Finding root cause of failure

by Drew D. Troyer

When a machine fails, evidence of the failure is often destroyed along with the component. The incipient evidence is so mangled by the actual failure itself, it becomes indistinguishable. The destruction of incipient failure evidence often leads one to blame the lubricant for a failure that was caused by another mechanism. Conversely, failures that are, in fact, caused by the lubricant or the lubrication are often attributed to something else. There are many possible cause-effect sequences where the evidence about the cause is lost in the evidence of the effect.

The absence of good evidence is what leads to costly poor decisions to act — or not act. Moreover, you can’t even determine if the event is addressable, or if it is random and should be accepted as such. Often, in the absence of good evidence and a sound understanding about what went wrong, individuals make somewhat arbitrary decisions to add new lubrication PMs, or modify the interval or method of existing PMs.

Absent a clear understanding about the nature of the failure, any beneficial effects associated with the change will be random (dumb luck). More often, the new and often costly changes fail to add value or, in some cases, actually cause problems themselves. For instance, the arbitrary but unjustified decision to switch to a synthetic lubricant adds cost but no value. The unfounded decision to increase the amount of grease applied to a bearing and/or the interval with which it is applied adds cost and, more often than not, creates problems rather than solving them.

So, how can you improve the quality of evidence and your ability to examine it?  Often, the lubricant or the lubrication system contains evidence even though the evidence on the component itself has been destroyed. Seize that evidence!  I have outlined several items below for you to think about:

1) Oil analysis: Despite the mangled appearance of the component, the lubricant still contains evidence about the time leading up to and including the catastrophic event. While not suitable for routine oil analysis, sump or tank bottom sampling can be useful in the root cause analysis process. The debris accumulates in the tank bottom, creating a veritable history book of the machine’s operation since the last oil change or tank cleaning. Many of the particles contained will be incipient wear particles. Others will be catastrophic. They can help you piece together the story.

2) Filter analysis: The filter is also a history book. It captures the particles generated since the last filter change and leading up to the failure event. By opening up the filter, liberating the particles with an ultrasonic bath and depositing them onto a slide or filter patch, the evidence of the incipient event leading up to the failure can be evaluated.

3) Component inspections: REALLY inspect components in response to condition monitoring. Frequently, condition monitoring detects a failure in its early stages, but when the mechanics pull the component and inspect it, everything looks fine. They reassemble the unit and, a few weeks later, the machine fails. Naturally, the assumption is that the intrusive act of inspecting the machine caused the failure, and the condition monitoring technicians look like dopes.

The typical inspection of a bearing is visual (often with the lubricant still on it) and/or may involve “giving her a spin” to see if it turns freely. Lubrication experts analyze five- to 50-micron particles with wear debris analysis. This means the machine has pits or grooves that are roughly the same size. It takes a microscope or other special instruments to evaluate the particles. How is a mechanic going to see the little pits with the naked eye?  Once a component starts to fail, the progression usually accelerates. Inspect pulled components with a microscope after cleaning the surfaces to see what’s going on.

4) Train your staff: Millwrights and mechanics need knowledge about failure mechanisms to understand how machines reach a failed state; as well as methods and techniques for reducing failure, including proper lubrication, condition monitoring and failure analysis. This enables them to find and interpret evidence about machinery failure and to employ their knowledge in pursuit of improvement.

Many organizations have thrown out the old book on equipment maintenance and are writing a new one. You can’t create new practices that eliminate problems at the root without evidence that accurately describes the problem. The lubricant and lubrication system offer clues even though the evidence on the machine has been destroyed. Access and use this evidence. It’s the basis for sound decisions.

Drew Troyer is the senior editor of Machinery Lubrication Magazine. If you have a lubrication or oil analysis question, contact Coach Troyer at 800-597-5460 or e-mail dtroyer@noria.com. 

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