A novel experimental arrangement for corrosion study of X60 pipeline steel weldments at turbulent flow conditions

Electrochemical noise (EN) measurements were carried out to study the effect of turbulent flow conditions on corrosion kinetic of API X60 pipeline steel weld immersed in synthetic seawater. In order to control the hydrodynamic conditions, two rotating cylinder electrodes were used. The EN data were analysed by three different statistical methods: currents transients, noise resistance and localisation index (LI). On the other hand, the spectral method was used in order to get the noise impedance. The superficial analysis using a scanning electron microscopy was carried out. According to EN analyses, the current transients indicate that the aggressiveness of the corrosion increased as the rotation speed also increased. The highest corrosion rate values were obtained at turbulent flow conditions. In the superficial analysis, a localised corrosion form was found in all corrosion processes; these results are agreed with the results obtained by LI.     

Electrochemical noise analysis for estimation of corrosion rate of carbon steel in bicarbonate solution

We have investigated the electrochemical noise behavior of carbon steel in fully deaerated aqueous bicarbonate solutions, and discussed the optimum conditions of the noise analysis for estimating corrosion rate of the steel. Noise of the potential difference and of the short-circuit current between two identical steel coupons were successfully measured. The time-series noise patterns were transformed into frequency domain by fast Fourier transformation, and then their power spectrum densities (PSDs) at a frequency were determined to be compared with the corrosion rate. The PSDs of the potential and of the current varied with changing environmental factors of bicarbonate concentration, pH, and immersion time. The factors also controlled the corrosion rate of the steel. The PSDs were associated with the corrosion rate, and then it was found that the PSDs of the potential and of the current showed linear correlation with the corrosion rate in log-log scale. There was also linear relationship between the corrosion rate and a spectral noise resistance obtained from the PSDs of the potential and the current. The linearities of the three correlations were better at a lower analyzed frequency. Furthermore, the PSDs of the current and the noise resistance indicated more linear correlation with the corrosion rate than that of the potential. As the simplicity of the measurement system is additionally considered, it is concluded that the PSD of the current noise at an analyzed frequency of 3 mHz is the optimum conditions for estimating the corrosion rate from 10⁻² to 10⁰ A m⁻² in this study.     

Study of colored anodized aluminum with calcon in sulfuric acidic solution using cyclic voltammetry and impedance measurement methods

The effect of coloring condition of Al with Calcon (sodium 2,2'‐dihydroxy‐azonaphthalene‐4‐sulfonate), on the corrosion resistance of Al in 0.1 M sulfuric acid solution was studied, using cyclic voltammetry and measurement of impedance noise methods. The changes in the corrosion resistance of colored aluminum electrodes were evaluated by measuring the magnitude of impedance and cyclic voltammetric responses of anodized and colored electrodes. An irreversible corrosion response was observed at the cyclic voltammogram of the colored aluminum electrode. The current and threshold potential of corrosion responses strongly depends on the applied conditions during anodizing, coloring and sealing stages. In addition, significant changes in impedance at the ac voltammogram and noise level at some ac frequencies were observed, when the electrodes were colored under various conditions. In this regard, the surface of the electrode was studied by Scanning Electron Microscopy (SEM). Comparison of SEM images of the colored and uncolored aluminum specimens showed that the colored surface contained a significant numbers of pits. The results indicated that coloring aluminum with Calcon could reduce corrosion resistance of aluminum and increase roughness of the oxide film.     

Electrochemical noise during non‐stationary corrosion processes

In the present work, electrochemical noise (EN) was measured in three different types of experimental set‐ups in order to obtain and compare various types of corrosion. Simultaneously with EN measurements, a parallel technique was used, regarding the type of experimental set‐up: a computer visualization system combined with optical microscopy, or measurements of mechanical changes. In order to distinguish between these corrosion types and to assess corrosion rate, the measured EN signals were analysed by two different techniques: spectral and statistical. On the basis of estimated significant spectral parameters (power spectral densities of current and voltage noise, spectral noise resistance) and statistical parameters (standard deviation, localisation index and noise resistance), the passive state, localized corrosion types and uniform corrosion can be recognized. However, by these parameters it is not possible to distinguish between certain localized corrosion processes: metastable pitting, initiation and growth of stable pits, stress‐corrosion cracking. It was ascertained that these corrosion processes exhibit unstable nature, and consequently generated EN signals are usually non‐stationary. Since stationarity is required for spectral and statistical analysis, the unstable nature of these processes was recognized as the main reason for unreliable results. It is believed that these types of signal analysis give poor information about corrosion processes which can be easily identified from EN signal itself: transient corrosion processes and transitions between different corrosion processes.     

Field Corrosion Detection of Nuclear Materials using Electrochemical Noise Techinique

Some critical issues when applying electrochemical noise (EN) in field corrosion detection of nuclear materials are solved. In this work, a portable EN measurement system for field test is established by using Compact RIO modular instrument and zero resistance ammeter (ZRA) module. The electrode system for EN measurement is built by using platinum wire or stainless steels coated with thermal sprayed ceramic coatings as counter electrode. Two EN sensors are developed based on the electrode system mentioned above, and field corrosion detection is successfully achieved. The corrosion of stainless steel pipeline surface in nuclear power plant and internal-surface corrosion of continuous blowdown piping are successfully evaluated by the established new EN measurement system.     

