Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1206285
22 | January - February 2020 | www . machinerylubrication.com CONTAMINATION CONTROL Phosphate Ester 1 st Stronger Acid 2 nd Stronger Acids Alkylphenols Alkylphenols Alkylphenols 3 rd Stronger Acids Varnish Varnish Varnish Figure 2. Hydrolysis reactions in phosphate ester fluid Figure 4. Acid titration curves of new, contaminated and in-service phosphate ester fluids Figure 3. Metal soap formation due to the leaching of metals from traditional acid-scavenging media reacting with acids lower prolonged temperatures of 100 to 120 degrees C. erefore, it is recommended to maintain water content of less than 500 ppm and acid numbers below 0.2 milligrams of potassium hydroxide per gram (mg KOH/g). Microdieseling Microdieseling involves compression of an entrained air bubble as it passes through a high‐pressure pump. Upon collapsing, the air bubble releases a high amount of thermal energy, which causes high temperatures in the range of 800 to 1,000 degrees C. ese temperatures break down the phosphate ester fluid into its constituent molecules and lead to fluid darkening. In some cases, microdies- eling may result in the formation of soot and incomplete combustion products. Soot particles are carbonaceous, black and submicron in size. ey may remain in suspension or form deposits and varnish in the system internals. ese particles have the potential to clog servo valves, thus causing severe reliability issues. e presence of soot particles impacts the performance of the acid-scavenging media and the fluid's resis- tivity as well. For this reason, it is crucial to monitor the color of the fluid. Metal Soaps in Phosphate Esters EHC system users frequently employ traditional acid-scavenging media tech- nology such as fuller's earth for faster acid removal. is technology leaches various metals like aluminum, silicon, calcium, sodium and magnesium. erefore, it is important to monitor the fluid's elemental analysis. e leached metals react with acids in the fluid to form soaps, as shown in Figure 3. Metal soaps may be alkaline or neutral. ey generally are insoluble but may dissolve in the fluid based on its condition. When produced, these soaps tend to precipitate and form deposits in the system. ey also affect the fluid's resis- tivity and other performance properties. Systems using fuller's earth often see a decrease in resistivit y upon initial appli- cation of ion-excha nge technolog y. The reduced resistivity is due to the removal of metals from the system. Deploying modern acid-scavenging media technolog y, such as ion-exchange resins, can eliminate existing leached metals and avoid further leaching of metals in the fluid. Condition Monitoring A proactive condition monitoring program is essentia l for successf ully ma inta ining phosphate ester fluids. Traditional oil anal- ysis reports for these types of fluids fall short of providing crucial information about the health of in‐service fluid. Newer or nontra- ditional test methods are recommended to monitor the fluid's health proactively. Acid titration curves, linear sweep voltammetry Leached Metals Acids Metal Soaps Water + + = 400 EP Values (mV) Titration Curves Volume (ml) 300 200 100 Contaminated Phosphate Ester In-service Phosphate Ester Virgin Phosphate Ester -100 -200 -300 -400 0 0 0.2 0.4 0.6 0.8 1