A traditional oil analysis provides valuable indications as to changes in the lubricant and its effects, providing the maintenance engineer with timely information about any change in viscosity, rising water content, acids in the oil, or contaminants. However, the question of why the darkened oil in our example showed such a high copper content could not be answered with the analysis included in a traditional OELCHECK analysis kit. Instead, the OELCHECK tribologists had to develop an all-new approach. To inspect the gear oil, they employed high performance liquid chromatography (HPLC) for the first time. The HPLC device is normally used to test whether the expected number of inhibitors is still present within a coolant. An inhibitor is added to a coolant to slow down or inhibit chemical or physical changes.
The inhibitors used are azoles like tolytriazole and/or benzotriazole, which protect components with non-ferrous metal-containing surfaces from corrosion. Non-ferrous metal inhibitors are also used to protect surfaces in lubricants. These additives can, however, break down and lose effectiveness as usage time continues. If it is possible to detect the breakdown of these protective ingredients accurately and ahead of time, an impending corrosive attack on the lubricated elements can be identified and documented. Non-ferrous metal inhibitors cannot be identified with an element analysis, FT-IR spectroscopy or other standardised process. With high performance liquid chromatography, however, OELCHECK already has the perfect laboratory device in place. The two synthetic gear oil samples taken at 43,000 and 52,700 operating hours, respectively, were tested together with a fresh oil sample using the HPLC method. The results confirmed the OELCHECK tribologists‘ hunch. The HPLC graph for the fresh oil (blue) shows its high tolytriazol content. A significant decline is evident in the graph for the sample taken after 43,800 operating hours (grey). Finally, after 52,700 operating hours (red), the content of the non-ferrous metal inhibitor tends towards zero. In other words, the wear has already begun. This information about the significant decline in the non-ferrous metal inhibitor at 43,000 operating hours would have made it possible to halt the rising copper wear in time, e.g. by performing an oil change.
Examples in the OELCHECK database, which contains over 3 million data records, shows that increases in non-ferrous metal content can be even more striking. Sample comparisons show that copper and zinc values have risen within the space of fewer than 2,000 operating hours to concentrations of well over 100 mg/kg without a cause being identified. With the HPLC method, OELCHECK now has a method at its disposal for identifying non-ferrous metal wear at an earlier stage. The process itself is relatively expensive due to the fact that after every analysed sample, the device has to be recalibrated with the oil to be inspected; however, these advance warnings will enable damage and cost-intensive repairs to be avoided.