The abnormal copper deposition occurred on the inner wall of the wellhead tubing leads to wellhead failure following acidizing operations in a certain block of an oilfield in western China. The deposition mechanism of copper introduced by acidizing corrosion inhibitors is systematically studied using both experimental and numerical simulation methods in this work. Deposits collected from the steel tubular sample in wellhead are analyzed and the results indicate that the deposits primarily consist of metallic copper (Cu) and cuprous oxide (Cu2O), exhibiting a multi-layered composite structure. Molecular dynamics and density functional theory approaches are conducted to simulate the structural evolution and adsorption behavior of copper-containing Mannich base corrosion inhibitor under varying pH and temperatures. The simulations demonstrate that the copper deposition mainly originates from the copper-containing Mannich base corrosion inhibitor. Throughout the acidizing, flowback, and production process, the wellbore environment transitions to higher pH and lower temperatures, the corrosion inhibitors may agglomerate and release Cu+ ions. These ions subsequently deposit on the inner wall of the wellhead tubing via disproportionation and replacement reactions, forming multi-layered copper-containing scale, which induces under-scale corrosion. The work may provide a crucial theoretical guidance for the selection of corrosion inhibitors and corrosion control strategies in oil and gas well acidizing operations.

Gas well deliquification is a key technology for mitigating liquid loading and restoring or enhancing production capacity in ultra-deep, high-temperature, and high-pressure gas wells. The abnormal corrosion behavior observed in the gas lift tubing of the Well X-1 oilfield in western China, within the 50–70 °C interval (1000–1500 m), was investigated. By analyzing the asymmetric wall thinning and axial groove morphology on the inner surface of tubing and then establishing a two-dimensional model of the vertical wellbore, the gas–liquid flow behavior and associated corrosion mechanisms were also elucidated. Results indicate that the flow pattern evolves from slug flow at the bottomhole, through a transitional pattern below the gas lift valve, to annular-mist flow at and above the valve. The wall shear stress peaks at the gas lift valve coupled with the significantly higher fluid velocity above the valve, which markedly elevates the corrosion rate. In this regime, the resultant annular-mist flow features a high-velocity gas core carrying entrained droplets, whose impingement synergistically enhances electrochemical corrosion, forming severe groove-like morphology along the inner tubing wall. Therefore, the corrosion in this well is attributed to the synergistic effect of the mechano-electrochemical coupling between multiphase flow and electrochemical processes on the inner surface of the tubing.

In the present work, novel Al2O3 particles were used to reinforce heterogeneous CoCrFeMnNi high-entropy alloy (HEA) matrix composites with nano- (5.0 wt.%) and nano- + micro- (5.0 wt.% + 10.0 wt.%) specimens. Al2O3 particles were fabricated via gas atomization and spark plasma sintering. The microstructure evolution and properties, i.e., density, hardness, and room temperature compression, were systematically investigated. The results indicate that the concentration of the Cr element in the pure CoCrFeMnNi HEA and the HEA matrix composite can be effectively reduced by using a gas-atomized HEA powder as the matrix. The formation of an impurity phase can also be inhibited, while the distribution uniformity of matrix elements can be improved. The composites prepared via gas-atomized powders formed a network microstructure composed of continuous Al2O3-rich regions and isolated Al2O3-poor regions, exhibiting good plasticity and improved density. The relative densities of the pure HEA, nano- (5.0 wt.%), and nano- + micro- (5.0 wt.% + 10.0 wt.%) composites were 98.9%, 97%, and 94.1%, respectively. The results demonstrate a significant improvement in the relative densities compared to the values (97.2%, 95.7%, and 93.8%) of the composites prepared via mechanical alloying. In addition, compared to the compressive fracture strains of nano- (5.0 wt.%) and nano- + micro- (5.0 wt.% + 10.0 wt.%) composites based on the mechanically alloyed HEA powder, the values of the nano- (5.0 wt.%) and nano- + micro- (5.0 wt.% + 10.0 wt.%) specimens prepared via gas atomization and spark plasma sintering increased by 80% and 67%, respectively.

