文摘
In recent years, the fuel system icing inhibitor (FSII) diethylene glycol monomethyl ether (DiEGME) has been implicated in an increasing incidence of peeling of topcoat material in the ullage space of integral wing tanks in the B-52 and other military aircraft. Work has indicated that, for the combination of DiEGME in JP-8 fuel, the icing inhibitor additive can concentrate in the tank ullage and condense at elevated concentrations on cooled tank walls. These high concentrations of DiEGME cause swelling and subsequent peeling of the epoxy-based topcoat. Here, we report on detailed studies of the compatibility of DiEGME and FSII replacement candidate triethylene glycol monomethyl ether (TriEGME) with BMS 10-39 fuel tank topcoat material. Tests were designed to simulate fuel tank wall exposures with subsequent topcoat degradation measured by icing inhibitor uptake analyses and pencil hardness evaluations. The lower volatility of TriEGME relative to the JP-8 fuel components results in it being less able to concentrate in the tank ullage and promote topcoat failure, as compared to DiEGME. This was confirmed with lower additive levels measured in the ullage, condensed vapors, and the exposed topcoat material. The pencil hardness of topcoat material exposed to fuel vapors was significantly improved upon changing from DiEGME to TriEGME exposure. Simulation experiments were able to reproduce the fuel tank topcoat peeling observed in the field as well as determine the conditions (concentration and temperature) required for topcoat degradation.