• 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.

• For systems with large oil fillings of more than 2,500 liters.
• For an extremely long oil life of more than 10,000 hours.
• For turbine, hydraulic and gear oils. For gas and steam turbines, turbo compressors and blowers.
• For oil circulation systems in the paper industry, steel and rolling mills. For hydraulics and planetary gears (capacities from 500 liters).
• If oil analyses provide evidence of residue formation.
• When first indications arise in practice.

ASTM (American Society for Testing and Materials), which is comparable to DIN, has submitted a draft standard for the MPC test. The ASTM standard does not yet specify how the results or the measured value should be presented.

OELCHECK therefore gives the maximum possible information for the MPC test:

• MPC index: Numerical value between 0 and 100, for turbine oil max. approx. 60. The higher the MPC index, the greater the risk of sludge and varnish-like deposits formation (see limit values table). * Luminance – L: the blackness or whiteness of the residue remaining on the membrane. The lower the L-value, the higher the proportion of black particles in the oil. These may indicate a diesel effect due to too much air in the oil or soot particles generated at "hot spots."
• Red value – a: is influenced by corrosive wear and degraded EP agents. The higher the a-value, the greater the risk from sludge-forming corrosion particles or degraded EP agents.
• Yellow value – b: is influenced by degraded or ineffective oxidation inhibitors and by oxidized base oil components. The higher the b-value, the more susceptible the oil is to sticky deposits.
• Solid contaminants: Weight increase of the filter by filtering off 50 ml of oil. The higher the weight gain, the dirtier the oil.

Obviously, each MPC lab report includes an image of the membrane under study. In addition, the course of the L-value and the a- and b-values in the color spectrum are mapped. Trend monitoring of color values can be used, for example, to assess the effectiveness of a filtration method in removing specific contaminants. For example, if an electrostatic filter method removes mainly the polar oxidation particles, the b-value becomes lower, but the L-value and the a-value do not improve. Additional measures may then become necessary.