Corrosion of X65 steel in CO2-saturated oilfield formation water in the absence and presence of acetic acid

Electrochemical corrosion behavior of X65 steel in CO₂-saturated formation water in the absence and presence of acetic acid was studied by electrochemical measurements, scanning vibrating micro-electrode (SVME), localized electrochemical impedance spectroscope (LEIS) and surface analysis techniques. It is found that, when steel is immersed in formation water, the dissolution of Fe dominates the anodic process and the steel is in active dissolution state. Adsorption of intermediate product on the electrode surface results in generation of an inductive loop in the low frequency range of EIS plot. As corrosion proceeds, the concentration of Fe²⁺ in the solution increases. When the product of [Fe²⁺] × [] exceeds solubility product of FeCO₃, FeCO₃ will deposit on the electrode surface, and protects the steel substrate from further corrosion. The steel is in a “passive” state. When the electrode surface is completely covered with FeCO₃ film, the inductive loop in the low frequency range disappears. In the presence of acetic acid in formation water, the cathodic reaction will be enhanced due to the direct reduction of undissociated acetic acid. Addition of acetic acid degrades the protectiveness of corrosion scale, and thus, enhances corrosion of steel by decreasing the FeCO₃ supersaturation in solution.     

The growth mechanism of CO2 corrosion product films

Carbon steel usually has high corrosion rate in water with dissolved CO₂ however the steel surface can be covered by protective corrosion product film. Therefore the carbon steel can be widely used in oil and gas industry. This paper discusses the structure, electrochemistry performances, initiation and growth of protective corrosion product films. A duplex layer structure of FeCO₃ films was found by electrochemical impedance spectrum (EIS). The physical and chemical situations of solution near carbon steel surface were investigated by ultraviolet spectrophotometry and chronopotentiometry. According to crystallography the growth mechanisms of protective CO₂ corrosion product films were discussed.     

Comparison of corrosion scales formed on KO8OSS and N8O steels in CO2/H2S environment

Abstract

Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were applied to analyse the microstructure and composition of the corrosion scale formed on KO80SS and N80 tubes with carbon dioxide (CO₂) and hydrogen sulphide (SO₂). The corrosion scales of both KO80SS and N80 tubes were of the double layer structure, and not only uniform corrosion but also localised corrosion was observed. The crystal of the surface layer is laminar. The main phase in the outer layer is calcium carbonate (CaCO₃), and the inner scale consisted of iron carbonate (FeCO₃) for KO80SS steel and FeS_0·9 with a little amount of FeCO₃ for N80 steel respectively. Additionally, the electrochemical techniques were used to investigate the characteristics of the corrosion scales. The results indicated that the polarisation resistance R_p of KO80SS steel film was nobler than that of N80 steel film. Finally, the corrosion current I_corr of KO80SS steels was lower than that of N80 steels. Corrosion scale of KO80SS tube steels is more protective to the matrix than that of N80 tube steels.     

Corrosion inhibition of mild steel by ethylamino imidazoline derivative in CO2-saturated solution

The corrosion inhibition and adsorption behaviour of 2-undecyl-1-ethylamino imidazoline (2UEI) on N80 mild steel in CO₂-saturated 3% NaCl solutions was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy techniques and SEM observation. Inhibitor efficiency increased with increase in 2UEI concentration. Temperature studies revealed an increase in inhibition efficiency with rise in temperature and corrosion activation energies decreased in the presence of 2UEI. A mechanism of chemical adsorption of 2UEI on the metal’s surface is proposed. The adsorption characteristics of the inhibitor were approximated by Temkin isotherm. The inhibition efficiency of 2UEI was enhanced in the presence of iodide ions.     

The inhibition of CO2 corrosion of N80 mild steel in single liquid phase and liquid/particle two-phase flow by aminoethyl imidazoline derivatives

The inhibitory behaviour of 2-undecyl-1-aminoethyl imidazoline (AEI-11) and 2-undecyl-1-aminoethyl-1-hydroxyethyl quaternary imidazoline (AQI-11) on CO₂ corrosion of N80 mild steel in single liquid phase and liquid/particle two-phase flow was investigated using weight loss, linear polarization, potentiodynamic polarization, EIS methods and SEM observations. The two compounds inhibited the CO₂ corrosion of N80 steel and the extent of inhibition was dependent on the flow conditions and particulate content. In both phases, AQI-11 exhibited better inhibition ability than AEI-11 due to the polycentric adsorption sites on its structure. Theoretical calculation on the inhibition abilities of the compounds and their modes of adsorption are reported.     

