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TX31 (Mg-3Sn-1Ca) is an alloy with promising future applications. This study enhances the corrosion resistance of the TX31 alloy through the addition of Zr and Zn and compares the effects of individual Cu addition and Zn/Cu composite addition on the corrosion resistance of the TX31 alloy. This study investigates the corrosion properties of TX31 alloys, focusing on the effects of the grain size, second phase, corrosion product film, and texture intensity. The addition of Zr and Zn changed the second-phase area fraction, while Cu introduced a new Mg2Cu phase. The TXZ311 alloy (Mg-3Sn-1Ca-1Zn) exhibited the best corrosion resistance, with a corrosion rate as low as 1.68 mm·year−1, a significant reduction compared to other alloys. This improvement is attributed to its higher fraction of high-angle grain boundaries (HAGBs) and the enhanced stability of the corrosion product film. The TXK311 alloy (Mg-3Sn-1Ca-1Zr) showed superior corrosion resistance, with a rate of 2.97 mm·year−1, due to its uniform and fine grain structure. In contrast, the TX31 alloy had the poorest corrosion resistance, with a corrosion rate of 3.66 mm·year−1, due to its bimodal microstructure. The addition of Cu in the TXC311 (Mg-3Sn-1Ca-1Cu) and TXCZ3111 (Mg-3Sn-1Ca-1Cu-1Zn) alloys resulted in micro-galvanic corrosion between α-Mg and Mg2Cu, which decreased the corrosion resistance. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A new weathering steel suitable for low salinity conditions was developed in this paper. The corrosion evolution of test steel under simulated tropical marine atmosphere was studied by alternating dry/wet corrosion tests, electrochemical techniques, morphology characterization and component analysis. It was indicated that the relative corrosion performance ratio of Mo-alloyed Ni-advanced weathering steel is superior to that of 3Ni steel due to the adsorption of Mo's oxide by NiFe2O4 in the rust layer. This interaction prevents NiFe2O4 from disintegrating, enhances the density of the rust layer, and improves its protecti0ve properties.

The effect of sulfides on the pitting corrosion behavior and film chemistry of 70/30 copper-nickel alloys in aerated seawater was investigated. Sulfides in seawater prevent the formation of protective oxides on the surface of the alloy and alter the morphology and composition of the corrosion products. It results in the corrosion product film consisting of the double layer structure of the loose and porous sulfide-containing outer layer and the dense inner layer. This double-layer structure of the corrosion product film can't alleviate corrosion, but instead accelerates the development of pitting corrosion. The statistical analysis method is used to study the corrosion process of 70/30 copper-nickel alloy in sulfide-containing environment. This work records the trend of pitting corrosion towards the horizontal and longitudinal directions.

TX31 (Mg-3Sn-1Ca) is an alloy with promising future applications. This study enhances the corrosion resistance of the TX31 alloy through the addition of Zr and Zn and compares the effects of individual Cu addition and Zn/Cu composite addition on the corrosion resistance of the TX31 alloy. This study investigates the corrosion properties of TX31 alloys, focusing on the effects of the grain size, second phase, corrosion product film, and texture intensity. The addition of Zr and Zn changed the second-phase area fraction, while Cu introduced a new Mg2Cu phase. The TXZ311 alloy (Mg-3Sn-1Ca-1Zn) exhibited the best corrosion resistance, with a corrosion rate as low as 1.68 mm·year−1, a significant reduction compared to other alloys. This improvement is attributed to its higher fraction of high-angle grain boundaries (HAGBs) and the enhanced stability of the corrosion product film. The TXK311 alloy (Mg-3Sn-1Ca-1Zr) showed superior corrosion resistance, with a rate of 2.97 mm·year−1, due to its uniform and fine grain structure. In contrast, the TX31 alloy had the poorest corrosion resistance, with a corrosion rate of 3.66 mm·year−1, due to its bimodal microstructure. The addition of Cu in the TXC311 (Mg-3Sn-1Ca-1Cu) and TXCZ3111 (Mg-3Sn-1Ca-1Cu-1Zn) alloys resulted in micro-galvanic corrosion between α-Mg and Mg2Cu, which decreased the corrosion resistance.

