Overall Lubrication Effectiveness (OLE) is a leading maintenance metric that evaluates the timeliness of lubrication PMs, contamination control, and lubricant health to ensure optimal machine reliability and performance.
Along with its companion leading metrics illustrated in the figure below, OLE is intended to drive proactive behaviors on the plant floor to ensure that the lubricant and lubrication process are effectively protecting machine components from the effects of abrasive, adhesive, fatigue, and erosive wear, and other performance-degrading mechanisms.
Ultimately, by managing essential root causes of failure, Overall Lubrication Effectiveness drives up Mean-Time-Between/To-Failure (MTBF/MTTF), which is our goal.
What OLE Is and Why It’s Important
The lubricant is the lifeblood of the machine. It provides a lubricant film that rarely exceeds five microns in thickness (about the diameter of a red blood cell) that is responsible for separating machine component surfaces and serves to reduce friction and wear.
It’s also essential for controlling ingested contaminants and generated heat. In hydraulic systems, it’s the mechanism by which force and motion are transferred to accomplish work. Effective lubrication is crucial in managing the reliability of a site’s equipment assets.
OLE is calculated by multiplying the following three factors (figure below):
- Percentage of lubrication PMs that are done on time.
- Percentage of contamination targets met.
- Percentage of lubricant and lubrication health targets met.
The simple formula for OLE, which is the product of multiplying the ‘behavioral inventories’ for the three input factors.
As with Overall Inspection Effectiveness, consider each of the three OLE components/metrics as an inventory process. We’re simply adding up the complying events and dividing by the total.
1. Lubrication PMs Completed on Time
Lubrication PMs include greasing bearings; performing time- or condition-based oil changes, changing filters and performing periodic decontamination; checking lube levels and topping up as appropriate; monitoring lubricant temperature, pressure, and pressure-differential across filters; taking representative samples for oil analysis; inspecting lubricant-film quality for greased bearings using surface-borne ultrasonic analysis, and a host of other tasks.
Precision maintenance demands rigor—lubrication PMs must always be done on time.
Lubrication PMs are time-sensitive: They must be done on time. The Lubrication PMs completed on time metric is binary and straightforward to calculate. It’s the number of lubrication PMs scheduled for a given week and finished that week, divided by the total number of lubrication PMs scheduled for the week.
If a PM is scheduled for a certain week, but we elect to push it into the next week, it’s not compliant. And if this week’s PM is completed next week, it doesn’t count as a PM completed this week (it’s removed from the equation). This may seem like a harsh interpretation of PM compliance, but precision maintenance demands rigor in completing time-sensitive tasks.
2. Contamination Targets Met
Contamination in the form of particulate, water, glycol/antifreeze, soot, fuel, air, and excessive heat are the scourge of lubricated and hydraulic systems. The percentage of contamination targets met, like the percentage of lube PMs done on time, is binary and simple to calculate.
Contaminants are the scourge of lubrication systems—control them, control reliability.
Based upon the most recent oil-analysis report, we inventory the number of machines that have no alarm condition for particle contamination (e.g., ISO 4406 cleanliness code), water contamination, glycol/antifreeze, soot (engines), or fuel dilution (engines) and divide that by the current number of machines included in the oil-analysis initiative.
Excessive heat and air are often overlooked contaminants in lubricated and hydraulic systems. Heat accelerates the rate at which lubricants oxidize, seals and elastomers thermally degrade, and other chemical processes.
As a rule of thumb, a 10°C (18°F) increase in temperature doubles the rate of most chemical reactions. Compliance on lubricant temperature in the metric is simply the number of machines that are at or below their target temperature divided by the total number of machines for which temperature is being monitored.
The monitoring can be accomplished with in-line/on-line sensors, gauges, or walkaround devices such as a non-contact pyrometer. The temperature component includes both oil and grease-lubricated machines.
A fair rule of thumb for grease-lubricated machines is that the grease temperature is about 10°C (18°F) higher than the housing temperature. Take your readings from the same place each time for walkaround temperature measurements.
Air in a lubricant can be a very dangerous contaminant (particularly in hydraulic systems). The presence of entrained air increases the rate of oxidation. In hydraulic systems, it can cause spongy response and vapor lock and lead to adiabatic compression-induced thermal failure of the product.
Checking for air contamination is a visual inspection. Look for excessive opacity (cloudiness), which can signal a high degree of mechanical agitation or a failure of the oil to release its air (possibly due to a reduction in surface tension).
Also, excessive foaming should be looked at, particularly in hydraulic systems and gearboxes. Foam compromises a lubricant’s heat dissipation properties and, in extreme cases, can exit the sump or reservoir to create slip-fall and fire hazards.
3. Lubricant and Lubrication Health Targets Met
To effectively function as a lubricant or hydraulic fluid, the product must be present in sufficient quantity and be healthy with respect to its physical, chemical, and performance properties.
Healthy lubricants are the lifeblood of reliable machinery.
For all lubricated machines, the number with the correct amount of oil-based upon site-glass, bullseye, or dipstick inspection is divided by the total number of oil-lubricated machines.
For those oil-lubricated machines, we divide the number with no alarm for oxidation, additive depletion, thermal degradation, or cross-mixing with the wrong oil (cross-mixing could just as easily be included in contamination control). I would also add transformer oil to this group.
This oil serves as a dielectric medium (insulator) in transformers. As it degrades, however, a transformer oil’s dielectric strength diminishes, and potentially flammable volatile organic compounds (VOCs), such as acetylene, can be formed. Therefore, transformer oils should be added to the inventory of practices equation.
For grease-lubricated systems, we rely primarily on surface-borne ultrasonic analysis tools. In properly lubricated bearings, a heterodyned signal of ultrasonic acoustic emissions at about 30 kHz produces a swishing sound of white noise and a decibel (dB) reading that’s normal for the application (baseline-dependent).
The dB reading increases if the ultrasonic noise level increases beyond a specified limit. If the lubricant is further compromised, one will hear the cracking sound of asperity contacts because the rolling elements are contacting the raceways.
To determine if lubricant and lubrication health targets are being met, simply divide the number of bearings that are compliant on the dB reading and not exhibiting any cracking sounds associated with surface-to-surface contact by the total number of grease-lubricated bearings being monitored.
If you want to refine this number, you may subtract the bearings that are defective per vibration analysis because we’re primarily focused on the proactive aspects of machine health.
BTW: If you want to get sophisticated about the health of grease-lubricated machines, check out some of the innovative grease-analysis techniques pioneered by Rich Wurzbach and the team at MRG Laboratories.
It isn’t easy to conceive of world-class asset-reliability management without a solid foundation of great lubrication practices. OLE focuses on driving the fundamental behaviors necessary to achieve lubrication excellence. Get your lubricants and hydraulic fluids working for you, and not against you, ASAP. And say “Olé” to Overall Lubrication Effectiveness.
Initially published in The RAM Review.
Drew Troyer is a seasoned expert with over 30 years of experience in sustainable manufacturing, physical asset management, energy management, and reliability engineering. He has a proven track record of helping companies in the mining, resource, process, and manufacturing industries optimize their operations to be more sustainable, reliable, and profitable. Drew is a thought leader and a prolific author, with over 350 published works and extensive experience as a keynote speaker at global conferences. He is also a Certified Reliability Engineer (CRE) and Certified Energy Manager (CEM), holding advanced degrees in business administration and environmental sustainability.