It is difficult for traditional aluminum alloy manufacturing technology to meet the requirements of large-scale and high-precision complex shape structural parts. Wire Arc additive manufacturing technology (WAAM) is an innovative production method that presents the unique advantages of high material utilization, a large degree of design freedom, fast prototyping speed, and low cast. As a result, WAAM is suitable for near-net forming of large-scale complex industrial production and has a wide range of applications in aerospace, automobile manufacturing, and marine engineering fields. In order to serve as a reference for the further development of WAAM technology, this paper provides an overview of the current developments in WAAM both from the digital control system and processing parameters in summary of the recent research progress. This work firstly summarized the principle of simulation layering and path planning and discussed the influence of relative technological parameters, such as current, wire feeding speed, welding speed, shielding gas, and so on. It can be seen that both the welding current and wire feeding speed are directly proportional to the heat input while the travel speed is inversely proportional to the heat input. This process regulation is an important means to improve the quality of deposited parts. This paper then summarized various methods including heat input, alloy composition, and heat treatment. The results showed that in the process of WAAM, it is necessary to control the appropriate heat input to achieve minimum heat accumulation and improve the performance of the deposited parts. To obtain higher mechanical properties (tensile strength has been increased by 28%–45%), aluminum matrix composites by WAAM have proved to be an effective method. The corresponding proper heat treatment can also increase the tensile strength of WAAM Al alloy by 104.3%. In addition, mechanical properties are always assessed to evaluate the quality of deposited parts. The mechanical properties including the tensile strength, yield strength, and hardness of the deposited parts under different processing conditions have been summarized to provide a reference for the quality evaluation of the deposition. Examples of industrial products fabricated by WAAM are also introduced. Finally, the application status of WAAM aluminum alloy is summarized and the corresponding future research direction is prospected.

ABSTRACTAs an important infrastructure for oil and gas transportation, the safe and stable operation of long‐distance pipelines is significant for guaranteeing national energy security and economic development. However, pipelines are susceptible to corrosion due to various factors. Therefore, it is crucial to take effective corrosion protection measures. Pulse current cathodic protection technology, as an advanced pipeline corrosion protection technology, is superior to traditional cathodic protection technology. This paper mainly summarizes the research progress of pulse current cathodic protection technology for long‐distance pipelines in recent years. It briefly discusses the protection mechanism, characteristic parameters, challenges, and development trends of pulse current cathodic protection technology, which provides a useful reference for the further promotion and application of pulse current cathodic protection technology for long‐distance transport pipelines.

Battery interface research can effectively guide battery design and material selection to improve battery performance. However, current electrode material interface studies still have significant limitations. In this paper, by employing DFT-D method, the influences of doping elements (boron, nitrogen, phosphorus, sulfur, and silicon) on the properties of C60 fullerene, such as structural stability, electronic properties, and the adsorption and migration of lithium ion, are comprehensively investigated. It is demonstrated that doping can bolster the fullerene molecule’s structural integrity and enhance charge transfer comparing with C60, thereby augmenting the material’s electrical conductivity. Among the five doping elements, B-doping exhibits the most favorable adsorption energies, indicating a strong lithium binding affinity. This observation is supported with energy barrier of lithium ion migration. B-doping leads to an elevated barrier (0.37 eV) comparing with pristine C60 (0.19 eV), whereas Si-doping significantly reduced barrier (0.038 eV) indicates enhanced lithium-ion mobility. These findings solid the efficacy of doping as a strategy to enhance the performance of fullerene electrodes. All DFT calculations were performed using the VASP software package. The chosen computational technique was a combination of the generalized approximate gradient function PBE with the dispersion correction (DFT-D3) developed by Grimme. The results of the calculations were analyzed with the help of VASPKIT.

An in-depth understanding of the bimodal scale particle reinforced composites, including the particle content and size, phase constitution and distribution, and their effects on mechanical properties and deformation mechanisms, is essential to advance the study of high performance high entropy alloys (HEAs). In this study, the bimodal-sized (nano + micron)(N + M)-Al2O3P/CoCrFeMnNi reinforced composites and monomadal-sized micron(M)-Al2O3P/CoCrFeMnNi reinforced composites were successfully fabricated using a two-step ball milling process in conjunction with spark plasma sintering (SPS) technology. Results showed that the Al2O3P/ CoCrFeMnNi composites primarily consisted of fcc structure, with Al2O3 and MnAl2O4 as secondary phases. The M-Al2O3P reinforced composites contained obvious heterogeneous structure while (N + M)-Al2O3P reinforced composites exhibited a multi-scale grain structure comprising of double-sized reinforcement and multiple-sized matrix grains. The yield strength (YS) of bimodal-size particle reinforced composites was higher than that of monomadal particle reinforced composites. For example, the YS of (N-5)/(M - 5) and (N-5)/(M - 10) composites was 117% and 133% higher than that of HEA, respectively. Intriguingly, (N + M)-Al2O3P reinforced composites effectively addressed the issue of reduced material strength caused by a high concentration of particles with a monomadal size. Moreover, the composites of (N-5)/(M - 5) and (N-5)/(M - 10) with a high content of lightweight Al2O3P effectively contributed to the reduction in density of HEA, exhibiting a decrease by 11% and 17% compared to pure HEA, respectively.

