Effect of particle size on the electrochemical corrosion behavior of X70 pipeline steel

In this study, by using a standard quartz replace of sandy soil particles, the effect of soil particle size (0.1–0.25 mm, 0.6–1.0 mm) on the electrochemical corrosion behavior of X70 pipeline steel in sandy soil corrosive environment simulated by 3.5 wt% sodium chloride (NaCl) was investigated through polarization curve and electrochemical impedance spectroscopy (EIS) technology. The results indicated that the polarization resistance of X70 steel decreased with decreasing particle size. For all polarization curves, the right shift of cathodic branch with decreasing particle size, suggesting that the cathode oxygen reduction process is accelerated. The corrosion of X70 steel is controlled by the process of cathode diffusion and oxygen reduction. This can be attributed to the effect of gas/liquid/solid three‐phase boundary (TPB) zone on cathodic process of X70 steel, and the corrosion rate is mainly determined by the cathodic reaction. EIS of X70 steel consisted of two capacitive loops with 7, 60 and 90 days buried corrosion, and the charge transfer resistance of X70 steel increased with increasing particle size.     

辽河油田原油输送温度对管线钢内壁腐蚀行为的影响

为了探究高强度钢与低碳钢在原油输送过程中腐蚀性的差异,采用动电位极化和电化学阻抗技术,并结合金相显微镜,研究了辽河油田不同原油输送温度对X70钢和Q235钢电化学腐蚀行为的影响规律。结果表明:2种管线钢在原油中的极化曲线均呈活化溶解特性;当温度变化范围为40~70℃时,随着输油温度的升高,X70钢和Q235钢的腐蚀速率均增大,腐蚀现象越来越显著;相同温度条件下,X70钢的腐蚀速率明显低于Q235钢,X70钢在辽河油田原油中的耐蚀性优于Q235钢。     

含缺陷涂层X80钢热影响区的电化学阻抗分析

为了进一步探讨X80钢涂层缺陷对耐土壤腐蚀性能及使用寿命的影响,将有无涂层缺陷的X80钢浸泡在玉门土壤模拟溶液中,采用电化学方法分析了其电化学阻抗谱。结果表明:无缺陷涂层的X80钢具有良好的防腐蚀效果;线缺陷涂层在不同测试期内的阻抗谱曲线都呈现为具有2个时间常数的双容抗弧特征;存在涂层缺陷时,外界腐蚀性介质会到达基体,使之腐蚀,随着腐蚀时间的延长,腐蚀产物会在缺陷处堆积;阴极反应形成的OH-增加会促使局部碱性环境的形成,进而导致X80钢涂层与基体界面剥离,发生缝隙腐蚀。     

碳钢在中性土壤中的腐蚀行为研究

总结了碳钢在不同湿度中性土壤介质中腐蚀初期的电化学阻抗谱特征 ;同时讨论了湿度对钢铁土壤腐蚀电化学行为和土壤腐蚀控制特征的影响。     

Understanding the effect of soil particle size on corrosion behavior of natural gas pipeline via modelling and corrosion micromorphology

The effect of particle size on the electrochemical corrosion behavior of natural gas pipeline steel in a 1.5 wt% NaCl sandy soil corrosive environment was investigated by standard quartz sand. A mathematical model of gas/liquid/solid three-phase boundary (TPB) zone and the soil particle size was developed, and then the theoretical calculation indicated that a critical particle size corresponded to 1.2 mm radius. The laboratory experiments indicated that the corrosion rate of natural gas pipeline steel increased with decreasing soil particle size to < 1.0 mm and was mainly determined by a cathodic reaction. Whereas the corrosion rate of pipeline steel increased with increasing soil particle size exceeding 1.0 mm and the dominant reaction was metal dissolution in the bulk zone and the corrosion rate was determined by anodic reaction. The modelling result is in good agreement with experimental data.     

Cl~-和应力对X80管线钢电化学腐蚀行为的影响

目前,对于Cl~-和应力同时作用时钢铁腐蚀行为及机理的研究不多。采用动电位极化和交流阻抗谱,研究了Cl~-和应力对X80管线钢在高pH值溶液中腐蚀行为的影响。结果表明:Cl~-对X80管线钢的钝化行为有显著影响,当Cl~-浓度小于0.10 mol/L时,X80管线钢表面会形成稳定的钝化膜,当Cl~-浓度大于0.10 mol/L时,则不会形成稳定的钝化膜。在自腐蚀电位下,少量的Cl~-可增加X80管线钢的腐蚀倾向,但大量Cl~-可降低其腐蚀倾向。外加应力使交流阻抗谱低频区出现第二段容抗弧,并且提高自腐蚀电位下X80管线钢的溶解速率。     