In order to analyze the impact of the waste heat utilization environment in phosphate compound fertilizer industrial production on the corrosion behavior of steam turbine rotors, various methods such as the mass loss method, laser scanning confocal microscopy (CLSM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical tests were employed. The corrosion behavior and patterns of the steam turbine rotor material, 2Cr-1Ni-1.2Mo-0.2V steel in 120 mmol/L NH4H2PO4 solution at an external temperature of 25 ℃ were investigated. Results showed that 2Cr-1Ni-1.2Mo-0.2V steel underwent uniform corrosion. The corrosion rate first rapidly decreased and then slowly decreased, gradually stabilizing towards 0.2 mm/a. When the NH4H2PO4 concentration was 120 mmol/L and the temperature was 25 ℃, the service life of 2Cr-1Ni-1.2Mo-0.2V steel was determined to be 7.5 a. The corrosion product film of 2Cr-1Ni-1.2Mo-0.2V steel in NH4H2PO4 solution was composed of Fe3(PO4)2, FePO4, Fe(OH)3, FeOOH, and Fe3O4. As the immersion time prolonged, the coverage, compactness and thickness of the corrosion product film were observed to increase, and Cr was found to be enriched in the corrosion product film, thereby enhancing the corrosion resistance of 2Cr-1Ni-1.2Mo-0.2V steel.

Based on corrosion thermodynamics and kinetics, considering the multi-field coupling effects of fluid flow, electrochemical reaction and mass transfer process, a new corrosion prediction mechanistic model was proposed by introducing the influence factor of corrosion product film on diffusion coefficient of ion mass transfer, which is based on the CO2 corrosion prediction model proposed by Nesic et al. The influence of temperature, flow rate and pH value on CO2 corrosion behavior on 20# steel was studied by orthogonal tests. Scanning electron microscopy (SEM) and energy spectrum analysis (EDS) was used to analyze the surface and cross section morphology of the corrosion product film, and the thickness of the corrosion product film was measured. The results show that the introduced influence factor can simplify the ion mass transfer calculation in the presence of corrosion product film, and the relative error between the predicted value of the modified model and the experimental results is satisfactorily controlled less than 10%. Compared with the prediction model without considering the influence of corrosion product film, the influence factor can effectively correct the high prediction value of the mechanistic model under the influence of corrosion product film, improve the accuracy and applicability of corrosion prediction, and provide important theoretical guidance for the design, manufacturing, operation and maintenance of oil and gas production pipelines and related facilities.

Micro-alloying Mg alloys with rare earth elements is an economical and promising way to improve their corrosion resistance. It is of great importance to understand their corrosion behavior for designing corrosion-resistant Mg alloys. In this work, Mg-11Al-0.2Y alloy was prepared for exploring its corrosion behavior in 3.5 wt.% neutral NaCl solution. It exhibits a low corrosion current density of 2.3 µA/cm2 after immersion for 1 d due to the formation of a protective surface film containing Al2O3, MgO and Mg(OH)2. However, nano-scaled pores exhibit at the film/matrix interface, which undermines integrity and protectiveness of the surface film after long-term exposure to chloride solution.

FeMnAlC low-density steel (LDS) is considered to be a promising material due to its good mechanical properties and light weight, its corrosion resistance, however, needs to be improved. In this paper, the effect of Cr and Ni on the electrochemical and early corrosion behavior of a Fe–25Mn–10Al–1.5C LDS in a 3.5% NaCl solution was studied through microstructure characterization, electrochemical tests and immersion tests. The results showed that Cr and Ni alloying reduced the austenite grain size and promoted the formation of the B2 phase. Adding 2% Cr or Ni to the Fe–25Mn–10Al–1.5C LDS clearly inhibited the electrochemical activity and initial micro galvanic effect between the second phases and the austenite. Moreover, the properties of the corrosion product film were optimized, and the local corrosion process beneath the product film was mitigated. Compared with 2% Cr addition, 2% Ni addition improved the corrosion resistance of the FeMnAlC LDS better from the aspects of electrochemistry, corrosion product film and corrosion mode.

In this study, the corrosion behavior of X52 pipeline steel affected by H2O content in supercritical CO2 streams containing O2, H2S, SO2 and NO2 impurities was investigated by the weight loss test and surface characterization. The corrosion differences of the steel in impure supercritical CO2 streams containing different H2O contents were analyzed. The influence of the variation of H2O content on the corrosion mechanism of steel in the complex impurity-containing supercritical CO2 streams was discussed. The results show that the H2O content limit is 100 ppmv in supercritical CO2 streams containing 200 ppmv O2, 200 ppmv H2S, 200 ppmv SO2 and 200 ppmv NO2 at 10 MPa and 50 °C. The impurities and their interactions significantly promote the formation of corrosive aqueous phase, thereby exacerbating the corrosion of X52 steel. The corrosion process of X52 steel in the environment with a low H2O content is controlled by the products of impurity reactions, whereas the impurities and the products of impurity reactions jointly control the corrosion process of the steel in the environment with a high H2O content. [ABSTRACT FROM AUTHOR]

