BEHAVIOR OF HASTELLOY-C22 STEEL IN SULFATE-SOLUTIONS AT PH-3 AND LOW-TEMPERATURES

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 potentia I was found to increase with temp erature. In the neighbourhood of the active-passive potentials, Hastel loy steel was corroded by means of a transient form. In addition, the potentials of the active and transpassive peaks shifted towards more n egative values with increasing temperature. The transpassive peak incr eased with temperature and its potential shifted towards smaller value s. The temperature increase led to a reduction of the passive region a nd a higher current in the passivity. As shown by current instabilitie s during the backward scan and a higher current than those in the forw ard transpassivity scan, all of the oxide layer could not be destroyed at the breakdown transpassive potentials. From electrochemical impeda nce 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 tempe ratures. At the passivity-transpassivity limit potentials, an inductiv e loop may be the result of adsorption. It was found that the diameter of the capacitive semi-circle and the inductive loop decreased when t he 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.