In the present work, 15 Mo/VC interfaces were investigated using first-principles calculations based on density functional theory. Four possible interface orientations, two terminations, and three stacking sites were considered. The adhesion energy (Wad) and interfacial energy (Eint) of these interface models were computed. The results indicate that the C-terminated hollow-site Mo(110)/VC(111) interface exhibits the highest stability with a larger Wad value of 10.64 J m−2 and the lowest Eint value of 2.98 J m−2, followed by the V-terminated central-site Mo(211)/VC(220) interface. Analysis of the electronic structure reveals the formation of strong polar covalent bonds at these interfaces. Additionally, simulations of tensile fracture processes were performed, demonstrating that at strains reaching 22% and 32%, respectively, the ideal tensile strengths for the C-terminated hollow-site Mo(110)/VC(111) interface and V-terminated central-site Mo(211)/VC(220) interface are ∼26.01 and 35.53 GPa. In particular, in the C-terminated hollow-site Mo(110)/VC(111) interface, fracture occurs in the Mo slabs due to concentrated strain when external strain is applied; meanwhile, uniform strain is observed in both Mo(211) and VC(200) slabs within this system. Notably, the V-terminated central-site Mo(211)/VC (220) interface demonstrates excellent tensile strength as well as toughness. These findings suggest that explaining solely based on adhesion work is insufficient to account for the observed tensile strength at these interfaces.

In the present work, Mo/VC multilayers with constant period (10 nm) and different modulation ratios (from 6:4 to 9:1) were deposited by dc magnetron sputtering. We investigated the microstructure and mechanical properties of Mo/VC multilayers. XRD and TEM results indicated that Mo was a bcc structure and VC was a NaCl B1 (fcc) structure. An HRTEM image revealed the coherent interfaces between the Mo and VC layers. Hardness and toughness were studied using the Nanoindent and Microindent methods, respectively. It was found that the multilayers hardness remained as high as ~22 GPa, while the toughness increased from 2.91 to 4.70 MPa·m1/2 and the modulation ratio varied from 6:4 to 9:1. The enhancement of both hardness and toughness is attributed to the interfaces and the lamellated structure. The first-principles method was also used to determine the most stable interface model and the formation mechanism of the interface between the Mo and VC layers.

For the internal corrosion problem of oil well casing， high-temperature and high-pressure weight loss tests， polarization curves， AC impedance spectroscopy， and potentiostatic polarization electrochemical testing techniques were used， combined with finite element simulation calculations， to study the casing internal corrosion protection technology of solid corrosion inhibitors combined with cathodic protection and its synergistic promotion mechanism.Results showed that the corrosion inhibition rate of J55 casing was 85.91%when the on-site concentration of solid corrosion inhibitor was 120 mg/L， meeting the standard requirements， but the corrosion rate was relatively high， which was 0.307 9 mm/a.The selected solid corrosion inhibitor belonged to the cathodic corrosion inhibitor.Therefore， cathodic protection could significantly promote the adsorption and retardation effect of corrosion inhibitor particles.After adding－50 mV cathodic polarization potential，the adsorption polarization resistance of corrosion inhibitor increased from 505.59 Ω·cm2 to 1 878.50 Ω·cm2.The protection distance of the high-temperature aluminum anode to the J55 bare steel pipe was calculated by finite element simulation software， which was only 11.104 m.After applying the solid corrosion inhibitor combined with sacrificial anode cathodic protection， solid corrosion inhibitor extended the protection distance of the sacrificial anode.The effective protection distance continued to extend as corrosion inhibitors coverage increased continuously.When the corrosion inhibitor coverage reached 98%， the effective protection distance was above 100 m.The solid corrosion inhibitor and cathodic protection had a synergistic promotion effect.Indoor experiments showed that under the combined action， the uniform corrosion rate of J55 casing decreased to 0.010 2 mm/a， and the corrosion inhibition rate reached 99.53%， demonstrating excellent protective effects.

