Corrosion of the Heat-Affected Zones (HAZs) of API-X100 pipeline steel in dilute bicarbonate solutions at 90 °C – An electrochemical evaluation

•Oxygen reduction interference with the 0.05 mV/s active–passive transition.•Lowest passive currents of the 10 °C/s HAZ of a three-time-constant passivation.•Evidence for thin, unstable passivation for the 30 and 60 °C/s HAZs.

This research explores for key correlations between the microstructures of API-X100 steel HAZs, simulated by Gleeble© thermal cycles, and their electrochemical corrosion behavior in dilute bicarbonate solutions at 90 °C. The potentiodynamic polarization revealed the role of ferrite of a HAZ cooled at 10 °C/s with the lowest passive currents, and those of acicular ferrite and martensite of the 30 and 60 °C/s HAZs with unstable, thin passivation. The 0.5 V vs. SCE potentiostatic currents suggested also a slow passivation growth, of repetitive breakdowns and repassivations, for the 30 and 60 °C/s HAZs. EIS equivalent circuits and time-dependent interfaces were proposed for each of the HAZ microstructures.