Influence of temperature and agitation on the electrochemical corrosion behavior of 2.25Cr–1Mo Steel in 0.5 M HCl

Abstract

In this work, the electrochemical corrosion behavior of a 2.25Cr–1Mo low-alloy steel was systematically evaluated in 0.5 M aqueous hydrochloric acid solution under different temperature and agitation conditions. Tests were performed at 25, 45, and 65 °C under stagnant conditions, as well as at 25 °C under controlled agitation of 350 and 700 rpm, using aerated solutions. Potentiodynamic polarization (PDP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) techniques were used for electrochemical characterization. The results show that, under all evaluated conditions, the steel exhibits an active dissolution regime, without the formation of a stable passive region. The increase in temperature significantly accelerates corrosion kinetics, with corrosion rates increasing from approximately 1 mm·year−1 at 25 °C to values ​​on the order of 12–16 mm·year−1 at 65 °C, depending on the electrochemical technique used. Agitation of the medium at 25 °C also increases the corrosion rate, although its effect is less dominant than the thermal effect. Nyquist plots obtained by EIS exhibit a single depressed capacitive arc, consistent with a process controlled primarily by charge transfer at the metal-solution interface. Furthermore, EFM tests show causality factors close to theoretical values, confirming the reliability of the determined kinetic parameters. Comparison of corrosion rates obtained using different electrochemical techniques demonstrates good agreement between the methods. These results provide relevant information for evaluating acid attack on Cr–Mo steels during industrial chemical cleaning processes and for optimizing operating conditions to minimize corrosion damage.