Electrochemical and kinetic analysis of corrosion of a 1.25Cr–0.5Mo steel in acidic media

Resumen

This work presents an electrochemical and kinetic assessment of the corrosion behavior of a 1.25Cr–0.5Mo steel in 0.5 M HCl under controlled temperature and hydrodynamic conditions, representative of acidic cleaning environments. Potentiodynamic polarization (PDP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) were applied at 25, 45, and 65 °C, and at 25 °C under agitation (350 and 700 rpm), using triplicate measurements. The steel exhibited active dissolution without passivation in all conditions. Corrosion rates increased markedly with temperature, reaching ~13–15 mm·year−1 at 65 °C, compared with ~1.15–1.23 mm·year−1 at 25 °C (static). Agitation at 25 °C accelerated corrosion from ~1.2 mm·year−1 (static) to ~3.5–3.7 mm·year−1 (350 rpm) and ~5.6–5.8 mm·year−1 (700 rpm), indicating a strong hydrodynamic enhancement of mass transport and surface renewal. EIS spectra showed a single depressed capacitive loop, consistent with charge-transfer control; Rct decreased and Cdl increased with temperature and agitation. Corrosion rates obtained by PDP, LPR, EIS, and EFM agreed well. Arrhenius analysis yielded apparent activation energies of ~50–52 kJ·mol−1 across techniques (R2 ≈ 0.99–0.999), supporting a consistent kinetic regime dominated by interfacial charge transfer. These results provide quantitative evidence of the critical impact of temperature and flow conditions on metal loss in hydrochloric acid environments for Cr–Mo boiler steels.