by Drew D. Troyer 

When a machine fails, the evidence of the incipient stages of the failure is usually lost. Anyone who has examined the mangled mess of a failed bearing or gearbox realizes this as a truth.

Root cause analysis is an investigative process that is very similar to solving a crime. The first thing detectives do when arriving at a crime scene is to carefully rope off the area. The purpose, of course, is to preserve the evidence so that it can be collected and analyzed later. When normal sources of evidence are destroyed or mangled, forensic criminologists look even more closely at the crime scene to uncover evidence that may be hidden from obvious view.

For the maintenance and reliability professional, the used oil and the filter represent important sources for clues about the incipient stages of the failure event. Regrettably, in their rush to get the machine quickly up and running, the maintenance team often disposes of the oil and filter, or allows them to become contaminated to the point that they are useless in the failure investigation.

Let’s look more closely at the use of oil analysis and used filter analysis within the context of failure root cause analysis.

Oil analysis
We commonly think of used oil as it is applied to operating machines. It is equally applicable to post mortem root cause analysis. Despite the mangled appearance of the component where evidence is destroyed, the lubricant still contains evidence about the time leading up to and including the catastrophic event. Sometimes, sump or tank-bottom sampling can help in the process. The debris accumulates in the tank’s 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.

A word of caution: This approach to sampling does not enable you to categorize the particle with respect to which component created it, nor the point in time when it was created. If you want to learn more about oil analysis, visit the Noria Web site and sign up for a free subscription to Practicing Oil Analysis.

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, you can evaluate the evidence of the incipient event leading up to the catastrophic failure.

Don Searles authored a nice article on filter analysis in the March/April 2002 issue of Machinery Lubrication, and Robert Whitlock and others discuss a method for filter debris analysis in “X-ray Fluorescence Spectroscopy: The Next Generation of Wear Debris Analysis,” found in the November/December 1998 issue of Practicing Oil Analysis. Like tank-bottom sampling, this method does not segregate the particles with respect to component or time of production.

Many organizations have thrown out the old book on equipment maintenance, and are rewriting a new, very different one. You can’t create new practices that eliminate problems at the root without evidence that accurately describes the problem. The lubricant and the lubrication system offer clues even though the evidence on the machine itself might have been destroyed.

Train your team to carefully preserve this evidence and learn how to access it to support your root cause analysis investigations, which should be the basis for sound equipment maintenance management decisions.

Drew Troyer is the senior editor of Machinery Lubrication Magazine. If you have a lubrication or oil analysis question, contact Coach Troyer at or e-mail . 

This article appeared in the June/July 2003 issue of MRO Today magazine. Copyright, 2003.

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