such as improved fluid cleanliness as means of justifying the program’s cost.
To realize a significant reduction in lubricant usage KPIs, such as consumption ratio, an aggressive lubricant conservation plan must be developed and implemented. The required steps will vary depending upon the organization’s current lubrication practices.
Leakage Control and Management
All too often, leaks are considered benign and normal. However, even a fairly slow leak can cause significant overall lubricant replacement cost. Consider the chart shown in Figure 3.
Figure 3. Determining Leakage Volumes Based On Drip-Rate.
Even Seemingly Small Leaks can Result in Significant
Lubricant Losses Over an Extended Time Period.
What is the impact of a slow leak, producing on average, five 1cm3 drops per minute? Over the course of a day, such a leak would result in the loss of 0.7 liters of oil - perhaps not a significant amount; but what about loss over a month? Assuming a 30-day month, a leak of five drops per minute will result in the loss of more than 20 liters of oil. Now, what about over a whole year? Over a 12-month period, a leak of five drops per minute will result in a total loss of close to 400 liters - or $2,000, assuming the lubricant cost nearly $5 per liter. Amortized over the number of leakage “bad-actors” throughout the plant, small, seemingly insignificant leaks have a way of adding up.
So how can leaks be controlled? Step No. 1 is to recognize their presence and tag the leak for inspection and corrective action during the next available maintenance outage. More often than not, poor seal maintenance is the primary culprit. Poor installation, hardening due to extended service life, seal incompatibility with the lubricant or working environment, or excessive contamination causing seals to wear are all major factors and should be carefully considered and corrected where appropriate. In situations where the cause of the leak is hard to pinpoint, the use of fluorescent dyes also offers some advantages.
Condition-based Oil Changes
One of the most effective ways to maximize oil life is to use oil analysis to scientifically determine when the oil should be changed. Tests such as acid number (AN), base number (BN) and rotating pressure vessel oxidation test (RPVOT) can all be used to ascertain the point at which the oil begins to degrade, allowing an oil change to be scheduled.
Condition-based oil changes are not for all organizations or all equipment. For example, a small hydraulic power pack may contain 20 gallons of oil that is changed once per year during a scheduled maintenance outage. By using oil analysis to carefully monitor the oil, it may be possible to extend this interval to every other year, halving the annual oil change expense - but at what cost? The cost to test this system to allow oil drain intervals to be safely and scientifically extended may far exceed the benefits associated with extending the oil drain interval.
A clear illustration of the savings that can be realized from condition-based oil changes comes from a large Canadian pulp and paper mill. Heading into a routine annual shutdown, the steam plant engineer called for an oil change on the main turbo generator lube system. The rationale was that the oil had not been changed for five years, so the estimated cost of changing the oil (not including manpower and disposal costs) of $54,000 was justifiable, given the criticality of this system to the mill’s operational profitability. After all, even one day without the turbo-generator required power to be purchased from outside sources at a cost of close to $30,000/day. Fortunately, the mill’s reliability team leader got wind of the pending work order and sent a sample of the in-service oil to a lab for analysis. In addition to routine tests for wear metals, viscosity and contaminants like water and particles, the reliability leader requested more detailed performance related tests such RPVOT, demulsibility, foam stability and corrosion inhibition tests.
Data from RPVOT measurements indicated that 90 percent to 95 percent of the oil’s oxidation resistance was intact. In addition, the oil had no serious foam, water, demulsibility, particle contamination or incipient wear problems. The decision was made to cancel the proposed oil change and retest prior to the next year’s shut down. In this instance, less than $500 in oil analysis tests helped avert changing $54,000 of “good” oil, not to mention freeing up valuable shutdown maintenance man-hours for other necessary tasks.
Don’t Change Oil; Filter It
The most common response to a problem identified through oil analysis is the recommendation to change the oil. It is true that problems resulting in chemical changes to the oil, such as oil oxidation or thermal failure or the presence of certain contaminants, such as fuel or glycol, are nearly impossible to remove from the oil and usually necessitate an oil change. Problems such as water or particle ingress, however, rarely require a complete oil change unless the water or particle ingression has resulted in additive and/or base oil degradation.
