Electrochemical noise analysis of PbSCC of Alloy 600 SG tube in caustic environments at high temperature

An electrochemical noise (EN) monitoring technique was applied to analyse an initiation and a propagation of Pb-assisted stress corrosion cracking (PbSCC) of Alloy 600 material in a simulated environment of steam generator (SG) sludge piles at high temperature. A typical electrochemical potential decrease concurrent with a current increase was observed during the EN measurements, indicating the occurrence of localized corrosion events. The EN data were analysed for the processes of a uniform corrosion, an initiation and a propagation of PbSCC using a stochastic theory and microscopy.     

模拟污染潮湿大气环境下LY12CZ、LC4CS铝合金腐蚀行为研究

建立了基于电化学噪声测试技术(EN)的铝合金大气腐蚀实时监检测方法.设计并制作了配套的电解池.运用所建立方法测试并计算得到了LY12CZ、LC4CS铝合金在pH值为中性恒温恒湿的模拟近海、海洋大气以及工业污染大气环境中的噪声电阻Rn和电位噪声功率密度谱高频线性部分斜率K,从腐蚀速度和腐蚀类型两方面研究了两种铝合金在模拟污染潮湿大气环境下的腐蚀行为,以及Cl-、NO3-和SO42-对铝合金大气腐蚀行为的影响和协同作用.     

基于Hilbert-Huang变换的电化学噪声解析及其应用

借助Hilbert-Huang变换 (HHT) 研究了Q345B碳钢在模拟混凝土孔隙液中的电化学噪声信号的时频谱,发现相比离散小波变换 (discretewavelet transform,DWT),HHT在噪声信号识别过程中具有更高的时频分辨率和稳定性,能够从本质上提高对电化学噪声中耦合的亚稳态点蚀信号的解析精度。针对Q345B碳钢处于钝化态、亚稳态点蚀萌发和稳态点蚀生长等不同阶段的噪声特点,提出了一套基于HHT边界谱的腐蚀状态量化指数与腐蚀特征识别方法。借助于在线电化学噪声监测装置,HHT算法将可用于诊断工业环境的腐蚀形态和腐蚀发展趋势。     

The application of electrochemical noise resistance to evaluate the corrosion resistance of AISI type 304 SS in nitric acid

The paper presents the application of noise resistance to evaluate the corrosion behaviour of sensitized AISI type 304 SS in nitric acid of varying concentration (4 N, 12 N, 16 N) and temperature (298 K, 323 K, 348 K). Electrochemical noise data was acquired from a three identical electrode configuration in the required conditions at open circuit potential. The noise resistance was evaluated as the ratio of the standard deviation of the potential to that of the current noise after removing the DC component. The inverse relationship between noise resistance and corrosion rate was exploited to qualitatively assess the corrosion behaviour of AISI type 304 SS in nitric acid. Noise resistance decreased with increase in concentration implying an increase in corrosion rate with increase in nitric acid concentration. An increase in temperature from 298 K to 323 K and 348 K decreased the noise resistance in 4 N and 12 N nitric acid implying higher corrosion rates at higher temperatures. The corrosion rates were similar at 323 K and 348 K in these concentrations. The simultaneous measurement of current and potential noise facilitated the evaluation of the frequency dependence of the noise data to determine the spectral noise resistance (R_sn) and the DC limit of the spectral noise resistance . The results from R_sn and also indicated higher corrosion rates at higher concentration and temperature. Also R_n and correlated well in 4 N and 12 N nitric acid at 323 K and 348 K while disparity was observed at room temperature in 4 N and 12 N nitric acid.     

The effect of electrolyte stirring and laminar flow on measured electrochemical noise

In the present paper the influence of various types of electrolyte movement on the characteristics of measured electrochemical noise (EN) has been investigated. For this reason the measurements were performed during different phases: in a still solution, during stirring, as well as in laminar flow. In order to relate the measured EN to the development of corrosion processes, digitized images of the electrodes were recorded continuously during these measurements. After the tests were finished, the corroded electrode surfaces were examined also by the scanning electron microscope (SEM). It was established that the characteristics of EN, in general, change significantly with the movement of the solution. On the other hand, no clear difference was observed between the EN signals measured during stirring and those obtained during laminar flow. This observation, combined with the results obtained in a passive environment and in a very aggressive still solution, confirmed that the main source for the change of EN characteristics during electrolyte movement is the transformation of corrosion processes. The direct effect of the electrolyte movement on the measured EN (modulation of signals due to spatio‐temporal flow disturbances) was found to be insignificant compared to the influence of the corrosion processes themselves.     

Possibility of detection of crack initiation in high temperature water

The initiation of stress corrosion cracks in sensitised austenitic stainless steel under high temperature water conditions (simulated boiling water reactor environment) was detected, applying electrochemical noise measurement technique. The stress corrosion cracks were generated on pre-oxidised, unnotched standard tensile round bar specimens under constant load conditions. The elementary transients associated with stress corrosion crack initiation were found to be embedded in the basic noise pattern coming from the oxide growth reaction on the tensile specimen. Thus a simple calculation of standard deviations to identify localised corrosion phenomena under high temperature water conditions cannot be used. The changes in the track of power density spectra proved to be much more suitable to indicate stress corrosion crack initiation under high temperature water conditions.     

