CO2 Corrosion Mechanism Research Articles

Ex‐situ synchrotron X‐ray diffraction study of CO2 corrosion‐induced surface scales developed in low‐alloy steel with different initial microstructure

The CO2 corrosion-induced scale developed in the surface region of the low-grade carbon steel is thoroughly investigated to understand the corrosion mechanisms involved during exposure to CO2-saturated aqueous environments. In this work, in addition to the electron microscopy and lab-source X-ray diffraction (XRD) methods, ex-situ depth-resolved phase identification of the corrosion scales developed on steel with different initial microstructures is performed using synchrotron grazing incidence XRD at different incidence angles. The CO2 corrosion mechanism is discussed considering the observed distribution of the corrosion products formed at a different depth relative to the time of electrochemical exposure of the steels.

Failure analysis of CO2 corrosion of natural gas pipeline under flowing conditions

The CO2 corrosion mechanism of pipelines is a controversial topic, especially under flowing conditions. In this work, the CO2 corrosion behavior of X80 steel under static and flowing conditions was studied by the electrochemical measurement and computational fluid dynamics (CFD). The results showed the CO2 corrosion was controlled by charge transfer in static conditions and mass transfer in flowing conditions. Localized damage of corrosion product film under flowing conditions is caused by CO2 bubble cavitation rather than wall shear. The failure process under flowing conditions can be divided into three stages: localized corrosion, bubble cavitation-film rupture and enhanced localized corrosion. The corrosion behaviors of CO2 under static and flowing conditions were described, and the corrosion mechanism was expounded.

Simulation of CO2 Corrosion of Carbon Steel in High Pressure and High Temperature Environment (HPHT)

In HPHT environments, the mechanism of CO2 corrosion faces a challenge as an effect of chemical-physical reactions on the metal surface. The presence of other elements in the CO2 system complicates corrosion behavior. To provide a realistic mechanism for corrosion process, some corrosion prediction models have developed software using fundamental theories such as electrochemical reactions and thermodynamics theories. Existing methods to predict corrosion rate models in HPHT environments have shown reasonable results. This paper reviews software of corrosion predictions which calculate corrosion rate based on mechanistic theories that study effects of H2S, acetic acid (HAc) concentrations, shear stress, pH in temperature from 25oC – 100oC and pressure from 1–10 bar. From the simulation, corrosion rate increased significantly in the high pressure CO2 environment. Corrosion rate at pH 4 increased to 30 mm/y at a temperature from 15oC to 90oC. While at pH 8 corrosion rate reached 4 mm/y. This lower corrosion rate indicated a tendency for deposits formation at higher pH. Corrosion rate behaves in a different mechanism at high temperatures. The corrosion rate decreased to 4 mm/y when the temperature increased to more than 90oC. Effects H2S gas and HAc were identified to increase corrosion rate. Both elements provide extra cathodic reaction and create limiting current density in the cathodic reaction process based on polarization sweep models. However, the polarization graph calculated using corrosion models could not display passive behavior in the anodic polarization process. Thus, further, improvement should be considered. From the data calculation, it can be shown that corrosion prediction software can predict corrosion rate in HPHT conditions.

Failure Analysis on Leakage and Perforation of Natural Gas Pipeline

CO2 corrosion is one of the most common corrosion forms in the process of oil and gas field development and oil and gas gathering and transportation. In the process of natural gas gathering and transportation, the problem of pipeline corrosion caused by CO2 is widespread, which often leads to serious local thinning, even perforation and fracture of the pipe body. Once it occurs, it will cause great economic losses and disastrous consequences to the actual production. Therefore, it is of great practical significance to study the mechanism of CO2 corrosion and analyze the influencing factors of CO2 corrosion in order to prevent the safety accidents and improve the efficiency of natural gas transportation. In this paper, a natural gas pipeline wall perforation failure analysis as an example, the sample from the natural gas pipeline corrosion product morphology and composition of micro analysis, and the CO2 corrosion mechanism, influencing factors and other aspects are described in detail.

