FeCO3 Formation Research Articles

Effects of H2S content on the corrosion behavior of gas storage reservoir injection and production pipeline steel in CO2-H2S environment

The effects of H2S content on the corrosion behavior of gas storage reservoir injection and extraction pipeline steel in a CO2-H2S environment were investigated by surface characterization and ultrasonic thickness measurement. The results show that the corrosion products of gas injection and extraction pipelines under real conditions are more complex. In the CO2-H2S environment, with the increase of H2S content, the corrosion rate of gas storage reservoir gas injection and extraction pipeline steel firstly increases and then decreases. At a partial pressure ratio of CO2 to H2S of 550, corrosion resulted mainly in the formation of FeCO3, FeS2, and Fe3O4, with limited generation of stabilizing protective films. This led to severe localized corrosion, mainly driven by CO2. In contrast, when the CO2 to H2S partial pressure ratio was reduced to 5.2, the corrosion mainly produced Fe7S8, FeS2, and BaSO4, which promoted the formation of a more stable protective film on the inner wall of the tube, while the presence of gums reduced the severity of the localized corrosion and shifted the corrosion control to H2S.

Corrosion behavior of N80 carbon steel in CO2 environments: Investigating the role of flow velocity and silty sand through experimental and computational simulation

The effects of flow velocity and silty sand on CO2 corrosion of N80 carbon steel were studied using a small flow loop. Silty sand does not change the electrochemical characterization of corrosion but reduces the corrosion rate of steel. Under the low flow velocity, silty sand embeds in the sample surface, reducing active area for iron dissolution and delaying the formation of FeCO3 in corrosion product layer. At medium and high flow velocity, silty sand erodes the sample surface, and wall shear stress damages the integrity of the corrosion product layer, but do not lead to greater corrosion rate.

Iron transformation and hydroxyl radical production during mixing surface water and groundwater in the riparian zone: Effects of bicarbonate and surface water-groundwater ratio

The interaction between surface water and groundwater in the riparian zone significantly influences iron (Fe) transformation. This study characterized the Fe mineral composition of sediments collected from the riparian zones upstream and downstream of the Xinglong Dam of Han River, China. The coexistence of divalent (Fe–CO3) and Fe(III) minerals in the sediments suggested varying redox conditions of the riparian zone. Furthermore, the transformation processes of dissolved Fe(II) under different bicarbonate concentrations and surface water-groundwater ratios during the interaction between surface water and groundwater were investigated by laboratory batch experiments to understand the formation of Fe–CO3 and Fe(III) minerals in the riparian zone. The results demonstrated that elevated bicarbonate concentrations (0–20 mM) and surface water ratios promoted the transformation rate and amount of dissolved Fe(II) to solids. The predominant minerals of the formed solid were lepidocrocite, goethite, and Fe–CO3, according to the results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The rising bicarbonate concentration facilitated Fe–CO3 synthesis. The Fe(III) mineral (goethite) was more likely to develop when dissolved oxygen (DO) and bicarbonate concentrations were high. The generated hydroxyl radical (•OH) during dissolved Fe(II) oxidation was also increased with elevated HCO3− concentration and surface water ratio, indicating higher oxidative potential in the riparian zone with higher bicarbonate and surface water ratio. These findings offer insights into the Fe transformation in redox-fluctuating zones.

The CO2 corrosion behaviour of 25Mn2 and 2Cr steels under certain downhole condition

An economical 2Cr steel tubing was prepared for application in a certain downhole corrosion condition, and the CO2 corrosion behaviour was investigated by employing the 25Mn2 steel for comparative study. The corrosion films of the two steels under different corrosion conditions were analysed by optical microscope, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). It is revealed that the corrosion rate of 25Mn2 steel at static solution is about 2.5 times higher than that at the dynamic solution with the flow velocity of 1 m/s, while the corrosion rate of 2Cr steel keeps almost the same. It is found that both steels show two layers of corrosion film at static corrosion, and the corrosion film is mainly composed of FeCO3, α-FeOOH and dotted Fe3C in the inner layer. It is inferred that carbon pickup phenomenon observed in the corrosion film is attributed to the formation of FeCO3, as well as may also be due to phenomenologically the reaction of Fe3C with carbonic acid.

