Hydrolyzed polyacrylamide (HPAM) is being used for Enhanced oil recovery (EOR), and increased corrosion rates of carbon steel were observed during corrosion monitoring in flow lines, even though standard corrosion inhibition was applied. Moreover, the corrosion pattern was found to change from acceptable uniform corrosion to critical localized corrosion under polymer back production. Based on these observations, laboratory investigations in an artificial environment simulating flow line conditions were carried out, addressing the influence of HPAM on carbon steel corrosion in the inhibited and non-inhibited fluid. Corrosion data were gained from electrochemical impedance spectroscopy and potentiodynamic scans with a rotating cylinder electrode, and a specific experimental procedure was developed that provides robust and reproducible results. Localization of attack was assessed by accelerating corrosion gently in the potentiostatic mode for some time. It was possible to demonstrate that the interaction of HPAM with carbon steel and corrosion inhibitor may cause a heterogeneous surface state and lead to undesired changes in corrosion processes with locally increased corrosion rates.