通过模拟井下环境的均匀和局部腐蚀试验,结合电化学测试分析,研究了J55 套管钢的腐蚀行为和腐蚀机理.结果表明:随着温度的升高,J55 套管钢的CO2 均匀腐蚀速率逐渐增大,当温度达到 60℃时,其腐蚀速率达到最大值,即 1.0175 mm/a,并且局部腐蚀最为严重.SRB、TGB导致J55 套管钢的均匀腐蚀速率明显增大,局部腐蚀程度显著增强.在单独CO2 腐蚀环境中,J55 套管钢的阴极和阳极均表现为活化反应,自腐蚀电位下的腐蚀电流密度为阴极反应过程所控制.随着温度的升高,其电化学腐蚀热力学趋势增强,当温度达到 60℃时,J55 套管钢动力学阻力达到极小值点,自腐蚀电流密度最大.SRB、TGB使J55 钢在CO2 腐蚀环境中的自腐蚀电位明显降低,并显著促进了CO2 腐蚀的阴极氢去极化过程,导致J55 钢的阳极溶解加速.

The new Cu-bearing High Frequency Welding （HFW） steel for welded pipes is prepared by Cu alloying,using a 150 kg vacuum induction furnace,forging the ingot into a billet,followed by solution treatment at 1 050℃.The treated billet is made into a steel plate using a controlled rolling and cooling process,with a 1 h ageing precipitation at 550℃.The treated steel plates are rolled into round tubes which are welded by high frequency welding technology.The Cu alloying improves the surface properties of the material and gives it good antibacterial properties.This paper investigates the corrosion behaviour of the new Cu-bearing HFW welded pipe base material and welded joint,conventional welded pipe material L360,in the SRB environment for simulated corrosion experiments to explore its corrosion resistance and reveal the bactericidal mechanism of the antibacterial relative microorganisms in the material.The experimental solution is a simulated microbial corrosion environment solution,the microorganism used in this paper is sulfate-reducing bacteria （SRB） for corrosion experiments.The SRB strain was activated by using SPX-250B biochemical incubator at 37℃.The activated SRB solution was injected into a Cl - solution at a concentration of 34 000 mg/L.Corrosion specimens were taken from welded Cu-bearing steel base material,welded joint and L360 pipeline steel and machined using high-precision wire-cutting to produce 50 mm×10 mm×3 mm corrosion hangers.The corrosion weight loss test was selected at a temperature of 37℃ and the test period was 30 days.Before the experiments,the specimens were ground with steel sandpaper to eliminate mechanical processing traces,and the de-oiled and dehydrated specimens were placed in a dryer to dry,and the size and mass of the experimental hangings were recorded to 0.001 mm and 0.1 mg respectively.The corrosion products were removed from the specimens for weighing and calculating the corrosion weight loss rate,the uniform corrosion rate was calculated according to NACE SP 0775-2018 standard,the samples Cu-bearing steel and L360 immersed in SRB solution were removed after the experiment,the specimens with biofilm were first immersed in 2.5%glutaraldehyde/phosphate （NaCl content 8.7 g/L;KH 2 PO 4 content 0.4 g/L;K 2 HPO 4 1.23 g/L） buffer solution for 30 min.The specimens were dehydrated and fixed in alcohol at 20%,50%,75% and 100% concentrations for 10 min and then dried and stored.The surface information of the specimens was subsequently observed using a GIMI500 field emission scanning electron microscope and energy spectrum analysis of the relevant areas.The microstructure of Cu-bearing steel is granular bainite and polygonal ferrite with a small amount of pearlite.The analysis of the microstructure of Cu-bearing steel reveals that the Cu-bearing steel precipitated phase is nano-Cu-rich phase and the matrix is α-Fe;the microstructure of L360 is polygonal ferrite and lamellar pearlite.The results of SRB corrosion experiments showed that the corrosion rates of Cu-bearing steel base material,welded joint and L360 in SRB solution were 0.007 1 mm/a,0.023 9 mm/a and 0.010 0 mm/a,respectively,and their maximum pitting rates were 0.025 9 mm/a,0.174 0 mm/a and 0.254 0 mm/a,respectively,with the pitting rate of L360 being 10 times higher than that of Cu-bearing steel.Through corrosion products,bacteria distribution and morphology of scanning electron microscopy observation found that the surface of Cu-bearing steel ladle corrosion products in Cu elements aggregation,the surface was not found to be structurally intact biofilm,corrosion media in the material surface hydrolysis generated by Cu ions effectively destroy the corrosion of the initial rapid attachment to the metal surface biofilm,thus forming a residue on the metal surface,near the shrinkage and tissue fluid spillage of bacteria found.Cu-bearing steel weld zone biofilm structure is intact,there are a large number of bacteria adsorption and good bioactivity,microbial corrosion under the film to produce corrosion pits caused by local film rupture,pitting corrosion is serious.After HFW welding joint weld zone pitting corrosion susceptibility is enhanced and corrosion resistance is reduced.Cu-bearing steel will form biofilm by rapid adsorption of SRB on the material surface at the early stage of corrosion,and the non-uniformity of SRB biofilm increases the active site of corrosion.The surface Cu-rich phase at the bottom of the biofilm is hydrolyzed,and the Cu ions from the hydrolysis are purposefully aggregated at the center of the biofilm.When free Cu ions come into contact with bacteria,they enter inside the biofilm to disrupt its cell wall and membrane structure or disrupt the biological environment,and the bactericidal effect of Cu ions from the center of the biofilm to the outside is from strong to weak.The aggregation of Cu ions had the most significant bactericidal effect at the center of the biofilm,and partially shriveled and dehydrated bacteria were found at the edge of the envelope produced after biofilm death.

