Effect of sodium chloride on corrosion of mild steel in CO2-saturated brines

Abstract

Corrosion rates of mild steel were measured in oxygen-free, CO 2 -saturated brines as a function of NaCl concentration employing electrochemical techniques. Decreased corrosion rates were observed as salt concentration increased. However, at high salt concentration (C20 wt% NaCl), corrosion rates were independent of the flow rate of CO 2 -saturated brine. To understand this phenomenon, corrosion surfaces were analyzed by scanning electron microscopy and X-ray diffraction and showed only residual iron carbide for salt concentrations of 0.5-5 wt%. However, at 20 wt% NaCl, a porous corrosion scale with embedded crystals, possibly magnetite, was observed. No iron carbonate was observed and water chemistry showed it was 10,000 times below saturation. A numerical model of corrosion in CO 2 -NaCl systems was able to predict the reduced corrosion rates with salt concentration increase as a consequence of reduced solubility of CO 2 (''saltingout''). However, the model did not predict that corrosion rates were flow-independent at high salt concentration. These results demonstrate that flow-independent corrosion is a consequence of a diffusion barrier created by magnetite scale, present only at high salt concentrations.

Effect of bicarbonate on corrosion of carbon steel in CO2 saturated brines

“…The first observation can be explained by the "salting-out" effect of NaCl in reducing CO 2 solubility (Han et al, 2011a(Han et al, , 2011c: lower dissolved CO 2 at higher salt concentration leads to lower carbonic acid concentration and corrosion rate. The second observation (higher corrosion rate at pH 7-8 in higher salt concentration solution) reflects the increased bicarbonate concentration in the presence of higher salt concentration, resulting in higher corrosion rate.…”

“…However, at pH 6-8, corrosion scale can develop in a few hours. Therefore, corrosion data for bare surface corrosion were collected once the corrosion rate and potential stabilized at around 20 min, long enough to reach steady state and short enough to avoid corrosion scale formation (Han et al, 2007(Han et al, , 2011c.…”

Summary Report on CO{sub 2} Geologic Sequestration & Water Resources Workshop

“…Much of this work has focused on carbonation of cement, including the studies of Kutchko et al (2007Kutchko et al ( , 2008Kutchko et al ( , 2009, Duguid and Scherer (2010), and the Schlumberger group (Barlet-Gouédard et al 2006, Rimmelé et al 2008, Fabbri et al 2009. Corrosion of steel in wellbore environments has received less attention, but includes experimental studies by Carey et al (2010) and Han et al (2011b).…”

CO2 Corrosion of Low Carbon Steel Under the Joint Effects of Time-Temperature-Salt Concentration

“…Han et al also reported decreased corrosion rates with an increase of salt concentration from 0.5 to 20 wt. % (Han et al, 2011). They proposed a model showing that cathodic reactions were decelerated by NaCl but anodic reactions were not significantly affected.…”