Insight into the role of silty sand in FeCO3 precipitation on carbon steel during CO2 corrosion: Experiments, theoretical simulation and modelling

The role of silty sand in FeCO3 precipitation on carbon steel during CO2 corrosion is investigated. Silty sand has a decreasing effect on the kinetic constant and activation energy to mitigate FeCO3 formation. This effect is more significant with the increase of silty sand content, FeCO3 supersaturation and temperature. This is because silty sand can adsorb Fe2+, repel CO32- and change ions distribution. A new and ultimately more accurate kinetic model for the corrosion layer accumulation rate of FeCO3 considering the effect of silty sand is proposed and verified, presenting an advancement in the understanding and prediction of CO2 corrosion.

Effect of H2S on CO2 Corrosion of Mild Steel in High-Temperature Supercritical CO2 Conditions

The effect of H2S on the aqueous corrosion behavior of mild steel was evaluated at high-pressure and high-temperature (HPHT) conditions at a partial pressure of CO2 of 12 MPa and a temperature of 160°C. The corrosion rate of steel samples was determined by electrochemical and weight loss measurements. The surface and cross-sectional morphology and the composition of the corrosion product layers were analyzed by using surface analytical techniques (scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction). Results showed that the corrosion rate decreased with time and no significant difference was observed in the presence of 1,000 ppm and 2,000 ppm of H2S at HPHT CO2 conditions. Surface and cross-sectional analyses revealed that the corrosion process was governed by the formation of FeCO3 regardless of the presence of H2S. Furthermore, the corrosion behavior of mild steel in these conditions did not depend significantly on flow velocity.

Study of a Local Structure at the Interface between Corrosion Films and Carbon Steel Surface in Undersaturated CO2 Environments.

Industries transporting CO2 gas-saturated fluids have infrastructures made of carbon steel. This is a good material with great mechanical properties but prone to corrosion and potential failure. Corrosion in sweet environments involves the formation of FeCO3 as a corrosion film, which is recognized to play a protective role under certain conditions. This work on the dissolution of corrosion films in sweet environments, under acidic and undersaturated conditions, demonstrates that the effects on the integrity of steel are far more significant than the damage observed on the surface of the corrosion film. Our results prove that dissolution of FeCO3 involved the presence of an amorphous phase, the intermediate formation of FeCl2 or FeCl+, and the presence of a phase with short distance atom-atom correlations. The amorphous phase was identified as a mixture of retained γ-Fe and Fe3C. Partially broken α-Fe and Fe3C structures were identified to prove the damage on the material, confirming the interface zone without evident damage on the corrosion film. Dissolution affected both the α-Fe and FeCO3, with the lattice [102̅] from the FeCO3 crystalline structure being the fastest to dissolve. The damage of steel at the molecular scale was evident at the macroscale with pit depths of up to 250 μm. The impact on the integrity of steel can be, therefore, more drastic than frequently reported in industrial operations of CO2 transport industries that use cleaning procedures (e.g., acid treatment, pigging) as part of their operational activities.

Hydrogen generation by soluble CO2 reaction with zero-valent iron or scrap iron and the role of weak acids for controlling FeCO3 formation

This study points out a new perspective on CO2 sequestration and H2 gas generation in a system of either zero-valent iron (Fe0) or scrap iron along with NaHCO3 and citric acid. Under a high bicarbonate environment, micro-size Fe0 (5–40 g/L) is oxidized at mild anaerobic conditions, generating hydrogen gas with a production rate in the range of 0.09–0.55 g(H2)/kg(Fe0)·h. At the same conditions without bicarbonate, the generation of H2 was negligible. At the end of the reaction, the pH was alkaline so it can be used to absorb CO2. Carbonate ions create a passivation layer on the Fe0 surface, called siderite (FeCO3), that entrapped Fe0 and hindered H2 production. By comparing citric, oxalic, and ascorbic acids for their ability to remove the siderite layer, citric acid was found to be the most effective. In a system of scrap iron-NaHCO3/citric acid, for seven consecutive cycles, it was found that by replacing the media solution with a new media after the end of each cycle and flushing with CO2 in the beginning of each cycle resulted in higher than 85 vol% H2 after one day of exposure and higher than 94 vol% H2 at the end of each cycle.

