Hydrothermal liquefaction represents a promising thermochemical technology for the conversion of wet biomass and biowaste streams into bioenergy products. However, the realization of its full potential is impeded by significant knowledge gaps related to corrosion damage experienced by reactors in the conversion environment. In this study, we investigated the influence of alloying elements on corrosion processes through a combination of thermodynamic calculations and autoclave tests. The impact of various amount of corrodants were also assessed. Our findings indicate that chromium plays a dominant role in corrosion resistance in both Fe-based steels and nickel-based alloys. Additionally, the corrosion resistance of a specific nickel-based alloy, UNS N08825, also depends on the existence of corrodants and amount of chromium present, leading to varying performance in different HTL conversion environments.