Unit tripped on high vibes and also got a low coolant level alarm. Found considerable amount of coolant in oil when sample taken. Have pressurized the heat exchanger to see if leaks in tube or tube sheet, but do not see evidence of tube leak large enough for this much coolant in oil. I'm looking for any other places where this coolant interfaces with lube oil. Any help would be greatly appreciated
Have you used the Cooling Water P&ID (Piping Schematic) drawing to see if there are other ways cooling water interacts with lube oil?
Usually, L.O. pressure in the L.O. heat exchangers (coolers) is higher than Cooling Water pressure, to prevent the possiblity of leakage of cooling water into the L.O., which is less desirable than if L.O. leaked into the cooling water.
You also haven't told what the GE-design Frame 5 heavy duty gas turbine drives: a generator or a compressor or a pump? If it's a generator, then the likely culprit is the L.O. heat exchanger. But, if it's a compressor (natural gas compressor or some other gas in a process plant) then the cooling water might be used for other purposes which could involve L.O. (such as seal oil).
But, the best thing to do is to use the Cooling Water system drawings to investigate what interfaces there are with L.O. and check them all.
It's also possible that your pressurization test wasn't effective or wasn't performed correctly and yielded questionable results.
But, in any case, it's not likely the turbine control system is involved in mixing cooling water and L.O.
Please write back to let us know what you find!