Machinery Lubrication magazine published by Noria Corporation
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A helicopter's planetary gearbox conveys power between the main drive shaft (from the engine) to the main rotor, giving the helicopter aerodynamic lift and thrust. e condition of the lubricant (the right health, cleanliness and supply) is essential for reliable, safe operation. Any failure of the lubricant can quickly start a disastrous chain of events, from lube failure to bearing failure to gear failure to rotor failure to lift failure to helicopter failure (crash and burn). While the helicopter example may be an extreme case, it is still an important and vivid illustration of the seriousness of early detec- tion and response. What might seem like a mild condition now (rising varnish potential, cloudy oil, elevated particle count, uptick in fuel dilution, out-of-grade viscosity, low oil level, etc.) can abruptly worsen to a runaway catastrophic outcome. Root Cause Alarms Proactive maintenance should always be "job one" in condition monitoring. To do well, it requires a solid understanding of root causes that are ranked by likelihood (the Pareto prin- ciple). ere is also a need to understand the criticality of each machine. What you perceive as "the cause" may be nothing more than a transitional step in a sequence of many in route to functional failure. e real root cause you are seeking is the one that could have been controlled or prevented. at is not to say your purpose is to look for someone to blame. I was once surveying a steel mill and noted that the needles on most of the pressure- differential gauges (used on filters) were in the yellow or red zones. My escort quickly commented that the maintenance staff no longer used the gauge readings to schedule oil changes. Instead, all oil filters were changed on six-month intervals regardless of the gauge reading. Needless to say, I was shocked. On-condition maintenance should always take precedence over scheduled maintenance. See the fault tree in Figure 1 used to trou- bleshoot the root cause of a large process pump failure. Asking the "repetitive why" takes you to the pump (and not the coupling or motor) that failed. Next, the pump bearings were found destroyed. An examination of the lubricant revealed heavy contamination. An effective functioning filter would have prevented such contamination. In fact, the filter was found to be plugged, as indicated by the red-alert pressure gauge reading that went unnoticed. Had an operator reported the high gauge reading and followed up with a filter change, the pump might have been saved. A red-alert gauge reading is not a pump failure unless it does not get reported with corrective action. If the filter became plugged prematurely, it should have been examined. Analyze the used filter to deter- mine the type and source of particles. How have they invaded the machine and the oil? Don't just change the filter. Correct the ingression points, i.e., the source of particles that plugs the filter. Many root causes can be detected by oil analysis. ese include various types of contam- inants, wrong oil and degraded oil. If cleanliness targets and other alerts are adjusted to promptly weed out root causes, they won't advance to even the earliest state of failure. I recently finished a case related to diesel engine failures. e lab was using a 5-percent alarm limit for fuel dilution. Anything less than 5 percent was reported as normal. No wonder the many defective fuel injectors were not detected until catastrophic engine failure had occurred. Coolant leak detection is also poorly deployed in diesel engine oil analysis. In my opinion, even the slightest amount of coolant leak is cause for concern. Weak Signal Alarms Long ago, researchers and tribologists discov- ered that the strength of signals being emitted during machine failure depends on the state of failure. Incipient failure produces weak signals, while precipitous (advanced) failure creates strong signals. is applies to various types of signals, including wear debris generation, vibra- tion, heat and acoustics. Hence, if you want to catch failure early, you need to be good at detecting and responding to weak signals. Sadly, many oil analysis programs are struc- tured to do the opposite. You can't fix a problem that you can't see. Rather than setting tight alarms and limits that are a slight offset from normal conditions, some programs don't alarm until problems advance to a state of imminent danger, such as two or even three standard devia- tions over the mean based on data history. Loose alarms equate to failure blindness. Some of the best oil analysis programs use cautionary alarms to alert condition-based main- tenance (CBM) technicians of abnormal lab data or a reportable inspection condition. is way, the alarm results in a more measured or throttled response. People who wrongly push the panic button often discredit the value of condition ML PUBLISHER Mike Ramsey - mramsey@noria.com GROUP PUBLISHER Brett O'Kelley - bokelley@noria.com EDITOR-IN-CHIEF Jason Sowards - jsowards@noria.com SENIOR EDITOR Jim Fitch - jfitch@noria.com TECHNICAL WRITERS Wes Cash - wcash@noria.com Alejandro Meza - ameza@noria.com Bennett Fitch - bfitch@noria.com Loren Green - lgreen@noria.com Michael Brown - mbrown@noria.com Garrett Bapp - gbapp@noria.com Devin Jarrett - djarrett@noria.com CREATIVE DIRECTOR Ryan Kiker - rkiker@noria.com GRAPHIC ARTISTS Patrick Clark - pclark@noria.com Josh Couch - jcouch@noria.com Greg Rex - grex@noria.com ADVERTISING SALES Tim Davidson - tdavidson@noria.com 800-597-5460, ext. 224 MEDIA PRODUCTION COORDINATOR Libby Bahlinger - lbahlinger@noria.com CORRESPONDENCE You may address articles, case studies, special requests and other correspondence to: Editor-in-Chief MACHINERY LUBRICATION Noria Corporation 1328 E. 43rd Court • Tulsa, Oklahoma 74105 Phone: 918-749-1400 Fax: 918-746-0925 Email address: editor@noria.com MACHINERY LUBRICATION Volume 18 - Issue 1 January-February 2018 ( USPS 021-695) is published bimonthly by Noria Corporation, 1328 E. 43rd Court, Tulsa, OK 74105-4124. 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