The corrosion behaviors of self-designed Ni-containing low-alloy steels with Mo addition in tropical marine atmosphere was investigated by surface analysis and electrochemical methods. The results showed that with the increase of Ni content, the weight gain rates of low-alloy steels gradually decreased and the composition phases of inner product films changed from γ-FeOOH to α-FeOOH. The synergistic effect of Ni and Mo on the corrosion resistance of low-alloy steel was related to the Ni content in the steel matrix. The corrosion resistance can be significantly improved by adding Mo when the Ni content was in the range of 1.72 to 2.87 wt.%. The enhanced synergistic effect of Ni and Mo could further promote the formation of more protective corrosion products, such as α-FeOOH, NiFe2O4 and Mo6+. [ABSTRACT FROM AUTHOR]

Based on corrosion thermodynamics and kinetics, considering the multi-field coupling effects of fluid flow, electrochemical reaction and mass transfer process, a new corrosion prediction mechanistic model was proposed by introducing the influence factor of corrosion product film on diffusion coefficient of ion mass transfer, which is based on the CO2 corrosion prediction model proposed by Nesic et al. The influence of temperature, flow rate and pH value on CO2 corrosion behavior on 20# steel was studied by orthogonal tests. Scanning electron microscopy (SEM) and energy spectrum analysis (EDS) was used to analyze the surface and cross section morphology of the corrosion product film, and the thickness of the corrosion product film was measured. The results show that the introduced influence factor can simplify the ion mass transfer calculation in the presence of corrosion product film, and the relative error between the predicted value of the modified model and the experimental results is satisfactorily controlled less than 10%. Compared with the prediction model without considering the influence of corrosion product film, the influence factor can effectively correct the high prediction value of the mechanistic model under the influence of corrosion product film, improve the accuracy and applicability of corrosion prediction, and provide important theoretical guidance for the design, manufacturing, operation and maintenance of oil and gas production pipelines and related facilities. [ABSTRACT FROM AUTHOR]

The corrosion behavior of CoCrFeMnNi high entropy alloy in 3.5 wt.% NaCl solution with and without 0.05 M NaHSO3 was studied by electrochemical measurement, immersion test, and atomic force microscope. The results show that with the addition of HSO3−, the state of activation indicated by the anodic reaction evolves to the passivation state. Corrosion resistance is related to the state of the film on the HEA surface. The addition of HSO3− may produce a protective composition that transforms the corrosion product film into passive film. With the presence of HSO3−, the dense and highly protective passive film is formed, which improves the corrosion resistance of the HEA. Without HSO3−, the loose, incompact and incomplete corrosion product film produced on the surface of the HEA exhibits a low protective effect. [ABSTRACT FROM AUTHOR]

Oxygen-reducing air flooding is a low-permeability reservoir recovery technology with safety and low-cost advantages. However, in the process of air injection and drive, carbon in the air is oxidized through the crude oil reservoir to generate CO2, and this can cause serious corrosion in the recovery well. In this study, experiments on the corrosion of J55 tubular steel in a fluid environment with coexisting O2 and CO2 in an autoclave are presented. In particular, a weight loss method and a 3D morphometer were used to determine the average and the local corrosion rate. The corrosion surface morphology and composition were also measured by means of scanning electron microscopy (SEM) and an X-ray diffractometer (XRD). The corrosion pattern and morphological characteristics of J55 steel were analyzed in the O2/CO2 environment for different degrees of oxygen-reduction. As made evident by the experimental results, the corrosion products were mainly ferrous carbonate and iron oxide. In general, air injection increases the degree of oxygen reduction, from oxygen corrosion characteristics to CO2 corrosion-based characteristics. As a result, the corrosion product film becomes denser, and the corrosion rate is lower. [ABSTRACT FROM AUTHOR]

The corrosion behaviour of equiatomic CoCrFeNi and CoCrFeNiMn high entropy alloys manufactured by the vacuum arc melting were studied in 3.5 wt-% NaCl solution. And the reasons for the differences in corrosion resistance were investigated in terms of microstructure, electrochemical behaviour and oxide film. The results show that the two alloys exhibit different corrosion characteristics, with CoCrFeNi alloy displaying typical passivation characteristics and CoCrFeNiMn alloy exhibiting activation behaviour. The CoCrFeNi HEA with compact and protective passive film has lower corrosion current density, larger film resistance and polarisation resistance, meaning a lower corrosion rate and superior corrosion resistance compared with those of CoCrFeNiMn alloy. Moreover, CoCrFeNiMn alloy forms a discontinuous and loose corrosion product film with higher Mn content and lower contents of Cr, Fe and Co compared to the matrix, which decreases its protection performance. The addition of Mn changes the electrochemical behaviour, and higher Mn oxides/hydroxides within oxide film are unfavourable to forming a stable passive film. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to reveal the corrosion behavior of J55 and N80 carbon steels in formation water under oil wells at different partial pressures, explore the formation process of corrosion product films under supercritical CO2 conditions, and analyze the reasons why the microstructure of carbon steel affects the corrosion behavior. The results show that the corrosion rate gradually increases with the increase in CO2 partial pressure. When the pressure exceeds 10 MPa, the corrosion rate of J55 increases slightly, and that of N80 decreases slightly. Under different partial pressures, the surface composition of the corrosion product film of J55 steel is FeCO3, and that of N80 steel is FeCO3 with a small amount of Fe3C. The analysis shows that the corrosion product films of two kinds of carbon steels can be divided into three layers under the condition of supercritical CO2. There are holes in the middle layer, which are formed first, and then the inner layer and the outer layer are formed at the same time. It is believed that the difference in the morphology and distribution of Fe3C is the reason why the corrosion rate of J55 steel is lower than that of N80 steel. Fe3C in J55 steel is lamellar, which can anchor FeCO3, promote the formation of corrosion product films, and improve the compactness of corrosion product films. However, the Fe3C in N80 is granular and dispersed in the ferrite matrix, which makes it easy to fall off the surface, form pits, and destroy the integrity of the corrosion product film. [ABSTRACT FROM AUTHOR]

