167 Expo Road
Fishersville, VA 22939
(T) 800-447-7747 (F) 540-337-4901
AS the EHC system ages, varnish is deposited on the inner walls of the piping, valves, actuators and system components. The varnish is generally a very hard, tenacious deposit that is accumulated over time. Varnish can occur in oils that appear healthy and clean, with no visible signs for concern through normal oil analysis. It cannot be identified by the typical in-service turbine oil tests. Low total acid number (TAN), a low ISO particle count and a high RPVOT does not guarantee that the lubricant is immune from varnish. The varnish deposits that form on machine surfaces cause numerous operational issues by interfering with the reliable performance of the fluid and the machine’s mechanical movements. They can also contribute to wear and corrosion or simply just cling to surfaces.
Other potential problems include: restriction and sticking in moving mechanical parts such as servo or directional valves, servovalve failure, increased component wear due to varnish’s propensity to attract dirt and solid particle contaminants, loss of heat transfer in heat exchangers due to varnish’s insulation effect, catalytic deterioration of the lubricant, plugging of small oil flow orifices and oil strainers, increase of friction, heat and energy because varnish acts as a heat insulator, reduction in filter efficiency and potential filter plugging, damage to mechanical seals, increased maintenance costs due to cleanup and discard of oil.
FLUSHING, CHANGING FLUID AND ELECTROSTATIC PURIFICATION/ IONIC EXCHANGE FILTERING SYSTEMS WILL NOT REMOVE ALL VARNISHING, nor in any way will it help worn parts, such as cylinder piston rings that lead to internal leakage, another contributing factor to varnishing. The only way to remove the varnish from your system in conjunction with proper filtration, fluid monitoring and some of the above ideas is to remove the hydraulic controls such as the cylinders and servovalves from the turbine and have them disassembled, extensively cleaned, re-sealed, worn parts replaced, and machine honed to remove the baked in varnishing, a process that ServoCon ALPHA has perfected. This is normally done during an outage.
While ServoCon ALPHA is disassembling, inspecting, taking photos of as found parts, extensively cleaning, machine honing baked in varnish, replacing seals and worn parts, you should drain old fluid from turbine, thoroughly clean reservoir tank, flush hydraulic lines and hoses and install new filtered/test fluid. It is important to maintain the proper OEM filter recommendations after the units have been re-installed on steam turbine.
Brian K. Supinger