An Electrochemical Study of the Effect of High Salt Concentration on Uniform Corrosion of Carbon Steel in Aqueous CO₂ Solutions

Abstract

Uniform C O 2 corrosion of carbon steel facilities is often a major problem when handling produced water in the oil and gas fields. High amounts of dissolved salts are often present in produced water. A limited number of research studies has been conducted on the effect of salt concentration on uniform C O 2 corrosion. In this study, the effect of NaCl concentration on uniform C O 2 corrosion of X65 carbon steel was investigated in C O 2 saturated aqueous solutions using a rotating cylinder system at 30 °C, autogenous pH, and 1 bar total pressure in an NaCl concentration range of 0‒4.27 molality (m) (0‒20 wt.%). With increasing NaCl concentration, the corrosion rate increased sharply and reached its maximum value at ∼0.17 m (1 wt.%) NaCl and then decreased with further increase in NaCl concentration. The observed trend in the corrosion rate with increasing NaCl concentration was primarily a consequence of the change in the cathodic limiting current density, which was the main factor controlling the rate of the overall corrosion process. The additional factor was the change in the rate of the anodic reaction with salt concentration.

Understanding the Role of NaCl Concentration on the Corrosion of Carbon Steel and FeCO3 Formation in CO2-Containing Electrolytes

“…Nevertheless, with further increasing concentrations, 5–30% w/v, a decrease in corrosion rate was observed . Madani Sani et al, also found that under dynamic conditions, at 30 °C, corrosivity increased with NaCl concentration increase and reached a maximum rate at 1% wt NaCl then decreased at greater concentrations (3–20% wt)) attributed to NaCl impact on both CO 2 speciation and electrochemical processes . Fang et al similarly demonstrated that under dynamic conditions, at 20 °C, increasing NaCl concentration (3–25% wt) reduced the corrosivity as electrochemical processes were hindered .…”

“…32 Madani Sani et al, also found that under dynamic conditions, at 30 °C, corrosivity increased with NaCl concentration increase and reached a maximum rate at 1% wt NaCl then decreased at greater concentrations (3−20% wt)) attributed to NaCl impact on both CO 2 speciation and electrochemical processes. 33 Fang et al similarly demonstrated that under dynamic conditions, at 20 °C, increasing NaCl concentration (3−25% wt) reduced the corrosivity as electrochemical processes were hindered. 34 At relatively higher temperatures (i.e., 80 °C), studies generally suggest that, under static conditions, corrosion rates decreased with increasing NaCl concentration (1−10 wt %) for pH <6.6.…”

“…The corrosion of carbon steels due to CO 2 in the presence of NaCl has been widely studied over an extensive range of salt concentrations (i.e., 0.1–25 wt %), most of which were intended to simulate conditions relevant to the oil and gas industry. The impact of pH, temperature, and flow regimes have also been considered. − The majority of studies, however, focused on understanding the severity of corrosion, initiation of localized corrosion attacks, and impact of NaCl on electrochemical processes at relatively low temperatures (20–30 °C) in the absence of FeCO 3 . Few studies have specifically probed the role of NaCl concentrations on the FeCO 3 layer, particularly the nature and characteristics of the crystals and layer formed. …”

Improvement to Water Speciation and FeCO3 Precipitation Kinetics in CO2 Environments: Updates in NaCl Concentrated Solutions

“…Experimental values for K ca were determined by collecting measured pH over different temperatures (5–80 °C) in solutions containing dissolved CO 2 (0.53–0.99 bar) and with various salt concentrations (0.1–25 wt %) from the literature. ,, Equation is plotted against I 0.5 as dots in Figure , where the dotted line is the best fit obtained over the entire range of temperature selected. As can be seen from the figure, rather than the quadratic correlation with I 0.5 as suggested by eq , as well as proposed by the expressions of Oddo and Tomson and Gao, the best fit involves a linear dependency with I 0.5 .…”

“…Figure4. pH comparison between model calculations7 and experimental results12,36,37 at different temperatures.…”