Machinery Lubrication


Machinery Lubrication magazine published by Noria Corporation

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20 | January - February 2020 | www . Phosphate ester fluids have been used to control thousands of steam turbines over the last 60 years. With this much user experience, one would assume that their operational challenges would be well-understood and that power plants would be able to maintain the quality of these fluids with ease. On the contrary, phosphate ester fluids are often the Achilles' heel of most lubrication programs. Degradation Modes e primary degradation modes of phosphate ester fluids are hydrolysis and microdieseling. ese fluids may also degrade due to oxidation, thermal degradation and the formation of metal soaps. e cause and effect of phosphate ester fluid degradation in steam turbine electro-hydraulic control (EHC) systems is illustrated in Figure 1. How to Monitor and Maintain Phosphate Ester Fluids CONTAMINATION CONTROL By Greg Livingstone and Jatin Mehta, Fluitec International Phosphate ester fluids are often the Achilles' heel of most l ubrication programs. Figure 1. Degradation modes of phosphate ester fluids in steam turbine EHC systems. Phosphate Esters Degradation Cause Microdieseling Oxidation Hydrolysis Leached Metals Phosphate Esters Degradation Eect Soot Varnish Acids Metal Soaps Hydrolysis Hydrolysis is the most common source of degradation in phosphate esters. High operating temperatures, intermittent steam leaks and the hygroscopic nature of the fluids provide an ideal environment that favors hydrolysis reactions. e saturation limit of phosphate esters at operating temperature is approximately 3,000 to 5,000 parts per million (ppm) of water. During hydrolysis, the fluid produces a stronger and a weaker acid. e stronger acid undergoes a series of reactions, forming subsequent phosphoric acid derivatives and alkylphenols. Temperature, water and fluid are the three prin- cipal parameters controlling hydrolysis reactions, with the consumption of water the limiting factor. ese reactions are autocatalytic and initiate at

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