The integrity of CO2 injection wells is crucial for the long-term safety of carbon capture, utilization, and storage (CCUS) technology. This study investigated how impurities such as H2S, SO2, and O2 affect the passivity and localized corrosion of 13Cr stainless steel (SS) under simulated injection well conditions (30 MPa, 80 °C), via high-temperature and high-pressure (HTHP) corrosion simulation experiments, coupled with surface characterization techniques, including 3D profilometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and simulation calculations. Results show that the stability of the passive film decreases with the increase in impurity types in the CO2 fluid. 13Cr SS remains passive in the impurity-free supercritical CO2 system, while all impurity-containing systems induce localized attack, with the most severe corrosion in the CO2-O2-SO2-H2S system. The presence of impurities and their interactions significantly enhances the corrosivity of the wellbore environment. On the one hand, trace amounts of HS- and S2- formed by the hydrolysis of H2S tend to induce an increase in defects within the passive film. On the other hand, elemental sulfur and H2SO4 produced by reactions among impurities lead to a significant decrease in the system pH, resulting in a marked increase in the passive current density of 13Cr SS in the multi-impurity system. With increasing impurity types, the main components of the passive film, originally composed of Fe2O3, Cr2O3, and Cr(OH)3, are gradually doped with corrosion products such as FeS2, FeS, FeSO4 and FeOOH, leading to a progressive decline in its stability.

This study systematically investigates the corrosion behavior and mechanisms of 9Cr and S13Cr martensitic heat-resistant steels under the simulated service conditions of shale oil in-situ conversion heating wells, using high temperature and high pressure corrosion experiments (600 degrees C, 18.82 MPa, H2O-CO2-H2S-H2) combined with microstructural characterization techniques. The results indicate that, due to the competing oxidation and sulfidation reactions, both materials develop a double layer corrosion product film. The outer scale mainly consists of FeS and Fe3O4 and undergoes severe spallation, while the inner layer is composed of (Fe, Cr)3O4 and FeS. S13Cr exhibits superior corrosion resistance compared with 9Cr, with an average corrosion rate approximately 60% lower than that of 9Cr. This improvement is primarily attributed to its higher Cr content, which promotes the formation of (Fe, Cr)3O4 in the inner layer, resulting in a denser and more protective film and thereby reducing the corrosion rate. This study provides important guidance for the selection and design of corrosion resistant oil-casing materials for shale oil in-situ conversion under complex service environments.

The influence of temperature on the service safety of downhole production equipment cannot be ignored in the harsh corrosive environment containing CO2 and H2S during ultra-deep oil and gas exploitation. This study investigated the effects of temperature on the corrosion behavior and surface film characteristics of 028 alloy exposed to CO2 and H2S environments under high-temperature and high-pressure conditions by in-situ electrochemical measurement, immersion test, surface analysis technique and thermodynamic calculation. The results show that the corrosion resistance of 028 alloy gradually decreases with increasing temperature, which is closely associated with the protective property of the surface film. When the temperature is below 200 °C, the charge transfer process exhibits a high activation energy and acts as the rate-determining step of the corrosion reaction. The surface film presents a low tendency to transform into a corrosion product film and retains the nature of an amorphous passive film, which is mainly composed of Cr2O3 and Cr(OH)3. Nevertheless, the competitive adsorption of corrosive ions increases the defect density of the passive film, accompanied by the local deposition of small amounts of NiS and FeS2. When the temperature exceeds 200 °C, the reduction in surface activation energy makes the diffusion process dominate the corrosion reaction. Meanwhile, the enhanced adsorption of sulfur-containing species accelerates the transformation of the passive film into a double-layered corrosion product film. The inner layer is a dense CrOOH film that inhibits the growth of outer sulfides, while the outer layer is composed of NiS and FeS2 with nanocrystalline characteristics.

In this study, a water chemistry model applicable to supercritical CO2-H2S-Cl- environments is developed to quantitatively characterize the species information in solution. Based on this, the electrochemical corrosion thermodynamic and kinetic models are established to determine possible electrode reactions and predict the corrosion rate of bare carbon steel. The accuracy and reliability of corrosion prediction model are validated by the results of high-pressure electrochemical tests. The contributions of various cathodic reactions to corrosion and their rate-determining steps are determined by the mechanistic model. Concurrently, the role of H2S in altering the electrochemical reaction mechanism of bare carbon steel is elucidated.

