Relationship between electrochemical characteristics and SCC of X70 pipeline steel in an acidic soil simulated solution

Stress corrosion cracking (SCC) of X70 pipeline steel in simulated solution of the acidic soil in Yingtan in China was investigated using slow strain rate test (SSRT), SEM and potentiodynamic polarization technique. Experiment results indicate that X70 steel is highly susceptible to SCC as applied potential reduces, which is manifested in loss of toughness and brittle fracture. Constant polarization current can detect the occurrence of SCC. The lower the polarization current is the sooner stress corrosion cracking occurs. The SCC mechanisms are different at varying potentials. When potential is higher than open circuit potential, anodic process controls SCC, whereas when potential is far lower than open circuit potential, cathodic process controls SCC, and between these two potential regions, a combined electrochemical process controls the SCC. Stress or strain has a synergistic effect with electrochemical reactions to accelerate the cathodic hydrogen evolution process, which makes the X70 pipeline steel to be more susceptible to SCC.     

Electrochemical corrosion behavior of X80 pipeline steel in a near‐neutral pH solution

In this work, the electrochemical corrosion behavior of X80 pipeline steel was investigated in a near‐neutral pH solution using electrochemical impedance spectroscopy (EIC) and photo‐electrochemical (PEC) measurements as well as X‐ray photo‐electron spectroscopy (XPS) technique. The effects of hydrogen‐charging and stress were considered. The results show that the steel is in an active dissolution state, and a layer of corrosion product is formed and deposited on the electrode surface, which is subjected to further oxidation to form ferric oxide and hydroxide. Photo‐illumination enhances anodic dissolution of the steel when it is under anodic polarization due to destroying of the corrosion product film. When the steel is under cathodic polarization, the cathodic current density decreases upon laser illumination due to the photo‐oxidation of hydrogen atoms generated during cathodic reactions, which behaves as an anodic reaction to offset the cathodic current density. Hydrogen‐charging and stress decrease the corrosion resistance of the steel and enhance the dissolution rate of the steel.     

外部电位对蚀孔或裂缝扩展阶段闭塞区腐蚀行为的影响

采用恒电位模拟闭塞电池装置研究外部电位对局部腐蚀闭塞区的影响，在蚀孔或裂缝的扩展阶段，即当闭塞区溶液的ｐＨ值已经降到临界值以下时，外表面阴极极化使闭塞区电位负移，腐蚀率变小，闭塞区电位与外部电位呈线性关系，闭塞区腐蚀率与外部电位呈指数关系，对外表面施加阳极极化时，闭塞区的电位和腐蚀率不随极化电位而变化，闭塞区内外的电位差主要来自内外溶液的扩散电位差和离子的电迁移欧姆降。     

X70钢在酸性土壤模拟溶液中的应力腐蚀行为

在不同的阴极保护电位下,采用慢应变速率拉伸实验、动电位极化方法以及SEM研究了X70钢在酸性土壤模拟溶液中的应力腐蚀行为.结果表明: X70钢发生穿晶应力腐蚀裂纹;应力腐蚀开裂(SCC)萌生与外加保护电位有关,完全受阳极过程控制时X70钢的SCC敏感性较低,但会发生点蚀和严重的均匀腐蚀;受混合电极过程控制和全受阴极过程控制时均能发生SCC;受混合电极过程控制时,SCC二次裂纹与点蚀伴生,裂纹形核密度大;而完全受阴极过程控制时,SCC裂纹附近未见点蚀坑,裂纹形核密度低;混合电极过程控制时比完全阴极电极过程控制下更容易发生SCC裂纹.     

外加电位下X80双相管线钢在模拟沿海土壤环境中的应力腐蚀行为

采用交流阻抗谱、极化试验、慢应变拉伸试验研究了不同外加电位下在模拟沿海土壤环境中X80双相管线钢的应力腐蚀行为,对拉伸断口和极化后试样进行SEM表面形貌及能谱分析。结果表明,与慢扫极化(模拟的非裂尖区域)相比,X80双相管线钢快扫极化模拟的裂尖腐蚀电位较负且腐蚀电流较大。-750 mV外加阴极电位处于裂尖自腐蚀电位范围,不足以起到阴极保护的作用,对应力腐蚀仍十分敏感。外加电位为-1050 mV时,阴极反应速率显著大于阳极反应,阴极反应产生的氢被金属吸收且扩散,慢应变拉伸未经颈缩即发生断裂,为准解理断裂。外加阴极电位为-900 mV,阴极电流有效抑制了阳极溶解反应,因此管线钢在模拟沿海土壤溶液中慢应变拉伸抗拉强度和断面收缩率都最高,断口表现为韧性断裂,侧面裂纹细小,阻抗模值最大,应力腐蚀敏感性最小。     

