Long-distance transmission of oil is usually carried out in large-diameter steel pipelines; water present therein may cause severe internal corrosion. An effective method of mitigating such corrosion is to inject organic corrosion inhibitors (CIs). Their surface adsorption, via heteroatom functionalities, can markedly enhance the corrosion resistance of metals. In this study, three CI model compounds with the same alkyl tail length (-C14H29), specifically benzyl-dimethyl-tetradecyl-ammonium (BDTA), tetradecyltetrahydropyrimidinium (TTHP) and tetradecylphosphate ester (TPE) were synthesized, their purities being determined using nuclear magnetic resonance spectroscopy (NMR). The critical micelle concentrations (CMCs) of each compound were measured using surface tensiometry (Du Noüy ring) and fluorescence spectroscopy techniques, and differences were found between these indirect and direct methods. In addition, linear polarization resistance was used to determine inhibition efficiencies (IEs) for carbon steel immersed in a NaCl electrolyte saturated with CO2. CI surface saturation concentrations, with maximum IEs, were compared with the determined CMCs. Excellent IEs were observed at concentrations of TTHP and TPE significantly less than their CMCs. These results imply that there is no direct link between CMC and corrosion efficiency and that the selection of the appropriate CI concentration for an industrial application should not be based solely on CMC. Further work is ongoing to confirm this absence of correlation at higher temperature (T>30°C) and different water chemistry.

Subject
Chemical compounds, Steel surfaces, Water, Corrosion rate, Saturation, Spectroscopy, Micelles, Synthesis, Mixtures, Sodium chloride solution, Phosphates, Corrosion modeling, Corrosion inhibitors
Keywords:
corrosion inhibitors, critical micelle concentrations, inhibition efficiency, surface saturation concentration
© 2021 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2021
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.