Oxide films were formed on A508-3 steel in simulated PWR primary water at the temperature of 561 ± 1 K for 168 hours with zinc and/or aluminum injection. Corrosion behaviors of oxide films were analyzed by electrochemical polarization, electrochemical impedance spectroscopy (EIS), Mott-Schottky plots, photocurrent measurement, scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The results showed that zinc and aluminum simultaneous injection technology decreased the corrosion current density, increased the impedance value, made the oxide film more compact, and affected the semiconductor properties of the oxide film. The increase in zinc concentration improved the corrosion resistance to some extent. ZnAl2O4 phase, with extremely low solubility and high stability, had been detected in the oxide film, this substance changed the composition of the oxide film and effected the corrosion behavior of A508-3 steel.

Passive films were formed on A508-3 steel (A508-3), 304L stainless steel (304L) and Incoloy 800 (In800) with blank/zinc/zinc–aluminum treatments in air at 300 °C. The electrochemical corrosion behaviors of different metals were investigated through potentiodynamic polarization, electrochemical impedance spectroscopy and the Mott–Schottky technique. The morphology and composition of passive films were analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The zinc–aluminum treatment effectively reduced the corrosion current and increased the impedance of A508-3 and 304L, but had a weak effect on In800. The zinc–aluminum treatment reduced the carrier concentration of A508-3 and changed the semiconductor property of 304L and In800. The order of zinc–aluminum treatment for improving the corrosion resistance of three metals was: A508-3 > 304L > In800. In addition, the zinc–aluminum treatment enhanced the density and smoothness of passive films. According to the composition analysis, spinel ZnAl2O4 was formed on three metals; however, the amount of spinel varied with the content of nickel and chromium in different metals, which affected the results of using this technology.

Alloy 508-III steel and 304L stainless steel are often used in pressure vessels found in nuclear power plants, and when both are exposed to boric acid, galvanic corrosion will occur and affect operational safety. The corrosion behavior and galvanic corrosion behavior after pairing these two metals in different boric acid solutions were studied by open circuit potential, polarization curve, AC impedance, zeroresistance ammeter, weight loss and SEM methods. The results showed that the differences in electrochemical properties between the two metals made A508-III act as the anode and 304L act as the cathode to form a galvanic couple that promoted the occurrence of galvanic corrosion. Compared with a single corrosive environment, the corrosion rate of A508-III was significantly accelerated under galvanic corrosion and the surface oxide composition also changed. An increase in the concentration of boric acid solution exacerbated galvanic corrosion. An excessive anodic area could slow down the galvanic corrosion current and quickly stabilize the corrosion. Ultimately, a galvanic corrosion model of A508-III and 304L in boric acid solution was described.