温度对X90管线钢及其焊缝电化学腐蚀性能的影响

为了明确X90钢的腐蚀变化规律,利用电化学阻抗技术(EIS)和动电位极化测试技术,研究了X90管线钢母材及其焊缝在不同温度下的电化学腐蚀行为。结果表明:在不同温度下,随着温度的升高,X90管线钢母材及其焊缝越容易发生腐蚀,电化学阻抗逐渐减小;母材与焊缝相比,焊缝在溶液中更容易发生腐蚀,且电化学阻抗值小于母材的。     

X100钢在模拟碱性土壤溶液中的腐蚀行为

为了给X100钢在工程中的应用提供数据参考,采用电化学方法,选用典型模拟碱性土壤溶液,通过改变Cl-浓度、浸泡时间以及极化恒电位值,研究X100钢的电化学腐蚀行为。结果表明:X100钢的腐蚀为活化-钝化过程,其交流阻抗谱包括高频容抗弧和低频容抗弧,在低频段出现Warburg阻抗;CE浓度从0.15mol/L增大到0.25mol/L时,溶液中的电荷转移电阻增大,反应形成的钝化膜越来越致密,导致腐蚀速率减小;浸泡时间从2h增加到8h时,电荷转移电阻减小,导致电极表面腐蚀加剧;在-0.60~0.40V极化扫描下,电荷转移电阻明显增加,钝化膜变得致密,导致腐蚀抗力增大,腐蚀速率减小。     

Characterization and corrosion behavior of electroless Ni–P/nano-SiC coating inside the CO2 containing media in the presence of acetic acid

In this research, Ni–P and Ni–P/nano-SiC coatings were applied on the X70 steel substrate successfully without any surfactant. Then, CO₂ corrosion in the presence of acetic acid (HAc) was investigated using electrochemical techniques. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were used for surface analyses of the coatings. The electrochemical behavior of corrosion was investigated using polarization test and electrochemical impedance spectroscopy (EIS). XRD pattern of Ni–P/nano-SiC coating was very similar to that of Ni–P coating. EDS results demonstrated the presence of SiC particles in the coating. SEM images confirmed the presence of SiC nano-particles with almost uniform distribution in the coating. The corrosion current density was less in the Ni–P and Ni–P/nano-SiC coated samples than uncoated X70 steel. Ni–P/nano-SiC coated sample had the most corrosion resistance because of less effective metallic area available for corrosive media. The overall protection mechanism of Ni–P and Ni–P/nano-SiC coatings was achieved by formation of a layer of adsorbed hypophosphite anions (H₂PO₂⁻).     

Corrosion monitoring of galvanized steel in soil extract solutions by electrochemical impedance spectroscopy

The chemical and structural complexity of soils, coupled with their heterogeneity, contributes to the increase in soil aggressiveness, which can in turn result in severe corrosion of underground materials. The understanding of corrosive processes of underground structures is important in aiding the development of methods, as well as in monitoring and maintenance, in an attempt to minimize environmental, social, and economic impacts. In this work, electrochemical impedance spectroscopy (EIS) was used to monitor the corrosive process of galvanized steel when in contact with soil extracts, aimed at evaluating the potentiality of applying electrochemical impedance spectroscopy when monitoring underground structures. To accomplish this, the behavior of the galvanized steel when undergoing corrosion was studied for 105 days, examining the variations in the eletrochemical parameter values obtained through EIS assays over this period. EIS proved to be effective in the study of corrosive processes of galvanized steel when in contact with soil extracts, identifying the different stages of the corrosive process, controlled by mass and/or charge transfer reactions.     

Electrochemical corrosion properties of Ti–6Al–4V implant alloy in the biological environment

The electrochemical corrosion behavior of Ti–6Al–4V implant alloy was investigated in three biological solutions, i.e. urine, serum and joint fluid. The corrosion properties of Ti–6Al–4V implant alloys were examined by using electrochemical techniques, such as the potentiodynamic method, cyclic voltammetry, electrochemical impedance spectroscopy (EIS). The electrochemical corrosion characteristics of Ti–6Al–4V implant alloys in three biological solutions were measured in terms of the corrosion potential (E_corr), the corrosion current density (i_corr), and ac polarization resistance (R_p). The corrosion kinetic parameters were calculated from both the Tafel plot analyses and EIS analyses. The dependence of impedance versus potentials was studied at 37 °C at various offset potentials in three biological solutions. The ac circuit model for Ti–6Al–4V implant alloy at corrosion interface in biological solution was proposed, which was based on a simple Randles equivalent circuit. It was found that the Ti–6Al–4V implant alloy in three biological solutions showed a characteristic of a capacitive behavior. The experimental results of Tafel plot analyses were found in good agreement with that of EIS analyses.     

