A reader at a refinery sought our advice and we answered. He wrote: “I am working to set up a lube program step here to begin sampling the lube oil we receive from our supplier upon receipt before deploying to field. My question is, from your experience, have you run across or know of a statistic that shows approximately what percentage of bearing failures are typically attributed to “unclean” lubrication? Basically, if we don’t sample our lube oil, we “don’t know what we don’t know,” and may have contributed to shortening bearing life on rotating equipment by introducing oil that, while new, may not be as clean as the ISO code for that product would indicate, or not even be the correct viscosity as the label indicates is necessary to properly support the bearing, things we would try to catch before we introduced [the product] to the equipment. What I’d like to show leadership is, given X pump failures over some time period [what is the] Y% of those we would expect to either reduce drastically or eliminate by taking this oil sampling measure. Does this sound like the right approach?
1. Sampling the incoming oil is indeed recommended. Depending on the original source, mode of transport, and chain of custody, an estimated 50% to 60% of lubricants do not meet the buyer’s specifications or the cleanliness claims made by lube providers.
2. Looking at all bearing failures, somewhere between 40% and 60% of all bearing failures are attributed to dirty oil. SKF and others have published these data.
3. The origin of dirty oil in a refinery’s equipment is equally divided between occurrences outside of the recipient’s gate and bad practices tolerated inside the recipient’s gate. Very often the tanker trucks delivering oil are left dirty.
4. Bearings in pump-bearing housings with open vents and/or cheap bearing-housing protector seals (the ones with radially moving O-rings) almost always experience premature bearing failure. Pump-bearing housings incorporating closed/plugged vents and/or superior bearing-housing protector seals (the ones with axially moving O-rings) almost always experience reduced rates of bearing failure.
5. Oil with inadequate viscosity will have too thin an oil film. Consequently, the bearings will run hot and fail prematurely. Oil with excessive viscosity will not remove enough heat from a bearing. In many instances, oil rings will experience speed retardation with oils that are too thick. In that instance, failure risk increases exponentially because the oil ring may swing back-and-forth like a pendulum. If, in addition, an oil ring slews sideways and contacts other surfaces, abrasive particles will definitely contaminate the oil.
6. Sampling alone may help a bit. Violating the other requirements will cause failures. It’s a bit like putting better tires on an automobile while allowing the front end to be out-of-alignment and not replacing cracked rubber boots surrounding the con-vel joints. Better tires alone will be a move in the right direction; however, by themselves the new tires will be a disappointing expense if other causes are not addressed.
7. The attached book list [from The RAM Review] may be of interest to you. Your average API pump repair costs $13,000. Avoiding even a single repair by consulting a $130 book results in 100:1 payback. Does this not encourage reading?
ABOUT THE AUTHOR
Heinz Bloch’s long professional career included assignments as Exxon Chemical’s Regional Machinery Specialist for the United States. A recognized subject-matter-expert on plant equipment and failure avoidance, he is the author of numerous books and articles, and continues to present at technical conferences around the world. Bloch holds B.S. and M.S. degrees in Mechanical Engineering and is an ASME Life Fellow. These days, he’s based near Houston, TX.
Tags: reliability, availability, maintenance, RAM, lube oil, oil sampling, bearings, bearing housings, O-rings