Inhibition of erosion corrosion of pipework steel in descaling solution using 5-hydroxytryptamine-based additives: Empirical and computational studies

Mildly HCl (5%) used in formulating acid wash and descaling solution in the oilfield corrodes steel pipework especially at elevated temperatures. 5-Hydroxytryptamine (5-HTM) was tested as alternative non-toxic and eco-friendly anticorrosion additive for protection of steel in 5% HCl at different temperatures. Experimental corrosion monitoring techniques, quantum chemical calculations and molecular dynamics simulations were employed to probe corrosion inhibition, adsorption phenomenon and binding characteristics of 5-HTM to steel surface. It was observed that 5-HTM acts as mixed type inhibitor with domino effect on anodic half reaction. Addition of 5-HTM decreases corrosion current and double layer capacitance but increases charge transfer and polarization resistances. Kinetic, thermodynamic and adsorption parameters were determined and used to further explain the interaction of 5-HTM species with X80 steel surface species. Frontier molecular orbitals energies, ELUMO and EHOMO values reveal high and low electron density sites. At the atomic and molecular levels, interaction and binding energies and mechanism are predicted based on results of geometry optimization, quantum chemical calculations and molecular dynamics (MD) simulations. Some N, O and CC sites in 5-HTM are predicted as active adsorption sites from FTIR, EDS analyses and MD simulations while surface morphology is screened by SEM.