Surfactants are well known as an active ingredient of corrosion inhibitors; however, the molecular structure and its content of commercial inhibitors are not disclosed to users. The performance of commercial inhibitors was studied by treating the whole aspect of inhibitor as a kind of surfactant. The corrosion rate was measured with an autoclave by using an electrochemical measurement; namely, linear polarization resistance (LPR) in an oil flowline condition solution. Firstly, the corrosion rate was measured only with a corrosion inhibitor, and a hydrocarbon solvent was added afterwards. The decrease of the corrosion rate was observed after an addition of the solvent. Aliphatic, alicyclic and aromatic solvents with different octanol-water partition coefficients, KOW, were tested in the same manner. The inhibitor efficiency was saturated remarkably after the addition of a solvent with high KOW. The synergistic effect with a specific solvent in this test can characterize the hydrophobicity and the adsorption tendency of the commercial inhibitor without close chemical analysis to specify the surfactant in it.
Corrosion inhibitors are used to prevent pipeline corrosion in oil and gas industry. The evaluation of corrosion inhibitors is one of the most important tasks for the corrosion engineers. Corrosion of the metal is suppressed by the inhibitor adsorption on the metal surface. Active ingredients of corrosion inhibitors are, in general, surfactants. A surfactant can adsorb on the internal metal surface of piping and makes a hydrophobic film preventing the contact of water with the metal surface. Most corrosion inhibitors consist of organic solvents and organic compounds. The inhibitor efficiency can be determined by corrosion tests such as weight loss measurements and/or electrochemical techniques under simulated conditions. The recommendation and its feedback on a corrosion inhibitor are exchanged between a laboratory and a field, consequently the experience is acquired for the individual field in a general practice.