A fully coupled model of hydrodynamic-chemical-electrochemical processes for CO2 uniform corrosion in multi-physics environment

Carbon dioxide uniform corrosion occurs widely in the petroleum industry and threatens the safe production and transportation of petroleum resources. It is a complex issue involving a variety of physical, chemical and electrochemical processes in multiple temporal and spatial scales. A fully coupled model, taking into account all involved processes in a coupled fashion, such as fluid flow, multi-ion transport, multi-component chemical/electrochemical reactions, is established to comprehensively investigate the mechanism of CO2 corrosion in multi-physics environment. The reliability of this model is validated by the good consistency between the predicted corrosion rates and the experimental results in the literature, and this model performs better in corrosion rate prediction than the previous models due to the explicit solution for the convective mass transfer. Based on this fully coupled model, the corrosion mechanism in the multi-physics coupled environments is revealed in terms of the time-dependent ion concentration field, mass transfer and electrode reaction kinetics. The interrelationship between the corrosion kinetics and the flow effect is explored. The results indicate that the time-dependent corrosion behavior is determined by the combined effect of the solution chemistry and electrical field. By accelerating the mass transport of corrosive species and the involved multi-component reactions, the fluid flow can significantly promote the corrosion process, while the promotion effect weakens gradually at higher flow velocities. Additionally, the flow effect at lower pH values is much more pronounced due to the transformation of the predominant controlling factors for electrode kinetics.

Effect of FexCayCO3 and CaCO3 Scales on the CO2 Corrosion of Mild Steel

Calcium ions are usually present at high concentrations in brines produced with oil and gas. Such brines are typically saturated with respect to CaCO3. Consequently, precipitation of CaCO3 as scale on the internal wall of the pipeline can readily occur due to changes in operational and environmental parameters as produced fluids are transferred from downhole to surface facilities. Despite its importance, there is minimal research in the literature addressing the effect of calcium ions, and specifically CaCO3 scale, on the CO2 corrosion mechanism. The main objectives of this research are to further broaden the mechanistic understanding of CO2 corrosion of mild steel in the presence of high concentrations of calcium ions and evaluate the protectiveness that FexCayCO3 and CaCO3 scale confers against further corrosion. The corrosion behavior was studied in situ by electrochemical methods, including linear polarization resistance and open-circuit potential, along with weight loss using a UNS G10180 steel with ferritic-pearlitic microstructure. Surface characterization of the scale and corrosion product was performed using scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. A descriptive model is proposed for the CO2 corrosion mechanism of mild steel in the presence of high concentrations of calcium ions. Unprotective FexCayCO3 (y>x) and CaCO3 scales were observed to act as a mass transfer barrier that could promote surface conditions favoring FeCO3 precipitation. The presence of uniform CaCO3 scale did not result in the onset of localized corrosion at the conducted experimental conditions.

A New Narrative for CO2 Corrosion of Mild Steel

The conventionally accepted mechanism of CO2 corrosion considers the direct reduction of carbonic acid as the main process that results in the higher corrosion rates as compared to that observed in strong acid solutions with the same pH. The present study is an attempt to further elucidate the underlying electrochemical mechanisms of CO2 corrosion. In this regard, the mechanism of CO2 corrosion was investigated based on the cathodic and anodic polarization behavior of mild steel in CO2-saturated solutions at elevated pressures. The examination of charge transfer controlled cathodic currents showed that the direct reduction of carbonic acid is insignificant at the condition of the present study. Additionally, the iron dissolution reaction was found to be significantly affected by the presence of CO2, particularly over the transition and pre-passivation ranges. A comprehensive mathematical model based on the presented mechanistic understanding of the system was developed and used for further quantitative examinations. The present mechanistic model was shown to be able to represent the main mechanistic features of polarization curves and predict the corrosion rates with reasonable accuracy.

