Boiling mercury corrosion has been studied in natural-circulation once-through 2¼ Cr-1Mo steel loops operating at 315 to 703°C and 300 psi for 5000 h at a flow rate of ≈11.5 kg/h. The corrosion inhibition resulting from the presence of solid titanium or zirconium at the boiler inlet was determined by comparison with an uninhibited loop operating under similar conditions. No boiler corrosion was found in the inhibited loops, but the uninhibited loop had 20–25 µ boiler corrosion.