Above: gas turbine fired power plant
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Info Centre >> Fuel and Lube Oil Technical Manual >> 7. Lube Oil - Test Results >> 7.7 Turbine Oil >> 7.7.1 Contamination
Many characteristics of turbine oils are the same as hydraulic oils and in essence they are both doing the same job, although at different rates of shear. Hence the interpretation of the analysis results is similar. Degradation of both types of oil are associated with rising acidity and viscosity. Trend measurement of TAN can identify whether the lubricant is spent, and a check on the viscosity usually confirms this.
An often-overlooked form of contamination in turbine oils is silicones, which exacerbate the problems experienced with air release. As little as 2ppm silicone can dramatically increase the time in which air is released from the fluid. Silicone is sometimes added to oils as an antifoam additive but always at very low levels (<2ppm). At levels above this the effect is reversed.
To effectively lubricate, turbine oil must rid itself of entrained air in as short a time as possible. This only takes place in the oil reservoir and the residence time of the oil here is generally fairly short. Air entrapment causes lack of lubrication at the bearings, which leads to catastrophic failure.
High-speed turbine breakdown can be extremely hazardous, so care with the selection of oil-wetted components is very important, especially high-pressure hoses (which should not be silicone-coated).