- The FT-IR spectrum shows oxidation.
- The acid number (AN or NZ) of the oil increases.
- The color number shows: The oil becomes darker.
- The air release behavior worsens.
- The viscosity increases.
- The RULER values for oxidation inhibitors decrease.
- The cleanliness class for particles > 4 μm increases.
- The solid impurities on a 0.45 μm filter increase.
All values are an indication that increasingly soft particles, mostly of higher molecular weight, are suspended in the oil. When they conglomerate with each other, they easily form deposits on all oil-wetted components in the system. Thus, they can stick together valves and complicate the oil-based control of the turbine. However, the deposits can also cause damage in the filters. Not only is it necessary to change the relatively expensive, fine filter cartridges frequently. Often the impurities are also the reason for electrostatic charging. The following discharge (ESD) causes sparking and local burning of the filter material. Because of the holes caused in the process, the filter loses its effectiveness.
Until now, it has not been possible to predict the risk of deposit formation based on standard tests alone. For several years, the QSA test has been experimented with in the U.S., where a spectrometer is used in an in-house test of an oil laboratory to evaluate filter discoloration. The interpretation of QSA values is very subjective.
OELCHECK therefore began working on the development of an independent standard years ago as a member of an ASTM turbine oil working group. This has the aim to objectively display a forecast of the further available oil application time. OELCHECK is currently the only European service laboratory to offer the MPC test as an additional special test. This test is the only examination method in the world that not only detects the problem-causing insoluble oil residues, but also quantitatively evaluates them.