Water heat pipes were fabricated from 316, 347, and 430 stainless steel, Monel 400, CDA 715, Inconel 600, and Incoloy 800. All of these materials generated varying amounts of hydrogen gas during the first few days of operation. However, as the heat pipes continued to operate, the amount of gas in each heat pipe, excluding 430 stainless steel, decreased by permeating through the heat pipe walls. Inconel 600 appeared to be the most acceptable material for water heat pipes by returning to isothermal operation over a short time period. An equation based on a diffusion dependent mechanism was developed that predicts heat pipe performance recovery rates.

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