Machinery Lubrication

Machinery Lubrication July - August 2018

Machinery Lubrication magazine published by Noria Corporation

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34 | July - August 2018 | www . GREASES "We shoved cable ties into the housing and wiped them off on the mouth of your oil sample bottles." Over the next hour, we both came to the realization that the sampling method was at the heart of the problem. It was likely that the grease that was adhering to the cable ties was "opportunity grease," the material closest to the access plug. As we began to understand how the grease moved in the housing, it became clear that the samples I analyzed were in many cases grease that was not currently active in the lubrication of the valve gears. A few of the "dirty dozen" turned out to be valves that had failed in the past but had since been rebuilt and were operating very well. What we had discovered was old particulate from the previous damage that was not completely cleared from the housing and ended up on the cable tie. We learned a lot through this failed project about the va lve grease and how it functioned in the gearbox, but we learned very little about the condition of the valves. I found that my failure to first address the sampling challenge had resulted in the previous month of my career producing very little actionable data for my company. Several years later, I was afforded the opportunity to participate in a research project for the Electric Power Research Institute (EPRI). EPRI member utilities had identified a need to better understand greases and how they worked in power plant equipment. From this, the Nuclear Maintenance Application Center (NMAC) of EPRI assembled the funding for the "Effective Grease Practices" research project and guideline. Among a number of areas of investigation was a focus on the challenges and best practices for motor-operated valve (MOV) grease sampling and analysis. is gave me the opportunity to determine where my prior efforts to sample MOV grease had gone wrong and share those findings with the industry. Nick Camilli of EPRI provided the insight and leadership that resulted in the construction of an MOV test stand (Figure 1). is test stand allowed us to try various methods of sampling and characterize the movement of the grease in the valve while in operation. Sampling tools and methods were developed that were incorporated into a new ASTM standard for in-service grease sampling (ASTM D7718). Additionally, the test stand was used to create a known higher wear condition to see if this could be detected by the grease sampling and analysis process. After the motor to the gearbox was deliberately misaligned, the result was a clear change in the measured wear content of the grease obtained by the new recommended sampling method, as seen in Figure 2. A fe w ye a rs later, wh i le attending an MOV conference, I overheard some engineers discussing the lubrication of MOV valve stems. Their concern was with short- stroking valves and the challenge in ensuring that an effective coating of grease was being delivered to the valve stem and stem nut when it was impossible to move the stem to expose most of the threads. Why was the application of grease so crit- Baseline Misalignment Linear (Misalignment) Linear (Baseline) Cycles 0 0 100 200 300 400 500 600 700 50 100 150 200 250 300 350 400 450 R 2 = 0.0173 R 2 = 0.7386 Iron Wear (ppm) Figure 2. A grease wear trend in a misaligned MOV gearbox

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