Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/120548
3 days of settling is included in a Membrane Patch Colorimetry (MPC) test to allow varnish material to agglomerate within the oil, which is cooling from its operating temperature. foaming and the oil oxidation rate may be greatly compromised. As system design and operating conditions also vary, their impact should be considered as it relates to the select formula as well. This parameter of additive chemistry adds to existing varnish challenges for both oil performance and service life. In addition, current alarm limits and action criteria focus on the effect of varnish accumulation on lubricated machinery. This approach discounts the impact of varnish on the design and function of the oil as well as the potential effect of this material on other oil failure modes. A more fundamental approach to setting alarm and action limits that includes the impact of varnish on the oil's performance is needed. The criteria should consider when the oil has lost its design performance, and these performance failure modes should be the point of initial action. Laboratory Testing The lubricant condition-monitoring community has developed a laboratory test (ASTM D7843) to assess the degree of accumulated varnish load within in-service oil. This Membrane Patch Colorimetry (MPC) test measures the overall load of varnish type material in the oil sample and includes a threeday settling period to allow varnish material to agglomerate within the oil, which is cooling from its operating temperature. The oil is then filtered through a 0.45micron cellulose patch with the aid of a solvent. Varnish material collects and deposits on the patch. The patch is checked for color, which is influenced by the volume of material deposited. A dark brown color is visible when more varnish from the fluid is on the patch surface. Figure 5 shows side-by-side examples of a split sample of turbine oil that was allowed to sit for a two-week settling time under controlled conditions. The sample on the left was stored in the dark, while the sample on the right was left in the sun. The contribution of the sun is the difference in these samples, which have different colors and very different varnish loads. Alarm Limits and Criteria The lubricant test community is currently using various versions of the color patch test to assess the volume of varnish within oil and the likelihood of damaging deposits occurring. Unfortunately, the test variations in use may scale the color differently and provide differing warning and alarm limits. These differences can lead to significant confusion in the marketplace. www.machinerylubrication.com | March - April 2013 | 17