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The properties of an adsorbed corrosion inhibitor - Tall Oil Fatty Acid (TOFA) imidazolium chloride, on mica, gold and X65 steel were studied using in-situ atomic force microscopy (AFM). Topography images and thickness measurements show that the structure of inhibitor film changes from monolayer to bi-layer as inhibitor concentration exceeds its Critical Micelle Concentration (CMC). Further kinetic study indicates that the developing of a full film takes about 6 hours. Quantitative force measurements were performed to evaluate the mechanical and adhesion properties of inhibitor films. Results show that the stress, needed to physically remove adsorbed inhibitor molecules is of the order of MPa. © 2013 by NACE International.

Electrochemical behavior of localized carbon dioxide (CO2) corrosion of X65 mild steel at 80°C in 0.1, 1.0, 10, and 20 wt% sodium chloride (NaCl) solutions have been investigated using electrochemical techniques including linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). Surface morphology of specimens was observed using scanning electron microscopy (SEM). Pit depth and its corresponding 3D optical measurement were undertaken using infinite focus microscopy (IFM). The results showed that Cl- concentration had only a slight effect on general corrosion rate. It also revealed that increasing Cl- concentration did not accelerate the initiation of localized corrosion; localized corrosion rate did not change with increasing NaCl solution concentrations; and chemical dissolution of corrosion product film could initiate localized CO 2 corrosion. © 2013, NACE International.

During the transportation of wet gas, temperature gradient between the internals of the pipeline and the outside environment leads to the condensation of water vapor. Freshly condensed water is very corrosive and can lead to the so-called Top-of-the-Line Corrosion (TLC). However, a certain fraction of hydrocarbons will co-condense along with the water vapor resulting in two immiscible liquids at the pipe wall with a different wettability and different corrosivity. To elucidate the role of co-condensation, corrosion tests in the absence and presence of hydrocarbon were conducted. In the experiments, hot vapors of water and n-heptane saturated with CO2 were generated and transported through a one-inch internal diameter condenser tube, with 2 carbon steel samples located at the inlet and outlet of the tube. Condensation took place on the inner surface of the tube and was related to the TLC. Corrosion rate was evaluated by the weight loss method. In the absence of co-condensation, corrosion rates increased with water condensation rates. In the presence of n-heptane co-condensation, water condensation rates had less influence on the corrosion rates. Iron carbonate (FeCO3) was observed only in the co-condensation scenario, suggesting the change of the chemistry of condensed water

An atomic force microscopy (AFM) study is presented to investigate the adsorption on mica and gold of a corrosion inhibitor tall oil fatty acid (TOFA) imidazolium chloride in aqueous solution. The formation of a continuous flat layer was observed at half and twice the critical micelle concentration (CMC). The thickness of the corrosion inhibitor films were accurately measured by the height variation between the inhibitor surface and the bare surface where the inhibitor molecules were scratched away using the AFM tip. At half CMC, the film thickness was approximately equal to the length of the surfactant inhibitor molecule, while at twice CMC, the film thickness was twice the molecular length. The latter is consistent with a bi-molecular layer. The mechanical properties of the inhibitor films were studied by quantitatively measuring the force to penetrate the film in the vertical direction and the force to remove inhibitor molecules in the lateral direction. The interfacial inhibitor film significantly changed the surface properties, providing a protective, mechanical barrier, in both vertical (normal) and lateral directions. Calculations based on the radius of the AFM tip showed that 2 and 4 nm thick inhibitor films can provide mechanical resistances of the order of 1 to 10 MPa. The vertical force to penetrate inhibitor films increased with film thickness. The lateral force to remove inhibitor molecules from the surface was over one order of magnitude higher than the normal forces and appeared to be independent of film thickness. As well as the mechanical properties, the kinetics of inhibitor re-adsorption can be measured after scratching inhibitor molecules from the surface.

Surfactant molecules are commonly used to prevent corrosion of steel by acid producing gases such as CO 2 and H 2 S. The mechanical properties of corrosion inhibitor films formed by tall oil fatty acid (TOFA) imidazolium chloride on mica at 0.5 and 2 times the critical micelle concentration (CMC) were studied using atomic force microscopy (AFM). Film thickness was determined by measuring the depth in an area where the inhibitor molecules were removed by scratching with the AFM tip. Internal structures were resolved by comparing film thickness to molecular length. The kinetics of molecular re-adsorption or film formation was also studied using the scratching technique. The vertical force to penetrate the inhibitor films was dependent on film thickness. Forces of 0.3 and 0.8 MPa were determined for mono and bi-molecular layer films of 2 and 4 nm thick respectively. The lateral force to remove inhibitor molecules from the surface was measured at 14-15 MPa, i.e. over one order of magnitude higher. The measurements suggest that inhibitor molecules would not be removed from steel pipe surfaces by the force of fluid flow alone.