Analysis of Acid Number in Phosphate Esters by FTIR Spectroscopy

In the nuclear power sector, electricity is generated from the steam generated by large turbines which are highly reliant on efficient electro-hydraulic turbine speed control systems (EHC). These systems offer a wide range of control options and operate at pressures of over 1000 psi to ensure rapid hydraulic response. At these pressures the potential for leaks of hydraulic fluid is greater as is the attendant fire hazard, leading to the use of phosphate esters as the hydraulic fluid of choice. Their selection was based on their auto-ignition temperatures being high, having have a low heat of combustion which makes them self extinguishing as well as having less compressibility, making them more responsive than mineral oils. Although phosphate esters have positive attributes, in operation they have been problematic due to fluid deterioration resulting in poor fluid quality. Once phosphate esters deteriorate significantly, problems arise in the form of operating problems with the EHC, commonly caused by sticky servo valves, which makes them unable to respond to the control system commands governing the emergency and sop valves. According to a study in 1992, 240 EHC failures in the US nuclear industry over a 5 year period, with over half of those resulting in a reactor scram or manual shutdown and about one quarter in a forced power reduction. A more recent study traced these problems to hydraulic fluid quality and the few utilities which did not experience EHC problems had taken ongoing action to ensure that the phosphate ester quality was maintained.