Compatibility Test and Residual Gas Analysis on 4130 Steel and Methanol Thermosyphons

Testing has been carried out to determine the material compatibility of methanol and 4130 steel. This fluid/material combination is of interest for rotating heat-pipe applications associated with cooling of electrical generators. Thermal soaking at 150°C of four methanol thermosyphons made of type 4130 steel was accomplished. Two of the thermosyphons have nickel-brazed joints and two have laser-welded joints. The temperature profiles indicated the generation of noncondensable gases (NCGs) in all four thermo- syphons for a thermal soak test time exceeding 14,000 h. The analysis showed that the NCG-generation rate accelerated up to 7.4 /xl/h initially and then dropped to a nearly constant rate of 2.5 /nl/h. Three NCG-generating regions were identified: accelerating, decelerating, and stable. The qualitative residual gas analysis using a mass spectrometer after 4000, 8700, and 14,000 h of thermal soak indicated the existence of the NCGs: hydrogen, formaldehyde, methane, and carbon monoxide. The corrosion and oxidation theory-based passivating film growth model and methanol catalytic decomposition model were qualitatively supported by the decelerating and stable regions defined in this experiment. It was also shown that burping is not a viable option to prolong the contaminated heat-pipe's life. Data obtained will provide important information for determination of the life and reliability of a rotating methanol heat pipe made of 4130 steel, and also, for the evaluation of the assembly processes used for fabricating rotating heat pipes.