In this work, the coupling effect of H2S and SO2 on the corrosion mechanism of X65 steel under gaseous and supercritical CO2 phase states was clarified. The impurities in supercritical CO2 make the corrosion of steel more serious. At the same conditions, SO2 causes more corrosion than H2S by promoting greater H+ formation in the aqueous phase, which enhances the hydrogen evolution reaction. Noteworthy, under the coupling effects of H2S and SO2, their reaction products alter the corrosion film of steel. Especially, the formation of H2SO4 intensifies the hydrogen evolution reaction, causing more severe corrosion than with a single impurity.

The corrosion behavior of X52 steel in high-pressure CO2 environments with multiple impurities was investigated using weight loss tests and surface analysis techniques. The effects of temperature, pressure, impurity concentration and H2O content on the corrosion of X52 steel were analyzed. The results show that the influence of various factors on the corrosion rate of X52 steel follows this order: H2O content > CO2 pressure > temperature > H2S concentration > NO2 concentration > SO2 concentration > O-2 concentration, with H2O content and CO2 pressure identified as the dominant factors. The corrosion mechanism of X52 steel does not change with the variation of temperature, pressure, impurity concentration, and H2O content, which is primarily controlled by the reaction products among impurities. Additionally, a corrosion prediction model is developed based on experimental data, with an overall average error of 10.3 %.

In this study, the corrosion behavior of X52 steel in liquid and supercritical CO2 environments with different water contents and coexistence of O2, SO2, NO2 and H2S gas impurities was investigated by means of mass loss method, surface analysis techniques and water chemistry simulations. The results show that benefiting from more corrosive substances and more corrosive aqueous phase, the corrosion degree of X52 steel in a liquid CO2 environment is larger than that in a supercritical CO2 environment. The formation of corrosion products is not affected by the changed CO2 phase state environment but is greatly affected by the water content in CO2 fluid. The impurities, the product of impurity reactions and the further oxidation of corrosion products jointly dominate the formation of corrosion products on the steel.

In this paper, the corrosion behaviour of nickel-based Alloy 028, 825 and 718 in a H2O-CO2-H2S-H2 mixed-gas atmosphere at 400 degrees C, 500 degrees C and 600 degrees C was investigated by corrosion simulation experiments, and the effect of temperature on the film structure of the corrosion products was investigated by microanalysis techniques. The results showed that the weight gain and thickness of the corrosion product film of nickel-based alloy increased rapidly with temperature. Alloy 825 has the best comprehensive corrosion resistance at three temperatures. The corrosion of nickel-based alloy was mainly caused by the combined effect of H2O oxidation and H2S sulphation, with CO2 and H2 having less influence on the formation of corrosion products. Cr is susceptible to oxidation at all three temperatures, forming an inner Cr2O3 film. Fe and Ni are more susceptible to forming an outer (Fe/Ni)S film at 400 degrees C and 500 degrees C and Fe3O4 and Ni3S2 film at 600 degrees C.

The corrosion evolution behavior of X65 steel in water-saturated supercritical CO2 streams with the impurities of 1000 ppmv O2 and 1000 ppmv SO2 at 8 MPa and 50 degrees C was investigated mainly by in-situ observation and electrochemical measurement. H2SO4 generated by impurity reaction promotes the precipitation of aqueous phase and dominates the FeSO4 film formation at the initial corrosion stage. With the corrosion proceeds, the corrosion product film with outer FeOOH layer and inner FeSO4 layer ultimately forms due to the oxidation of FeSO4. The time-dependent variation of corrosion kinetics is closely associated with the evolution of corrosion product film characteristics. A schematic model is established to depict the corrosion evolution process.

In this study, slow strain rate tension tests were conducted on an X80 steel weld in 12 MPa mixed gases with 2 %- 75 % H2 ([H2]) and 0 %-0.75 % CO ([CO]). The influence mechanism of CO on inhibiting hydrogen embrittlement (HE) was explored with the aid of the first-principles method and hydrogen permeation tests. The results show that the HE index first decreases rapidly with the increase of [CO] or [CO]/[H2], and then tends to stabilize. CO can restore the hydrogen induced plastic loss to a certain value, and the recovery degree decreases with the increase of [H2]. CO preferentially occupies the hydrogen adsorption site when co-existing with H2, and can reduce but not completely inhibit hydrogen permeation, this is the essential reason why the change of [CO] affects HE susceptibility.

The effect of HNO3 and H2SO4 impurities on hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of X70 steel in CO2-saturated water environment was investigated. Concurrently, a method for characterizing the contribution of corrosion-produced hydrogen to SCC was developed. HNO3 and H2SO4 boost the hydrogen permeation through promoting cathodic hydrogen evolution. The hydrogen embrittlement induced by corrosion-produced hydrogen, together with anodic dissolution, dominates the SCC process of X70 steel. The steel has much higher SCC susceptibility in H2SO4-containing environment than in HNO3-containing environment, which is closely related to the much stronger hydrogen embrittlement effect caused by H2SO4 than HNO3.

