Corrosion behaviour and characterisation of iron in hot flowing Bayer liquors

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 degreesC to 230 degreesC and equivalent pipe velocities between 0.84 ms(-1) to 3 ms(-1) were used in this work. Techniques, such as, weight loss, ac impedance, potential measurements and electron microscopy were used to characterise corrosion behaviour during the experiments and also any surface corrosion products formed. Corrosion rates measured by weight loss were in good agreement with those obtained through ac impedance measurements. The results showed evidence of a peak in the corrosion rate with increasing temperature for iron. Such peaks were also observed as a function of increasing velocity. The effects of these variables were demonstrated by constructing a corrosion map in which regions of "high", "medium" and "low" corrosion rate for the material, under specific conditions, were identified. This method may be a useful way of providing a guide to optimise the process conditions when using materials in high temperature alkaline flowing environments such as those found in Bayer plants.