静载荷对30CrMnSiA在中性及酸性溶液中腐蚀速度的影响

    用电化学测量技术通过加载时30CrMnSiA在中性溶液中自腐蚀电位和阳极极化曲线负移,及在酸性溶液中电化学阻抗谱的不同变化,研究了静载荷对腐蚀速度的影响.并提出外力是否影响腐蚀速度,应视腐蚀的控制步骤而定的观点.结果表明,当腐蚀体系阴阳极都为活化控制时,外力增加腐蚀速度;当腐蚀体系控制步骤为扩散控制时,外力不影响腐蚀速度;对吸氧腐蚀而言,在外力较大时,还需考虑外力是否导致阴极控制过程的转变.     

X100管线钢在酸性土壤模拟溶液中的应力腐蚀行为

采用慢拉伸(SSRT)、动电位极化和SEM观察等方法,研究了在不同的阴极保护电位条件下X100钢在酸性土壤模拟溶液中的应力腐蚀行为.结果表明,X100钢发生穿晶裂纹的应力腐蚀,裂纹的萌生和发展与阴极保护电位有关.完全阳极过程控制时,X100钢无裂纹出现,但出现晶间腐蚀;在混合过程控制时,应力腐蚀敏感性较低,裂纹发展缓慢;在完全阴极过程控制时,氢脆机制起主要作用,裂纹扩展迅速.     

碳钢在含硫化氢及高压二氧化碳饱和的NaCl溶液中的腐蚀行为

利用自制的高温、高压腐蚀试验及电化学测试装置,通过失重法、电化学极化曲线法及电子探针微观分析等方法,研究了温度、硫化氢浓度对碳钢在高压二氧化碳饱和的39％NaCl溶液中腐蚀的影响．结果表明较低温度(80℃)下,升高温度及增大硫化氢浓度均加速腐蚀反应的阴、阳极过程,失重腐蚀速率增大;高浓度的硫化氢抑制了腐蚀反应的阴极过程;120℃时碳钢CO2腐蚀产物膜对金属基体起很好的保护作用,失重腐蚀速率减小了3～4倍,随硫化氢浓度的增大,失重腐蚀速率缓慢增长,腐蚀产物FeCO3膜逐渐转变为以硫铁化合物为主的腐蚀产物膜．     

Factors affecting the corrosion rate of steel in carbonated mortars

The corrosion of steel in carbonated mortar has been investigated by monitoring polarization resistance, corrosion potential and mortar resistivity. The results suggest that factors such as relative humidity and chloride contamination affect the corrosion rate via their influence on mortar resistivity. To account for the observed electrochemical relationships, most notably the linear correlation between corrosion rate and conductivity, and the exponential increase in corrosion rate with fall in corrosion potential, it is proposed that the corrosion kinetics of steel in carbonated mortar are subject to anodic control with the anodic reaction rate being limited by the resistance of the mortar. In this model, termed anodic resistance control, resistivity is viewed as a factor which may limit a half reaction rate in a similar way to diffusion and activation polarization. It is also shown that, when such a model is operating, the use of polarization resistance to monitor corrosion rate changes may still be justified provided the cathodic reaction rate is an exponential function of potential.     

阴极极化下X80钢在鹰潭土壤模拟溶液中应力腐蚀行为研究

采用电化学阻抗和慢应变速率方法,结合扫描电子显微镜,研究了不同阴极极化电位下X80钢在鹰潭土壤模拟溶液中的应力腐蚀行为。结果表明：鹰潭土壤模拟溶液中,X80钢/溶液界面处电荷转移电阻随阴极极化程度增加先升后降。在自腐蚀电位条件下开裂机理为阳极溶解,当外加电位为-1000 mV (vs SCE),应力腐蚀敏感性最低,此电位为最佳保护电位;继续增大阴极极化程度,应力腐蚀敏感性增加,此时开裂机制为氢和应力协同作用下的氢致开裂。     

