Machinery Lubrication magazine published by Noria Corporation
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zones. Start by working down the failure mode ranking, beginning with process-critica l machines. Place each failure mode in one or two zones within the DZT. Highly ranked failure modes should be assigned to the green zone. Others may fit within the yellow zone. Lesser-ranked failure modes can be placed in the yellow or amber zones. Let's apply this to a hypothetical example. A high-speed centrifugal compressor has had chronic problems with bearing failures. An FMEA exer- cise ranked varnish and sludge to be the apparent root cause in most cases. e primary root cause was impaired lubricant air-release issues, which was made worse by entrained air sources. Adiabatic compressive heat from the entrained air was the cause of varnish. Figure 3 recasts the DZT to illus- trate how condition monitoring can detect and respond to this type of failure in different ways. e varnish example was used because I've seen the actions and results listed within the table's cells in many real-world cases. Following is a brief description of each of the cells. Cell 1A: Skillful and frequent inspection and oil analysis detect and recognize the aeration problem. The root causes (air induction a nd cros s- c ont a m i n ate d oi l) were eradicated. Cells 2A and 3A: The main difference here is the delayed detec- tion and response to aeration and the need to address the varnish problem that ensued. Early detec- tion prevents varnish. Late detection requires de-varnishing of the oil and machine. is leads to extra costs and extra risk. Cell 1B: Here, a lack of training on varnish and aeration resulted in treating the symptom (degas) and not the root cause (the source of air-re- lease and entrainment problems). Cells 2B and 3B: With the aeration problem undetected and unfixed, the aeration issue quickly escalates into a varnish and sludge problem. Removing the varnish and sludge followed by changing the oil is nothing but a short-term remedy. e root cause remains unchecked, so aeration and varnish will soon return. Cell 1C: While aeration was detected, the haphazard solution of changing the oil and filter did nothing to provide a real solution. How many times do you need to change an oil to fix an air- entrain- ment problem? Cell 2C: e time delay and poor condition monitoring skills lead to advanced varnish being detected but not the root cause. Once heavy varnish potential is present, the compressor's days are numbered. Cell 3C: A bearing failure and teardown revealed oil-way sludge and restricted oil flow to the bearing (starvation). e maintenance staff immediately declare the oil was AS I SEE IT