In view of the practical problem that the impressed current method fails to effectively protect the buried long-distance pipeline section crossingwater area, the joint cathodic protection method ofimpressed current and sacrificial anodewas used for the maintenance and treatment.Herein, the interaction law of impressed current with the magnesium alloy sacrificial anode for cathodic protection, as well as the influence of coating damage rate on the effect of joint cathodic protection, was studied through electrochemical experiments. Meanwhile, the protection effect of sacrificial anode was evaluated with finite element simulation and calculation. Besides, the laboratory research results were also verified in the field. The results show that there is anode output current at the sacrificial anode when the impressed potential is positive to the open-circuit potential of the sacrificial anode, and there is cathode input current at the sacrificial anode when the impressed potential is negative to the opencircuit potential of the sacrificial anode. With the increase of the impressed potential and the coating damage rate, the output current of the sacrificial anode decreases, the working potential shifts negatively, and the effect of cathodic protection is weakened. The cathodic protection potential of the under-protectedsection of the target pipeline near the water area could meet the-0.85 VCSE criterion under the joint cathodic protection of impressed current and sacrificial anode. Compared with the impressed current cathodic protection method, the joint cathodic protection effect is significantly improved, with the protection rate increased from 52.6% to 100%, and the pipeline potential is distributed more uniformly. Therefore, the sacrificial anode could be used as an auxiliary cathodic protection measure for the special environmental pipelines with local under-protected sections or positive potential.（10 Figures, 3 Tables, 20 References）

长输管道运行多年后局部防腐层会出现明显劣化,外加电流阴极保护系统已不能对全管段进行有效保护,需要在欠保护区域追加牺牲阳极辅助保护.本文通过仿真计算手段研究了涂层破损率、土壤电阻率和并行管道对牺牲阳极辅助保护措施效果的影响,并以镁合金牺牲阳极进行了现场验证.结果表明:在相同的牺牲阳极保护方案下,当防腐层破损率从0.05%增加到 10%时,管道的保护效果逐渐降低,且当长输管道防腐层破损率超过5%时,添加牺牲阳极的辅助阴极保护方法效果不佳,应考虑修补或更换防腐层;随着土壤电阻率的增大,牺牲阳极保护的管道距离缩短,且当土壤电阻率超过30 Ω·m左右时,需考虑在欠保护管段部位添置外加电流防腐站的方法,以保证管道的安全运行;当目标管道涂层破损率和土壤电阻率较小时,存在防腐层质量不高的并行管道可以提高目标管道的防护效果.现场试验同样表明:镁合金牺牲阳极可为涂层破损率和土壤电阻率较小的目标管道提供有效防护,且防腐层质量不高的并行管道提高了牺牲阳极保护效果.

采用基于密度泛函理论(DFT)的第一性原理研究方法,考察了DO22-Al3 Nb、L12-Al3 Y和DO22-Al3 V等3种金属间化合物的热力学稳定性、电子结构和力学性能.计算结果表明,Al3X(X=Nb,V,Y)金属间化合物的生成焓均为负值,表明三者均为热力学稳定态,且DO22-Al3 Nb的生成焓最负,其热力学稳定性最高,L12-Al3 Y和DO22-Al3 V次之.杨氏模量E和剪切模量G由大到小排序为DO22-Al3 Nb>DO22-Al3 V>L12-Al3 Y,可见三者中DO22-Al3 Nb强度较高.体模量(B)和剪切模量(G)的比值B/G可用以预测延展性,B/G值排序为DO22-Al3 V>DO22-Al3 Nb>L12-Al3 Y,可知三者中DO22-Al3 V延展性较好.各向异性指数AU的排序为DO22-Al3 V>L12-Al3 Y>DO22-Al3 Nb.根据电荷密度差分(EDD)和分波态密度(PDOS),考察了三者的原子间成键情况.Al原子倾向于失去电子,而V、Y、Nb原子倾向于得到电子.Al-3s3p轨道和V-3d、Y-4d、Nb-4d轨道的价电子具有强烈的杂化作用,所形成的Al-V、Al-Y和Al-Nb键具有显著的共价特征.

