Abstract

A homologous series of alkyldimethylbenzylammonium chlorides (BAC) was used as a model for a composite commercial corrosion inhibitor formulation. The homologous series consisted of three BACs with C12, C14 and C16 tail lengths. A 10-point, three-component mixture design experimentation was performed to determine the composition for achieving the ‘optimal’ corrosion inhibitor performance. The CMC of each mixture combination (single, binary or ternary) was firstly evaluated using the lipophilic dye Nile Red. The corrosion inhibition performance of each mixture was subsequently determined at the respective CMC in a 1 wt.% NaCl solution under approximately 1 bar partial pressure of carbon dioxide (CO2) at 30°C. In order to calculate the corrosion inhibitor efficiency for each mixture of components, the corrosion rates before and after the injection of the corrosion inhibitor mixture were measured by linear polarization resistance (LPR). The measured CMC values and corrosion inhibitor efficiencies for each mixture were plotted on a ternary diagram and a cubic response curve fitted to each dataset. The ‘peak’ in the mixture CMC response curve and the peak in the corrosion inhibitor efficiency response curve were then compared, and an optimal composition was estimated from the mixture response analysis.

Introduction
Background

Corrosion inhibitors provide a critical barrier to internal corrosion, presenting the most cost-effective form of mitigation and enabling operators to use carbon steel where it would otherwise be impractical. The correct selection and validation of inhibitors is essential to ensure successful field deployment, providing safe and reliable operation. However, the selection and optimization of a corrosion inhibitor for a particular field application is not trivial.

Many corrosion inhibitors are organic amphiphilic surfactants, featuring a hydrophilic head group and a hydrophobic hydrocarbon tail. In solution, the surfactant monomers exhibit adsorption to surfaces, with the hydrophobic tail of each monomer extending into the solution to provide a physical barrier between the substrate and the corrosive electrolyte.

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