Evolution of dissolution processes at the interface of carbon steel corroding in a CO2 environment studied by EIS

The evolution of interfacial phenomena during CO₂ corrosion of C1018 carbon steel was characterized by EIS (Electrochemical Spectroscopy Impedance) and LPR (Linear Polarization Resistance). Turbulent conditions were simulated by a channel flow cell with deoxygenated 3 wt.% NaCl solution at 80 °C and pH 6 during 158 h. EIS helped in the characterization of the dynamic mechanism during the formation of the unprotective porous Fe₃C layer, and subsequent precipitation of the protective FeCO₃ layer inside the cementite. The experimental response of the active states at the interface was characterized by electrical passive elements with constant phase parameter analogs showing good agreement with the experimental results.     

Investigation on carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water

The carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water is studied by potentiodynamic curve and electrochemical impedance spectroscopy (EIS); the micro-structure and composition of the corrosion scale formed at high-temperature and high-pressure are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that 13Cr stainless steel is in passive state in the stratum water, the passive current density increases and the passive potential region decreases with increasing temperature. The corrosion scale formed at high-temperature and high-pressure is mainly composed of iron/chromium oxides and a little amount of FeCO₃.     

On the fundamentals of electrochemical corrosion of X65 steel in CO2-containing formation water in the presence of acetic acid in petroleum production

Electrochemical corrosion behavior of X65 steel in CO₂-containing oilfield formation water in the presence of acetic acid (HAc) was investigated by various electrochemical measurements and analyses as well as thermodynamic calculations of ionic concentrations, reaction rate constants and equilibrium electrode potentials. A conceptual model was developed to illustrate corrosion processes of steel in oilfield formation water system. The anodic reactions of the steel contain a direct dissolution of Fe, Fe → Fe²⁺ + 2e, and the formation of corrosion scale, FeCO₃, by Fe + → FeCO₃ + H⁺ + 2e. The cathodic processes contain the reduction of H⁺, , H₂O and HAc, where reduction of HAc has the least negative equilibrium potential and thus dominates the cathodic process. With addition of HAc in the solution, both cathodic and anodic reaction rates increase remarkably. It is attributed to the fact that HAc inhibits or degrades the formation of protective scales due to the decrease of solution pH. Upon electrode rotation, the measured impedance decreases with the increase in HAc concentration. The FeCO₃ scale will not form on electrode surface. When HAc concentration is less than 1000 ppm, the adsorbed intermediate product is not significant, resulting in generation of a low-frequency inductive loop in EIS plots. When HAc concentration is more than 3000 ppm, the adsorption of intermediate product is significant, generating overlapped capacitive semicircles in EIS measurements.     

Abrasion resistances of CO2 corrosion scales formed at different temperatures and their relationship to corrosion behaviour

The abrasion resistances of CO₂ corrosion scales formed on API P110 grade carbon steel at different temperatures and CO₂ corrosion behaviour of P110 carbon steel have been investigated utilising weight loss method, scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that as the film forming temperature increased, the abrasion rate of CO₂ corrosion scales increased firstly and then decreased, the variation trend was similar to that of the corrosion rate, and the maximal abrasion rate was present at 70°C rather than 100°C, at which the maximal corrosion rate was obtained and CO₂ corrosion scales were loose and porous and were composed of FeCO₃, Fe₃C and CaCO₃. The abrasion resistances of CO₂ corrosion scales formed at 100°C was reinforced by the sand particles embedded easily in the loose and porous layer, together with a very hard residual skeleton, Fe₃C. In addition, CaCO₃ was worn out easily and substituted by SiO₂ during abrasive wear.     

Role of polyacrylamide concentration on corrosion behavior of N80 steel in the HPAM/H2S/CO2 environment

The effect of polyacrylamide on corrosion behavior of N80 steel in the HPAM/H₂S/CO₂ environment was studied by using weight-loss and electrochemical tests to simulate the environment of production wells in polymer flooding. The morphology and composition of corrosion scales were studied by scanning electron microscopy, energy dispersive X-ray spectrometer, and X-ray photoelectron spectroscopy. The results show that as the polyacrylamide concentration increases, the uniform corrosion rate of N80 steel decreases gradually. The safe service life of N80 steel grows along with the increase of the concentration of polyacrylamide. The corrosion scales of N80 steel in the HPAM/H₂S/CO₂ environment is split into two layers, an inner layer of O-rich composed of FeCO₃ and an outer layer of S-rich consisting of FeS. Polyacrylamide adsorbs on the surface of N80 steel to form a protective network, which blocks contact between the metal and the solution and then inhibits the anodic dissolution of the metal. Moreover, the growth of polyacrylamide concentration increases the pH value of the solution and promotes the ionization of H₂S, HS⁻, and H₂CO₃ in the solution.     

