Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/136253
OIL ANALYSIS Oil can be especially electrostatically charged if: • It is formulated with a base oil from Group II or III. • The oil level has dropped too low. • It contains no polarizing (zinc-containing) additives. Electrostatic Discharges and Possible Consequences • The conductivity of the new or old oil is less than 400 pS/m. • It is fed into pipes that are too small. • It is moved with too high a flow velocity. • It produces friction in poorly designed filter elements. • Pipes and hoses are not grounded. • It contains high proportions of undissolved air (bubbles). If the level of electric charge in the system becomes too great, an electrostatic discharge (ESD) will occur. In such cases, microsparks or sparking results. Typically, a crackling or clicking sound will be heard near the filter or in the tank. If the charge is high enough, the discharge could be repeated several times in quick succession. Discharges primarily take place in areas with vastly different material combinations. Modern filters with a high proportion of plastic are often affected. The microsparks caused by a static charge can lead to temperatures approaching 1,000 degrees C. This can be extremely dangerous if the fluids are even slightly flammable. In addition, if hydrocarbon vapors have formed in the tank ventilation area, the system could spontaneously combust. However, when discharge sparks occur within a turbine or hydraulic oilcirculation system, they are normally smothered very quickly by the oil. Nevertheless, these miniexplosions can burn holes in filters or even seriously damage the oil due to increased sludge buildup. Effects on Turbine and Hydraulic Oils In recent years, electrostatic charges and discharges have been occurring more frequently in turbine and hydraulic oil systems. Several developments are responsible for this, including: •Modern hydraulic fluids and turbine oils have become increasingly less conductive because of the global trend to use modern base oils and additives. Previously, turbine oils were based on relatively conductive, lightly refined Group I base oils. Currently, more oxidation-resistant, better refined Group II base oils or even partly synthetic Group III base oils are being used, especially for gas turbine oils. These oils are considerably less conductive. In addition, turbine oils normally contain very few metal-organic additives, which help to prevent the formation of unwanted deposits (varnish). • New systems feature a more compact design with a considerably smaller tank capacity and a proportionally larger displaced volume. 40 May - June 2013 | www.machinerylubrication.com