Effect of FeCO3 Supersaturation and Carbide Exposure on the CO2 Corrosion Rate of Carbon Steel

Abstract

The pH stabilization technique is a widely used corrosion protection method for multiphase gas pipelines with glycol as hydrate inhibitor. It implies to increase the pH by addition of  3 HCO in order to enhance the formation of protective iron carbonate films. The protection mechanism at ~20°C is of concern because the conditions for precipitating protective corrosion film are less favorable compared to higher temperatures due to the increasing solubility of FeCO 3 with decreasing temperature. The scope of the ongoing work is to investigate whether corrosion mitigation of pipelines at ~20°C relies on the formation of protective corrosion films or if the corrosion rate is sufficiently lowered by the elevated pH. This paper discusses the corrosion rate and corrosion potential observed on carbon steel exposed to varying concentrations of  3 HCO and Fe 2+ at 20°C in a 1wt% NaCl and 50wt% glycol solution purged with CO 2 at 1 atm partial pressure. The objective was to promote protective FeCO 3 films by high iron and bicarbonate concentrations and study the effect of supersaturation and variations in iron and bicarbonate concentration. Protective films did not form despite high supersaturation and long exposure times. The reason for this is discussed in light of exposed iron carbide (Fe 3 C) and prerequisites for iron carbonate growth.

Corrosion Behavior of Deep Water Oil Production Tubing Material Under Supercritical CO2Environment: Part 1—Effect of Pressure and Temperature

“…Similar corrosion product morphologies have been observed recently under different experimental conditions. [19][20] Furthermore, it is known that the nucleation and growth of the inner FeCO 3 typically starts at the steel surface because of the highest pH and FeCO 3 saturation values achieved there. 21 This is because of the Fe 3 C layer restricting the transport of acidic species in and ferrous ions out, so the most favorable conditions for the precipitation of a protective FeCO 3 layer are found inside the porous Fe 3 C layer at the steel interface.…”

Corrosion Behavior of Deep Water Oil Production Tubing Material Under Supercritical CO2 Environment: Part 2—Effect of Crude Oil and Flow

“…9 In Part 1 of this study, 7 the presence of iron carbide (Fe 3 C) on the steel surface was detected using XRD analysis. Farelas, et al, 10 and Berntsen, et al, 11 reported as well the presence of a Fe 3 C layer resulting from the preferential dissolution of ferrite over Fe 3 C. Fe 3 C is an electrical conductor 12 and its presence will increase the apparent crosssectional area of the ER element and decrease the element's electrical resistance (Equation [1]), which results in lowering the corrosion rate reading, as is observed in Figure 2.…”

Re‐examining the influence of chloride ions on electrochemical CO2 corrosion of pipeline steels—corrosion of the heat‐affected zones (HAZs) of API‐X100 steel

“…This affects the kinetics of dissolution and in turn the mechanisms the corrosion products precipitate with, and their properties. Depending on the local pH, and on the local and intermediate adsorbents concentrations, (resulting from the dissolution process), and on the applied potentials, the initially carbonate‐based corrosion products precipitate by supersaturation, (Equation (5)), or by direct oxidation, (Equation (6)). …”