Engineering of corrosion product-polymer hybrid layers for enhanced CO₂ corrosion protection of carbon steel part two: Computational investigation and surface characterisation

Carbon dioxide internal corrosion of carbon steel pipelines remains a major issue that is typically mitigated via the addition of corrosion inhibitors. In specific operational environments, a protective natural corrosion product layer known as iron carbonate (FeCO₃) can evolve on internal pipeline walls, providing comparable corrosion inhibitionefficiency to that achieved from surfactants. However, in some instances, incomplete corrosion product coverage can initiate localised corrosion. In our previous work, we demonstrated the ability of Poly (allylamine hydrochloride) (PAH) to act synergistically with FeCO₃ when the corrosion product exhibits partial coverage of ×65 carbon steel surfaces in an aqueous CO₂ corrosion environment. In this work, we employ density functional theory (DFT) to show that PAH is able to coordinate with both FeCO₃ and the bare carbon steel surface, producing a FeCO₃-PAH hybrid structure. The surface and chemical properties of a naturally formed FeCO₃ and the FeCO₃-PAH hybrid layers are characterised employing scanning electron microscopy (SEM) coupled with focused ionic beam (FIB), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS).