Machinery Lubrication

Machinery Lubrication May June 2014

Machinery Lubrication magazine published by Noria Corporation

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26 May - June 2014 | By andy sit ton and thanant sirisithichote, focusl aB VArNIsh the Varnish Issue: strategies for successful and acceptable levels S Several obstacles may be encountered when attempting to measure varnish in turbine or rust and oxidation (R&O) inhibited lubricating oils. Despite the recently published varnish potential test standard (membrane patch colorimetry, ASTM D7842), there are still real challenges to determine an acceptable level of varnish measurement that can provide trouble-free operation as well as an unacceptable level that would warrant taking measures to prevent and remove varnish from lubrication systems. Another obstacle to successful monitoring and establishing proper alarm levels is the constantly changing combination of oil and equipment types. Defining Varnish Varnish is a submicron-sized soft contaminant that is polar in nature. It is thought to be approximately 0.01 micron in size. This extremely small size has led to a whole new area of research called submicron particle counting. As a soft, insoluble contam- inant, it is not clearly definable as liquid or solid. In fact, temperature alone can move it from soluble to insoluble and back again. This makes physical trapping of varnish by mechan- ical means difficult. However, since it is polar in nature and can accept a positive or negative electrical charge, this polarity can be used in attempts to capture varnish. Root Causes The majority of root causes for varnish formation in R&O oils are foaming/air entrainment and bubble implosion, elec- trostatic spark discharges, and additive depletion/ incompatibilities. Adiabatic decompression is the technical term for the bubble implosion that takes place when oil bubbles do not completely rise out of the lubricant (from oil pressure) upon returning to the lubrication reservoir. These suspended bubbles get sent back into active lubrication duty before they have had time to rise and disperse at the surface. They become highly compressed in between gear and bearing surfaces. This can also lead to microdieseling. To understand the dieseling term, think of the main difference between a spark-ignition (gasoline) engine and a compression-ignition (diesel) engine. One uses a spark plug, while the other uses a high pressure/temperature rise as the source of igni- tion. Adiabatic compression causes a high heat source of the air/hydrocarbon monitoring Electrostatic sparking in oil (Ref. Pall Corp.) Samples with different levels of varnish potential 1. Don't purchase oil based on price specifications. Ask the manufacturer and outside third-party consultants for guidelines and seek general industry opinions. Remember, an approved vendor list does not indicate which oil is the best performer or which is the worst performer. 2. Keep the oil clean from the very moment of commissioning in the case of new units. For existing units, keep them clean from the very moment of replenishing oil. The worst assumption you can make is that the oil does not need to be kept clean because it is new oil. 3. Have your machine's oil analyzed to determine if there is an existing varnish problem or the potential for a problem. Apply the appropriate type of varnish-removal system according to your equipment type, oil type and reservoir size. 4. Continuously monitor your oil with a third-party oil analysis service. Do not depend upon "free oil analysis" from an OEM or an oil supplier. Best Practices for Managing varnish

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