Influence of Hydrocarbon on Stearic Acid as Corrosion Inhibitor in Synthetic Brine

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Corrosion inhibitors are used for carbon steel pipelines in the oil and gas industry. Based on current
understanding, the inhibitor molecules mitigate corrosion through adsorption to the internal surface of
the pipeline, forming a barrier film that impedes electrochemical corrosion reactions at the metal
surface. Micellization is a key factor of the surfactant distributions.

Product Number: 51323-19330-SG

Author: Susumu Hirano, Tatsuya Sei

Publication Date: 2023

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The role of corrosion inhibitor is explained by the function of surfactant, i.e., partition from oil to water,
dispersion in water and adsorption on metal surface. This study selected stearic acid as a surfactant
and paid attention to the effect of oil on corrosion inhibition. Stearic acid was treated as a single
component corrosion inhibitor. The corrosion inhibitor efficiency of stearic acid was observed in a
metal-oil-water system. An acyclic saturated hydrocarbon, i.e., an alkane was tested as oil because it
has a simple chemical structure. Stearic acid was dissolved in alkanes and injected into a synthetic
brine. The roles of alkane and water were evaluated by measuring corrosion rates of carbon steel. As a
result, the inhibitor efficiency increased, although stearic acid has low solubility in water. This can be
explained by hypothesizing that stearic acid forms mixed micelle with alkane and to disperse into the
brine. The effect was enhanced with the shorter carbon chain length of alkane having higher solubility
in water. The inhibitor efficiency was affected by pH, suggesting that the adsorption of stearic acid
depends on its dissociation in water.