Abstract
The time-dependent effect of temperature and salt (NaCl) concentration on the corrosion behavior of carbon steel in CO2-saturated environments were explored using various electrochemical techniques coupled with XRD, Raman spectroscopy and SEM/FIB examinations. At constant salt level, corrosion rate increased and stabilized when temperature was below 60 °C. When temperature was higher than 60 °C, corrosion rate firstly increased, reached an apex, and then started decreasing continuously. The magnitude of the decrease is inversely proportionally to the salt concentration, which is then attributed to the microstructure of dual-layer FeCO3 scale. Polarization experiments indicate the anodic process is more affected by salt concentration than temperature while the opposite is true for the cathodic kinetics. Although chloride is not detected in the corrosion scale, it is regarded to have significant influence on the nucleation and growth of FeCO3 and therefore the properties (e.g., thickness and compactness) of the corrosion scales. Lastly, a mechanism is proposed for the evolution of corrosion scales on carbon steel in CO2 saturated environment as a function of temperature and salt concentration.
Highlights
The corrosion of carbon steel caused by dissolved carbon dioxide (CO2) has been recognized to pose a serious threat to the oil and gas industry
Yin et al (2009) investigated the effect of temperature on the corrosion of carbon steel in CO2-saturated NaCl environments. They concluded that temperature affected the crystal size and thickness of the corrosion product layer and both high and low temperatures resulted in small amounts of cementite (Fe3C) and magnetite (Fe3O4) in the corrosion product layer
The depressed capacitive semicircles at high to medium frequency are related to the double layer capacitance and charge transfer resistance, while the inductive semicircles at low frequency can be attributed to the adsorption of intermediate corrosion products (Sun et al, 2012), or the relaxation of water-iron species on the steel surface
Summary
The corrosion of carbon steel caused by dissolved carbon dioxide (CO2) has been recognized to pose a serious threat to the oil and gas industry In our recent study of Cl− concentration on the corrosion behavior of carbon steel at room temperature, the results suggested that corrosion rate increased with decreasing Cl− concentration (Zeng et al, 2016). There was no protective corrosion scale formed at room temperature, and the increasing presence of Cl− resulted in the formation of more porous and non-protective corrosion product films on carbon steel (Liu et al, 2014; Zeng et al, 2016). We investigated the effect of salt concentration (0.001–10 wt.%) on the corrosion behavior of carbon steels (C1018 and C1010) in CO2-saturated NaCl solutions at various temperature levels (25 to 80◦C). A new corrosion scale formation mechanism was proposed based on all the results obtained
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