When we opened the bearings of our steam turbine this year we found a coating of varnish. As we opened other parts of the system we found that the coating was throughout the system including valves coolers and tanks. Thinking that the oil was oxidizing due to its age, 15 to 25 years, we sent samples to be tested. The results came back indicating that the oil had very little oxidation, a low oxidation number and the viscosity was similar to new oil. Any suggestions as to what is causing the varnish and what we should look for?
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