The anisotropic deposit film formed during the galvanic corrosion can impede the mass transfer of the involved species, thereby affecting the electro-chemical behavior and the evolution of galvanic corrosion. The limitations of experimental studies in the spatial-temporal scales restrict a deeper understanding of the corrosion mechanism, which can be complemented by numerical simulation. A multi-physics coupled model is proposed in this work to systematically investigate the temporal and spatial evolution of galvanic corrosion of the Mg-steel couple with the growing anisotropic deposition layer. By utilizing the multi-physics field coupled technique, various coupled physical-chemical processes underlying the corrosion behavior are built into the model, including chemical reactions, ionic mass transfer in the bulk solution and the deposition layer, interfacial reaction, deposition of corrosion products as well as the morphological transitions caused by metal dissolution and deposition. In particular, the anisotropic deposit film is considered to be a porous layer with a porosity varying in time and space as the corrosion evolves. The predicted corrosion morphology by this model is better than the previous models. The coupled relationship between the electrochemical behavior (e.g., electrode reaction kinetics, current density, surface potential) and the physical processes (e.g., ionic transport, geometric evolution of metal surface and film interface) is revealed. The results indicate that a porous deposition layer with a denser inner layer and a loose outer layer is generated, leading to more significant inhibition of mass transfer in the inner layer than the outer layer. The anisotropism of the deposition layer results in a non-uniform conductivity distribution and a discontinuous current density distribution in the electrolyte. The current density on the electrode surface is inhibited by the deposition layer and the variation in the cathode/anode area ratio during the corrosion process. The competition between the transport process and the electrochemical reaction determines the spatial-temporal evolution of the ion concentration.

The effect of 1.5% Cr on the corrosion resistance of low‐alloy steel in a simulated mine environment was studied. To clarify the effect of Cr on the corrosion of low‐alloy steel in the wet environment at the initial stage of corrosion, salt spray corrosion tests were performed to simulate the corrosion process in the field, and the bare steel and corrosion products were characterized. The results showed that the addition of 1.5% Cr reduced the surface potential and the kinetic tendency of the corrosion reaction, making the corrosion rate at the initial stage of the test lower than anticipated. An increase in Cr content significantly elevates the level of α‐FeOOH. The corrosion product film (CPF) had a bilayer structure, with α‐FeOOH of Cr‐rich and Cr(OH)3 were found in the inner layer and at the junction of the inner and outer layer. The CPF had a dense structure that effectively reduced electrochemical reaction activity and improved corrosion resistance. [ABSTRACT FROM AUTHOR]

The corrosion behaviors of Sb‐free and Sb‐added low‐alloy structural steels were comparatively studied in a real tropical marine atmosphere. And the role of Sb addition on corrosion resistance was clarified by electrochemical measurement and rust analysis. The results showed that the addition of 0.05% Sb increased the polarization resistance, reduced the cathodic current density, and slowed down the oxygen reduction process. Meanwhile, Sb addition optimized the physical structure, promoted the transformation of phase, and improved the protection of the rust. More importantly, 0.05% Sb addition inhibited the local acidification at the bottom of the pits, thus slowing down the local corrosion process at the rust/matrix interface. Accordingly, the corrosion resistance of the Sb‐added low‐alloy steel was enhanced, causing a lower corrosion rate than that of Sb‐free steel in a tropical marine atmosphere. [ABSTRACT FROM AUTHOR]

