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

Abstract

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 (FeCO 3 ) 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 FeCO 3 when the corrosion product exhibits partial coverage of ×65 carbon steel surfaces in an aqueous CO 2 corrosion environment. In this work, we employ density functional theory (DFT) to show that PAH is able to coordinate with both FeCO 3 and the bare carbon steel surface, producing a FeCO 3 -PAH hybrid structure. The surface and chemical properties of a naturally formed FeCO 3 and the FeCO 3 -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). • The PAH molecules adsorb onto the carbon steel surface and corrosion product (FeCO 3 ) via chemisorption and physisorption. • The PAH molecules interact with FeCO 3 through coordination and hydrogen bonding producing a hybrid layer. • The PAH centres of interaction with film-free carbon steel and FeCO 3 film are protonated and neutral amine groups. • The crystal structure and layer thickness of FeCO 3 and FeCO 3 -PAH hybrid layers are characterised and compared.