Organic acids, such as propionic, acetic, formic and butyric, have been found to be in formation waters of various gas and oil wells that have been chemically analyzed. The most predominant of the acids have been seen to be acetic. Acetic acid, acetate ions, and undissociated acid are of vital consequences in the electrochemical corrosion process of carbon steel in aqueous environments containing carbon dioxide gas. Recently published studies have established that acetate ions increase the cathodic current density associated with H+ diffusion.
Additionally, other related studies have pointed out that both acetic acid and acetate ion increase the corrosion rate of steel. All the studies undertaken about the corrosive effects of acetate on steel have been a success. However, there is no published information regarding the impact of acetic acid on API 5L X52 steel.
Recently, a team of researchers from the National Autonomous University of Mexico (UNAM) and Mexican Petroleum Institute (IMP) determined the effect of acetic acid on the electrochemical corrosion process of API 5L X52 steel samples, immersed in an aqueous solution saturated with carbon dioxide gas and at turbulent flow conditions. Their work is currently published in the research journal, Materials and Corrosion.
The researchers started by setting up a three-electrode system in a cylindrical glass cell filled with the test solution and placed on top of a controlled heating plate. Next, they set the temperature to a specific value and then bubbled nitrogen gas in the test solution to displace dissolved oxygen. Lastly, the employed various electrochemical techniques to determine the effects of acetic acid and turbulent flow on the corrosion process of pipeline steel in aqueous sodium chloride solutions saturated with carbon dioxide gas.
The authors observed that in the carbon dioxide gas-saturated sodium chloride solution, the corrosion kinetics were controlled by the mass transfer of reducible ions. The team also noted that the corrosion kinetics were considerably affected by the acetic acid addition. Furthermore, they discovered that the cathodic limiting current density could be described as the sum of individual limiting current densities for each reducible ionic species, and an independent flow term, associated with the carbon dioxide gas hydration.
In a nutshell, Juan Genesca and colleagues presented an in-depth analysis of the effects of acetic acid on cylindrical coupons of API 5L X52 steel. Generally, they observed that for all the rotation rates tested, the measured values of the limiting current density and the corrosion rate were similar. This indicated that the overall corrosion process could be regarded to be controlled by mass transfer. Altogether, a better understanding of how acetic acid affects and degrades API 5L X52 steel was achieved and presents crucial information for the design of oil and gas well systems.
María Elena Olvera-Martínez, Juan Mendoza-Flores, Francisco Javier Rodríguez-Gómez, Rubén Durán-Romero, Juan Genesca. Assessment of the effects of acetic acid and turbulent flow conditions on the corrosion of API 5L X52 steel in aqueous CO2 solutions. Materials and Corrosion. 2018, volume 69, page 376–385.Go To Materials and Corrosion