The corrosion modes and extents of three candidate alloys (UNS S31603, UNS S31000 and UNS N06625) was investigated under simulated hydrothermal liquefaction (HTL) conditions. The effect of alkaline catalysts (K2CO3), operating pressure and flow rate on corrosion was also examined. Results indicated that the three alloys underwent general oxidation in hot pressurized water, of which SS 316 exhibited worse corrosion resistance compared to SS 310 and Alloy 625. The addition of K2CO3 resulted in a significant increase in the corrosion rates of the alloys, likely due to the formation of soluble metal hydroxides in basic environment. Environmental loop tests showed that higher operating pressure led to a marginal increase in the corrosion rates of SS 310 and Alloy 625. Increasing flow rate from 9 to 15 had no noticeable effect on the corrosion rates of the alloys in hot pressurized water at 310 C and 10 MPa.