利用电化学方法研究纯镁在薄液膜下的腐蚀行为Ⅱ-薄液膜对纯镁腐蚀阳极过程的影响

利用电化学噪声研究了纯镁在不同厚度薄液膜下的腐蚀行为.结果表明:与本体溶液相比,薄液膜对纯镁腐蚀的阳极过程有使点蚀的孕育速度减缓作用的同时还有使点蚀生长的概率增加的作用;薄液膜下纯镁表面产生的亚稳态点蚀牛长成稳态点蚀的概率比本体溶液下的大.点蚀孕育速度比点蚀生长概率对阳极过程的影响更大;这导致r薄液膜下纯镁腐蚀的阳极过程减缓.     

Detection and characterisation of intergranular stress‐corrosion cracking on austenitic stainless steel

Intergranular stress‐corrosion cracking (IGSCC) on a sensitised type AISI 304 stainless steel specimen was monitored simultaneously by acoustic emission, electrochemical noise, elongation measurements and a digital imaging system. The specimen was exposed to an aqueous sodium thiosulphate solution in combination with a constant load. It was established that before the final fracture two large cracks and numerous smaller cracks had developed. Detection and characterisation of the stress‐corrosion processes which generated these cracks are discussed. The results confirm and generalise previously established correlations between various parameters obtained by the implemented characterisation methods and IGSCC processes. Additionally, a clear differentiation between crack related and crack non‐related AE signals was made based on an analysis of the AE signals. The relationship between the crack lengths calculated by means of digital image correlation analysis and the electrochemical current noise was also established.     

Study of pitting corrosion on mild steel during wet–dry cycles by electrochemical noise analysis based on chaos theory

Electrochemical noise (EN) was used to investigate the corrosion behaviour of mild steel (Q235) in 0.1 M Na₂SO₄ and 0.1 M NaCl aqueous solutions during wet–dry cycles. The positive fraction and value of the Largest Lyapunov Exponent (LLE) of electrochemical current noise (ECN) were found out to represent the number and isolation degree of the pits formed in two electrolyte conditions. The calculated results indicate that metastable pits are more plentiful and uniformly distributed in wet cycles and in Na₂SO₄ solution than those in dry cycles and in NaCl solution respectively.     

Identification of steel corrosion associated with sulfate-reducing bacteria by electrochemical noise technique

Deterioration of steel structures in natural waters can result from microbiologically influenced corrosion (MIC) such as that caused by sulfate-reducing bacteria (SRB). Corrosion pits associated with MIC have been recently observed in submerged steel bridge piles and there is renewed interest to assess their deterioration. Conventional electrochemical techniques to identify MIC have been complicated due to the effects of the surface films and the mechanism for charge transfer by the bacteria on the steel surface. An electrochemical noise (EN) technique to identify steel corrosion in an aqueous solution has been developed and the method ideally can identify the onset of local pitting, but complications and limitations relating to data acquisition, filtering, and interpretation exist. EN analysis was shown to differentiate SRB and corrosion activity including initial biofilm development, pitting corrosion development, and diminution of SRB activity. Electrochemical behavior, environmental characteristics, SRB activity, and corrosion modality provided consistent correlation to EN and localized corrosion development.     

Corrosion electrochemical behavior of brass tubes in circulating cooling seawater

Electrochemical impedance spectroscopy(EIS) and electrochemical noise(EN) were used to study the corrosion electrochemical behavior of brass tubes in circulating cooling seawater using the developed sensor. EIS study shows that the inhibitor can lead to the formation of corrosion products on metal surface, which will then inhibit the corrosion process. When the flow rate of the seawater increases, the diffusion of oxygen speeds up and the action of filming on HA177-2 tube accelerates, resulting in decrease of corrosion rate. EN analysis shows that the flow rate of the seawater has little effect on pitting susceptivity of HSn70-1 tube; however the pitting susceptivity of HA177-2 tube increases with increasing flow rate. Good agreement is observed between the spectral noise resistance R30(f) calculated from EN data and the modulus of impedance. It is shown that the electrochemical noise technique can be used in corrosion monitoring.     

Detection of SCC initiation in austenitic stainless steel by electrochemical noise measurements

The electrochemical noise (EN) measurement technique is one of the most promising tools for continuous in situ corrosion monitoring in technical systems with a certain potential to be used for the detection of stress corrosion cracking (SCC). To evaluate the suitability of the EN technique for the detection of SCC initiation, a small but systematic test programme was started, performing EN measurements on type 304 austenitic stainless steel during constant extension rate tensile tests in aqueous thiosulphate solution at room temperature. SCC could be detected by EN measurements, which was verified by interruptions of the experiments at different stages, by testing steel with different degrees of sensitisation and by post‐test fractography in the scanning electron microscope. Conclusions on the cracking mechanism could be drawn based on the current noise signal pattern.     