In order to clarify the top corrosion mechanism of X65 wet gas pipeline in Yanchang Gasfield and to improve thecorrosion protection effect of the pipeline, the coupon comparison test was carried out using a self-made tube top corrosionsimulation test device with high temperature and high pressure, and the variation of corrosion rate of bottom and topcoupons with the time and the morphology characteristics of the surface and cross-section of corrosion coupons were studiedby means of scanning electron microscope. The results indicate that the uniform corrosion rate at the bottom of pipelinedecreases with time, but that on the top has no obvious variation. The uniform corrosion rate at the bottom and on the topvaries greatly, close to 100%. The bottom corrosion is pitted and the corrosion pits tend to connect as a whole. However, obvious local corrosion can be observed on the top, and the top corrosion spots are greater than the bottom corrosion pits.The corrosion product film at the bottom is thick and distributed uniformly, generally having good protective effect to thecoupons. But the corrosion product film on the top is thin and distributed unevenly. No accumulation of corrosion productappears around the top corrosion, and the local corrosion expands rapidly. Most of the top corrosion is localized, with agreater threat to the safe operation of wet gas pipeline.

To obtain the influence rules of temperature on 5 typical steel corrosion behavior under supercritical CO2 condition, and improve the corrosion protection effect of pipelines that are used for transporting supercritical CO2, hightemperature autoclave was adopted to conduct the coupon corrosion comparison test. With the help of scanning electron microscope, the corrosion surface morphology of different stainless steel (DSS, 13Cr and austenitic steel) and carbon steel (X70 and P110) coupons, the surface morphology of metal matrix after removing corrosion products, the formation process of corrosion product film and the relation between coupon corrosion rate and corrosion product mass were studied under different temperatures. The results indicate that the solubility of water in supercritical CO2 presents an approximately linear increase with the pressure, or temperature rise. In supercritical CO2, the corrosion rate of stainless steel is one or two orders of magnitude lower than that of carbon steel. With the temperature rise, the inhibition of corrosion product film on metal corrosion exceeds the promoting effect of temperature, resulting in a reduction in uniform corrosion. However, the existence of honeycomb or striped cracks in the formation process of corrosion product film leads to serious local corrosion on the surface of the coupon. It is concluded that the influence of temperature on 5 typical steel corrosion behavior is bidirectional under supercritical CO2 condition, in other words, the temperature rise will lower the uniform corrosion rate of pipelines, but on the other hand, it may increase the local corrosion rate.

By means of an electrochemical workstation, hydrogen evolution device, optical microscope (OM) and scanning electron microscope (SEM), the corrosion behaviors of an as-rolled Mg-8%Li alloy with a dual phase structure in 0.9 wt.% NaCl and 3.5 wt.% NaCl solutions have been investigated and compared. The results show that when the immersion time exceeds 8 h, the hydrogen evolution rate of the alloy in the 0.9 wt.% NaCl is 3 times higher than that in the 3.5 wt.% NaCl solution. Moreover, the corrosion behaviors of the alloy are obviously different in the two differently concentrated NaCl solutions. In the 3.5 wt.% NaCl solution, the localized corrosion is much more severe and can occur simultaneously in the interior of both the α-Mg and β-Li matrix phases. However, the localized corrosion in the 0.9 wt.% NaCl solution is obviously weak and mainly occurs at the α-Mg phase. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Flue gas collection from steam generators and its utilization in enhanced oil recovery (EOR) can reduce CO2 emissions into the atmosphere and improve oil recovery efficiency. Under the environments of flue gas corrosion in oilfields, the effects of corrosion time, temperature, pressure, velocity, and concentrations of O2, SO2, H2O, and NaCl on corrosion rates of steels used for a downhole string were investigated through physical simulation experiments. The corrosion mechanisms were analyzed by component, and the morphology of the corrosion products tested by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). In the gas phase, the corrosion rates of X70, P110, and N80 notably increase with temperature and O2 concentration. The corrosion rates first increase rapidly with pressure from 1.0 to 3.0 MPa and then remain largely stable. Meanwhile, the corrosion rates of X70, P110, and N80 in the liquid phase first increase and then decrease with temperature and reach maximum values at 90°C. The corrosion rates of X70, P110, and N80 increase notably with velocity and the concentrations of O2, SO2, H2O, and NaCl. The corrosion rate of 13Cr is considerably lower than those of N80, P110, and X70, which shows good corrosion resistance performance. To reduce the flue gas corrosion of a downhole string, the relative humidity of the flue gas should be lower than 0.7, the temperature of the flue gas in the wellbore should avoid the range between 80 and 100°C, the excess air coefficient of the boiler should be kept at a reasonable value to reduce the O2 content in the flue gas, and the flue gas should not be coinjected into wellbores with brine. The injection of flue gas is technically feasible considering the corrosion of downhole string.

