Prediction of Sludge and Varnish Formation in Base-stock Lubricant Using an Experimental Package

One of the most prevalent problems in the application of lubricants and hydraulic oils is sludge and varnish formation from lubricant degradation. It is believed that thermal degradation is the main reason for sludge formation in lubrication systems. In this study, base-stock lubricant (group I API) underwent the thermal degradation within a temperature range of 90 to 150°C for a period of 1 to 48 hours. In order to obtain a clear justification about lubricant degradation, a new analysis package of experiments consists of FTIR (Fourier Transform Infrared Spectroscopy), viscosity, TAN (Total Acid Number), IFT (Interfacial Tension measurement) and UC (Ultra-Centrifuge) test has been conducted. The results showed that the amount of sludge increases with temperature. Furthermore, all obtained results were analyzed theoretically. We found that when the surface tension suddenly decreases, the amount of sludge in the lubricant has reached its dangerous limit. Since the results of these analyses were a good predictor of sludge production, it can be claimed that the proposed package can be applied for prediction of sludge formation conditions.