APU diaphragm testing

The Auxiliary Power Unit (APU) fuel (hydrazine) tanks were removed from the Columbia Shuttle during major modification of the vehicle, because of long-term hydrazine compatibility concerns. The three tanks had been in service for 11 years. As part of an effort to determine whether the useful life of the fuel tanks can be extended, examination of the ethylene propylene rubber (EPR) diaphragm and the metal casing from one of the APU tanks was required. NASA Johnson Space Center Propulsion and Power Division requested the NASA Johnson Space Center White Sands Test Facility to examine the EPR diaphragm for signs of degradation that might limit the life of its function in the APU tank and to examine the metal casing for signs of surface corrosion. No appreciable degradation of the EPR diaphragm was noted. A decrease in the tensile properties was found, but tensile failure is considered unlikely because the metal casing constrains the diaphragm, preventing it from elongating more than a few percent. The titanium casing showed no evidence of surface corrosion.