Machinery Lubrication

Machinery Lubrication November December 2016

Machinery Lubrication magazine published by Noria Corporation

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24 | November - December 2016 | www.machinerylubrication.com By BryAn JoHnSon, PAlo Verde nucleAr GenerAtinG StAtion As oil or oil additives degrade, they develop varnish and begin to accu- mulate this material within the oil. The amount of varnish carried by or within the oil will progressively increase as the oil continues its service. The oil's carrying capacity for varnish will also fluctuate based on temperature. As the oil becomes satu - rated, this material can settle from the oil and form harmful deposits. Fortunately, varnish can be extracted from oil and measured in a laboratory by its change in color. The ASTM D7843 standard provides requirements for performing membrane patch colorimetry (MPC) testing. However, this test has been found to be biased by exposure to ultraviolet (UV) light. A recent experiment demonstrated that overhead lighting, such as fluorescent lights, can have a similar effect. Therefore, caution is needed to avoid contact with all but incidental light when handling oil samples that will require an MPC test. Increases in MPC measurements of 50 to 100 percent have been demonstrated following several days of exposure to indoor lighting only. As such, seemingly benign sources like fluorescent overhead lighting can dramatically alter MPC varnish test data. For example, one oil sample increased from a measurement of 21 to 41 in a 16-day period due to exposure to fluorescent lighting. Case Study For a comparative study, a single oil sample drawn from a large turbine oil reser- voir was processed for an MPC measurement. The sample was split and placed into light-blocking and translucent sample bottles at the time of sampling. All the bottles were made of high-density poly- ethylene (HDPE). A series of tests was designed to deter- mine the impact of time and temperature with the sample limited to light exposure within the laboratory. Duplicate oil samples were drawn on the same day by the same personnel. One sample was placed into the standard semi-translucent sample bottle. The second sample was drawn into a light- blocking brown bottle. When the samples arrived at the labora- tory for testing, a 90-milliliter subsample was immediately removed from the translu- cent container and placed directly into a dark drawer to match the standard practice. OIL ANALYSIS Oil Analysis Light How Affects Results for Varnish Potential Caution is needed to avoid contact with all but incidental light when handling oil samples that will require an MPC test. OIL SAMPLES TRANSLUCENT CONTAINER MPC LIGHT-BLOCKING CONTAINER MPC As found, after 16 days (pre-heating) 39 26 Heated for 24 Hours at 60°C and Stored in a Dark Location 3 days after heating 38 22 7 days after heating 40 24 14 days after heating 41 26 Reheated Samples 7 days after second heating 40 27 MPC test data and test conditions

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