Cl~-对天然气管道内涂层破损处局部腐蚀的影响

为了进一步了解天然气管道内涂层破损处在含Cl~-电解质溶液中的破损机理,以X80管线钢为基材,利用EIS(电化学阻抗谱法)和SKP(扫描开尔文探针测试法)等电化学检测技术,通过获取内涂层破损处的腐蚀电化学参数的特性,研究了Cl~-浓度对特定缺陷尺寸内涂层破损处局部腐蚀的影响,并探讨其腐蚀机理。EIS谱结果表明,不同Cl~-浓度下的腐蚀过程经历了大致相同的规律,即随着浸泡时间延长腐蚀电阻出现先减小后增大的趋势;SKP测试表明,破损处周边的涂层/金属界面存在较大的电位差,在界面最易发生腐蚀,并随着浸泡时间延长,推动着腐蚀向涂层内部渗透,进而引发涂层不断剥离。     

The corrosion behavior of copper in acid soil during soil acidification by simulated acid rain

The corrosion behaviors of copper in acid soil during soil acidification by simulated acid rain (SAR) were studied by means of polarization curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The results indicated that the SAR increased the corrosion rate of the copper in the acidic soil. The corrosion rate of the copper increased with decreasing pH value of SAR. Corrosive characteristics of the soil obviously increased because of the leaching of the acid rain. For the leaching of the distilled water, the corrosion rate of the copper decreased. EIS of copper was a capacitive loop in the early stage of corrosion. After 60 days exposure, EIS consisted of two capacitive arcs for copper in the acidic soil leached with SAR, the control step for corrosion of copper was charge transfer process. For the distilled water, EIS consisted of a capacitive loop at higher frequency and a Warburg impedance at lower frequency, and the control step for corrosion of copper was diffusion process.     

温度对X80管线钢在0.5mol/L Na_2CO_3+1.0mol/L NaHCO_3溶液中电化学腐蚀性能的影响

目前,有关温度对CO_3~(2-)-HCO_3~-环境下X80管线钢腐蚀行为的影响规律尚无统一的认识。为了探究高强度钢在不同温度的0.5 mol/L Na_2CO_3+1.0 mol/L NaHCO_3溶液中的腐蚀行为,采用动电位极化、电化学阻抗技术,并结合金相显微镜观察研究了温度对X80管线钢在0.5 mol/L Na_2CO_3+1.0 mol/L NaHCO_3溶液中电化学腐蚀行为的影响规律,并通过Mott-Schottky曲线对不同温度下钝化膜的半导体性质进行探讨。结果表明:温度从30℃上升至75℃时,X80钢的点蚀电位和电荷转移电阻均逐渐减小,腐蚀现象越明显;当温度达到90℃时,点蚀电位和电荷转移电阻反而增大,腐蚀程度有所减缓;在0.3~0.7 V内,钝化膜呈现出典型的n型半导体特征;随着温度的升高,钝化膜内的施主电流密度和平带电位呈现先降低后增加的趋势,钝化膜稳定性先减弱后增强;在75~90℃之间存在一个临界温度,此温度下钝化膜的缺陷密度最大,保护性最差。     

油气输送管道钝化行为的交流阻抗谱研究

油气输送管道表面的钝化膜易遭受HCO-3破坏,从而引起管道报废造成重大损失.采用动电位扫描技术研究了管道用材(X70钢)在4种不同NaHCO3/Na2CO3浓度溶液中的极化曲线,并根据极化曲线确定其电位范围,测试了X70钢在NaHCO3/Na2CO3溶液中钝化膜的电化学交流阻抗谱(EIS),提出了X70钢在NaHCO3/Na2CO3溶液中的等效电路模型.结果表明:X70钢在NaHCO3/Na2CO3溶液中具有二次钝化行为,表面先后形成两种性能不同的钝化膜,随着HCO-3浓度的增加,一次钝化膜逐渐溶解,二次钝化膜逐渐增厚,耐蚀性增强,起到了很好的保护作用.     

管线钢在近中性pH值溶液中的应力腐蚀

为研究不同强度管线钢在近中性土壤环境中的耐腐蚀性能,模拟近中性土壤环境,采用C型环试样进行浸泡试验、电化学试验(极化曲线)来研究X80和X100这2种高强度管线钢在近中性环境中的应力腐蚀行为,采用扫描电镜(SEM)、X射线衍射仪(XRD)对试验后的试样腐蚀形貌、产物、结构进行了分析。结果表明:在模拟近中性土壤环境下,耐点腐蚀性能X100>X80,加载应力试样<不加载应力试样; 2种材料均表现出应力腐蚀开裂(SCC)敏感性,SCC敏感性X100>X80,说明随着管线钢强度的提高,SCC敏感性增大;应力腐蚀机制为阳极溶解(AD)+氢脆(HE)。     

