What Exactly is a Lubrication Failure?

Noria Corporation

If you ask anybody who's been around maintenance why precision lubrication is important, nine times out of 10 he or she will answer "to prevent failures." While this basic statement cannot be argued, let's stop to consider the actual meaning of a failure. The two most common types of failure are catastrophic and functional.

When referring to a catastrophic failure, we are usually talking about a sudden failure to a machine that causes it to cease operation. Catastrophic failures can cause damage not just to the specific component in question but also collateral damage. Take, for example, a piston ring seizing while an engine is operating causing the rod to push through the cylinder wall, or an ID fan bearing that failed due to lack of lubrication forcing the fan housing and motor to be ripped from the base and literally thrown across the plant. By anyone's definition, these two real-world examples would constitute catastrophic failures. A catastrophic failure may then be considered an event that causes significant collateral damage, production interruption and/or the occurrence of a safety hazard. Needless to say, catastrophic failure should be eliminated through reliability engineering, root-cause failure analysis and predictive tools, designed to reduce the severity of an event.

The second category to consider is functional failure. In my experience, a functional failure is often misunderstood. To obtain a better grasp of this subject, consider a pump designed to pump at 1,000 gallons per minute that is losing pumping capacity down to 800 gallons per minute. Assuming the lower pumping rate does not meet the process requirements for this pump, one might consider it to have functionally failed - the machine is still operating, but cannot function according to the required design specifications and likely needs to be shut down to correct the problem.

But it's a third type of failure that, in my experience, is the least understood and/or to a large extent ignored when it comes to lubrication-related failure. This type of failure is sometimes called premature failure. Typically, this term is associated with a catastrophic or functional event; however, this may not always be the case. To illustrate my point, consider the design life of a rolling element bearing. While several variants can be used to describe the expected life a rolling element bearing, the most commonly used is the L10 life. The L10 life, which is typically given in years, is the life expectancy of the bearing with a probability of 90 percent under given stressing conditions (load, speed, etc.), before the bearing fails due to fatigue. In other words, out of a population of 100 bearings, at least 90 of those bearings should reach their L10 life.

Now think about your plant. How many bearings actually reach their L10 life? While this will vary based on circumstances such as application and environment, a senior engineer from a major bearing company suggested that on average, fewer than 10 percent of bearings actually reach their L10 life, compared to the predicted 90 percent - an opinion I often hear validated by in-plant maintenance and reliability personnel.


Lubrication-related Failure?
Now consider that as many as 60 to 80 percent of all bearing failures (catastrophic, functional and premature) are lubrication-related, whether it's poor lubricant selection, poor application, lubricant contamination or lubricant degradation. Then you can start to understand the tremendous cost saving opportunities of eliminating not only catastrophic and functional failures which impact production, but to extend the life of many oil- and grease-wetted components through precision lubrication.

So, why is this often overlooked as a lubrication-related failure? In my opinion, the problem lies in the fact that predictive maintenance programs (vibration analysis, thermography and wear debris analysis) are so effective in finding problems that can be resolved during a scheduled outage, we lose sight of the fact that many components are failing early because lubrication best practices (right lubricant, right time, right quantity, clean, dry and cool) have not been established. Surely it makes sense, given the number of bearings and other oil- and grease-wetted components in a typical plant, that if the life expectancy of every component can be increased by just 10 to 20 percent, this will have a significant impact on maintenance costs. Call it the hidden cost of lubrication malpractice.

So, the next time you or someone else in your plant claims "we really don't have any lubrication-related failure," consider the underlying facts of this statement. Are you truly stating that every single bearing, gear, valve and guide lasts as long as can be expected based on it's design specifications, or is there an opportunity to reclaim some of the remaining useful life of oil- and grease-lubricated assets that may be squandered due to a less-than-ideal approach to lubrication?

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