Info Centre >> Fuel and Lube Oil Technical Manual >> 7. Lube Oil - Test Results >> 7.7 Turbine Oil >> 7.7.3 Gas Turbine Oil
Gas Turbine Oil
Gas turbine oil is usually derived from aircraft turbines and is often used in naval or other high speed vessels (hence the term aero-derivatives). The main additive types used in gas turbine oil are oxidation inhibitors, which prevent the oil from ageing prematurely. Very highly-refined base oils must be used and synthetics are often specified for the lighter viscosity grades. The viscosity of gas turbine oil is usually between 2.5 - 30 cSt @ 40°C.
Steam Turbine Oil Technology
In general, industrial gas turbine system oil requirements are satisfied by steam turbine oil technology. Viscosity grade selection is largely determined by any associated transmission gearing as for steam turbines. The major difference between the way in which the oil is required to work between steam and gas turbine is that a gas turbine lubricant will be operating in a ‘dry’ environment unless water is entering the system via leakage.
Oil Temperature
Within the gas turbine oil, there is at least the potential of increased stress via oxidation because of the higher cycle temperatures across a gas turbine. Typical oil temperature at full load often exceeds 200°C. Control of oil temperature and flow at critical points within the system can however limit oxidative stress. Stress of the oil due to oxidation will be evident as a rise in viscosity and TAN.
Generally the same default limits apply as for hydraulic oils. It should be particularly noted, however, that some equipment may be more sensitive to viscosity change (especially viscosity reduction) and water contamination and lower default limits may apply. Synthetic oils are susceptible to acidification from water contamination.