All too often, the comment is made that oil is cheap compared to unscheduled downtime, so why not change oil more frequently? However, changing oil costs more than just the raw cost of the new oil. The sidebar in this page illustrates the estimated cost to change just five gallons of oil at a nuclear power plant. When the cost of ancillary labor, paperwork, used oil disposal costs and other factors are considered, what began as a $65 oil change ends up costing almost $1,000.
When trying to maximize oil life, it is important to recognize and control factors that directly impact oil life. Contaminants such as air, heat, water and catalytic metal particles all have a direct impact on an oil’s rate of oxidative degradation and must be carefully controlled if oil life is to be maximized.
Because air is the driving force behind oil oxidation, it stands to reason that air entrainment is directly correlated to oil oxidation. Even though up to 10 percent of a lubricating oil’s volume may be air, every attempt should be made to prevent excessive air entrainment through proper sump management, controlling suction line leaks and avoiding contaminants such as water and particles that can result in air entrainment.
Heat generation in any lubricating system is inevitable due to mechanical and fluid friction, as well as compressive heating effects. However, based on the Arrhenius rate rule, the rate of oil oxidation - simply a chemical reaction between base oil and oxygen - increases exponentially at higher temperatures. For mineral-based oils, the rule of thumb is that the rate of oxidation doubles for every 18°F rise in temperature above 170°F.
In the chemical manufacturing industry, catalysts are used to provide an alterative reaction pathway allowing a chemical reaction to occur at a faster rate. For oil oxidation, certain metals - particularly nascent copper - provide just such a catalytic effect. In fact, for an uninhibited mineral oil, the rate of oxidation as measured by the increase in acid number has be found to be five times higher when a copper catalyst is present than when no metal is present (Figure 4).
For this reason, a clean coil of copper wire is used in the RPVOT test to help induce premature oil oxidation.
Blow-by in Engines
It is well-known that contaminants in engine oils contribute to excessive oil consumption. Ingressed particles such as dirt and wear particles cause abrasive wear, particularly between rings and cylinders, leading to excessive blow-by. Blow-by, of course, allows oil to pass from the sump into the combustion chamber where it burns and leaves the engine through the tail pipe. Coming in from the other direction, blow-by increases soot loading in the oil, rendering the antiwear additives less effective. In turn, this increases ring-to-cylinder wear, resulting in yet more blow-by and creating a vicious cycle of lubricant degradation and engine wear.
In one extreme case, a marine engineer was asked how often the oil was changed on large marine diesel engines operating 12 to 16 hours a day. The answer was once a year. After discussing the issue further, it was learned that based on an extremely high oil consumption rate, an oil change was essentially being performed every seven days. Even though additives were being replenished due to the high make-up rate, replenishing the oil still didn’t remove contaminants in the engine like soot and particle build-up, which were likely exacerbating the problem by causing abrasive wear, leading to even more blow-by and an even higher oil consumption rate.
Particle contamination is one of the leading causes of poor equipment reliability. In hydraulic systems particularly, high levels of particle contamination results in premature pump, valve and component wear. Whenever maintenance work needs to be performed due a premature failure, it is inevitable that at least some of the hydraulic fluid will be lost when the system is drained resulting in fluid consumption.
Similarly, excessive particle ingression can result in valve stiction and seal wear, both of which can lead to progressive or sudden fluid loss. At operating pressures from several hundred to several thousand psi, it takes only a few seconds for tens or even hundreds of gallons of hydraulic fluid to be lost.
Most contamination control efforts are motivated by an attempt to control the direct impact of particle contamination on abrasive, erosive and particle induced fatigue wear rates. However, many organizations that have adopted an aggressive approach to contamination control have realized significant overall savings in fluid consumption (Figure 5), often enough to justify the upfront cost of the contamination control program.