Abstract During offshore oil production, O2 could be introduced into the multiple thermal fluid, and the temperature of the wellbore can reach up to 200°C, which may result severe corrosion of tubing. However, the corrosion mechanism of downhole pipes in such aggressive environment remains unclear in the high-temperature and high-pressure CO2-O2-H2O mixed environment. Herein, we investigated the corrosion behaviour of N80 steel with different temperatures in CO2-O2-H2O environment. The influence of temperature on composition and structure of the corrosion product film of N80 steel was characterized by scanning electron microscope, energy-dispersive spectroscopy and X-ray diffraction. The results show that the corrosion rates of N80 steel performed a downward trend with the increase of the temperature, but it increased slightly at 180°C. The corrosion rate of N80 steel was up to 1.6 mm/y at 60°C, owing to the damage to corrosion product film by O2 and reduced its protection at lower temperature. As the temperature increased, the formation of Fe3O4 enhanced the protection of the inner corrosion product film, thereby greatly reducing the corrosion rate. However, the product of (FeCa)CO3 in the corrosion film completely lost its protection at 180°C, and the corrosion rate increased slightly to 0.84 mm/y. With the temperature increased to 240°C the corrosion rate of N80 steel reduced to 0.24 mm/y on account of the formation of dense and complete Fe3O4.

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.

This study explored the microstructure evolution of 2205 duplex stainless steel (DSS) and further probed its effects on microhardness and corrosion performance. The results show that the dislocation multiplication, strain-induced martensite generation and grain refinement resulted from pre-stain increase the microhardness of DSS. Compared with the degradation of corrosion resistance at 7% pre-strain, the improved corrosion resistance at 14% and 21% pre-strain is related to the smaller surface energy difference, more strain-induced martensite and more low-angle grain boundaries. The changed pitting nucleation sites with the rise of pre-strain strongly depend on the increased dislocation density and strain-induced martensite.

In this study, the corrosion behavior of N80 steel exposed to 80 bar supercritical CO2 and 0 -15 bar H2S environments was investigated by weight loss test, surface analysis, water chemistry simulation, corrosion thermodynamic and kinetic calculations. The results show that a very low H2S pressure of 0.004 bar in supercritical CO2 environment boosts the corrosion rate of N80 steel, whereas the rate is considerably reduced with further increasing the H2S pressure. The variation of corrosion rate with H2S pressure largely depends on the changes in cathode process and overall protectiveness of corrosion product film caused by H2S. As the H2S pressure rises, the evolution of corrosion product film on the steel is as follows: FeCO3 dominated film below 0.16 bar H2S, FeCO3 and FeS mixed film within 0.16-4 bar H2S, and FeS dominated film over 4 bar H2S. Benefiting from the integrity of film structure and the uniformity of film composition, N80 steel experiences uniform corrosion in the formation environment of FeCO3 or FeS dominated film. However, the localized corrosion easily occurs in the formation environment of FeCO3 and FeS mixed film owing to the loss of film integrity induced by uneven precipitation of FeCO3 inside the corrosion product film.& COPY; 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 this study, the evolution of microstructure and its correlation with hardness and pitting corrosion resistance in duplex stainless steel (DSS) welded joints were investigated. The results showed that the precipitation of chromium nitride, refined grain size and large residual deformations contributed to the increase of microhardness in the heat affected zone (HAZ) and weld metal (WM). Poor pitting corrosion resistance was found in the HAZ, especially in the high temperature heat affected zone (HT-HAZ). The chromium nitride precipitates and secondary austenite were the main pitting nucleation sites.

