Investigating the corrosion of the Heat-Affected Zones (HAZs) of API-X70 pipeline steels in aerated carbonate solution by electrochemical methods

The electrochemical investigations were carried out to link between the quantities of selected microstructural features, of the weld metal, near-fusion, coarse grain and fine grain HAZs, and their corrosion behavior. The weld and HAZs were made of API-X70 steels by the longitudinally submerged-arc welding process. The electrochemical tests were the potentiodynamic polarization and electrochemical impedance spectroscopy. They were used to evaluate the cathodic reduction, corrosion kinetics, dissolution, the passivation process, and the stability of the passive films – in comparison to the base API-X70 steels – in naturally-aerated solutions containing 0.5 M bicarbonate and 0.01 wt% chloride at 25 °C.