March 1, 2013

Dissolved Soft Contaminants and Oil Degradation Precursors
by David Doyle, CLS, OMA I & II
Vice President & Operations Manager

The formation of soft contaminants from oil degradation can present significant operational issues to circulating systems, which can compromise equipment reliability and result in considerable maintenance action. Soft particle contaminants form over time as a result of lubricant oxidation and degradation due to water, aeration and foaming, high temperatures, and wear particles acting as catalyst. Micro-dieseling is also a common cause of thermal degradation.


Oil decomposition by-products are the result of lubricant degradation which forms soft polar particles. These soft particle contaminants are very small, often less than 0.1 mm in size, and easily transition in and out of solution, depending upon temperature and pressure.  Soft contaminants are initially soluble at operating temperatures and become insoluble at lower temperatures.

Eventually soft particle contaminants can agglomerate together due to their polar nature and form a thin insoluble film that develops throughout the internals of a machine’s lubrication system over time. The polar compounds are attracted to one another and can begin to accumulate into high molecular weight materials in the oil and deposit onto metal parts as varnish.  Once these soft contaminants begin to agglomerate together they will often condense on valve spools and sleeves, bearing surfaces, gears and other internal surfaces of the lubricant system as a sticky film, causing significant operational impairment of these system components due to varnish formation. Further damage to the system can result by attracting other hard contaminants such as dust and wear metals to component surfaces.


System temperature affects how these soft particle contaminants behave. Hot spots accelerate the formation of these soft particles through oil degradation, and then settle out when the oil temperature decreases during outages. Their polar nature attracts the particles to metallic surfaces in cooler spots, such as valves and coolers. These soft contaminants also have lower thermal stability and tend to bake onto hot surfaces such as journal bearings.


Soft contaminants can be removed during their dissolved and suspended phases to avoid varnish formation using proper filtration practices, which differs from those used for removing particulate contamination. Many times problems from accumulated soft contaminants can manifest themselves with the changeover to a new oil formulation in the system. This could be due to product incompatibility or differences in base stock used in the formulations.


ALS can test for potential issues resulting from soft contaminants with a standardized varnish potential analysis package. This service is beneficial in monitoring the health of hydraulic and turbine oil circulating systems where the lubricant is meant to stay in service over an extended period of time. Corrective action can be accomplished through system design modifications and proper filtration techniques.


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