Effect of a Small Amount of Cr and Mo on Aqueous CO2 Corrosion of Low-Alloyed Steel and Formation of Protective FeCO3 in Near-Saturation Conditions

The effect of a small amount (1 wt%) of Cr or Mo on aqueous CO2 corrosion of low-alloyed steel and the formation of protective FeCO3 corrosion product layers was investigated under controlled water chemistry conditions, where the bulk saturation value of FeCO3 was maintained at near-saturated condition. Changes in CO2 corrosion rate with exposure time were monitored by linear polarization resisitance measurements. The surface morphology and the composition of the corrosion product layers were analyzed by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and transmission electron microscopy. Results showed that the emergence of a continuous Fe3C layer created favorable conditions at the surface of nonalloyed steel (containing no Cr and Mo) for semiprotective FeCO3 to form even though the bulk saturation value of FeCO3 was maintained at near-saturated condition. However, semiprotective FeCO3 was not observed on the surface of 1% Cr steel and 1% Mo steel, but rather discontinuous and porous corrosion product layer was formed. Due to the hydrolysis reactions of Cr3+ and Mo3+, and the discontinuous structure of the corrosion product layers, the surface conditions for 1% Cr steel and 1% Mo steel were not favorable for the formation of FeCO3 under the experimental conditions of this study.

Understanding the local pitting corrosion characteristics of carbon steel in CO2 corrosion environment using artificially machined pits

Carbon steel remains the most commonly used material in CO2 – containing oilfield, and other energy applications. Pitting corrosion is a prominent form of corrosion attack on carbon steel, and linked to the formation of non – protective iron carbonate (FeCO3) films and/or their breakdown. The conditions for local breakdown of FeCO3, and other fundamental aspects of pitting corrosion are still not clearly understood; particularly in relation to the evolution of the local chemistry within active pits. Local distribution of corrosion activities/species is likely to influence FeCO3 formation; evolution and properties to support and/or impede pit propagation. This study investigates the local corrosion environment within an artificially machined pits to understand the local pitting corrosion behaviour. It focuses on the local evolution of FeCO3 and pitting corrosion. Pits with specific geometry on X65 carbon steel samples are exposed to two different environments: pH of 4 and 5.9 for 168 h. Tests were performed at atmospheric pressure and 60 °C in 1 M NaCl solution. Linear polarization technique was implemented in combination with a suite of post-experiment surface analysis: Scanning Electron Microscopy, X-ray diffraction, 3D-profilometry and Raman spectroscopy for assessing overall corrosion rate, localised corrosion products and pitting characteristics. Results show that at both pH levels, more crystalline FeCO3 was formed within the pits than at the top surfaces. The size and compactness of FeCO3 decrease from the base of the pits towards the top surfaces, which correlates with the extent of pitting corrosion within the pit and the spatial variation in the local chemistry.

Modelling of CO2 corrosion and FeCO3 formation in NaCl solutions

The corrosivity of carbon dioxide (CO2) corrosion and iron carbonate (FeCO3) layer formation in sodium chloride (NaCl) solutions (1–12 % w/v) were investigated through electrochemical experiments and modelling. Relying on electrochemical measurements (Potentiodynamic polarisation) and simplified current density expressions (employing only H+ activity), reaction enthalpies (ΔH) and rate constants (Kr) for Fe dissolution, H2 evolution and H2O reduction reactions were estimated over a temperature range of 40–80 °C. Additionally, a revised FeCO3 precipitation rate expression was developed based on a newly derived FeCO3 solubility product (Ksp), integrating the effects of temperature and ionic strength (using activity coefficients). Collectively, this yielded a new CO2 corrosion prediction model accounting for the presence of a developing layer of FeCO3 in NaCl solutions. The model was validated over a broad range of conditions (pH, temperature, pressure and NaCl concentrations) by employing the corrosion rate and FeCO3 characteristics as metrics. Notably, it was shown that the activities of dissolved CO2 and Cl− were not essential to predict the electrochemical response of anodic processes. Furthermore, it was demonstrated that increasing NaCl concentration resulted in a complexly evolving environment where porous, less protective FeCO3 layers were formed.

Removal of Iron Carbide in Turbulent Flow Conditions and Influence of Iron Carbonate Formation in Aqueous CO2 Corrosion of Mild Steel

Iron carbide or cementite (Fe3C) is often classified as a “corrosion product” but it is originally found in the material’s microstructure and, unlike iron carbonate (FeCO3), it is not precipitated on the steel surface. Rather, it represents the leftover steel structure once the ferrite phase has corroded away. Various researchers have found that Fe3C acts as a diffusion barrier between iron and carbonate ions, which aids in the precipitation of FeCO3. Previous studies have also considered various material compositions and microstructures favoring FeCO3 formation. However, the effect of flow has not been considered previously although it plays a critical role in Fe3C adherence to the steel surface as it is a fragile leftover layer. In this study, a ferritic-pearlitic UNS G10180 material was exposed to flow velocities (0.4 m/s, 2 m/s, and 6 m/s) and shear stresses (0.8 Pa, 20 Pa, and 100 Pa) in a thin rectangular flow channel at favorable layer formation conditions (T = 80°C, pH 6.6, initial [Fe2+] = 2 ppm, initial S(FeCO3) ≈ 10). A critical velocity for Fe3C removal was identified, which further prevented the formation of FeCO3, although it is fully expected that its value should depend on the operating conditions.

