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How often do you change the oil in your car? One of the most common answers is "every three months or 3,000 miles." Another answer may be "5,000 miles" or even "7,500 miles."
I recently asked a client why he performs oil analysis on industrial equipment. His reply was to look for wear and contamination in his machines. I then asked him how often lubricant changes are performed on the equipment, and he replied that his equipment is placed in the CMMS on either a six- or 12-month lubricant change interval.
These answers are typical of plant maintenance managers, and do not vary from the common answers for automobile oil changes. Both utilize the same maintenance strategy - scheduled maintenance. Neither schedule takes into account the actual condition of the lubricant.
To fully implement and realize the benefits of condition-based maintenance, utilizing oil analysis results to drive lubricant changes is essential.
An article in the January issue of POA defined some of the typical tests employed for used oil analysis.1 The following are examples of how using the results of some of those tests to determine lubricant health can help optimize lubricant changes.
Case Study No. 1 From Noria Training
Figure 1 graphs a case study of viscosity trending of an ISO VG 68 bearing oil. In this graph, the viscosity decreases over time due to VI shear thinning. However, the viscosity showed a significant increase in August. After investigation, it was found that an incorrect lubricant was placed in this bearing; however, following research and data confirmation, the mixed viscosity lubricant was allowed to remain in the bearing. Subsequent to rebaselining for viscosity, new alarms were put in place and monitoring continues.
Over time, there is a visible increase in viscosity. After proper testing, it was noted that the oxidation was also increasing in lock-step fashion. In January, it was determined that the lubricant could no longer provide adequate protection to the metal surfaces and a lube change was performed. It is important to note that after the lube change was performed, a new baseline of viscosity was established. A baseline viscosity should be set based on an actual oil sample and not from the manufacturer's product manual.
Case Study No. 2
A customer was using an ISO VG 320 lubricant in several hard-to-reach agitator gearboxes. After introducing lubrication specialists to perform a complete lubrication program design, it was determined that the optimum lubricant for these gearboxes was an ISO VG 220 lubricant.
This customer is currently making equipment modifications to adhere to the recommendations of the design process. These modifications include performing a lubricant drain and flush prior to refilling with a lubricant containing the properties recommended for that specific component.
After completing the modifications, the gearboxes get resampled. In many of these gearboxes, it was noted that some of the additive levels were not consistent with the additives measured in the new lubricant. Additionally, the viscosity was not always in grade for the new lubricant.
Similar to the bearing example, significant data research was performed. Knowing that as much as 15 percent of the old lubricant may be left behind when a lubricant change is performed, it was confirmed that the additive levels and irregular viscosity were caused by a residual lubricant left over from an incomplete flush. It was also confirmed that the two lubricants were compatible with one another, making another lube change unnecessary. A new baseline was established for the components and appropriate monitoring takes place from this point. The customer will utilize oil analysis to decide a time period for the next lubricant change.
Benefiting from Oil Analysis
Oil analysis is a valuable technology used in both predictive and proactive maintenance strategies. While focus is placed on the actual machine condition and contamination, the proactive approach regarding lubricant health should not be forgotten. With the proper test slate, a well-established oil analysis program can reduce oil consumption. Some facilities can save enough in oil consumption costs to cover the costs of the oil program. This does not take into consideration the costs saved in allowing maintenance personnel to focus on other tasks rather than lubricant changes during planned outages.
Simply put, allowing oil analysis to help drive contamination control measures is only part of the savings. Allowing oil analysis to drive lubricant changes enables the user to experience additional savings offered by this technology.