We recently replaced the lube oil (oil in service for more than 8 yrs.) of a C3 compressor train from Total 46 to Total GT 46 which is deemed to perform better. Lube oil tank and piping inspection during oil replacement; reservoir/cooler/pipe internals did not show up any abnormal deposition of contaminant or varnish and was fairly clean. Old used oil TAN was about 0.7 & residual life of oil was still acceptable but the decision to change was made. the gearbox internal inspection also did not reveal any varnish or deposits on gears/bearings during oil replacement.
Whole system was flushed and drained of new oil type once an again new oil was charged through a filtration cart.
1. the oil filter DP started gradually increasing and now resulting in frequent filter replacements. MPC values are in single digit and ISO particle counts are in range of 17/15/12 without any change but filter DP indicates an increase.
2. with increase in oil filter DP, bearing temperatures are also indicating a trend up to level of 3-4 deg C
3. kidney loop filtration with deep filtration or ESP unit is helping to stabilize the issue of oil filter DP surprisingly is even reducing the oil filter DP to normal levels.
4. once kidney loop filtration is stopped again the oil filter DP starts gradual increase!! oil is clean, new no varnish, no particles ..
your comments are highly appreciated. lets take it forward experts.