目的 确立一种用于油田采出水中咪唑啉类缓蚀剂残余浓度检测的技术方法.方法 采用紫外–可见分光光度法测量了咪唑啉类缓蚀剂的紫外吸收光谱和吸光度,研究了油田采出水模拟溶液中矿化度、pH值及Fe3+等对缓蚀剂吸光度的影响,分析了不同因素影响下缓蚀剂浓度与吸光度之间的相关性.结果 采出水矿化度的变化及Na+、K+、Ca2+、Mg2+、Cl?、SO42?、HCO3?等离子的存在对缓蚀剂的吸光度值影响很小,对缓蚀剂浓度检测的影响轻微.然而,采出水中可能存在的悬浮物对缓蚀剂吸光度的测量具有显著影响,检测之前需要对采出水进行过滤处理.在碱性环境中pH值的变化(7～11)对缓蚀剂的吸光度基本无影响,而在酸性介质中pH值的变化(2.5～7)导致缓蚀剂的吸光度在–0.02～0.02范围内波动,引起的缓蚀剂浓度检测误差约为±5 mg/L.采出水中可能存在的Fe3+对缓蚀剂吸光度的测量影响很大,在缓蚀剂浓度检测过程中需要消除Fe3+对吸光度测量的干扰.结论 提出了油田采出水中咪唑啉类缓蚀剂残余浓度检测技术方案:取缓蚀剂样品配制至少2种浓度的缓蚀剂溶液,测定特征吸收峰波长λ和吸光度A,确定缓蚀剂浓度与吸光度的关系式A=kC;取未知浓度缓蚀剂采出水样;过滤处理;采用紫外–可见分光光度法在波长 λ 处测量水样吸光度A;Fe3+检测及浓度Fe3C+测定;不含Fe3+时,依据CR=A/k计算缓蚀剂残余浓度CR,含有Fe3+时,依据CR=(A-0.0565C Fe3+)/k计算缓蚀剂残余浓度CR.

In this study, the corrosion behavior of carbon steel in crude oil–water–CO2/H2S multiphase environments simulating the service conditions of a production well and ground gathering pipeline of a carbonate oilfield was explored by weight loss tests and surface analysis techniques. The results show that the presence of crude oil significantly reduces the corrosion rate of 80SS casing and L245 pipeline steels, but it favors the occurrence of localized corrosion at middle-high water cuts. The corrosion of 80SS steel with the variation in the water cut obeys a similar pattern under different environmental conditions. When the water cut is higher than 50%, the corrosion rate obviously enhanced, and the corrosion form changes from uniform corrosion to localized corrosion due to the inhomogeneous wetting of crude oil and water under the test conditions. Benefiting from the synergistic corrosion inhibition of crude oil and a protective sulfur-rich film, the steel demonstrates a relatively low corrosion rate at a high water cut of 80%, however, this is higher than that at middle-low water cuts.

13Cr stainless steel is commonly used as the material of downhole tools in the field of offshore oil &gas exploitation,but it is prone to be corroded when stored in marine atmospheric environment.In order to improve the corrosion resistance of 13Cr stainless steel in marine atmosphere,the single citric acid passivation and citric acid-hydroxide composite passivation were selected to deal with the surface of L80-13Cr stainless steel,and their effects on the corrosion resistance of L80-13Cr stainless steel were investigated by polarization curve,FeCl3 pitting corrosion test,neutral salt spray test,outdoor exposure test in marine atmospheric environment and etc.Additionally,the reasons for the improvement of the corrosion resistance of L80-13Cr stainless steel resulting from citric acid passivation treatment were analyzed.Results showed that the two citric acid type passivation methods could significantly improve the marine atmospheric corrosion resistance of L80-13Cr steel and could ensure that the L80-13Cr steel presented no obvious corrosion in marine atmospheric environment for at least 3 months.This improvement was attributed to the fact that the citric acid passivation greatly increased the content of Cr-related compounds in the passive film of L80-13Cr steel,and thus improved the protectiveness of passive film.More importantly,the addition of hydroxide passivation treatment on the basis of citric acid passivation was helpful to improve the proportion of metal oxides in the passive film,thus further intensified the stability and corrosion resistance of passive film.Therefore,the comprehensive protection effect resulting from the citric acid-hydroxide composite passivation treatment on L80-13Cr steel was superior to that of single citric acid passivation treatment.

To detect the corrosion resistance of a friction stud welding (FSW) joint in simulated seawater (a 3.5 wt% NaCl solution), the pulse electrochemical deposition method was used for electroplating Ni coating with different duty ratios (50%, 80%, and 100%) on the surface of FSW joint. The microstructure and surface structure of the coating were observed by micro-spectroscopy and other characterization methods. The corrosion behavior of the coating was analyzed by means of macroscopic electrochemical testing. The local corrosion law of joint surface and coating surface defects were innovatively explored by using micro-zone electrochemical scanning system. The coating characterization results showed that, as the duty ratio continues to increase, the coating surface becomes denser and smoother, and the corrosion products such as Fe 2 O 3 , Fe 3 O 4 , and FeOOH are generated. The results of macroscopic electrochemical experiment indicated that the coating with 100% duty ratio has the lowest corrosion current density and the maximum polarization resistance. The scanning vibrating electrode technique results showed that the corrosion current density in the defect area is higher than that in the coating area, and the maximum corrosion current density decreases with the increase of duty ratio. The localized electrochemical impedance spectroscopy results indicated that the localized impedance at the welded zone was the largest, and with the increase of the pulse duty ratio, the impedance diffusion in the defect area was decreasing.