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.     

采用聚类分析研究X70钢在库尔勒土壤中初期电化学噪声特征

采用电化学噪声（EN）技术研究了X70管线钢在库尔勒原土（含水量1.04%）中腐蚀初期（0 d~7 d）的腐蚀行为。通过时域谱分析、统计量分析和Q型聚类分析研究了电化学噪声特征以及相应的腐蚀状态信息,并与实际腐蚀状态和电化学阻抗谱（EIS）结果进行了对比。结果表明,基于EN统计量的谱系聚类分析法可用于解析土壤EN数据。聚类分析结果与时域分析、腐蚀形貌特征和EIS结果相吻合,且更加精确。根据聚类分析结果,可将研究体系中初期土壤局部腐蚀过程分为不稳定萌发期、快速发展期和稳定发展期三个阶段。     

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.     

表面粗糙度对304不锈钢早期点蚀行为影响的电化学方法

采用动电位扫描、电化学阻抗谱和电化学噪声等方法研究了4种不同表面粗糙度304不锈钢电极在质量分数为3％的NaCl溶液中的早期腐蚀行为.随着不锈钢电极表面粗糙度的下降,304不锈钢自腐蚀电位与点蚀电位均有所上升;电荷转移电阻噪声电阻明显升高,而电位标准偏差与电流标准偏差则有所降低;粗糙度0.25μm的电极在阻抗谱低频区出...     

Monitoring of vitreous enamel degradation by electrochemical noise

Vitreous coatings are widely used for protecting steel at temperatures up to 600 °C in applications where high oxidation- and wear-resistance are required. However, the action of alkaline chemical agents such as household cleaning products can cause the devitrification and spalling of these coatings, with the consequent loss of their protective properties. In such cases, corrosion of the substrate is accelerated due to the heat treatment applied during the manufacturing process of the coating — tempering or curing. The present work characterizes the initial stages of this deterioration using the electrochemical noise technique (EN). When coatings are undamaged the current noise is very low, with current intensity values of the order of picoamperes. However, when defects appear as a result of chemical attack, the systems electrical activity changes considerably and there is an increase in both current and potential noise. This work also establishes the loss of the coatings protective nature as a function of spectral noise resistance, R_sn, finding good concordance with values obtained by other more conventional techniques such as electrochemical impedance.     

Effect of microcrystallization on pitting corrosion of pure aluminium

A microcrystalline aluminium film with grain size of about 400 nm was prepared by magnetron sputtering technique. Its corrosion behaviour was investigated in NaCl containing acidic solution by means of potentiodynamic polarization curves and electrochemical noise (EN). The polarization results indicated that the corrosion potential of the sample shifted towards more positive direction, while its corrosion current density decreased compared with that of pure coarse-grain Al. The EN analysis based on stochastic model demonstrated that there existed two kinds of effect of microcrystallization on the pitting behaviour of pure aluminium: (1) the rate of pit initiation is accelerated, (2) the pit growth process was impeded. This leads to the enhancement of pitting resistance for the microcrystallized aluminium.     

Effect of SO2 in flue gas on coal ash hot corrosion of Inconel 740 alloy – A high temperature electrochemical sensor study

Our newly developed high temperature electrochemical sensor was applied to study the effect of SO₂ in flue gas on thin film coal ash corrosion of Inconel 740 superalloy at 750 °C. The response of electrochemical noise (EN), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) test data from the sensor is compared with the results from a weight loss test. There is a good correlation between the electrochemical data and the actual degradation processes. The current noise analysis in time and frequency domains for the quantitative determination of hot corrosion rate in service is discussed.     

WBE联合LP技术研究海水/海泥界面碳钢的腐蚀行为

利用阵列电极技术捕获了在不同浸泡时间下每个微电极与其它99个微电极整体的电偶电流,分析获得了海水/海泥界面附近阴、阳极分布区域的变化规律;利用线性极化和电化学阻抗技术对垂直海水/海泥界面的一行微电极进行测试,获得了距海水/海泥界面不同距离的微电极的腐蚀电流、腐蚀电位,并观察了腐蚀形貌,探讨了其腐蚀机理。结果表明：平行于海水/海泥界面的海泥区域为电偶腐蚀阳极区、对应的海水区域为电偶腐蚀阴极区域;海水/海泥界面区金属的腐蚀是由电位差、溶解氧浓度、海泥阻抗等多因素控制;腐蚀主要区域是近海水/海泥界面的海泥区域及远海水/海泥界面的海水区域。海水中较高浓度的氧促进了腐蚀产物的致密化,而海泥中缺氧环境及微生物抑制了腐蚀产物的致密化。     

消除稳态极化曲线测量中介质电阻影响的一种实验技术

设计了一种新型电解池，配有两支参比电极，参比电极到工作电极之间的距离可精确调节。在进行极化曲线测量时，通过测量工作电极相对于两支参比电极的电位，可求得不同电流密度的下溶液电阻，从而消除溶液电阻的影响。模拟电路和实际体系的测量证明了本实验技术的可行性。     

