The flow-induced corrosion of iron, in spent Bayer liquor at high temperatures, was investigated using a rotating cylinder electrode (RCE) in an autoclave facility. A temperature range of 100-230 degreesC and equivalent pipe velocities in the range 0.84-3 m s(-1) were used. AC impedance technique was applied to monitor in situ the entire corrosion process. Corrosion rates measured by a.c. impedance expressed as average 1/R-p were in good agreement with those obtained by weight loss measurements. The results suggest that a.c. impedance is a suitable method to monitor the corrosion process of steels exposed to flowing Bayer liquor at higher temperatures.