Failure Analysis of a Heat Exchanger

摘要

The rupture of a heat exchanger inside an inert atmosphere glovebox threatened to damage a radioactively fueled heat source intended to generate electricity on a future US space flight. Because of the potential for damage to heat sources in other gloveboxes, it was necessary to identify the cause of failure. The failure analysis was effected by listing possible causes of rupture and then determining which possibilities were consistent with evidence obtained from the failed heat exchanger. Macroscopic evaluation of the heat exchanger provided information as to the nature of the failure. Scanning electron microscopy and energy dispersive x-ray analysis were used to confirm the failure mechanism. Metallographic sections of both ruptured and deformed tubes gave clues as to the history of the material, as did microhardness measurements. Tensile tests on undeformed tubing provided estimates of strength. Burst tests on similar tubing were used to confirm the validity of the tensile data. Finally, the tensile data were used in models to determine which of the proposed scenarios of failure were most likely. It was concluded that failure had occurred because, periodically during the life of the heat exchanger, both the inlet and outlet valves had deliberately been closed. The subsequent rise in temperature caused expansion of the coolant, and a corresponding rise in hydrostatic pressure occurred which was sufficient to deform the tubing upon each repetition. (ERA citation 11:007058)