Investigation of the local response of the steel–concrete interface for corrosion measurement

An equivalent circuit representation for the steel–concrete interface is determined from direct potential measurements at the steel surface. The local response of steel–concrete interface to a given polarization applied at the concrete surface is investigated using an Ag/AgCl embedded reference electrode and a test system which allows simultaneous measurements at the steel–concrete interface and on the concrete surface. It is shown that the impedance spectrum on Nyquist plot for the steel–concrete interface comprises of a single arc. The equivalent circuit representation of the steel–concrete interface comprising of a parallel combination of a constant phase element (CPE) and a resistance was found to be suitable for representing the observed frequency response above 10 mHz. The parameters for the equivalent circuit obtained from the frequency-domain impedance measurements are shown to provide close prediction of the transient time-domain response from a linear polarization resistance measurement. The equivalent circuit was found to be suitable for interpreting the transient response of the steel–concrete interface during the linear polarization measurements. Available results indicate that while the response of steel undergoing active corrosion exhibits a distinctive CPE behavior, the passive steel approaches a pure capacitor. The value of resistance when the measured current increases linearly with time during a linear polarization measurement from the concrete surface provide acceptable measurements of the charge transfer resistance, and the Ohmic resistance of the concrete.     

Corrosion monitoring of nickel-containing steels in marine atmospheric environment

Corrosion monitoring of nickel-containing steels has been performed in a natural atmospheric environment using AC impedance technique. A pair of identical comb-shape steel electrodes embedded in epoxy resin was used as a probe electrode for the corrosion monitoring. Three different probes of ordinary carbon steel, 2.5%Ni- and 5%Ni-containing steels were exposed to a natural marine atmosphere for the period of 14 months. The instantaneous corrosion rate of the steels was monitored by continuous measurements of the polarization resistance, and time of wetness of the steel surface was determined from high frequency impedance. The measurement was automatically carried out with an AC corrosion monitor placed at the exposure site, and data transmission between the exposure site and laboratory was performed through cellular phones.     

Linear polarisation resistance measurements using a potentiostatically controlled guard ring

The use of a sensor controlled guard ring has been developed in recent years to enhance the accuracy of linear polarisation corrosion rate measurements on reinforced concrete structures. The established method of measurement uses a galvanostatically controlled guard ring device. In the method reported in this article the reinforcing steel is polarised potentiostatically by an inner auxiliary electrode and the real time plot of the current response is displayed on a laptop computer which controls the guard ring device. The area of steel polarised is confined by a current applied from an outer guard ring electrode which is controlled by two sensor electrodes positioned between the inner auxiliary and outer guard ring electrode. The potential between the two sensor electrodes is continually monitored, and the current output from the guard ring electrode varied to maintain a constant potential difference between the two sensor electrodes. The method has been validated on an electrical test circuit simulating active and passive reinforcement corrosion. Further testing has been conducted on a reinforced concrete specimen and the results compared with those of commercially available galvanostatically controlled equipment and those of standard unconfined linear polarisation resistance measurements.     

Assessment of intergranular corrosion (IGC) in 316(N) stainless steel using electrochemical noise (EN) technique

In the present work, an attempt was made to demonstrate the use of electrochemical noise (EN) technique in assessment of intergranular corrosion (IGC) in 316(N) stainless steel (SS). Degree of sensitization (DOS) in the specimens aged at 923 K for 24, 40, 50 and 100 h was determined using double loop electrochemical potentiodynamic reactivation (DLEPR) technique. Immediately after applying a prior preconditioning treatment, current and potential noise measurements were made. The DOS was determined from standard deviation of current noise (σ_I) versus time plot and it was found to bear a good correlation with the values obtained by DLEPR. Shot noise analysis of the EN data confirmed the above results.     

Variation of carbon steel corrosion rate with flow conditions in the presence of an inhibitive formulation

This work is an extension of studies into the mechanism of inhibition of a carbon steel by a non-toxic multicomponent inhibitor (fatty amines associated with phosphonocarboxylic acid salts) used for the treatment of water in cooling circuits. In a previous work [N. Ochoa, F. Moran, N. Pébère, B. Tribollet, Corros. Sci. 47 (2005) 593], it was shown that the properties of the protective layers formed on the metal surface were dependent on the electrode rotation rate. Moreover, two distinct surface areas were visualised on the metal surface and the ratio between the two zones was dependent on the flow conditions. The present study focuses on the measurement of the corrosion rate from impedance diagrams obtained at the corrosion potential for different electrode rotation rates. The measured polarisation resistances correspond to the anodic process. A non-monotonic variation of the corrosion current densities was observed and explained by the variation of the ratio between the two layers, which each have different intrinsic protective properties. From the polarisation curves plotted in the same conditions, the non-monotonic variation was not shown. Independently of the electrode rotation rate, the corrosion current densities remained low. This study brought an original approach to the influence of flow on the corrosion rate in the presence of inhibitors.