电化学噪声技术检测核电环境材料的腐蚀损伤

探讨和解决了电化学噪声技术在核电环境材料腐蚀损伤检测应用的关键问题,建立了基于零阻电流（ZRA）检测的SCC电化学噪声测试体系。采用小面积的Pt或表面热喷涂陶瓷涂层的工作电极材料作为对电极,研制适用于核电现场检测的多种电化学传感器。运用Compact RIO模块化仪器和设计制作的基于ZRA电路的电化学噪声测试模块,实现电位一电流噪声的同步测量和采集。成功研制出便携式核电材料损伤检测系统。应用研制的测试系统和电化学传感器研究了高温高压和动态水环境304不锈钢的电化学噪声谱特征。并初步实现了在役核电站辅助车间不锈钢管道表面直接腐蚀检测和钢厂动力锅炉连续排污管的现场腐蚀检测,取得了比较满意的结果。     

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.     

断电流分析测量技术监测钝化膜小孔腐蚀破坏过程

利用建立的断电流暂态测量系统和提出的由-t·dV/dt～lg(t)图判断腐蚀体系时间常数个数和弛豫过程类型的判断方法,定性地确定了钝化膜随时间的变化情况。用这项技术连续监测了20~#碳钢和1Cr18Ni9Ti不锈钢的小孔腐蚀破坏过程。     

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 studies of austenitic and duplex stainless steels in aqueous lithium bromide solution at different temperatures

The corrosion behavior of three stainless steels EN 14311, EN 14429 (austenitic stainless steels) and EN 14462 (duplex stainless steel) was studied in a commercial LiBr solution (850 g/l LiBr solution containing chromate as inhibitor) at different temperatures (25, 50, 75 and 85 °C) by electrochemical methods.Open circuit potentials shifted towards more active values as temperature increased, while corrosion potentials presented the opposite tendency. The most resistant alloys to general corrosion were EN 14429 and EN 14462 because they had the lowest corrosion current for all temperatures. In all the cases corrosion current increases with temperature.Pitting corrosion resistance is improved by the EN 14462, which presented the highest pitting potential, and the lowest passivation current for the whole range of temperatures studied. The duplex alloy also presents the worst repassivation behavior (in terms of the narrowest difference between corrosion potential and pitting potential); it does not repassivate from 50 °C.     

The influence of the cathodic process on the interpretation of electrochemical noise signals arising from pitting corrosion of stainless steels

The use of electrochemical noise (EN) measurements for the investigation and monitoring of corrosion has allowed many interesting advances in the corrosion science in recent years. A special advantage of EN measurements includes the possibility to detect and study the early stages of localized corrosion. Nevertheless, the understanding of the electrochemical information included in the EN signal is actually very limited. The role of the cathodic process on the EN signals remains uncertain and has not been sufficiently investigated to date. Thus, an accurate understanding of the influence of the cathodic process on the EN signal is still lacking. On the basis of different kinetics of the oxygen reduction it was established that the anodic amplitude of transients arising from pitting corrosion on stainless steel can be decreased by the corresponding electron consumption of the cathodic process. Therefore, the stronger the electron consumption, the weaker the anodic amplitude of the EN signal becomes. EN signals arising from pitting corrosion on stainless steel can be measured because the cathodic process is inhibited by the passive layer. This was confirmed by means of EN measurements under cathodic polarisation. Since the cathodic process plays a decisive role on the form of transients arising from pitting corrosion, its influence must be considered in the evaluation and interpretation of the EN signals.     

Guideline for an assessment of electrochemical noise measurement devices

Pro‐active ageing management is becoming more and more important for the economical and safe operation of industrial plants. A key element for a pro‐active ageing management approach is to apply in situ corrosion monitoring. The electrochemical noise (EN) technique is an example of a promising method, especially for monitoring localised corrosion phenomena. Currently, research work on the EN technique is carried out in several laboratories worldwide for different kind of industrial applications but also for the investigation of corrosion mechanisms. A prerequisite for performing serious research on the EN measurement technique is a careful evaluation of the measuring system, even if commercially available EN measurement instruments are used. Therefore, testing on well‐defined dummy cells should always be a preliminary step to assess the baseline noise of the EN measurement equipment and to ensure data validity. For this purpose a guideline has been developed by the European Cooperative Group on Corrosion Monitoring of Nuclear Materials (ECG‐COMON 1 ) as an outcome from round‐robin testing on EN. The current guideline describes a simple procedure for the performance and evaluation of EN measurement equipment using dummy cells.     

Applications and experience with a Superaustenitic 7Mo stainless steel in hostile environments

A new superaustenitic stainless steel is described in terms of chemical composition. mechanical properties and corrosion resistance. Results obtained by using this highly alloyed stainless steel, EN 1.4652, in a number of hostile environments are reported. Applications include neutral and acid chloride containing environments such as those existing in e.g. – pulp bleach plants, – ventilation systems of pharmaceutical plants, – equipment for flue gas cleaning in power plants and municipal waste incineration plants, – equipment for recovery of chlorinated hydrocarbons, – sea water piping, – nuclear power plant condenser tubes. The paper also contains laboratory corrosion test results positioning this steel in relation to other highly alloyed stainless steels and nickel base alloys, mainly in terms of its resistance to chloride induced localised corrosion.     

