Traditionally, varnish build-up has been a problem in hydraulic and turbine applications. For example, sensitive hydraulic and turbine systems can come to an abrupt halt if varnish is undetected. Identifying this threat has previously been limited to physical inspections. Unfortunately, these inspections force system shutdowns resulting in loss of availability and revenue.
The consequences of varnish build-up can be both time-consuming and costly. System failures due to varnish include sticking or seized control servos, restricted oil flow, increased oil temperatures, plugged or partially blocked strainers, overall deposit formation as well as increased wear and component failures. The causes of varnish deposition—which include thermal degradation, severe oxidation and coking—are natural occurrences in the operation of heavy-duty hydraulic & turbine operations. Historically, visual inspections were performed to identify varnish buildup. While traditional oil analysis testing has its value, it has not offered a reliable, cost-effective procedure to identify the presence of varnishing conditions—until now.
Bureau Veritas has developed an innovative program called QSA® (Quantitative Spectrophotometric Analysis) that can accurately determine the likelihood of a used lubricant producing harmful sludge and varnish build-up. The QSA® program is based on a series of new procedures that determine a specific rating for the used lubricant. Based on the lubricant type and the application, this rating allows a trained diagnostician to determine the presence or likelihood of internal sludge and varnish build-up.
There are numerous types of insoluble contaminants found in lubricating systems. Insoluble contaminants are those materials that will not dissolve in oil. The two most general classifications of insoluble contaminants are hard contaminants (dirt, debris and wear particles) and soft contaminants composed of various oil degradation by-products. Varnish originates from the soft contaminants. It is a thin, insoluble film that slowly deposits throughout the internal surfaces of a lubrication system. The degradation process accelerates as the lubricant undergoes continued exposure to air, water, and high temperature.
The presence of varnish in hydraulic and lubrication systems causes a host of serious problems. These include:
Reduced clearance zones affecting lubrication
This often means a transition from full film to boundary lubrication, resulting in increased wear in pumps, bearings, gears and valves
This results in higher energy requirements and can cause stuck or seized valves
Higher operating temperatures
Varnish acts as an insulator, decreasing the cooling effect of heat exchangers
Restriction or impedance of oil flow
Varnish clogs strainers, filters and lines
Increased wear rates
Varnish captures hard contaminants, creating an abrasive surface that accelerates wear
System corrosion and accelerated degradation
Accelerated deterioration due to acidic constituents
Increased maintenance resources and costs
Required to clean varnished systems
All of these factors can contribute to conditions that end in failure. For example, a sticking gas turbine control valve can cause the entire unit to go offline—the potential revenue loss for the utility company can amount to hundreds of thousands of dollars. Or in a manufacturing facility, deposits in an injection-molding control servos may cause the system to malfunction, resulting in damage to finished parts—costing the operation thousands of dollars in time and material.
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|Bureau Veritas Inc.
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