Clove waste-derived green corrosion inhibitor for API 5L Grade B steel in acidic HCl environment

This study investigates the corrosion inhibition performance and dynamic adsorption mechanism of clove waste extract ( Syzygium aromaticum ) as an eco-friendly organic inhibitor for API 5L Grade B steel in a 0.5 M HCl environment. The primary focus of this work lies in the integrated evaluation of low inhibitor concentrations (15–25 ppm) and prolonged immersion times (12–20 h) to elucidate the correlation between evaluation methods, protection efficiency, and film stability. Inhibition performance was systematically assessed using Potentiodynamic Polarization (PDP), Electrochemical Impedance Spectroscopy (EIS), and Weight Loss methods, while the interfacial characteristics were analyzed through Langmuir adsorption isotherms, Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The experimental results demonstrate that the clove extract effectively reduces the corrosion rate, achieving optimal initial inhibition efficiencies of 98.29% (PDP), 89.92% (EIS), and 98.29% (Weight Loss) at 25 ppm after 12 h of exposure. Electrochemical analyses confirm that the extract functions as a predominantly mixed-type inhibitor that simultaneously suppresses both anodic metal dissolution and cathodic hydrogen evolution. Thermodynamic evaluation reveals standard free energy of adsorption (-ΔG°ads) values ranging between 7.56 and 17.66 kJ/mol, explicitly confirming a spontaneous, physisorption-dominated mechanism driven by weak electrostatic interactions. This physical nature accounts for the high initial surface coverage (θ ≈ 0.98) and the subsequent susceptibility of the film to dynamic adsorption–desorption fluctuations and molecular rearrangements observed at extended immersion periods (16–20 h). SEM and FTIR analyses corroborate these findings, confirming that the mitigation is achieved through a concentration-dependent organic adsorbate layer. The results demonstrate regarding the capabilities and temporal limitations of clove extract, highlighting its functional profile as a bio-based corrosion inhibitor for carbon steel pipeline systems under specific acidic conditions.

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