Nickel-Co nanocrystalline coatings were electrodeposited onto a carbon steel substrate with and without saccharin addition. In the absence of saccharin, current density and adsorption of hydrogen complexes and/or intermediate components were distinguished as two effective parameters causing nanocrystalline electrodeposits. In the latter case, the growth active sites can be blocked easily at low current densities. By increasing the current density, a lower degree of adsorption was associated by a significant increase in surface diffusion of adions resulting in grain growth. Although, the nucleation rate is expected to increase with current density, it seems that the Ni-Co grain size is not reduced by the nucleation rate. Adsorption of saccharin molecules and/or decomposed sulfide species occurred in the saccharin contained bath, resulting in slow surface diffusion of adions. Therefore, finer grains were obtained which produced a smooth morphology instead of the pyramidal forms obtained in the absence of saccharin.
The effects of sand erosion on inhibitor performance have been examined in a flow loop using an impinging jet test cell and different techniques such as long-term weight loss (WL), linear polarization resistance (LPR), potentiodynamic polarization (PDYN), 3-D profilometry, and electrochemical impedance spectroscopy (EIS). Inhibition mechanisms and the relation between inhibitor concentration and corrosion penetration rate are described by the Flory-Huggins, Frumkin, Temkin, and Langmuir adsorption isotherms. Flow loop tests indicated that sand particle erosion can decrease the efficiency of an imidazoline-based inhibitor by removing the inhibitor protective layer from the surface. Therefore, an increased concentration of inhibitor is needed during sand production to achieve the same effectiveness. It was shown that an inhibitor adsorption isotherm can be integrated into a mechanistic model for prediction of carbon dioxide (CO2) corrosion to predict CO2 corrosion rates as a function of inhibitor concentration. Also, the inhibitor adsorption isotherm has been modified as a function of erosivity to predict the effect of erosivity on corrosion inhibition. One novel approach is discussed for predicting the inhibited erosion-corrosion rate based on the modified inhibitor adsorption isotherms combined with mechanistic models for predicting CO2 corrosion rates and sand particle erosion rates.
Erosion-corrosion deterioration of carbon steel in carbon dioxide (CO 2 )-saturated systems with sand is a problem in the oil and gas industry because the combined effects of erosion and corrosion can reduce the protection provided by iron-carbonate scale formation or inhibitors. Oil and gas production can be accompanied by the formation water (typically chloride containing brine). Some effects of chloride concentration on corrosion are not widely known, and this can result in misleading conclusions. The goal of this paper was to contribute to a better understanding of the effects of chloride concentration in CO 2 corrosion. Previous studies reported in the literature and experimental and theoretical studies conducted in the present work have shown that increasing the sodium chloride (NaCl) concentration in solution has three important effects on corrosion results. First, standard pH meter readings in high NaCl concentration solutions require corrections. Second, increasing the NaCl concentration decreases the CO 2 concentration in solution and therefore contributes to a decrease in the corrosion rate. Third, increasing the NaCl concentration increases the solubility of FeCO 3 and therefore reduces the likelihood of forming an iron carbonate scale. High NaCl concentration also decreases the sand erosion rate of the metal slightly by increasing the density and viscosity of the liquid.
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