Electrochemical noise analysis: detection of electrode asymmetry

One major application of electrochemical noise (EN) analysis for corrosion studies is the estimation of corrosion rate via impedance measurement. The measurement involves coupling two electrodes, whereupon the associated EN is measured and the noise resistance and the spectral noise impedance are computed. However, the two electrodes are required to be “nominally identical” (i.e. symmetrical) for the noise resistance and spectral impedance techniques to be valid. This paper proposes that the correlation between the measured potential and the current noise can be used to detect an asymmetric electrode pair and thus provides a necessary but not sufficient test for electrode symmetry. The potential/current coefficient of correlation is derived based on an equivalent circuit to demonstrate the concept and experimental data is presented to support the theory.     

The effect of passive layer stability on electrochemical noise signals arising from pitting corrosion of stainless steels

Electrochemical noise (EN) enables corrosion research and monitoring in real time and with high sensitivity. In the case of submicroscopic nucleation events of pitting corrosion it has been observed that the cathodic process plays a decisive role in the mechanism as well as in the origin of EN signals, which depend not only on the metallic dissolution reaction but also on the electron‐consuming process. EN signals arising from the nucleation process of localized corrosion on stainless steels can only be recorded due to the inhibition effect on the cathodic process achieved by the spontaneous formation of the passive layer. In consequence, passive layer stability becomes a significant factor in influencing EN signals. The way in which the passive layer stability affects the acquisition and analysis of EN signals arising from pitting corrosion on stainless steels is discussed in detail.     

Rauschdiagnostik bei Korrosionsprozessen Teil 2: Problemanalyse

Noise diagnostics at corrosion processes Part 2: Problem analysis Although the phenomenon of electrochemical noise (EN) is known in corrosion research for almost 30 years it only reaches attention of a growing number of prospective buyers as a relatively new measurement procedure within the last few years. Some problems concerning the use of electrochemical noise measurements in corrosion research are shown and discussed. Based on the results of a round robin test the task regarding arrangement of the EN measuring technique, particularly the choice of a suitable frequency range, a suitable data acquisition and different methods for evaluation of data are presented. On the basis of experimental investigations regarding pit initiation and inhibition of aluminium as well as pitting of stainless steel arising problems are analyzed and solutions are suggested. The evaluation of the measurement results of the round robin test makes it clear that a uniform numeric assessment of the readings is of decisive meaning for the comparability of the results. The example of calculation of standard deviations for various assessment time periods demonstrated that very different results can be determined from the same data set by the same evaluation method. It became clear that the complex interaction between the way in which EN data are recorded (sampling rate, filtering, online data manipulation, baseline noise level) and the subsequent data evaluation should be taken into account in any case.     

Rauschdiagnostik bei Korrosionsprozessen Teil 1: Ergebnisse eines Ringversuches

Noise diagnostics at corrosion processes Part 1: Evaluation of a round robin test The Institute of Materials Engineering and Materials Testing of the University of Magdeburg (IWW) organised a round robin test on the measurement of electrochemical noise (EN) and obtained the participation of 17 organisations (universities, commercial firms, R&D laboratories) from 5 countries. The experiment involved the investigation of EN signals from aluminium and stainless steel exposed under conditions in which pitting corrosion can occur. The data provided by the participants were analysed at IWWaccording to various criteria. Evaluation methods included visual inspection of the noise in the potential or current versus time curves, calculation of the standard deviation, counting of transients and transformation of the measurements into the frequency domain. Almost all of the participants were able to detect differences in EN behaviour during different stages of the experiment qualitatively. Quantitative evaluation, however, revealed a more complex situation. At times, differences in measured EN signal intensity of two orders of magnitude were obtained as a result of different apparatus used (sensitivity, frequency range, etc.). Nevertheless, the fact that more than half of the participants reported data within a relatively narrow scatterband is a positive result. The experience gained from the round robin test provides a basis for further development of EN as a tool both for the fundamental understanding of various aspects of corrosion and for the solution of practical problems of corrosion protection, in particular in the area of corrosion monitoring.     

Corrosion behavior of engineering alloys in synthetic wastewater

The corrosion behavior of 1018, 410, and 800 steels exposed to synthetic wastewater have been studied using linear polarization resistance, cyclic potentiodynamic curves (CPCs), electrochemical noise (EN), and electrochemical impedance spectroscopy (EIS) tests. The conditions were: a biochemical oxygen demand of 776 ppm; a chemical oxygen demand of 1293 ppm; a pH of 8; and a cell temperature of 25 °C. From the CPC and EN results, no localized corrosion was found for the stainless steels. However, small indications of a possible localized corrosion process were detected for the 1018 steel. The EIS results revealed that different corrosion mechanisms occurred in the carbon steel compared with the stainless steels. The results show that the corrosion mechanism strongly depends on the type of steel. Overall, the 1018 steel exhibited the highest corrosion rate, followed by the 410 alloy. The highest corrosion resistance was achieved by the 800 alloy. In addition, scanning electron microscopy analyses were carried out to explain the experimental findings.     

