Perhaps your facility has a well-established oil analysis program that is providing great results, but are you utilizing all of the information available in the reports? If everything in a report is correct and within the specifications, do you do anything else with the information? Do you still allow the time-based preventive maintenance work order to change the oil and filter? If you answered “yes” to this question, you could be wasting thousands if not hundreds of thousands of dollars per year on unnecessary oil changes. You could also be introducing human error and creating more problems through this needless maintenance.

What are Condition-based Oil Changes?

There are three types of oil changes: reactive, preventive and proactive or predictive. So which of these is a condition-based oil change? It is a proactive or predictive oil change performed at the right time and for the right reason. 

In the “old days” before oil analysis was common in most larger facilities, the original equipment manufacturer (OEM) set up guidelines for recommended oil change frequencies. They usually erred on the safe side, which left nearly 50 percent of the useful life in the lubricant. Sometimes even the warranty was involved, requiring that the lube be changed at specific time intervals to maintain the warranty. In recent years, most OEMs will recognize a good oil analysis program and allow extended oil drain intervals without compromising the warranty. Of course, this is something that must be discussed and agreed upon before establishing extended drain intervals.

Condition-based oil changes are not to be taken lightly. You can reap the benefits of major cost avoidance or experience the wrath of catastrophic failures if not done correctly. You must also have a champion over your oil analysis program. 

Not all equipment is a candidate for extended drain intervals. You need to have an understanding of the equipment, material makeup of internal components and the operating parameters. You must also incorporate proper oil sampling techniques, the right slate of analysis tests and special tests performed periodically to ensure you are not missing any valuable information when making decisions on extending drain intervals. 

With a well-established oil analysis program, you will have trend information on the equipment, which will help you decide what pieces are eligible for extended drain intervals. It is true that the larger the reservoir, the bigger the potential savings. However, if you are performing oil analysis on smaller reservoirs due to criticality, why not take advantage of that information as well? Other factors that should be considered for extended oil drains include reservoir volume, the amount of makeup oil, operating temperatures and the quality of filtration and breather systems.

In addition, you should have a good understanding of how different oil analysis tests are performed and the strengths and weaknesses of each test. This is why it is important to have good communication with your oil analysis laboratory and discuss concerns as well as which special tests may need to be performed to obtain all the information to help make your decisions on the drain intervals. The more you let your lab know about your program and what you are trying to accomplish, the better your results will be. 

It is also critical to have an established baseline from new, unused oil samples. If you or your lab does not know what the new oil is supposed to look like, how will you know when something is wrong, since you have nothing against which to compare your current samples? 

Limitations of Oil Analysis Tests

One of the weaknesses of oil analysis tests is that they can give you a false sense that everything is fine. For instance, spectroscopic analysis only identifies particles smaller than 7 microns (depends on particle composition and analysis method), so you could have visible metal in the sample but only get results of 100 parts per million (ppm) of iron on the analysis report. A few alternate methods to obtain the necessary information would include acid or microwave digestion. This would break down the larger particles so that a more complete spectral burn can identify and quantify them. 

Analytical ferrography is another great method to detect and characterize large ferrous and other particles in your samples. This not only quantifies a particle amount but also can identify shapes, sizes and morphology of the particles, which can help determine the type of wear occurring.

After switching to condition-based oil changes,
the Seminole Electric plant was able to achieve
a cost avoidance of $1.27 million over a
five-year period.

It is also important to keep in mind that a high copper value may not be actual wear but leaching from a cooler. Zinc dialkyldithiophosphate (ZDDP) is an additive that sometimes causes copper leaching and thus high copper results. Silicon is another very common false positive. Unless you are used to seeing silicon in your analysis, a drastic increase is most likely from a repair job that utilized room-temperature vulcanizing (RTV) silicone or a silicone sealer. 

Water can be another misleading result in your oil analysis report. Most labs perform a crackle test on all samples, while some rely on Fourier transform infrared (FTIR) spectroscopy to detect water. A crackle test can identify water at around 500 ppm and higher, although a good lab technician can sometimes catch it at a lower ppm in certain oils with low additive levels (e.g., turbine oil). The crackle test is approximate and not considered quantitative. If you need to know the exact amount of water, have a Karl Fischer titration performed, but understand that there can be interferences with this as well. Also, be sure to specify the evaporator or drying method, especially with engine oils (also called co-distillation). 

Particle counts are usually obtained with a laser particle counter. While this is an accurate method, darker oils, water and air entrainment can sometimes cause problems. The pore blockage particle count can be performed in place of the laser particle count when the oil condition is extremely dark or contaminated with water. This method is not as accurate as a laser particle count, but it is a viable option in assessing fluid cleanliness to avoid the previously mentioned interferences. 

Another less common way to perform a particle count is with a Millipore patch. This can be time-consuming and expensive, but in specific situations, the Millipore patch can be used to help with wear debris analysis in place of analytical ferrography.

