Varnish and Sludge Potential: Strategies for Successful Gas Turbine Oil Condition Monitoring

One growing concern in power plants nowadays is the presence of one of the lubricant degradation by-products that can affect the lubrication system, which is sludge and varnish. Membrane patch colorimetry (MPC) was performed to determine both soluble and insoluble varnish in used lubricating oil. The varnish potential index (SI-MPC) is the new guideline to evaluate the overall varnish and sludge formation, and it helps in detecting early signs of possible varnish and sludge problems in the system. Viscosity, FTIR, linear sweep voltammetry (LSV), total acid number, and particle count were also performed to monitor the correlation between varnish and sludge formation. The result shows that the early detection of soluble varnish (S-MPC, ΔE 13.0) before it transforms to insoluble varnish can help the power plant make an action plan before the varnish problem becomes worse (I-MPC, ΔE 68.5), and an increase in the varnish potential index also relates to the depletion of antioxidant additive (50.8%) and increased particle count (ISO 21/17/14) of the lubricant. Thus, proper monitoring of soluble varnish (S-MPC), insoluble varnish (I-MPC), and varnish potential index (SI-MPC) can improve the diagnostic and corrective actions for varnish problems in gas turbines.