This paper presents the investigation on the effect of calcium on the corrosion behavior of 1Cr carbon steel under various levels of initial CaCO3 saturation (SCaCO3) of the bulk solutions. All the experiments were performed at 80°C in 1 wt% aqueous NaCl solution saturated with CO2. Four initial SCaCO3 levels were investigated, namely 0, 0.6, 2, and 10. The corrosion process was followed using linear polarization resistance, potentiodynamic sweeps, and electrochemical impedance spectroscopy. The surface morphology of the corrosion products was analyzed with scanning electron microscopy and structural information using X‐ray powder diffraction. Precipitation of a substitutional solid solution of FexCayCO3 (x + y = 1) was found on the steel surface. The growth of this layer was delayed by Ca2+ ions in the solution, but its protectiveness was not affected and was comparable with the pure FeCO3 corrosion product. No signs of localized corrosion were detected on the material. [ABSTRACT FROM AUTHOR]

• A multi-physics model for galvanic corrosion with anisotropic deposition layer is proposed. • The morphology evolution, ion mass transfer and reactions are coupled in model. • The predicted corrosion morphology matches well with experiment data. • The competition between ion transport and reactions determines concentration field. • The relation between corrosion kinetics and deposition layer growth is revealed. The anisotropic deposit film formed during the galvanic corrosion can impede the mass transfer of the involved species, thereby affecting the electro-chemical behavior and the evolution of galvanic corrosion. The limitations of experimental studies in the spatial-temporal scales restrict a deeper understanding of the corrosion mechanism, which can be complemented by numerical simulation. A multi-physics coupled model is proposed in this work to systematically investigate the temporal and spatial evolution of galvanic corrosion of the Mg-steel couple with the growing anisotropic deposition layer. By utilizing the multi-physics field coupled technique, various coupled physical-chemical processes underlying the corrosion behavior are built into the model, including chemical reactions, ionic mass transfer in the bulk solution and the deposition layer, interfacial reaction, deposition of corrosion products as well as the morphological transitions caused by metal dissolution and deposition. In particular, the anisotropic deposit film is considered to be a porous layer with a porosity varying in time and space as the corrosion evolves. The predicted corrosion morphology by this model is better than the previous models. The coupled relationship between the electrochemical behavior (e.g., electrode reaction kinetics, current density, surface potential) and the physical processes (e.g., ionic transport, geometric evolution of metal surface and film interface) is revealed. The results indicate that a porous deposition layer with a denser inner layer and a loose outer layer is generated, leading to more significant inhibition of mass transfer in the inner layer than the outer layer. The anisotropism of the deposition layer results in a non-uniform conductivity distribution and a discontinuous current density distribution in the electrolyte. The current density on the electrode surface is inhibited by the deposition layer and the variation in the cathode/anode area ratio during the corrosion process. The competition between the transport process and the electrochemical reaction determines the spatial-temporal evolution of the ion concentration. [ABSTRACT FROM AUTHOR]

Research progress on corrosion behavior (localized corrosion, corrosion type and corrosion products) and the effects of processing methods and alloying on the corrosion resistance of hexagonal close packed (HCP) singular phase, body cubic centered (BCC) singular phase and (HCP+BCC) duplex structured Mg-Li alloys were summarized. The future research directions about how to improve the corrosion resistance of Mg-Li alloys were pointed out and the research on corrosion behavior of Mg-Li alloys should focus on the structure, main components and evolution of surface product layers. Meanwhile, it is necessary to consider the effect of alloying elements on the protective effect of surface film layers, and to study the influence of the crystallographic texture of Mg-Li alloys due to the severe plastic deformation on their corrosion behavior.

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The influence of slug flow on local corrosion of pipeline was studied, and the protection measures for slug flow corrosion were well done to improve the safety of oil-gas-water-humidity mixed pipeline. An indoor loop test was designed to simulate the slug flow in real undulating pipelines. The surface microstructures of X70 hanging pieces were studied by scanning electron microscopy (SEM) under slug flow conditions at different test stages. At the beginning of the test, there was much pitting corrosion on the surface of the hanging pieces, but at the end of the test, only some pitting or pitting spots developed into serious local corrosion. The flow corrosion of slug in pipe had obvious characteristics of cavitation corrosion. Its occurrence was the result of synergistic action of various mechanisms. The strong impact force, high impact velocity and mechanical action of multi-frequency micro-jet produced by cavitation annihilation significantly affected the development process and characteristics of electrochemical corrosion, which resulted in that the cavitation corrosion was mostly pitting corrosion. The damage of corrosion product film caused by high-speed micro-jet impact caused by cavitation cracking was local, and the pitting tendency increased at the local damage of corrosion product film. However, with the formation of electrochemical corrosion products, the destroyed corrosion product film was repaired continuously, but did not develop into local corrosion. Local corrosion occurred only when the high-speed micro-jet with cavitation breakdown repeatedly impacted a point of pitting tendency, but this probability was smaller than that of pitting tendency. [ABSTRACT FROM AUTHOR]

