This paper investigates the stability and growth of the passive films on the heat-affected zones (HAZs), of API-X100 pipeline steel, in dilute bicarbonate solutions containing 100 and 300 ppm chloride ions at 363 K. The investigations were carried out by electrochemical methods, and the kinetics and corrosion rates were evaluated. The HAZs were simulated by thermal Gleeble cycles of heating up to 1223 K peak temperature, followed by cooling at 10, 30, and 60 K/s. The 30 and 60 K/s HAZs showed evidence of thin, highly sensitive passive films towards the increased chloride concentration, and evidence of increased charge-transfer resistance over immersion time at the OCP conditions. The corrosion rates of the 30 K/s HAZs, of which acicular ferrite is the main constituent, were the lowest, among other samples, as revealed by the slow 0.05 mV/s potentiodynamic polarization and EIS. The passive films of the 10 K/s HAZ, at the open circuit potentials, were of the highest resistance to deteriorate/facilitate for mass transport.