AFRL Develops Money-Saving Methods for Aircraft Fuel Tank Repair

  • Published
  • By Heyward Burnett
AFRL researchers developed a program aimed at reducing the cost of aircraft fuel tank repair. Their research results indicate that using a diethylene glycol monomethyl ether (DiEGME)-resistant coating to line the interior of aircraft fuel tanks decreases repair frequency and, consequently, cost. The new coating requires just a single application, dramatically reducing maintenance costs for aircraft such as the B-52, which presently undergoes fuel tank refurbishment every 4 years, at a cost of $120,000 per aircraft. In terms of the current B-52 fleet size, a projected aircraft service life extending to the year 2040, and the tank's existing 4-year repair cycle, the savings would approach $90 million.

In recent years, the fuel system ice inhibitor (FSII) additive in military aircraft fuel has caused fuel tank topcoat peeling, wherein the protective coating applied to the tank's interior surfaces delaminates. The FSII additive, a DiEGME-based substance, is added to JP-8 and JP-5 jet fuels at concentrations ranging from 0.1% to 0.15%. Because the DiEGME is more volatile than the fuel, its vapors dominate fuel tank headspace in concentrations detrimental to paint. The condition causes the tank's interior coating to swell and peel, and the resulting debris clogs aircraft filters. In turn, the unscheduled maintenance required to decontaminate the filters and repair the tank raises costs and reduces aircraft availability.

AFRL guided the collaborative effort with Applied Coating Technologies, Inc.; Axon Products, Inc.; NIC Industries, Inc.; Boeing; Naval Air Systems Command; and the B-52 Program Office to identify a protective coating resistant to DiEGME. The lab-led research received funding from the Office of the Secretary of Defense Corrosion Prevention and Control Group.

During the first phase of program activity, AFRL worked with commercial coating manufacturers to identify a DiEGME-resistant fuel tank coating compatible with current fuel tank coatings--specifically, BMS 10-39 and AMS-C-27725. Researchers also developed a test method for determining DiEGME resistance, as well as test parameters and requirements for inclusion in the AMS-C-27725 coating specification.

With the second program phase now under way, researchers have applied each of three test coatings to the interior of an active B-52 fuel tank for further monitoring and testing. Each coating will undergo evaluation after 1 year in order to determine its suitability for long-term use. Meanwhile, the researchers will continue to pursue the funding needed for qualifying any promising coating to AMS-C-27725 specification, a process that ultimately authorizes its use aboard Department of Defense aircraft.