Determining the Failure Mechanisms in Water-Absorbing Filter Monitor Elements, 03-9416Printer Friendly Version
Inclusive Dates: 08/25/03 - Current
Background - The aviation industry currently faces a major threat to fuel quality with water-absorbent fuel monitors prematurely failing in the field. Aviation pipelines and airport terminals use water-absorbent monitor elements to remove free water from the aviation fuel during aircraft re-fueling. Recent inspections of monitors in the field reveal that they are potentially performing to only one-third of their advertised life. Industry has performed limited research, with no success, to determine the cause of these failures.
Approach - New and used water absorbent monitors were obtained from manufacturers and a major air carrier. These monitors were evaluated according to API 1583 to determine how they function in accordance with the standardized test method. Results were then compared to determine if the used monitors were actually depleted. Laboratory analysis was performed to determine if the water-absorbent polymer could be detected. Results for both new and used monitors were compared.
Accomplishments - The air carrrier provided used monitors from three manufacturers. New monitors from two manufacturers have been received, and other new monitors are expected. The API flow loop has been re-configured to perform the API 1583 tests.
Scanning Electron Microscope (SEM) images of one of the monitors removed from service indicate the water-absorbent polymer is no longer present. Energy Dispersive X-ray (EDX) and diffractive x-ray were also performed to reveal particulate debris on the monitors. Various clay-like minerals were detected.
Nuclear Magnetic Resonance Spectroscopy (NMR), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimeter (DSC) analysis have been performed on new and used monitors. NMR determines the chemical composition of the polymers, while TGA and DSC analyses determine the quantity of polymer in the new and used monitors. These results support visual data collected from the SEM images.
A literature search indicated that some water absorbent polymers are slightly soluble in aromatic compounds. Aviation fuels contain approximately 25-percent aromatics. An extraction was performed using a toluene/water azeotrope with a new monitor. ICP analysis was performed on both the water and toluene factions. An ion known to be present in this polymer was found in both fractions, indicating aromatic compounds very well may be gradually removing the polymer from the monitor.