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

Abstract

The formation of FeCO3 was studied as a function of NaCl solutions (1 and 3% w/v), saturated with CO2 (pH ∼ 6) at 80 °C. Individual crystal growth and properties, the formation of films, and the corrosion resistance of C1018 carbon steel were assessed. Immersion experiments were conducted from 6 to 168 h. Monitoring ex situ used the substrate weight loss method with dissolved iron concentration measurements (from bulk solution) by inductively coupled plasma-mass spectroscopy (ICP-MS). After exposure, scanning electron microscope (SEM), X-ray diffraction (XRD), and Raman spectroscopy were employed to understand FeCO3 amorphous/crystalline nature and surface composition. Complementary electrochemical measurements [open circuit potential (OCP), potentiodynamic polarization] were conducted to understand the impact of NaCl on cathodic and anodic processes. The role of NaCl was significantly more nuanced than the general corrosion rates might suggest (initially decreasing with increasing NaCl concentration). The induction time and nature of the FeCO3 formed are strongly influenced by the NaCl concentration. First, increasing NaCl concentration retarded the nucleation of FeCO3 crystals. Second, this same increase also induced crystal ripening and habit modification. Collectively, this leads to a porous, less protective layer of FeCO3.

Effects of Ca2+ Ions on the Localized Corrosion of Carbon Steel Influence of the Associated Anion

“…In our case study, the pH of the solution with 2% NaCl saturated by CO 2 at atmospheric pressure is 4.4. Additionally, it is well-known that solutions containing CO 2 in contact with low-alloy steel create a corrosion product protective layer on the material, basically formed by siderite (FeCO 3 ) [34,35]; however, the presence of certain ions, essentially chlorides, interfere with the formation of the protective layer, causing its dissolution [36] and resulting in an increase in the corrosion rate. Moreover, the presence of Na + promotes the action of chlorides.…”

Contribution of galvanic coupling with TiN, TiAlN, and CrN to the corrosion of steel in neutral and acidic chloride solutions

“…The polarization behavior of the steel in these electrolytes agreed with studies conducted in similar environments. [33][34][35][36][37][38]…”