高纯铝在含Cl~-溶液中电化学噪声的小波包子带能量特征

建立了基于小波包分解的电化学噪声子带能量表征方法 ,测试了高纯铝在含Cl-溶液中不同条件下的电化学噪声 ,分析了所测电化学噪声信号的时域特征、PSD特征及小波包分解子带能量特征 .PSD分析显示 :随着浸泡时间的增加 ,当蚀孔开始生长后 ,孔核的生长期缩短 ,消亡期延长 ,而SO2 -4 对孔核的生长期及消亡期没有显著影响 .与PSD方法相比 ,子带能量特征向量可以刻画电化学噪声信号的高频“指纹”特征 ,对腐蚀体系、腐蚀类型及腐蚀状态有较强的敏感性 .通过对第一子带能量变化分析显示 ,SO2 -4 会降低高纯铝在含Cl-溶液中孔核的发生频数 .     

Corrosion Behavior of Alloy 600 in Simulated Nuclear High Level Waste Medium

Nickel-based alloys are being considered as candidate materials for the storage of high level waste. In the present investigation, Alloy 600 was assessed by potentiodynamic anodic polarization technique for its corrosion behavior in the as-received, solution annealed, and sensitized condition in 3 M HNO₃ and 3 M HNO₃ containing simulated high level waste. From the results of the investigation, it was found that the solution annealed specimen possesses superior corrosion resistance compared to the as-received and sensitized specimen. Double loop electrochemical potentiokinetic reactivation test was carried out to study the degree of sensitization. The effect of different concentrations of chloride ions in 3 M HNO₃ at 25 °C indicated tendency for pitting as the concentration of chloride ions was increased. Microstructural examination was carried out by optical microscope and scanning electron microscope after electrolytic etching. X-ray photoelectron spectroscopy study was carried out to investigate the passive film formed in 3 M HNO₃ and 3 M HNO₃ simulated high level waste.     

敏化态304不锈钢慢速率拉伸腐蚀过程的电化学噪声检测

采用电化学噪声方法对敏化态304不锈钢在0．5mol／LNa2＆O3溶液的慢速率拉伸过程的腐蚀进行检测,同时得到腐蚀过程的电位与电流变化曲线,试验后试样表面出现了多处应力腐蚀裂纹。分别采用时域谱、频域谱及小波分解分析电流噪声数据,表明腐蚀过程经历了应力腐蚀裂纹萌生与裂纹扩展的过程。根据多种电化学噪声谱图及小波分解后的能...     

In situ study of dew point corrosion by electrochemical measurement

Dew point corrosion (DPC) is an electrochemical process in a dynamic electrolyte layer, which makes it difficult to carry out conventional electrochemical measurements and thus is not conducive to corrosion mechanism study. In situ electrochemical measurements including electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) are realized by a novel DPC simulation set-up and special electrode arrangements in this work. DPC of carbon steel is studied by in situ test method and ex situ test method, respectively. Different corrosion mechanisms are obtained from two methods. Thus, it is significant to study DPC by in situ test method so as to understand DPC essentially.     

ELECTROCHEMICAL NOISE ANALYSIS OF PURE ALUMINUM IN SODIUM CHLORIDE SOLUTION WITH WAVELET TRANSFORM TECHNIQUE

1．I口毗rodOCtlOOThe characterlzatlon and monltoringofcorroslon process usingelectrochemlcal noisetechnology has received considerable attention since 1968[1－41．One of*theion most imper－tant advantages offered by this electrochemlcal technique Is its l     

Detection and characterization of stress-corrosion cracking on 304 stainless steel by electrochemical noise and acoustic emission techniques

This paper focuses on the corrosion process of 304 stainless steel in acidic NaCl solution during slow strain rate testing experiment by using electrochemical noise (EN) and acoustic emission (AE) techniques. Meanwhile, the EN and AE characteristics of corrosion process were studied. The results show that stress corrosion occurs easily in the experimental system, and corrosion forms develops gradually from localized corrosion including stress corrosion and pitting corrosion to general corrosion. The AE signal characteristics of pitting corrosion, crack and bubble break-up are significantly different during the corrosion process.     

Corrosion protection of Mg–5Li alloy with epoxy coatings containing polyaniline

The protective ability of epoxy coating containing polyaniline (PANI coating) on Mg–5Li alloy in 3.5% NaCl aqueous solution has been studied by means of EIS and electrochemical noise measurements (EN). The results of EN and EIS revealed that the PANI coating protected Mg–5Li alloy from corrosion perfectly. XPS results indicated that the presence of polyaniline changed the chemical structure of the corrosion film on the alloy surface. An analysis of the electrochemical noise data based on stochastic analysis indicated that the corrosion growth probability of Mg–5Li alloy beneath the coating was decreased by the addition of polyaniline.