The effect of thiosulphate/H2S on crevice corrosion behaviour of P110 carbon steel in the CO2-saturated 3.5 wt% NaCl solution was investigated. The results showed that crevice corrosion of P110 steel could not occur in the CO2-saturated solution, likely due to the inhibition of both anodic and cathodic reactions inside crevice. Further, the structure of corrosion product film along the crevice wall is influenced by the concentration of thiosulphate. Increasing the concentration of thiosulphate to 10−2 mol L−1 promotes the formation of fine flake-like mackinawite outside crevice. In addition, crevice corrosion of P110 steel in the CO2-saturated solution is promoted by increasing the concentration of thiosulphate. This is because the dense and fine mackinawite film on the steel surface has a better protectiveness and could enhance cathodic reaction rate outside crevice. [ABSTRACT FROM AUTHOR]

The cause of pitting under dynamic DC interference is unclear. This paper studies the mechanisms of pitting in simulated solutions under neutral and alkaline conditions using weight loss, electrochemical testing, and microscopic characterization. The results indicate that the metal mainly undergoes active corrosion in the neutral solution, and the formation of millimeter-scale pits is due to local defects in corrosion products. Metals in the alkaline solution undergo passive corrosion, resulting in micro-scale pits. Initially, stable pits form at damaged areas of the passivation film. Then, pits can grow rapidly under self-catalysis, with the growth rate surpassing other surface locations. • Investigated the pitting corrosion of pipeline steel under dynamic DC interference. • Corrosion product film defects or passivation film induced pitting corrosion. • Evolution process of corrosion product film structure. • Greater risk of pitting corrosion in the neutral solution. [ABSTRACT FROM AUTHOR]

Flue gas collection from steam generators and its utilization in enhanced oil recovery (EOR) can reduce CO2 emissions into the atmosphere and improve oil recovery efficiency. Under the environments of flue gas corrosion in oilfields, the effects of corrosion time, temperature, pressure, velocity, and concentrations of O2, SO2, H2O, and NaCl on corrosion rates of steels used for a downhole string were investigated through physical simulation experiments. The corrosion mechanisms were analyzed by component, and the morphology of the corrosion products tested by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). In the gas phase, the corrosion rates of X70, P110, and N80 notably increase with temperature and O2 concentration. The corrosion rates first increase rapidly with pressure from 1.0 to 3.0 MPa and then remain largely stable. Meanwhile, the corrosion rates of X70, P110, and N80 in the liquid phase first increase and then decrease with temperature and reach maximum values at 90°C. The corrosion rates of X70, P110, and N80 increase notably with velocity and the concentrations of O2, SO2, H2O, and NaCl. The corrosion rate of 13Cr is considerably lower than those of N80, P110, and X70, which shows good corrosion resistance performance. To reduce the flue gas corrosion of a downhole string, the relative humidity of the flue gas should be lower than 0.7, the temperature of the flue gas in the wellbore should avoid the range between 80 and 100°C, the excess air coefficient of the boiler should be kept at a reasonable value to reduce the O2 content in the flue gas, and the flue gas should not be coinjected into wellbores with brine. The injection of flue gas is technically feasible considering the corrosion of downhole string. [ABSTRACT FROM AUTHOR]

The corrosion behavior of a high manganese steel in simulated marine splash zone environment was studied by dry-wet cyclic corrosion experiment and electrochemical experiment. Corrosion kinetics, composition, surface morphology, cross-section morphology, element distribution, valence state, polarization curve and electrochemical impedance spectroscopy were analyzed with the aim of characterizing the characteristics of corrosion product films. The results show that in chloride-containing environment, in the initial corrosion products, Mn oxides with porous structure lead to higher corrosion rate. As corrosion extends, the formation of alloy element oxides in corrosion products changes the corrosion properties of rust layers at different stages. Mo oxides form a stable passivation film, which reduces the influence of chloride ion on corrosion. Ni oxides in the inner rust layer facilitate the transformation of goethite, and Cr oxides in the outer rust layer increase the densification of the rust layer. The stability and compactness of Fe _3 O _4 , α -FeOOH and FeCr _2 O _4 in the later corrosion products inhibit the corrosion action of manganese iron oxides and slow down the corrosion rate. With the corrosion durations, the corrosion current density of the sample with the corrosion product film first increases and then decreases, and the corrosion potential first moves negative and then shifts in a positive direction subsequently, indicating that the protective effect of the corrosion product film is gradually significant.

