In situ SR-XRD study of FeCO3 precipitation kinetics onto carbon steel in CO2-containing environments: The influence of brine pH

Abstract

The growth of iron carbonate (FeCO3) on the internal walls of carbon steel pipelines used for oil and gas transportation can reduce internal corrosion significantly. Solution pH can be considered as one of the most influential factors with regards to the kinetics, morphology and protection afforded by FeCO3 films. This paper presents results from a recently developed in situ Synchrotron Radiation-X-ray Diffraction (SR-XRD) flow cell integrated with electrochemistry for corrosion measurements. The cell was used to follow the nucleation and growth kinetics of corrosion products on X65 carbon steel surfaces in a carbon dioxide (CO2)saturated 3.5 wt.% NaCl brine at 80 º C and a flow rate of 0.1 m/s over a range of solution pH values (6.3, 6.8 and 7). In all conditions, FeCO3 was identified as the only crystalline phase to form. Electrochemical results coupled with post-test surface analysis indicate that at higher pH, larger portions of the surface become covered faster with thinner, more protective films consisting of smaller, denser and more compact crystals. The comparison between XRD main peak area intensities and FeCO3 surface coverage, mass and volume indicates a qualitative relationship between these parameters at each pH, providing valuable information on the kinetics of film growth.

Fundamental aspects of the corrosion of N80 steel in a formation water system under high CO2 partial pressure at 100 °C

“…The coverage of the corrosion scale increased. Burkle 41 was also discussed the morphology and development of the FeCO 3 crystals over time. Burkle stated that the steel surface was almost entirely covered by FeCO 3 crystals aer several hours of exposure.…”

Effects of chloride concentration on CO2 corrosion of novel 3Cr2Al steel in simulated oil and gas well environments

“…As shown in Figure , with the increase in Cl − concentration, the amount of FeCO 3 deposited on the steel surface decreased, and the crystalline character of FeCO 3 also weakened. Some studies have illustrated that the development and morphology of FeCO 3 crystals were closely related to solution pH. The decrease in solution pH considerably increased the solubility of Fe 2+ , resulting in slower precipitation and thus a decreased rate of surface coverage.…”

Iron carbonate formation kinetics onto corroding and pre-filmed carbon steel surfaces in carbon dioxide corrosion environments

“…Dugstad [ 4] suggested that a 'high degree' of super saturation is necessary in the bulk solution to obtain appreciable levels of FeCO3 formation on the steel sur face. However, more recent studies have indicated that enough sur face deposition to provide suppression of carbon steel corrosion rates can occur in systems with a bulk saturation below [2,[5][6][7].…”

“…The ability of FeCO3 to achieve such a dramatic reduction in corrosion rate is believed to be achieved through a surface blocking effect as a result of the crystals being in direct contact with the steel substrate. However, it has also been suggested that the layer acts as a diffusion barrier to electrochemically active species involved in the cathodic reactions [2,3].…”