温度、Cl-浓度、Cr元素对N80钢CO2腐蚀电极过程的影响

利用电化学阻抗技术研究了温度、Cl^-浓度、Cr元素对N80钢CO2腐蚀电极过程的影响，结果表明，随着温度的升高，CO2腐蚀的阴极、阳极电极反应速率会明显增大，与此同时，温度的升高又容易使腐蚀产物膜在试样表面形成，对基体金属起到一定的保护作用，增加介质中的Cl^-浓度，会使阳极溶解速率先增加，后减小；阴极还原速率则缓慢减小；同时，Cl^-还会破坏腐蚀产物膜在试样表面的覆盖，N80钢加入Cr元素以后，CO2腐蚀阴极、阳极反应速率降低，材料具有一定的抗CO2腐蚀能力。     

Effects of corrosion product deposit on the subsequent cathodic and anodic reactions of X-70 steel in near-neutral pH solution

The effects of corrosion product deposit on the subsequent anodic and cathodic reactions of X-70 steel in a near-neutral pH solution were investigated by localized electrochemical impedance spectroscopy (LEIS), scanning vibrating micro-electrode (SVME) and macroscopic EIS measurements as well as surface analysis technique. It is found that the deposit layer formed on the steel surface is porous, non-compact in nature. The presence of a corrosion product layer would enhance adsorption, but significantly inhibit absorption and permeation of hydrogen atoms into steel. It is due to the porous structure of the deposit that generates a spatial separation of cathodic and anodic reaction sites, resulting in an increased effective surface area for hydrogen adsorption and, simultaneously, a “blocking” effect on hydrogen absorption and permeation. The deposit enhances greatly anodic dissolution of the steel, which is attributed to the adsorption of the intermediate species and the resultant “self-catalytic” mechanism for corrosion of the steel in near-neutral pH solution. In the presence of corrosion product deposit on the pipeline steel surface, pipeline corrosion, especially pitting corrosion, is expected to be enhanced. Stress corrosion cracks could initiate from the corrosion pits that form under deposit. However, deposit does not contribute to hydrogen permeation, although the hydrogen evolution is enhanced.     

碳钢在点蚀/缝隙腐蚀闭塞区模拟溶液中的腐蚀行为

研究了低碳钢在点蚀孔/缝隙腐蚀闭塞区模拟溶液中的腐蚀 行为.结果表明低碳钢在pH等于2～4的模拟闭塞区溶液中,阴极过程由氢离子的扩散步骤控 制,阴极去极化起着主要作用.当pH值小于2时,阴极过程表现为活化特征.阳极溶解过程遵 循着Bockris机理.碳钢在闭塞区的腐蚀不存在临界pH值和临界Cl-浓度,腐蚀速度(V c)的对数与pH值呈线性关系.闭塞区内溶液pH的微小变化,对腐蚀速度有明显的影响.外部 溶液中的Cl-离子迁入闭塞区后,会促使溶液pH下降.     

Corrosion behavior of titanium-clad carbon steel in weakly alkaline solutions

The electrochemical polarization curves and corrosion potentials during long-term immersion of Ti, carbon steel, carbon steel tightened-Ti and Ti-clad carbon steel specimens were investigated in bentonite-contacting solution (mixture of sodium sulfate and sodium carbonate solutions), sodium sulfate solution and borate solution adjusted to pH=9.0-9.84. Ti and carbon steel were passivated during immersion in borate solution, while carbon steel was corroded in the solutions containing SO₄²⁻ ions. The immersion potentials of Ti-clad steel and steel-tightened Ti specimens were controlled by the corrosion potential of carbon steel (about 0 V vs. RHE at 298 K). The Ti side of the clad specimen was, therefore, polarized cathodically at this immersion potential, and this caused hydration of and/or hydrogen penetration into the oxide film, resulting in degradation of its barrier property. Furthermore, the cathodic current on the Ti side was partially coupled with the anodic current in the corrosion reaction on the carbon steel side, resulting in acceleration of the overall corrosion rate.     

温度对N80和KO80SS钢在饱和CO_2地层水中电化学腐蚀的影响

利用极化曲线和电化学阻抗谱研究温度对N80和K080SS钢在饱和CO2地层水中电化学腐蚀阴阳极过程的影响.结果表明:N80钢和KO80SS钢随成膜温度的升高,腐蚀加剧,腐蚀电位下的电极反应速度分别由阳极和阴极控制.在30℃条件下N80钢的阳极交流阻抗谱显示活化区与腐蚀产物膜覆盖区并存,基体处于腐蚀状态;温度达到60和90℃时.N80钢腐蚀产物膜基本完全覆盖基体表面,KO80SS钢生成的腐蚀产物膜完整均匀;两种钢的阳极腐蚀均受活化控制.两种钢的阴极腐蚀反应均同时受扩散和活化控制,阴极反应以H2CO3、HCO-3的还原为主,H+的还原占从属地位.     