Ferryl for real. The Fenton reaction near neutral pH.

According to the literature, the Fenton reaction yields HO˙ and proceeds with 53 M-1 s-1 at 25 °C and low pH. Above pH 5, the reaction becomes first-order in HO-, and oxygen atom transfer has been detected, which indicates formation of oxidoiron(2+), FeO2+. These observations, and the assumption that the intermediate [FeHOO]+ decays approximately iso-energetically to FeO2+, allow one to estimate an Gibbs energy of formation FeO2+ of +15 ± 10 kJ mol-1, from which follows the one-electron E°'(FeO2+, H2O/[Fe(HO)2]+) = +2.5 ± 0.1 V and the two-electron E°'(FeO2+, 2H+/Fe2+, H2O) = +1.36 ± 0.05 V, both at pH 7. In the presence of HCO3-, formation of FeCO3(aq) occurs which may facilitate formation of the [FeHOO]+ intermediate, and leads to CO3˙-. At pH 7, the product of the Fenton reaction is thus FeO2+, or CO3˙- if HCO3- is present.

Modelling of Co2 Corrosion and Feco3 Formation in Nacl Solutions

Modelling of Co2 Corrosion and Feco3 Formation in Nacl Solutions

Electrochemical and molecular modelling studies of CO2 corrosion inhibition characteristics of alkanolamine molecules for the protection of 1Cr steel

Effects of alkanolamine molecules on the corrosion inhibition of L80–1Cr steel were studied in a CO2-saturated 1 wt% NaCl solution at well downhole temperatures of 20 and 80 °C. The electrochemical results showed lower corrosion rates at 20 °C, for which corrosion rates were more influenced by the alkanolamine injection. The experimental results and molecular modelling calculations using DFT revealed that alkanolamine adsorption/desorption played a determining role in the kinetics and characteristics of FeCO3 formation. Additionally, the dependency of inhibitor efficiency on both chemical structures and adsorption energy on Fe(110), FeCO3(104) and Fe3C(001) was demonstrated, resulting in the highest efficiency provided by ethanolamine.

Corrosion Behavior and Mechanism of Oil Casing Steel in CO<sub>2</sub> Salt Solution

The influence of temperature, flow rate, PH value, and oxygen content on the corrosion law in the carbon dioxide salt solution of J55 oil casing was investigated by the corrosion weight loss method. The results showed that with the increase of temperature, the corrosion rate of J55 steel first increased and then decreased and the corrosion rate reached the maximum at 100°C. The corrosion rate was closely related to the formation of corrosion products. The increase of the flow rate speeded up the transfer rate of the corrosive medium to the metal surface and hindered the formation of FeCO3 on the metal surface. The corrosion rate was significantly higher than the corrosion rate under static conditions, and as the flow rate increased, the corrosion rate of J55 steel increased accordingly. The increase of the pH value gradually reduced the concentration of hydrogen ions, and cathodic reaction of hydrogen ion depolarization during metal corrosion process was inhibited, and the tendency to form an oxidizing protective film on the surface of carbon steel increased, thereby reducing the corrosion rate of metals. With the increase of oxygen content, there were both hydrogen evolution reaction of CO2 and oxygen absorption reaction caused by O2 in the cathode process. The corrosion rate of J55 steel gradually increased, and at the same oxygen content, the higher the carbon dioxide content, the greater the corrosion rate is.

Electrochemical behaviour of N80 steel in CO2 environment at high temperature and pressure conditions

This study investigates the scale formation behaviour of N80 steel in CO2 environment at different temperatures and immersion time by in-situ electrochemical and surface analysis techniques. It shows that the temperature and immersion time have significant influence on electrochemical behaviour, which is due to the different scales formed on N80 steel surface. The scales formed at 60°C and 90°C are mainly corrosion products. At 120°C and 150°C, the scale consists of CaCO3. The formation of CaCO3 inhibits the corrosion and the formation of FeCO3. CaCO3, formed in 150°C, is aragonite, which provides better protection to substrate for its compact structure.