Special Tests

Even with an extensive oil analysis test slate, special tests are often needed to provide additional information when extending oil drains. For example, a rotating pressure vessel oxidation test (RPVOT) can be conducted to determine the oxidation stability of the in-service lubricant compared to a new lubricant. The RULER test offers another way of comparing new oil with in-service oil to estimate the remaining useful life. Other tests, such as the varnish potential rating, membrane patch colorimetry (MPC) and quantitative spectro analysis, can help identify the amount of oil degradation byproducts and depleted additives. These soft contaminants can create serious problems if left unattended. 

A demulsibility test is used to indicate a lubricant’s ability to shed water. Air release or foam tests are also important, as air does not provide a proper oil film to keep machine surfaces separated. Rust and copper strip corrosion tests can help identify a lubricant’s remaining anti-corrosive additives, while acid and base number tests measure the rate of change between a new and used lubricant. See Figure 1 for a list of the ASTM test methods.

These are just some of the special tests that can be performed on in-service lubricants to help make decisions about extending drain intervals. Once again, having good communication with your lab will be invaluable when it comes to making sure you are getting all the information needed to achieve cost avoidance and prevent catastrophic failures.

Cost Avoidance

With lubricants, there is the actual cost (what you pay the distributor per gallon, pound, pail or drum) and the real cost. The real cost of a lubricant is the total cradle-to-grave cost once it reaches your facility. This includes receiving, storing, dispensing, installing and disposal. Several years ago this cost was estimated to be an average of four to seven times per gallon. For contaminated special case oil (radioactive), the cost could be as much as 40 times per gallon. The average industry cost per gallon is $9 to $14 for mineral oil and $20 to $30 for synthetic lubricant, with the exception of specialty synthetics being $60 and more. For the purpose of this discussion, let’s estimate mineral oils at $10 per gallon and synthetics at $25 per gallon.

At the Seminole Electric facility, which is a two-unit, 1,300-megawatt combined coal-fired power plant, the equipment monitored for condition-based oil changes contains 6,043 gallons of oil (see Figure 2). Prior to condition-based oil changes, some of this equipment received oil changes every six months and some every 12 months. With these oil changes, the total increased to 7,948 gallons of lubricant per year. If you were to use the average of $10 per gallon and the real cost of seven times per gallon, the total would be a real cost of $70 per gallon. In a perfect world, if you could go one year without an oil change on all of the equipment, you would have a cost avoidance of $556,360. 

As can be seen in Figure 2, the average meantime between oil changes at the Seminole Electric facility is now closer to 1.5 years, with some equipment reaching five years. On the five-year oil change equipment, the total gallons of oil is 18,145, based on the six- and 12-month change frequencies over five years. Four to seven oil changes are avoided, since the equipment is usually inspected with an oil change at the fifth year of operation or around 40,000 runtime hours. This equals a cost avoidance of $1.27 million for those six groups of equipment over the five-year period. 

Please note that turbines, turbine control oil and boiler feed pumps are not included in these numbers. Due to their size, these reservoirs, which are more than 25,000 gallons combined, and filtration systems generally receive extended drain intervals.

Return on Investment

Now let’s consider the return on investment (ROI) for condition-based oil changes. The primary cost is the oil analysis. In Figure 2, there are 792 oil samplings per year for the equipment listed, at an average cost of $20 to $40 per sample analysis. A range of $15,840 at $20 per sample to $31,680 at $40 per sample provides an idea of the cost for the oil analysis. While $40 might be slightly high, that should more than make up for the few special tests needed to obtain additional information throughout the year. Even if you include the salary of the person managing the oil analysis program at the facility, you would still be well below the projected cost avoidance of $556,360 per year.

Additional Benefits

Now that you have seen the potential cost avoidance of condition-based oil changes, let’s examine some of the other benefits. First and foremost is the freeing up of man-hours to perform proactive work on equipment that really needs it. You may also have a reduction in machine failures or infant mortality, since you are not unnecessarily exposing equipment to human error. Unfortunately, too many times something is left out, left loose or leaks afterward. The system will remain cleaner if you are not opening it up in a dirty industrial environment and stirring up sediment that has settled to the bottom of the reservoir during operation. Filter usage likely will be reduced as well, as filters will not be changed on a time frequency but rather when they need to be changed based on differential pressure. You also will leave less of a footprint on the environment by reducing the number of new lubricants and the waste stream of used oil for disposal.

It is easy to see how you can create substantial cost avoidance by doing nothing more than utilizing all of the information your oil analysis report is providing. It should also be encouraging to know that you are generating enough cost avoidance to exceed the cost of the oil analysis program. If managed correctly, you can start reaping the benefits of condition-based oil changes by doing the right thing at the right time for the right reason.