Behaviour of Hastelloy C22 steel in sulphate solutions at pH 3 and low temperatures

Abstract

The behaviour of Hastelloy C22 steel (N06022 UNS) in solutions at pH 3 and different temperatures, for radioactive water reprocessing plants was studied. The corrosion potential was found to increase with temperature. In the neighbourhood of the active-passive potentials, Hastelloy steel was corroded by means of a transient form. In addition, the potentials of the active and transpassive peaks shifted towards more negative values with increasing temperature. The transpassive peak increased with temperature and its potential shifted towards smaller values. The temperature increase led to a reduction of the passive region and a higher current in the passivity. As shown by current instabilities during the backward scan and a higher current than those in the forward transpassivity scan, all of the oxide layer could not be destroyed at the breakdown transpassive potentials. From electrochemical impedance spectroscopy (EIS), apparently the thickness of the passive oxide decreased with temperature in the prepassive region. In passivity, the EIS showed an enhancement of corrosion for higher potentials or temperatures. At the passivity-transpassivity limit potentials, an inductive loop may be the result of adsorption. It was found that the diameter of the capacitive semi-circle and the inductive loop decreased when the temperature increased, indicating an enhancement of corrosion and a decrease in adsorption. The number of active sites and oxidation rate were determined at different potentials.