Organic molecules showing the characteristics of localised corrosion aggravation and inhibition

The behaviour of imidazoline and an acid functionalised resorcinarene as steel corrosion inhibitors in carbon dioxide (CO₂)-saturated brine solutions has been studied using an electrochemically integrated multi-electrode array namely the wire beam electrode (WBE). Both imidazoline and resorcinarene acid provided excellent inhibition to general CO₂ corrosion; however imidazoline was found to aggravate localised corrosion by creating a small number of major anodes that focused on a small area of the WBE surface, leading to highly concentrated anodic dissolution. The resorcinarene acid showed distinctively different behaviour by generating a large number of minor anodes randomly distributing over the WBE surface, leading to insignificant general anodic dissolution. These results indicate that resorcinarene acid provided effective localised corrosion inhibition by promoting a random distribution of insignificant anodic currents.     

Corrosion behavior of low-alloy steel containing 1% chromium in CO2 environments

Corrosion behavior of low-alloy steel containing 1% Cr (1Cr) with normalized (ferritic–pearlitic) and quenched-and-tempered (tempered martensitic) microstructures was investigated in CO₂ environments at 60 °C. The severe localized corrosion which was observed in N80 carbon steel, did not exist for 1Cr steel due to the formation of a compact and self-repairable Cr-rich scale. For 1Cr steel, the corrosion resistance with ferritic–pearlitic microstructure was better than that with tempered martensitic microstructure. An apparent corrosion scale spallation was observed on the surface of quenched-and-tempered 1Cr steel, while only slight scale spallation was seen for normalized 1Cr steel.     

Morphology and phase composition of corrosion products formed at the zinc-iron interface of a galvanized steel

The corrosion products formed on the inner wall of pipes made of galvanized low carbon steel, exposed for ∼2 years to water flowing in a large household heating system, were analysed using X-ray diffraction, Mössbauer and Raman spectroscopic techniques, as well as metallographic techniques. Products grew in the form of large-sized tubercles that gradually developed causing base metal losses up to perforation of the steel pipe. Considerable differences in the phase composition were found between the products formed in contact with the steel and those constituting the outer part of tubercles. The former were mainly made of FeCO₃ (siderite), with small amounts of Zn₅(CO₃)₂(OH)₆ (hydrozincite), ZnCO₃ (smithsonite), (Fe,Zn)CO₃ mixed carbonate and CaCO₃ (calcite), the latter mainly by Fe(III) oxyhydroxide goethite. Both parts of the tubercles also contained small amounts of other ferric oxyhydroxides, γ-FeOOH (lepidocrocite) and β-FeOOH (akaganeite), and very small amounts of hematite. The procedures used proved effective for an adequate identification of both the iron-containing and iron-free compounds in the corrosion products as well as for suggesting a corrosion mechanism.     

Mitigation of top- and bottom-of-the-line CO2 corrosion in the presence of acetic acid (I): pH control using methyl diethanolamine

Temperature differences between the top and the base of pipelines can, in specific circumstances, drive severe corrosion due to condensed fluids at the top-of-the-line. Here, we measure corrosion at the top-of-the-line in the condensate phase and, simultaneously, in the immersed phase at the bottom-of-the-line using an electrochemical approach. With CO₂-saturated chloride brine, corrosion at the top-of-the-line increased with fluid temperature (due to increased condensation rates), whereas at the bottom-of-the-line, the corrosion rate decreased (due to ferrous carbonate precipitation). The addition of acetic acid increased the corrosion rate at both top and bottom of the line, with any ferrous carbonate films being removed by dissolution. The addition of methyl diethanolamine (MDEA) reduced corrosion rates significantly because of the increased pH in both the condensate at the top-of-the-line and under immersion at the bottom-of-the-line, reducing the solubility of FeCO₃. Overall, the addition of acetic acid was confirmed to damage and remove protective FeCO₃ films. However, continuous films were not re-established after MDEA additions, rather porous and generally unprotective films were formed.     

A study of 4-carboxyphenylboronic acid as a corrosion inhibitor for steel in carbon dioxide containing environments

4-Carboxyphenylboronic acid (CPBA) has been found to be an efficient carbon dioxide (CO₂) corrosion inhibitor for steel in aqueous media. The results indicate that the addition of CPBA to CO₂ containing sodium chloride solutions at a low concentration is able to retard corrosion anodic reactions, reduce corrosion current densities, increase charge transfer and total resistances, resulting in more uniform and smoother steel surfaces. These effects are attributed to the formation of a barrier layer on steel surface, which provides metal surface protection. The inhibitor was also found to mitigate corrosion by promoting random distribution of minor anodes.     