The electrolyte renewal effect on the corrosion mechanisms of API X65 carbon steel under sweet and sour environments

Sweet and sour services are the most common media found inside the pipelines of petroleum industry. They are one of the main causes of degradation by corrosion that lead to several financial and environmental losses worldwide. They also are responsible for the formation of corrosion products that might play a protective feature on the metal surface diminishing the corrosive processes. However, conditions in the field are not necessarily favourable for the precipitation of protective structures given the physicochemical dynamism inside the pipes. Then, the need to address this issue that occurs inside the tubes becomes crucial for the correct assessment of the development of protective corrosion products hence to give a more realistic approach to the lab conditions. Therefore, this paper presents a methodology to investigate the electrolyte renewal effects on API X65 carbon steel corrosion under CO2 and H2S (thiosulfate) environments at 4,5 bar of pressure, temperatures of 90 °C and 120 °C over 150 h. Electrochemical techniques (LPR and EIS), weight loss and characterizations were conducted in two different average pH, 3,3 and 4,5. The proposed methodology was capable to delay the development of protective scales in renewed media. The corrosion rates were higher for conditions with electrolyte renewal and higher temperature. FeCO3 formation was favoured at high pH and 120 °C whilst FeS structures were dominant at 90 °C. Sulphides were more cracked and uneven in renewed media whereas carbonate crystals presented higher anchorage to the substrate and were able to develop in sizeable diameters. Unrenewed media presented the best electrochemical responses.

Electrochemical Behaviour of Steel in Aqueous Alkanolamines for CO2 capture

Carbon dioxide capture using absorption-desorption by alkanolamines can mitigate carbon dioxide emissions, but corrosion of the steel reactor systems remains a limitation that depends on the amine type. The primary amine, monoethanolamine (MEA), a commonly used solvent for this process, forms carbamate ions (CH2CH2OHNHCOO-)when it absorbs CO2 and has been reported to corrode carbon steel. CO2 absorption in another popular solvent, the tertiary amine, methyldiethanolamine (MDEA), does not form carbamate, but rather hydrogen carbonate ions (HCO3 -), which facilitate FeCO3 formation on steel surfaces (Fig.1), limiting their corrosion rates.The surface reactions on iron in CO2-aqueous alkanolamine solutions were investigated by measuring current transients at an applied potential of -0.350 V vs. SHE at temperatures of 25 – 80 °C, concentrations of 5 and 3 M and various pHs. In aqueous 5 M MDEA solutions, an electrically resistive film formed on iron, evidenced from the sharp decrease in current density to ca. zero (Fig.2); similar behaviour was exhibited in 3 M MDEA(aq). By contrast, current transients measured in aqueous MEA solutions did not decrease sharply. Ex-situ surface characterisation by SEM and EDX detected FeCO3 (Fig.1) on the iron exposed to MDEA, but not on the iron sample exposed to MEA.We shall explain the formation mechanisms of films, if present, and report impedance spectra used to define conditions corresponding to electrically resistive, stable film formation that could be used to inhibit steel corrosion in carbon capture plants. Figure 1

CO2 Corrosion of Carbon Steel: The Synergy of Chloride Ion Concentration and Temperature on Metal Penetration

This paper investigates the synergy of chloride ion concentration and temperature on the general and pitting corrosion of carbon steel in CO2-saturated environments. Experiments were conducted over 168 h in different concentrations of NaCl brines (1 wt%, 3.5 wt%, and 10 wt%) and temperatures (30°C, 50°C, and 80°C) with the aim of elucidating the combined effect of changes in chloride ion concentration and temperature on overall metal degradation, taking into consideration general and pitting corrosion. This also includes a correlation with the formation and properties of FeCO3 corrosion products. Linear polarization resistance was implemented to monitor the electrochemical responses. Corrosion product characteristics and morphologies were studied through a combination of scanning electron microscopy and x-ray diffraction. Pitting corrosion evaluation was conducted through the application of 3D surface profilometry to study pit geometries such as the depth and diameter. The results show that general and pitting corrosion are strongly correlated to the synergistic effects of changing chloride ion concentration and temperature in carbon steel as a result of their combined influence on ferrite (Fe) dissolution and FeCO3 formation. This represents a paradigm shift from the already established mechanisms on chloride ion and temperature effects on passive alloys such as stainless steel. Increasing chloride ion concentration and temperature up to 10 wt% NaCl and 50°C to 80°C, respectively, is observed to increase the rate of Fe dissolution and formation of semiprotective FeCO3 corrosion products, leading to the increased manifestation and severity of pitting corrosion. The results also show that a “threshold chloride concentration” exists at 30°C, above which there is no significant increase in corrosion rate. However, such “threshold effects” were not observed at higher temperatures evaluated in the range of chloride concentration considered in this study.