• Nuclear Engineering and Technology
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• v.41 no.10
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• pp.1315-1322
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• 2009

The present article is concerned with the application of an electrochemical noise (EN) monitoring technique to analyze the initiation and propagation of Pb-assisted stress corrosion cracking (SCC) of an Alloy 600 material in a simulated environment of a steam generator (SG) sludge pile at high temperatures. A typical increase of electrochemical current noise (ECN) and electrochemical potential noise (EPN) was frequently recorded from the EN measurement in a caustic solution with such impurities as PbO and CuO, indicating that there are localized corrosion events occurring. With the aid of microscopic and spectral analyses, the EN data involving information on such stochastic processes as uniform corrosion and the initiation and propagation of SCC, were analyzed based on a stochastic theory.

• Journal of Electrochemical Science and Technology
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• v.8 no.2
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• pp.115-123
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• 2017

Electrochemical noise signals in many cases exhibit a DC drift that should be removed prior to further data analysis. Polynomial fitting and moving average removal method have been used to remove trends of electrochemical noise (EN) in time domain. The corrosion inhibition of synthesized schiff base N,N'-bis(3,5-dihydroxyacetophenone)-2,2-dimethylpropandiimine on API-5L-X70 steel in hydrochloric acid solutions were used to study the effects of drifts removal methods on noise resistance calculation. Also, electrochemical impedance spectroscopy (EIS) was used to study the corrosion inhibition property of the inhibitor. The results showed that for the calculation of $R_n$, both methods were effective in trend removal and the polynomial with m=4 and MAR with p=40 were in agreement.

• Corrosion Science and Technology
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• v.9 no.2
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• pp.57-66
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• 2010

Since nuclear power plants are being operated under high temperature and high pressure, on-line monitoring technique to detect corrosion could be more effective than off-line method in shut-off period. In this operating condition, electrochemical noise method may be suitable to monitor the corrosion. This paper aims the analysis on the relation between the cracking and electrochemical noise signal of Alloy 600 under U-bending. When electrochemical noise monitoring technique was used during SCC test, it was judge to be obvious that if cracks generate, its generation can be detected by electrochemical current noise. Cracking-related noise was defined as the noise showing 5~10 times greater than the average value of background noise bands. On the base of crack noise, crack initiation time was determined. From SCC test and electrochemical noise monitoring in $25^{\circ}C$, 0.1 M $Na_2S_4O_6$ solution (Reverse U-Bended Alloy 600 SE+), average crack initiation time was obtained as 9,046 seconds and from its initiation time, it could be defined that net crack propagation rate is the crack length divided by ${\Delta}T$(= total test period - crack initiation time). Therefore, average net crack propagation rate was obtained to be $1.18{\times}10^{-9}\;m/s$.

• Corrosion Science and Technology
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• v.8 no.5
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• pp.203-207
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• 2009

Electrochemical methods have been widely used to study the performances and mechanisms for the degradation of organic and inorganic coatings. In this study, EN(Electrochemical noise) measurement was applied to the protective properties and review the parameters analyzed noise signals in the time and in the frequency domain for epoxy resin based coated steels during exposure to hot sea water($40^{\circ}C$) and salt spray for 200 days. It was also found that $R_n$(Noise resistance), $R_{sn}$($f_{min}$)(Spectral noise resistance) and 2H(Hurst exponent) represented the performance of epoxy coated steels. $R_n$ can be determined as the ratio of the standard deviations of potential and current noise signals and is decreased to exposure time. Data qualities can be easily checked by PSD(Power Spectral Density) plot and $V_{psd}$, $I_{psd}$ and $R_{sn}$($f_{min}$) is useful to research the protective performances and mechanisms of coated steels. Hurst exponent represents the degradation of coated steels. But, it is difficult to directly apply the protective criterion to the evaluation of epoxy coated steels used the shipbuilding processes.

• Corrosion Science and Technology
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• v.7 no.5
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• pp.296-299
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• 2008

High order statistical parameters were evaluated using the electrochemical noise data collected during corrosion of type 430 stainless steel coupled to a inert, platinum electrode in 3.5% NaCl solution. High order statistical parameters are shown to predict uniform corrosion properly. However, Localization index, skewness of current, kurtosis and skewness of potential are capable of predicting pitting corrosion only when the transients are large with long life time. Of the high order statistical parameters evaluated, kurtosis of current is found to be the most sensitive parameter for detecting uniform and pitting corrosion.

