Author : Angeire S. Huggins Gonzalez
Publisher :
ISBN 13 :
Total Pages : 231 pages
Book Rating : 4.:/5 (118 download)
Book Synopsis Galvanic Interactions in Sweet and Sour Environments by : Angeire S. Huggins Gonzalez
Download or read book Galvanic Interactions in Sweet and Sour Environments written by Angeire S. Huggins Gonzalez and published by . This book was released on 2019 with total page 231 pages. Available in PDF, EPUB and Kindle. Book excerpt: Corrosion of carbon steel exposed to aqueous environments containing dissolved carbon dioxide (CO2) and hydrogen sulfide (H2S) is responsible for many failures of equipment and pipelines in the oil and gas industry. Corrosion product films, e.g., iron carbonate (FeCO3) and iron sulfide (FexSy), play a major role in enhancing localized corrosion after breakdown of these films by either mechanical or chemical means. This has been attributed to galvanic effects driven by the difference in open circuit potential (OCP) between steel covered by FeCO3 or FexSy and bare uncovered areas. Upon localized breakdown of the films, a galvanic current flows between the bare metal areas (anodes) and the areas covered with FeCO3 or FexSy (cathodes). Although many studies have evaluated these galvanic effects, there are still some questions remaining related to the cathodic nature of corrosion product films and their role in enhancing localized corrosion. The present study focused on the evaluation of galvanic interactions of iron (Fe) in CO2 and CO2/H2S environments. The corrosion rate and OCP were measured over time for samples under various conditions, corrosion products on those samples were characterized, and galvanic currents were measured between samples exposed to different conditions. The test conditions were selected to favor the formation of protective films. Fe and steel samples were immersed in 1% NaCl saturated with 100% CO2 or 0.1, 1, 10% H2S/balance CO2. The pH of the bulk solution was adjusted to values between 6 and 8, while the temperature was controlled between 20°C and 80°C. Corrosion product layers were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The galvanic interactions were measured using a modified split cell that allowed customization of different environments in each of the half cells, along with simultaneous monitoring of the galvanic current and driving force as indicated by the difference in OCPs. The results indicated that the pH of the bulk solutions plays a major role in the formation of protective FeCO3 scales. Fe exhibited a passive-like behavior when immersed in a solution at 80°C with pH adjusted to 8. The split cell experiments showed that after reaching a passive-like behavior, Fe was cathodic when coupled to samples immersed in a solution with lower pH, and the galvanic current was approximately 2.4 μA/cm2. The galvanic current decreased with increasing temperature and pH gradient between the half cells. The study of artificial couples between Fe electrodes in 1% NaCl solutions saturated with 0.1, 1 or 10% H2S/balance CO2 and with CO2 showed that the galvanic current increased with temperature and %H2S in the gas mixture. At 20°C and 0.1-1%H2S/balance CO2, the FexSy-covered electrodes were cathodic compared to Fe in CO2-saturated solution. At higher temperature and H2S/CO2 ratio, the FexSy covered samples were anodic. The reversal in polarity in the evaluation of temperature, pH and H2S/CO2 ratio suggested that the cathodic or anodic nature of FexSy films may be influenced by the local chemistry in the film/metal interface.