Corrosion and Stress Corrosion Cracking Behavior of X70 Pipeline Steel in a CO2-Containing Solution

The electrochemical corrosion and stress corrosion cracking (SCC) behaviors of X70 pipeline steel in CO₂-containing solution were studied by electrochemical measurements, slow strain rate tensile tests, and surface characterization. The results found that the electrochemical corrosion of X70 steel in aerated, alkaline solution is an activation-controlled process, and a stable passivity cannot develop on steel. Corrosion rate of the steel increases with the CO₂ partial pressure. The enhanced anodic dissolution due to the additional cathodic reaction in the presence of CO₂, rather than the film-formation reaction, dominates the corrosion process. The mass-transfer step through FeCO₃ deposit is the rate-controlling step in corrosion of the steel. The susceptibility of steel to SCC and the fracture brittleness increase with the CO₂ partial pressure. The enhanced fracture brittleness is attributed to the evolution and penetration of hydrogen atoms into the steel, contributing to crack propagation. The formed deposit layer is not effective in reducing hydrogen permeation due to the loose, porous structure.     

Cover Picture: Materials and Corrosion. 4/2020

Cover: Hydrolysis of anionic polyacrylamide (HPAM) adsorbs on the surface of metal to form a network of protective fi lm. The corrosion scales of N80 steel includes an inner film which is composed of FeCO₃ and an outer film composed of FeS₂ in HPAM/H₂S/CO₂ environment. More detailed information can be found in: Baojun Dong, Dezhi Zeng, Zhiming Yu, Haixin Zhang, Huiyong Yu, Gang Tian, Yonggang Yi, Role of polyacrylamide concentration on Corrosion Behavior of N80 steel in the HPAM/H₂S/CO₂ environment, Materials and Corrosion 2020 , 71, 526.     

Characterization of corrosion of X70 pipeline steel in thin electrolyte layer under disbonded coating by scanning Kelvin probe

Scanning Kelvin probe technique was used to characterize the electrochemical corrosion behavior of X70 steel in a thin layer of near-neutral pH and high pH solutions, respectively. Results demonstrate that passivity can be developed on steel in the near-neutral pH solution layer as thin as 60 μm, which is attributed to the fact that Fe²⁺ concentration in aqueous phase could reach saturation in the thin solution layer. The solubility of FeCO₃ is reached to drop out of solution as a precipitate. With the increase of solution layer thickness, it becomes more difficult for Fe²⁺ concentration to reach saturation. Consequently, the passivity cannot be maintained, and the steel shows an active dissolution state. Anodic dissolution rate of steel increases with the immersion time. The electrochemical polarization behavior of X70 steel in high pH solution is approximately independent of the solution layer thickness and immersion time. In thin solution layer, diffusion and reduction of oxygen dominate the cathodic process, as demonstrated by the presence of cathodic limiting diffusive current. In the bulk solution, the absence of limiting diffusive current density in cathodic polarization curve indicates that the main cathodic reaction is reduction of H₂CO₃ and , and the formed film is thus mainly FeCO₃.     

Corrosion of carbon steel in concentrated LiNO3 solution at high temperature

The corrosion of carbon steel in concentrated LiNO₃ solution at high temperature was investigated by a weight loss method. Results showed that increasing temperature and pH would increase the corrosion rate, and increasing concentration and adding Li₂CrO₄ would reduce the corrosion rate. The corrosion in LiNO₃ solution was general corrosion and the corrosion products were composed of Fe₃O₄ and Fe₂O₃. A compact passive layer comprising of Cr₂O₃, Fe₃O₄ and Fe₂O₃ was observed with adding Li₂CrO₄, and it could effectively depress the corrosion. The carbon steel corrosion in LiNO₃ solution was much smaller than that in LiBr solution.     

Fe3C influence on the corrosion rate of mild steel in aqueous CO2 systems under turbulent flow conditions

The corrosion and corrosion inhibition of mild steel in CO₂ saturated solutions were studied under turbulent flow conditions at different pH. Electrochemical measurements using a.c. and d.c. techniques in uninhibited solutions of pH 3.8 indicated the formation of protective surface films (FeCO₃) in short immersion times. However, as the exposure time was increased the corrosion rate always increased, an effect attributed to the increased surface area of Fe₃C residue from corrosion of the steel. At pH 5.5, the corrosion rate always increased with time, behaviour also associated with the presence of Fe₃C surface film. The huge cathodic area of Fe₃C seems to have a more important impact on the electrochemical behaviour than the poorly formed FeCO₃ products. The effect of Fe₃C on inhibition by a quaternary amine inhibitor at pH 3.8 is to increase the corrosion rate as the pre-corrosion time is increased. The Fe₃C causes either (a) a cathodic area increase reflected in the corrosion rate increase with time or (b) a potential gradient in the pores of the Fe₃C layer that prevents positively charge amine ions from reaching all anodic sites.