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Title: Corrosion behaviour and characterisation of iron and steels in hot flowing Bayer liquors
Author: Lu, Qing
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 1999
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The flow-induced corrosion of steels, in flowing caustic Bayer liquor solutions at high temperatures, has been experienced in Bayer alumina production plants. The use of a rotating cylinder electrode (RCE) in an autoclave facility has been identified by previous workers as a suitable method to simulate the plant conditions. The characterisation of the corrosion behaviour of iron, mild steel and duplex stainless steel was investigated by using a RCE, in the temperature range of 100 to 230C^ and equivalent pipe velocities between 0.84 to 3m/s. Techniques such as, weight loss, polarisation measurement, ac impedance and surface analysis, were used to characterise corrosion behaviour during the experiments and also the corrosion products formed. The corrosion rates measured by weight loss techniques were in agreement with those obtained by using ac impedance measurements. At ISOC^ , the corrosion rates and the surface film morphologies of iron and mild steel have been found to vary significantly with the liquor flow velocity. This is in agreement with the proposed model of the process based on the active dissolution of the metals. However, for duplex stainless steel, the behaviour was different with little change observed between corrosion rates under the conditions studied. Corrosion processes including dissolution accompanied by adsorption, active-passive transition and passivation, were interpreted through a series of equivalent circuits. The combined effect of temperature and velocity on corrosion rate was demonstrated by the construction of corrosion maps for the materials tested. This method may be a useful way of providing a guide to optimise the process conditions in high temperature flowing environments such as those found in Bayer plants.
Supervisor: Stack, M. M. ; Newman, R. C. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available