The corrosion behavior of novel 3Cr2Al steel in simulated oil and gas well environments was investigated using scanning electron microscopy, electron diffraction spectroscopy, potentiodynamic polarization, and potentiostatic polarization. The results revealed that the corrosion rate of 3Cr2Al steel increased as the Cl− concentration increased. The thickness of the corrosion product film decreased as the Cl− concentration increased. The increase in Cl− concentration caused a decrease in pH value, subsequently causing an increase in the solubility of Cr(OH)3 and Al(OH)3 and hindering the deposition of corrosion product, eventually yielding a thinner corrosion film. The corrosion behavior of novel 3Cr2Al steel in simulated oil and gas well environments was investigated using SEM, EDS, and polarization. The results revealed that the corrosion rate of 3Cr2Al steel increased as the Cl concentration increased. The thickness of the corrosion product film decreased as the Cl− concentration increased. The increase in Cl− concentration caused a decrease in pH value. [ABSTRACT FROM AUTHOR]

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The surface corrosion behavior and reaction product film deposition mechanism of biodegradable as-extruded Mg-2Zn-0.6Zr- x Nd alloys with different Nd addition were investigated using electron backscattered diffraction (EBSD), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray diffraction (XRD), electrochemical test and immersion test. The results showed that 0.2–0.6 wt% Nd addition led to significant grain refinement of the alloys and the formation of fine MgZn and T phases. Excessive Nd addition (1 wt%) significantly resulted in large size Zr-rich precipitates and second phases as cathodes, causing micro-galvanic corrosion acceleration. The electrochemical measurements, immersion tests and corrosion morphologies proved that the alloy with 0.6 wt% Nd addition had the best corrosion resistance and exhibited a uniform corrosion mode, which were attributed to small grain size, fine second phases and formation of compact CaHPO 4 ·2H 2 O film. Moreover, corrosion models with different Nd contents were proposed to interpret the corrosion product film deposition mechanism. [ABSTRACT FROM AUTHOR]

The product film formed on Ni-advanced weathering steel in a tropical marine environment was investigated in detail through outdoor exposure by using diverse surface analysis techniques combined with electrochemical impedance spectroscopy and scanning kelvin probe measurements. The results showed that the product film was mainly composed of nanophasic goethite in the inner layer and maghemite, akaganeite, and hematite in the outer layer. Moreover, the resistance to atmospheric corrosion gradually increased from the outermost product film to the innermost film. Ni was significantly enriched in the inner layer in the form of the spinel phase NiFe 2 O 4 , which transformed lepidocrocite to fine-grained goethite, withstood the invasion of chloridion, and improved the corrosion potential of the product film in a tropical marine atmosphere. [ABSTRACT FROM AUTHOR]

The corrosion performance of low alloy steels with varying Cu contents (ranging from 0 to 1.2 wt%) was evaluated in a 10 wt% H 2 SO 4 solution at room temperature. By incorporating Cu, the active dissolution of the bare steel is effectively suppressed, leading to enhance corrosion resistance as the Cu content increases. However, during immersion, the corrosion product film transitions from CuO and Cu(OH) 2 dominance to Cu 2 O and Cu0 dominance. Simultaneously, hydrogen reduction induces cracks in the film, causing an uneven Cu distribution and gradual corrosion resistance degradation with higher Cu content and longer immersion duration. • Corrosion of low alloy steel with five Cu contents in simulated WFGD environment is studied. • As the Cu contents increased, the corrosion of bare steels is mitigated. • The dominance of Cu+ in the corrosion product film worsens corrosion. • The reversal of steel's corrosion resistance by Cu is discussed. [ABSTRACT FROM AUTHOR]

As-cast nickel-aluminum bronze is prone to suffering selective phase corrosion in marine environments. To solve this problem, chromium was introduced via ion implantation to modify its surface microstructure, which was characterized by high-resolution transmission electron microscopy and auger electron spectroscopy. The corrosion behavior was studied by electrochemical measurements and salt spray test. It was found that the inherent selective phase corrosion in as-cast NAB was inhibited effectively when the implantation fluence was 5 × 10 17 ions/cm 2 . The improved corrosion resistance after ion implantation was believed to stem from the rapid formation of a more protective film containing chromium oxides and hydroxides. [ABSTRACT FROM AUTHOR]

The corrosion behavior of a duplex-phase brass Cu40Zn in clean and sulfide-polluted 3.5% NaCl solutions was investigated by conducting electrochemical and gravimetric measurements. The corrosion product films were analyzed by scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction. The presence of sulfide shifted the corrosion potential of Cu40Zn toward a more negative value by 100 mV and increased the mass loss rate by a factor of 1.257 compared with the result in the clean solution. The corrosion product film in the clean solution was thin and compact; it mainly consisted of oxides, such as ZnO and CuO. By contrast, the film in the sulfide-polluted solution was thick and porous. It mainly contained sulfides and zinc hydroxide chloride (i.e., Zn(OH)Cl·HO). The presence of sulfide ions accelerated the corrosion damage of Cu40Zn by hindering the formation of protective oxides and promoting the formation of a defective film which consisted of sulfides and hydroxide chlorides. [ABSTRACT FROM AUTHOR]