Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/120548
The key to long-term varnish mitigation is in establishing a system free of varnish and then continuing a process that maintains both the oil and system in this condition. 81% Varnish is the product of a chemical reaction within oil which leads to a new chemistry being created that is different from both the oil and its additives. A prevalent varnish begins as an acid, which is typically caused by a reaction of the oil's additives as they become consumed or the base oil's chemistry as it is degrading. It may also result from a reaction of the oil with other chemistries, which may be present as contaminants within the oil or the system. As with other lubricant-related properties or associated machine conditions, condition-monitoring techniques can be used to assess the accumulation of varnish within oil and manage the detrimental effects that follow. Condition Monitoring Lubricant condition monitoring involves obtaining data that supports an evaluation of the acceptability of the machine performance and the viability of the oil. To date, deposits on lubricated equipment have been the focus with regards to the detrimental effects of varnish. Figure 1 shows examples of bearings with significant varnish accumulation. In general, the alarm and action criteria used within industry are set at levels to avoid power loss or machinery damage but may not include the prevention of varnish of lubrication professionals have experienced problems caused by oil degradation products such as varnish and oxidation, according to a recent poll at machinerylubrication.com deposits. This discounts the effect varnish has on the design and performance of the oil and may allow oil to remain in service when it has exceeded failure criteria. A principal area of lubricant condition monitoring that can often be overlooked is the suitability for continued use of the oil. This type of monitoring determines if the oil is able to meet its design properties. When outside of these criteria, the oil can be considered to be in a failure mode. Unfortunately, this aspect of lubricant condition monitoring appears to have become lost in comparison to the significant machinery impacts seen when varnish is found in turbine systems. If oil condition was the focus of monitoring rather than machine condition, then varnish likely would not progress to the point of accumulation and the oil would be much more capable of meeting its design. This type of lubricant condition monitoring should be emphasized when performing varnishrelated monitoring since oil with a high varnish load can be expected to have critical loss in key design characteristics such as water separability and inhibiting corrosion/rust, foam and air release. Loss of any of these properties can place the system at significant risk. Testing criteria that focus on these properties should be at the forefront of the varnish issue. www.machinerylubrication.com | March - April 2013 | 13