Technical Note: Electrochemistry of CO2 Corrosion of Mild Steel: Effect of CO2 on Cathodic Currents

The common understanding of aqueous CO2 corrosion mechanism considers carbonic acid as an electroactive species. The direct reduction of carbonic acid on a steel surface is believed to be the cause of the higher corrosion rates of mild steel, as compared to that observed in strong-acid solutions with the same pH. However, in-depth quantitative analyses based on comprehensive mechanistic models, developed in recent years, have challenged this idea. In an attempt to provide explicit experimental evidence for the significance of direct reduction of carbonic acid in CO2 corrosion of mild steel, the charge transfer controlled cathodic currents in CO2 saturated solutions were investigated in the present study. The experiments were conducted on three different surfaces: Type 316L stainless steel, pure iron, and API 5L X65 mild steel, in order to examine the possible effect of alloying impurities on the kinetics and the mechanism of cathodic currents. The experimental polarization curves showed that at a constant pH, the charge transfer controlled cathodic currents did not increase with increasing partial pressure of CO2 from 0 bar to 5 bar. This confirmed that the direct carbonic acid reduction was not significant at the conditions covered in the present study, and its sole effect was to buffer the hydrogen ion concentration.

The Research of Internal Corrosion Location Prediction Technology in the Typical Pipeline Components of Natural Gas Gathering Pipeline

Gathering pipeline is used for transporting crude gas without purification in natural gas mine, it has short transmission distance, small diameter, pressure changes and other characteristics . In the natural gas gathering and transportation process, the carrying effect of high pressure and high speed gas, water, sand, acidic medium and other untreated impurities could induce flow corrosion in gas pipeline, pipeline components (referred to as the tube), and other ancillary facilities interior. According to the actual failure case of an acidic gas mine pipeline, based on the CO2 corrosion mechanism, internal flow field analysis of the model and the actual test results, through comparison of numerical results and actual test results, the article gives a research on corrosion location prediction technology in the typical components of natural gas gathering pipeline. The technology has an important significance to guide field inspection, improve the detection efficiency and defect detection rate, and protect the natural gas mine gathering safety.

Corrosion Behavior of X52 Steel in High Pressure CO<sub>2</sub> Environment

Research in high pressure CO2 environment is important in oil and gas industry due to potential development of high pressure CO2 gas fields. Current understanding limits the use of carbon steel pipeline material in this high pressure CO2 environment due to excessive corrosion rates predicted by corrosion prediction software. The aim of this work is to elucidate the corrosion behavior of X52 steel in high pressure CO2 environment. Electrochemical methods of linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques were employed to study the CO2 corrosion mechanism at high pressures of 10-60 bar at ambient temperature. Surface morphology and chemical composition of corrosion film was studied by using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results obtained showed that the corrosion rates at high pressures were significantly influenced by CO2 pressure. However FeCO3 and F3C were the main component of the corrosion product film.

Discussion of the CO2 corrosion mechanism between low partial pressure and supercritical condition

The corrosion behaviour of X65 pipeline steel at various temperatures for different immersion time under low CO2 partial pressure and supercritical CO2 condition were investigated by weight loss measurements and surface analysis techniques. By comparing the characteristics of CO2 corrosion product scale formed under experimental conditions and the variation rule of corrosion rate with temperature, the CO2 corrosion mechanism under low partial pressure and supercritical condition was studied. To explain the big difference of corrosion rate between low CO2 partial pressure and supercritical CO2 condition, thermodynamic calculation of the solubility of CO2 in H2O were discussed.

Predicting Carbon Dioxide Corrosion of Bare Steel under an Aqueous Boundary Layer

Abstract The corrosion of bare steel under an aqueous boundary layer with dissolved carbon dioxide (CO2) was modeled to investigate the effect of CO2. The model incorporated the coupled effect of CO2 diffusion, hydration, local ionic equilibria, ferrous carbonate (FeCO3) precipitation, and steel corrosion. The model was verified against published experimental data under both FeCO3-saturated and unsaturated boundary layers. Good agreement was shown under a variety of conditions. For saturated boundary layers, the results show that the corrosion rate in carbonic acid (H2CO3) is greater than in hydrochloric acid (HCl)for a given pH and that H2CO3 reduction is the cause for the increase of corrosion rate in H2CO3. Increasing temperature was found to increase corrosion rate substantially. This work provides further understanding of the CO2 corrosion mechanism and is a reliable, convenient, and practical tool for predicting the rate of CO2 corrosion.