A synthesized pyrimidine derivative with highly efficient long-term corrosion protection for API X60 steel in CO2-saturated NACE brine ID196 under hydrodynamic condition

Abstract

This research investigates the CO2 corrosion inhibition characteristics of a synthesized pyrimidine derivative whose molecular structure is embellished with nitrogen-based functional groups with the intention of achieving highly effective and stable film formation, at low doses, after prolonged corrosion period under turbulent hydrodynamics. For this purpose, 5-(4-(dimethylamino)phenyl)-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d]pyrimidin-4(1H)-one (DPP) was synthesized using the one-pot method, and investigated as inhibitor against the corrosion of API X60 steel after instantaneous and prolonged (72 h) immersion in CO2-saturated NACE ID196 brine under 1000 rpm rotation speed. Results from potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements show that DPP is a mixed-type inhibitor which lowers the double layer capacitance and rate of charge transfer across the steel-solution interface with 97% efficiency. Its instantaneous adsorption blocks the steel surface from any noticeable microstructural damage, based on scanning electron microscopy (SEM) characterization. After prolonged exposure (72 h), the uninhibited steel experiences enhanced resistance, which inversely depreciated the DPP efficiency to > 73%. With DPP, however, the steel is significantly protected against surface microstructural degradation, based on SEM assessment. Computational modeling with density functional theory (DFT) and molecular dynamics simulation (MDS) provided molecular-level confirmation of the experimental results.