We had a failure of a sleeve bearing on a 400HP motor last week. The inspection revealed a small concentrated wear area with significant groving in the bearing material. Oil analyis was performed in the middle of August and showed a slight increase in wear metals. Iron went from 1PPM to 2PPM, Tin from 1PPM to 6PPM and copper from 1 to 2 PPM. We have 5 of these motors and the only difference in the analysis on the failed bearing was the 2 PPM of both iron and copper. This seems to be a very low threshold for calling a bearing problem so my question is what is the general criteria for sleeve bearing oil analysis? I wouldn't want to pull a motor and send it for a $15KV bearing rebuild based on a 4 or 5 PPM increase in tin. Vibration and acoustics showed indicated normal prior to the failure.
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