• Journal of the Korean Data and Information Science Society
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• v.11 no.2
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• pp.157-172
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• 2000

Metal containers represent a situation where a specific metal is exposed to a wide variety of electrolytes of varying degrees of corrosivity. For example, hundreds, if not thousands of different products are packaged in an aluminum beverage can. These products vary in pH, chloride concentration and other natural or artificial ingredients which can effect the type and severity of potential corrosion. Both localized (perforation) and uniform corrosion (metal dissolution without the onset of pitting) may occur in the can. A quick test or series of tests which could predict the propensity towards both types of corrosion would be useful to the manufacturer. Electrochemical noise data is used to detect the onset and continuation of pitting corrosion. Specific noise parameters such as the noise resistance (the potential noise divided by the current noise) have been used to both detect pitting corrosion and also to estimate the pitting severity. The utility of noise resistance and other electrochemical parameters has been explored through the application of artificial neural networks. The versatility of artificial neural networks is further demonstrated by combing electrochemical data with electrolyte properties such as pH and chloride concentration to predict both the severity of both localized and uniform corrosion.

• Corrosion Science and Technology
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• v.7 no.6
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• pp.319-323
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• 2008

The polarization resistance of mild steel in 0.5M hydrochloric acid has been evaluated by using impedance (Z) and linear polarization (LPR) techniques and compared to the noise resistance obtained from electrochemical noise data. The degree of localization of this general corrosion has also been discussed by evaluating localization index and power spectral density. Polarization resistance obtained by LPR technique ($28\Omega$) was higher than that obtained by impedance technique ($15\Omega$). Noise resistance ($11\Omega$) was much lower than polarization resistance measured by both of above techniques. Higher polarization resistance obtained by LPR technique is generally caused by passivation effect in the presence of scales or deposits which can introduce an increased resistance as can low conductivity electrolytes. The reason why noise resistance is lower than polarization resistance is the effect of background noise detected by using three platinum electrodes cell in 0.5M hydrochloric acid. Slope($-\beta$) of power spectral density (PSD) obtained from analysis of noise data ($-\beta$ = 3.3) was much higher than 2 which indicates mild steel corroded uniformly. Localization index (LI) calculated from statistical analysis (LI=0.08) is much lower than 1 which indicates that mild steel did not corroded locally. However, LI value is still higher than $1x10^{-3}$ and this indicates that mild steel corroded locally in microscopic point of view.

• Corrosion Science and Technology
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• v.16 no.4
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• pp.194-200
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• 2017

Stress-corrosion cracking (SCC) of alloy 600 and alloy 800 in 0.5 mol/L thiosulfate solution during constant strain was investigated using electrochemical noise (EN) combined with 3-D microscope techniques. The in-situ morphology observation and EN results indicate that the SCC process could be divided into three stages: (1) passive film stabilization and growth, (2) crack initiation, (3) and crack growth. Power Spectral Density (PSD) and the probability distribution obtained from EN were used as the "fingerprint" to distinguish the different processes. During passive film stabilization and growth, the current noise signals resembled "white noise": when the crack initiated, many transient peaks could be seen in the current noise and the wavelet energy at low frequency as well as the noise resistance decreased. After crack propagation, the noise amplitudes increased, particularly the white noises at low and high frequencies ($W_L$ and $W_H$) in the PSDs. Finally, the detection of metal structure corrosion in a simulated sea splash zone and pipeline corrosion in the atmosphere are established.

• Corrosion Science and Technology
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• v.3 no.1
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• pp.14-19
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• 2004

Crack growth rate and threshold stress intensity factor for stress corrosion cracking(SCC), $K_{ISCC}$ were measured for type 403 stainless steel in 3,5% NaCl solution at room temperature and SCC was monitored by electrochemical noise technique during $K_{ISCC}$ testing. In rising load test, pits were formed at the tip of pre-crack for the pre-cracked compact tension specimen unlike in smooth round specimen in which only unstable pits were observed and hence immune to SCC. Micro-cracks were found to initiate from the pits in the former specimen, and initiation of micro-crack as well as macro-crack was detected by electrochemical noise technique in rising load $K_{ISCC}$ tests. Crack growth rate increased with increasing either displacement rate or stress intensity factor at crack initiation and was higher in rising load $K_{ISCC}$ test compared to constant load $K_{ISCC}$ test at given stress intensities.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.4
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• pp.615-618
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• 2016

Electrochemical noise(EN) has been used to analyze the deterioration of coating films of offshore wind substructures. In this study, prototype sensors using EN have been developed to detect the corrosion rate. To verify the reliability of sensors, experiments were conducted both in the laboratory and offshore using probe and standard samples. New analysis and data processing techniques show that the sensor can provide useful information about the corrosion rate.