在对某油田套损井工况调研的基础上,通过采出水成分、腐蚀产物成分等分析,明确了套管内、外腐蚀环境及腐蚀原因.通过化学成分分析及模拟工况环境的腐蚀速率测试评价了在用套管材料的耐蚀性;通过有限元模拟方法计算得到套管内置和外置牺牲阳极在不同环境中的有效保护距离;通过释放率和缓蚀率测试评价了在用固体缓蚀剂的缓蚀性能.最后根据评价结果对防腐蚀措施提出了改进建议.

Metal materials are vulnerable to corrosion in the process of production and service, which often leads to serious disasters, including the decline of the performance of metal components and the shortened service life, and even causes catastrophic accidents and ecological damage. Adding a certain amount of corrosion inhibitors (CIs) to the corrosive medium is a simple, efficient, and economical anti-corrosion method to slow down and restrain the corrosion of metal materials. Organic corrosion inhibitors (OCIs) are considered to have good application prospects and are widely used for surface anti-corrosion of metal materials, as they generally have advantages such as good metal adsorption, low oxidation resistance, good thermal and chemical stability, and green environmental protection. This paper systematically summarized some major OCIs, including alkyl chains, imidazoles, and pyridines, and their structural characteristics, as well as the action mechanism of OCIs. Moreover, this paper discusses some natural compounds used as environmentally friendly CIs and provides a prospect for the development trend of OCIs.

In the present work, novel nano-Al2O3p reinforced heterogeneous CoCrFeMnNi matrix composites with 0-7.5 wt% Al2O3p were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) method. The microstructure evolution and properties, i.e., density, hardness and room temperature compression were systematically studied. The results show that different degrees of heterogeneous matrix organization occurred in the composites. The CoCrFeMnNi-2.5 wt%Al2O3p composite consists of CG region and UFG region of uniformly distributed nano-Al2O3p. And the addition of nano-Al2O3p can effectively refine the matrix grains. Compared to pure HEA, the grain size of CoCrFeMnNi-5.0 wt%Al2O3p composite is refined by 48.5%. With the increase of nano-Al2O3 content, the hardness values of the composites increased by 23.6%-56.7% than those of pure HEA. Among the nanocomposites, the CoCrFeMnNi-5.0 wt%Al2O3p composite exhibits the best strengthening effect, while the CoCrFeMnNi-2.5 wt%Al2O3p composite shows a superior strong plastic synergistic effect with yield strength, ultimate compressive strength and fracture strain of 913 MPa, 1935 MPa and 38%, respectively. However, with the Al2O3p content further increases to 7.5 wt%, both the strength and plasticity of the composite decrease due to the serious agglomeration of nanoparticles.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

In view of the CO2 corrosion environment of oil and gas fields, the corrosion behavior of 5Cr, 9Cr and 13Cr steels was studied by high temperature and high pressure weight loss test and electrochemical test with J55 material as comparison. Scanning electron microscopy (SEM) analysed the morphology of corrosion products. The corrosion resistance mechanism of Cr-containing steel was analyzed from the perspective of structural stability by firstprinciples. The results show that the uniform corrosion rate of Cr-containing alloy steel is lower than that of J55 steel, and the CO2 corrosion resistance of the material increases with the increase of Cr content. With the increase of temperature, the self-corrosion current density of different Cr-containing steels gradually increases, the pitting potential of 9Cr and 13Cr gradually decreases, and the pitting resistance decreases. The electrochemical corrosion kinetic resistance of Cr-containing steel increases under long-term immersion corrosion. Molecular dynamics and first-principles calculations show that the corrosion product preferentially formed by Fe is FeCO3, and the corrosion product preferentially formed by Cr is Cr(OH)(3). On the surface of the iron matrix, Cr (OH)(3) is more easily adsorbed on the surface of the iron matrix, thereby protecting the matrix from corrosion resistance.