Application of inhibitors is an established and cost-effective method to mitigate internal corrosion of mild steel pipelines in the oil and gas industry. Conventionally, surfactant-type organic inhibitors are frequently applied based on their critical micelle concentration (CMC) values and their adsorption to mild steel evaluated based on laboratory tests that show a reduction in corrosion rate. In this work, the relationship between reduction in corrosion rate, CMC and inhibitor surface saturation concentration on mild steel was studied using model quaternary ammonium inhibitors with different alkyl tail lengths. The quaternary ammonium model compounds were synthesized in-house and characterized by 1H-NMR before their use. Their CMCs were determined using surface tension measurements. Results showed that, although the CMC value and surface saturation concentration were the same for two of the inhibitors tested, there was no relationship observed between measured CMC values, surface saturation concentrations, and the calculated corrosion efficiencies for the five model inhibitor compounds tested. Consequently, using CMC values as a measurement for injection of inhibitors might not be considered as a reliable factor.
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Investigation of Corrosion Inhibitor Adsorption on Mica and Mild Steel Using Electrochemical Atomic Force Microscopy and Molecular Simulations
Electrochemical atomic force microscopy (EC-AFM) experiments, including simultaneous linear polarization resistance (LPR) tests and in situ AFM imaging, under a CO2 atmosphere, were performed to investigate the adsorption characteristics and inhibition effects of a tetradecyldimethylbenzylammonium corrosion inhibitor model compound. When the inhibitor bulk concentration was at 0.5 critical micelle concentration (CMC), in situ AFM results indicated nonuniform tilted monolayer formation on the mica surface and EC-AFM results indicated partial corrosion of the UNS G10180 steel surface. At 2 CMC, a uniform tilted bilayer or perpendicular monolayer was detected on mica, and corrosion with UNS G10180 steel was uniformly retarded. Consistently, simultaneous LPR tests showed that corrosion rates decreased as the inhibitor concentration increased until it reached the surface saturation value (1 and 2 CMC). Molecular simulations have been performed to study the formation of the inhibitor layer and its molecular-level structure. Simulation results showed that at the initiation of the adsorption process, islands of adsorbed inhibitor molecules appear on the surface. These islands grow and coalesce to become a complete self-assembled layer.
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- Award ID(s):
- 1705817
- NSF-PAR ID:
- 10416618
- Date Published:
- Journal Name:
- Corrosion
- Volume:
- 78
- Issue:
- 10
- ISSN:
- 0010-9312
- Page Range / eLocation ID:
- 990 to 1002
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5006/4136
