Seven Effects of Varnish on Turbines That Maintenance Teams Should Not Overlook

Technical Explanation

1. Reduced oil flow - Deposits in oil passages or small-bore piping reduce the available flow area, delivering less oil than required to lubrication points.
2. Filter plugging - Soft contaminants and degradation products can block the pores of the filter media, increasing differential pressure and shortening filter life.
3. Servo valve stiction - Varnish is tacky and increases friction between the spool and valve body, causing irregular movement or hysteresis.
4. Sandpaper effect - Sticky deposits can trap hard particles on a surface, creating a sandpaper-like layer that accelerates wear.
5. Reduced heat transfer - Varnish acts as an insulating layer. When it forms on coolers or bearing surfaces, it reduces heat dissipation.
6. Increased bearing wear - Deposits can disrupt the hydrodynamic oil film and increase the likelihood of intermittent metal-to-metal contact.
7. Higher risk of a machine trip - When valve response, bearing temperature, or oil flow moves outside operating limits, a problem that began with minor deposits can develop into an alarm or trip.

Impact on Machinery

• More downtime from frequent filter replacement or valve repair
• Shorter bearing and component life
• Reduced cooling and energy efficiency
• Higher maintenance costs from recurring corrective work
• Greater risk of production loss

Points to Consider

• Evaluate symptoms across multiple locations instead of analyzing each in isolation
• Correlate MPC, particle count, and filter differential pressure with machine condition
• Inspect filters, reservoirs, and components for deposits during inspections
• Perform root-cause analysis before replacing components or selecting treatment

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