An electrochemical study of the corrosion behaviour of metals in canola biodiesel

The corrosion behaviour of pure Al, Cu, 1018 carbon steel and 304 type stainless steel in Canola biodiesel during 528 hours has been evaluated by using electrochemical techniques. Techniques include open circuit potentials (OCP), electrochemical noise (EN) and electrochemical impedance spectroscopy (EIS) measurements at room temperature. These tests were complemented by scanning electronic microscopy, X-ray diffraction, infrared spectroscopy and gas mass chromatography analysis. Results have shown that carbon steel had the highest corrosion rate whereas Cu had the lowest corrosion rate. EN measurements indicated that 304 type stainless steel was moderately susceptible to pitting corrosion, whereas the rest of the metals were susceptible to either mixed or uniform type of corrosion. This was due to the degradation of the biodiesel as observed in an increase in its density, viscosity, acidity and water content at the end of the test.     

核电站用不锈钢在液态Pb-Bi合金中的腐蚀行为研究进展

核电系统中,液态金属腐蚀问题是影响加速器驱动次临界系统(ADS)稳定服役的关键.概述了液态Pb-Bi合金和不锈钢在核电中的应用背景.在此基础上,重点综述了近年来常用不锈钢材料在液态Pb-Bi合金环境下的腐蚀行为,其中不锈钢在液态Pb-Bi合金中的腐蚀机制包括:(1)不锈钢中Ni元素在液态Pb-Bi合金中优先溶解而发生的...     

Evaluation of a fractal analysis technique for corrosion studies

Corrosion tests were performed to obtain electrochemical noise (EN) data during general and pitting corrosion in NaCl solutions for type 316 and 403 stainless steels. The data were analyzed by the Hurst parameter (HP) based on the rescaled range analysis. A correlation of the HP with the noise resistance was found in general corrosion, and the variability in published HP data is in part due to the difference in the value of noise resistance. The variability is also attributed to the difference in the amount of high frequency components in EN data. The HP is, however, a useful parameter for assessing the effectiveness of an inhibitor based on the characteristics of EN spectra, but not for identifying changes in the mode of corrosion in the case where the level of EN is low.     

铁素体/奥氏体双相钢在旋转单相流体中腐蚀的数值模拟

引入现代流体力学方法，建立流体力学、传质过程、腐蚀电化学反应的综合数学模型，对双相钢在流动3．5％NaCl水溶液的腐蚀过程进行了数值模拟．探讨了近壁处流体力学参数对双相钢腐蚀过程的作用，模拟结果表明：双相钢的腐蚀主要受阳极过程控制，其中钝化膜中的传质过程是腐蚀的主要控制步骤．计算的腐蚀速度与实测值基本一致,验证双相钢的流体腐蚀机构．     

Using thionates for noise eperiments – a reasonable combination?

The detection of intergranular corrosion (IGC) initiation of austenitic stainless steel (AISI 347) coupon specimens was investigated using electrochemical noise (EN) measurements. The tests were performed in acidic sodium tetrathionate (Na₂S₄O₆) solution. The IGC initiation in tetrathionate solution could not be clearly detected by the electrochemical potential noise signal due to interferences of the noise signal with chemical processes which occurred in the test solution. This was confirmed by tests with inert platinum specimens. It was concluded that EN results obtained by tests in thionate or comparable sulfur containing solutions should be regarded with great care and verified, e.g., by tests with inert specimens.     

核电厂海水系统不锈钢焊接处腐蚀与防护

核电厂海水系统不锈钢焊接处是腐蚀失效的敏感部位,本文阐述了不锈钢焊接处的腐蚀机理,对核电厂海水系统不锈钢焊接选材设计、准备、实施和焊后处理过程中可能发生的腐蚀行为或存在的腐蚀隐患进行分析,并提出防护措施.     

指数律衰减电流极化电位响应的解析及其在测定金属的瞬时腐蚀速度方面的应用

本文为适应腐蚀体系中受力试样的腐蚀速度快速测定,对指数律衰减电流的电位响应进行了研究,从理论上导出指数律衰减电流极化的电位响应曲线上有极值点存在,这是用指数律衰减电流极化极值法测定金属腐蚀速度的理论基础。本文把用此方法和稳态方法得出的结果进行了比较,表明两种方法测得的结果比较接近,同时列出了321不锈钢在0.5mol/LHCI+0.5mol/LNaCl体系中不同应力水平时的瞬时腐蚀速度。