Machinery Lubrication


Machinery Lubrication magazine published by Noria Corporation

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16 | September - October 2020 | www . Deficiencies of membrane patch colorimetry (MPC) test The Varnish Potential Test Ghasem Shilati | Naham Pala Engineering " The high solubility of varnish at different lubricant temperatures makes varnish contamination a complicated problem to tackle. " OIL ANALYSIS API Group II oils have been commonly used in gas turbines during the past two decades. As a result, varnish contamination has been one of the most concerning problems for those who maintain them. These contaminants are sludge-like and sticky compounds that are the result of interactions of phenol and amine antioxidants in the oil environment. e high solu- bility of varnish at different lubricant temperatures makes varnish contam- ination a complicated problem to tackle. Because of this, gas turbines may experience numerous technical difficulties. Currently, the most common laboratory test for detecting varnish potential in the oil is the membrane patch colorimetry (MPC) test (ASTM D7843). Despite its overall value, it still suffers from some shortcomings. Understanding these shortcomings helps analysts prevent otherwise probable errors and mistakes. The Current Testing Method ASTM D7843 is intended to estimate the amount of risk that varnish contamination poses to gas turbine performance. According to this standard, the oil sample should first be kept at about 65° C for 24 hours prior to the test and then left for about 72 hours at 20° C. en a certain volume of the oil sample is diluted by a non-polar solvent such as petroleum benzene and passed through standard membranes with a 0.45-micron pore size. Depending on the amount of varnish contamination in the oil, the standard white membrane will discolor to varying degrees. The intensity of the color created on the membrane is measured by a spectro- photometer and a number ranging from 0 to 100 (in rare cases even above 100) will be assigned as an indicator of varnish potential. Despite the valuable results of this standard, there are some shortcom- ings in current practice. is article will address two of these weaknesses, as noted by two international experts. Observations on the current testing method In 2014 Professor Akira Sasaki authored an article pointing to a major flaw in the ASTM D7843 standard.

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