X80管线钢在近中性pH溶液中腐蚀行为研究

目的研究X80管线钢在近中性p H溶液中的腐蚀与应力腐蚀裂纹萌生行为。方法采用电化学实验和浸泡实验研究X80管线钢在近中性p H溶液中的腐蚀行为,采用慢应变速率拉伸实验研究X80管线钢在近中性p H溶液中,在自腐蚀电位和外加电位下的应力腐蚀裂纹萌生行为。结果 X80管线钢在近中性p H溶液中的极化曲线只有活化区,没有钝化区,其自腐蚀电位约为-750 m V,浸泡195天后,试样表面没有氧化膜出现,但是观察到点蚀坑。在自腐蚀电位下,X80管线钢试验表面有大量的应力腐蚀裂纹;在-500 m V阳极外加电位下,X80管线钢试验表面几乎没有观察到应力腐蚀裂纹;在-850 m V阴极外加电位下,X80管线钢试验表面的应力腐蚀裂纹很少,但是随着外加阴极电位负移到-1300 m V时,X80管线钢试验表面的应力腐蚀裂纹增多。结论 X80管线钢在近中性p H溶液中发生均匀腐蚀,但是夹杂物剥落能在X80管线钢表面形成点蚀坑。在近中性p H溶液中,在自腐蚀电位下,X80管线钢应力腐蚀裂纹萌生敏感性最强;外加阴极电位抑制应力腐蚀裂纹萌生,但是随着外加阴极电位的负移,应力腐蚀裂纹萌生敏感性增强;外加阳极电位下,由于均匀腐蚀的作用,应力腐蚀裂纹萌生敏感性较弱。     

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

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

混凝土结构中NO_2~-的不均匀性对钢筋宏电池腐蚀行为的影响

基于宏电池腐蚀理论,将阴极区钢筋和阳极区钢筋分别浇筑成两个独立的砂浆试块,并用导线将其连接成循环电路,通过断开和连接电路来控制钢筋的微电池腐蚀和宏电池腐蚀,再将不同浓度的NO_2~-溶液分别添加到阴极试块和阳极试块中以模拟其渗透过程,通过比较NO_2~-作用前后阴阳极钢筋之间宏电池腐蚀电流的大小,来评价阴阳极钢筋表面NO_2~-的不均匀性对钢筋宏电池腐蚀行为的影响。结果表明:当NO_2~-作用于处于腐蚀状态的阳极钢筋时,能够增加阳极钢筋的极化阻抗,减少阴阳极钢筋间的宏电池腐蚀电位差,降低宏电池腐蚀电流,从而有效抑制宏电池腐蚀;当NO_2~-主要作用于处于腐蚀状态的阴极钢筋时,阴阳极钢筋间的宏电池电位差的增大易使宏电池腐蚀电流增加,存在加速钢筋宏电池腐蚀的危险。     

应变幅与应变速率在形变加速腐蚀过程中的作用

采用应变电极技术研究了应变幅、应变速率与外加电位对形变中金属电化学腐蚀过程的影响。选用的体系为工业纯Ｆｅ－３．５％ＮａＣｌ水溶液和Ａ５３７钢－３．５％ＮａＣｌ＋１％ＮａＮＯ２水溶液结果表明，塑性变形对阳极过程的加速作用大于对阴极过程的加速作用，这种作用主要发生在自腐蚀电位附近。在强阳极与强阴极极化区，由于强的分反应驱动力，单个反应的电流增大，导致了形变电流的增加相对不重要。活化体系的金属溶解电流主要受应变幅控制，而钝化体系则主要由应变速率控制，取决于应变活化区域的再钝化动力学过程．     

海水及培养基中假单胞菌对45钢电化学腐蚀行为的影响

采用微生物分析、失重法、自腐蚀电位、EIS、动电位极化曲线和SEM等手段对比研究了45钢在无菌海水、无菌培养基、假单胞菌海水和假单胞菌培养基4种不同环境下的腐蚀行为。结果表明：腐蚀初期假单胞菌及培养基均对45钢有缓蚀作用。但随着时间的推移,假单胞菌新陈代谢作用引起了氧浓差腐蚀,且其代谢产物中的碱及铁载体的局部堆积加速了45钢的腐蚀。培养基环境对微生物腐蚀有促进作用。