Lube-Tech
Detecting Insoluble Varnish is Only Part of the Story Micropatch analysis is only part of the story, a few months later we were approached to see if we could detect soluble varnish. Currently, the Membrane Patch Colorimetry Test (ASTM D7843), can only detect varnish that is insoluble. POLARIS Laboratories’® Director of Technical Services, David Swanson, began researching various ways to see how we would be able to detect soluble varnish. The current testing method technique required heating the oil and then immediately placing it in the dark for 72 hours. In order to detect soluble varnish, the oil had to be hot, and the varnish was still suspended. Similar to ASTM D7843, we bake the oil in the oven at 60 degrees Celsius for 23 to 25 hours. Then, 1 drop of oil is placed on a 0.45-micron filtration patch and it is then placed in the dark to dry for 24 hours. Afterwards, we then take a reading of the colour and the CIE ∆ L*a*b* values. No filtering or solvent is utilised during this process, as the goal is to preserve as much of the soluble varnish as possible. By allowing the oil to dry, the soluble varnish will then plate out and be absorbed by the patch (see Figure 10). Up until now, no one has been able to detect the formation of varnish in its early stages. Just imagine the savings on downtime, labour, loss in revenue, maintenance and repairs that can result in this varnish testing. It would prevent serious failures like the one at the Nuclear Power Plant in the UK.
What is Soluble and Insoluble Varnish and why is it beneficial to detect both? Soluble varnish is the precursor that will lead to full-blown varnish formation. When the varnish is suspended in the oil, that is when to begin looking at varnish mitigation. Why? The sooner the varnish is detected, the longer the life of the oil and equipment. Less downtime, loss in revenue, production as well as maintenance and repair cost savings. If soluble varnish isn’t mitigated, in time, the oil will become overly saturated by varnish and begin to fall out
30 LUBE MAGAZINE NO.169 JUNE 2022
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.140 page 5
of solution, plate out and begin its agglomeration process to become insoluble varnish – leading to further operational and mechanical issues. The varnish will stay suspended so long as the oil is hot, however, once the oil has cooled, that is when varnish will plate out and gravitate to the cooler parts of the systems. This can lead to further thermal degradation and an increase in operational temperatures. The cycle is endless and continues to just get more detrimental over time. Therefore, we wanted to provide customers with a solution and the development of soluble varnish detection began. Figures 10 and 11 are some examples of soluble varnish patches.
Figure 10
Figure 11
L*a*b* Values and their significance During the research and development phase, S-MPC was ran alongside samples receiving the standard MPC testing and recorded the CIE ∆ L*a*b*. This allowed us to gather data, analyse it and determine valuable correlations with each MPC test and L*a*b* values. These values can also indicate other types of causes of the varnish and other properties that can identify the type of varnish formation and oil degradation. These values are detected during our reading of the MPC patch, within the CIE ∆ color scale. A description of each L*a*b* value is listed below.
L* (Lightness) the L* value detects the white and black on the colour scale ranging from 0-100. The closer a value is to 100, the brighter/whiter the colour on the patch should be. Values closer to 0 will have a darker colour. A low L* value can indicate one
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