Effects of phosphate on the chloride-induced corrosion behavior of reinforcing steel in mortars

The influence of phosphate as a corrosion inhibitor on the corrosion behavior of as-received and pre-rusted reinforcing steels in mortar specimens was investigated after 360 days exposure in 3.5% NaCl solution. This involved the use of electrochemical techniques for studying the steel surface reactions and microscopic observations of the steel–mortar interface. The electrochemical methods, including electrochemical impedance spectroscopy (EIS) and measurements of corrosion potential (E_corr) and linear polarization resistance (LPR), were employed to evaluate the corrosion tendency and general corrosion rate of steel. In addition, the pitting corrosion resistance of steel was also determined by cyclic polarization (CP) measurements. The results indicate that different from nitrite, which is generally accepted as an anodic inhibitor, phosphate may be a cathodic inhibitor according to its reduced corrosion rate and more negative E_corr at the same dosage as nitrite in mortar specimens. The study also reveals that the inhibiting efficiency of phosphate against general corrosion of both as-received and pre-rusted specimens is lower than 10%, which is inferior to nitrite in some respects. However, as indicated by cyclic polarization measurements, the presence of phosphate provides slightly higher pitting corrosion resistance in comparison to nitrite. Furthermore, it suggests that the corrosion inhibition mechanism of phosphate in mortars mainly depends on a dual effect occurring at the steel–mortar interface. Furthermore, it is confirmed that phosphate has little effect on the long-term mechanical properties of mortars.     

The effect of acetic acid on the CO2 corrosion of grade X70 steel

The effect of acetic acid (HAc) on the CO₂ corrosion of grade X70 steel was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), polarization tests and electrochemical impedance spectroscopy (EIS). In the absence of acetic acid, a fairly dense layer of iron carbonate (FeCO₃/siderite) was formed. At 500 ppm HAc, FeCO₃ layer became more porous. In addition, anodic/cathodic polarization curves were activated with the more pronounced effect on the cathodic side. By adding 1000 ppm HAc, similar polarization behavior was obtained and FeCO₃ layer became yet more porous than previous conditions. At 2000 ppm HAc, FeCO₃ layer disappeared completely, while polarization behavior changed and the limiting diffusive current density was observed in the cathodic side. There were two major increases in the corrosion rate at 500 and 2000 ppm HAc. The EIS results reflected similar behavior for the specimens exposed to the solutions with 0–1000 ppm HAc. Under these conditions, a charge transfer controlled behavior due to the FeCO₃ layer was observed which was accelerated by increasing HAc concentration. At 2000 ppm HAc, the corrosion behavior changed considerably and the formation/adsorption of corrosion product followed by the dissolution process was observed.     

Effect of bias voltage on the electrochemical properties of TiN coating for polymer electrolyte membrane fuel cell

The electrochemical properties of TiN film coated on AISI 316 stainless steel (SS) by the magnetron sputtering physical vapor deposition (PVD) were studied for application as a bipolar plate. The crystal structure and surface morphology of the coatings were examined by x-ray diffractometry (XRD) and atomic force microscopy (AFM), respectively. The corrosion behaviors of the TiN films were investigated by electrochemical methods, including potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) under + 600 mV_SCE application. The electrochemical behavior of the TiN coatings was enhanced with increasing bias voltage due to lower corrosion current density and higher R_ct values during an immersion time of 168 h. This result was attributed to the formation of crystalline-refined TiN(200) at high bias voltage, which increased the coating compactness and the protective efficiency, and decreased passive current density.     

反应溅射TiN纳米晶薄膜的结构特征和耐蚀性

利用直流反应溅射技术在不锈钢和硅基体上沉积了TiN纳米晶薄膜,采用场发射扫描电镜(FESEM)、X射线衍射(XRD)和电化学阻抗谱(EIS)技术研究了薄膜的表面形貌、相结构和耐蚀性与偏压的关系。结果表明,TiN薄膜的表面结构明显取决于所施加的偏压,适当提高偏压有利于获得细小、均匀、致密和光滑的膜层。XRD分析发现,TiN薄膜为面心立方结构,其择优取向为(111)面。实验显示,对应0V和-35V偏压的薄膜为欠化学计量比的,而偏压增加至-70V和-105V时的薄膜为化学计量比的TiN。EIS结果表明,较高偏压下的TiN薄膜几乎在整个频率范围内均表现为容抗特征,其阻抗模值明显高于低偏压下的膜层,这主要与较高偏压下的薄膜具有相对致密的微结构有关。较低偏压的TiN薄膜因结构缺陷较多其耐蚀性低于基体不锈钢。EIS所揭示的薄膜结构特征与FESEM观测结果一致。可见,减少穿膜针孔等结构缺陷有利于改善反应溅射TiN纳米晶薄膜耐蚀性。