Relationship of H₂O and CH4 Supply Rates in HTGR Helium to the Carburization of Hastelloy-X and Alloy 800H

A detailed study of the carburization of Hastelloy-X and alloy 800H in high-temperature gas-cooled reactor helium was made to determine the cause of the wide variability of data generated in retorts. Data for 1000°C and 2500-h exposure show that up to an order of magnitude difference in the carburization levels can be caused by changes in the flow rate of the test gas and/or the position of the corrosion specimen in the gas stream. The results are unambiguously explained by the parameters Ṡ(H₂O) and Ṡ(CH₄), the supply rates of water and methane, respectively.