An experimental program to investigate the corrosion compatibility of the high temperature thermal energy storage (TES) salts with Inconel‐617 container was initiated at the Thermal Laboratory of the Wright Research and Development Center (WRDC) in 1985. Three fluoride eutectic mixtures: LiF‐MgF2‐KF, LiF‐MgF2‐NaF, and LiF‐MgF2having melting points in the neighborhood of 1000 K and heats of fusion above 750 kJ/kg were chosen. High purity analytical grade component salts were processed in oxygen and moisture‐free inert atmosphere, and meltedin situin the Inconel‐617 containers. The containers were sealed by electron beam‐welding of the end caps thereby evacuating the void volume. The TES capsules thus formed were placed in a tubular vacuum furnace for continuous thermal cycle life testing by cycling them ±100 K from the eutectic temperature every 2 hours. The capsules have successfully undergone 40,000 hours and 10,000 cycles of testing as of April 1990 and continuing on the test. This is believed to be the longest record available on the TES corrosion compatibility data. The present results clearly indicate that careful processing and proper welding are key factors in obtaining a longlife TES salt‐containment system.