The Role of Microstructural Iron Carbide Content on Inhibition of Galvanic Coupling-Driven Localized Corrosion Propagation

The resistance of carbon steels to localized corrosion, especially in inhibited environments, might be influenced by their microstructure and composition, particularly the presence of iron carbide (cementite) phases. This study investigates the role of the cementite phase in C1018 and X65 carbon steels on the inhibition of galvanic coupling-driven pit propagation. Using a zero-resistance ammeter setup, galvanic coupling tests were conducted between an anode (pencil electrode) of C1018 and X65 steels and a cathode (C1018 block) in CO2-saturated, 5 wt% NaCl solution at pH 4.5, under produced water conditions at 55°C and 80°C. An imidazolinium-based corrosion inhibitor was applied to assess its effectiveness in mitigating corrosion in these settings. Results showed that increased exposure of the cementite phase compromised the inhibitor’s ability to suppress pit propagation under artificially sustained galvanic coupling. The finding highlights the critical influence of iron carbide content on inhibitor performance in galvanically coupled carbon steel systems. The extent of the pit propagation depends upon the amount of accumulated cementite phase inside the formed pit, the used ratio of anode to cathode surface, and also upon the ability to form a homogeneous corrosion inhibitor film on the corroding surface. Cleaning inside the pit by removing accumulated cementite phase, limited propagation of the pit. With respect to mechanisms, more tests are required to discriminate between the various parameters listed in this paper. Other parameters related to the test setup are also highlighted in this article and shall be covered in future work.