Figure 5. The Impact of Improved Fluid Cleanliness on Oil Consumption
Use Better Quality Lubricants
Many plants and individuals that have successfully implemented lubricant conservation programs have discovered an amazing fact - oil does not last forever, but eventually wears out. Depending on the quality of the base oil and additives and the environmental stressing factors, oils will have a finite life expectancy, even under the most ideal conditions. At this point, it is sometimes cost-beneficial to seek better quality products, such as synthetics and highly refined mineral oils. While the upfront cost of synthetic oils may be significantly higher, perhaps anywhere from five to 15 times higher, by managing factors related to oil degradation, it may be possible to extend oil drains to the extent that the additional cost can be justified based simply on an extend oil drain interval.
Whenever this type of strategy is evaluated, it is important to carefully eliminate or minimize all other forcing factors discussed previously, which contribute to premature oil degradation. It is also important to determine current oil change intervals using a condition-based oil analysis strategy and then evaluate the higher-end product using a similar approach based on a carefully selected oil analysis test slate. Simply replacing a conventional mineral oil with a highly-refined mineral or synthetic oil, based on some conceived notion that synthetic oils are necessarily “better” can lead to an increase, rather than a decrease in overall lubricant costs.
Single-point automatic grease dispensers offer significant advantages for providing “just-in-time” regreasing, particularly in hard-to-reach applications where accessibility or safety concerns make manual greasing difficult. However, it is important when using such devices to ensure that they are accurately calibrated and set to provide the correct amount of grease. It is also important to turn them off - either manually or using a relay device - when equipment is not running.
The impact of not accurately setting automatic grease lubricators can have a significant effect on overall lubricant costs. In one instance, a pulp mill was spending close to $140,000 per year on new lubricant purchases, with more than $21,000 attributable to automatic grease lubricator purchases. While this expense was justifiable to the mill for lubricating the hard-to-reach backside bearings of the paper machine, it was discovered that the amount of grease the single-point lubricators were calibrated to dispense far exceeded the bearings’ operational requirements. Based on a careful review of the volume of grease being delivered by each unit against standard formulas used to calculate the required grease volumes for large rolling element bearings of this kind, an annual savings of $7,000 was obtained. This was achieved by carefully setting automatic greasing systems to deliver the right amount of grease at the right time. These savings do not account for perhaps the biggest payback - the impact overgreasing can have on premature bearing failure.
Using Technology to Drive Relubrication Intervals - The Future is Here!
Aside from condition-based oil changes, other recent technological advances have allowed lubrication professionals the ability to apply just-in-time oil changes and re-greasing intervals and volumes. New tools, such as developments in Fourier transform infrared (FTIR) spectroscopy, the RULERTM instrument, which allows the rate of depletion of antioxidant additives to be determined, and numerous ultrasonic devices that allow for regreasing intervals and quantities to be carefully determined, offer the lubrication technician an unprecedented view inside bearings and other lubricated components.
Many newer cars come equipped with so-called smart systems that calculate the optimum oil change period using complicated algorithms based on factors such as speed, distance traveled and rpm. While these software tools may not be as stringent and fool-proof as we might like, the time is not far away when even the most basic vehicle will come equipped with a low-cost, smart sensor which evaluates oil condition and scientifically determines, based on measuring certain oil condition parameters, the optimum time to change the oil.
These are exciting times to be a lubrication professional. New developments, which better equip the knowledgeable lubrication engineer to be able to draw every last cent of value from a drop of oil or grease, are being introduced regularly. All it takes to improve your organization’s lubrication program is an open mind, an open ear and a desire to embrace change.
The Real Cost of Changing Oil at a Nuclear Power Plant
Apparent Oil Change Costs = New Oil + Labor = $65
Actual Oil Change Costs = $988.70
Rizo, L. (2002, May-June). Getting the Most from Single-Point Lubricators. Machinery Lubrication. pp. 46-51.
Fitch, E.C. (1992). Proactive Maintenance for Mechanical Systems. Stillwater, Oklahoma: FES Inc.