电化学噪声测试系统建立与研究

本文描述了电化学噪声模型,测试方法。并建立电化学噪声测试装置。     

小波变换及Hilbert-Huang变换在转子系统故障诊断中的应用

在故障诊断中,通常由于背景噪声较大,故障特征值常常淹没在噪声中不易识别.采用小波变换实现振动信号的信噪分离,提取淹没在噪声中的早期故障特征信息,并对提纯的信号进行经验模态分解(EMD)而得到若干个固有模态函数(IMF),同时求得相应的Hilbert时频谱及边际谱,从中可以判断非平稳信号的故障类型.理论分析及试验结果表明,按此方法得到的各固有模态函数突显了转子的故障特征信息,能有效诊断出转子的早期故障.     

混凝土中钢筋点蚀的电化学噪声特性研究

    采用Sym4小波分析氯离子环境下砂浆中碳钢电化学噪声的电流波动及电压波动信号,通过提取信号的小波能量,得到了信号的能量分布曲线.结果表明,电化学噪声的小波能量是点蚀监测信号解析的重要特征参数,根据能量分布曲线的变化可以判定点蚀的发生.     

304不锈钢点蚀行为的电化学噪声研究

本文利用电化学噪声技术检测了304不锈钢在6．0％（质量分数）FeCl3溶液中的点蚀行为。通过电化学噪声的时、频域分析和电化学噪声信号的统计分析以及相应的腐蚀形貌,研究了蚀点的生长过程。结果表明,浸泡初期噪声电阻Rn在较高水平波动,试样处于钝化状态;浸泡4～14h为点蚀诱导期,Rn开始降低,峭度和不对称度增大,出现明显的噪声峰,试样表面业稳态点蚀形核,生成的亚稳态点再钝化,通过扫描电镜观察未发现蚀点;浸泡14～32h为亚稳态点蚀向稳态点蚀过渡期;浸泡22h后,观察到电位噪声突然下降后不再恢复,功率密度（PSD）图低频区出现白噪声水平,亚稳态蚀点发展成为稳态的蚀点,通过扫描电镜观察到小而浅的蚀点;浸泡32～48h后材料处于稳定的点蚀阶段,通过扫描电镜观察到口径较大且较深的蚀点。     

304不锈钢点蚀的电化学噪声特征

使用电化学噪声技术,通过长期连续实时监测,对304不锈钢在0.5mol/L FeCl₃溶液中发生局部腐蚀的点蚀发展过程和腐蚀机理进行研究。综合谱图分析、时域统计分析、小波分析等诸多方法进行分析和论证。结果表明：电化学噪声的谱图可以明显地分为4个阶段,分别对应于点蚀发展过程中的钝态期、亚稳态点蚀期、稳态点蚀期及稳态点蚀后期。在时域分析时,先用3阶多项式拟合移除漂移,电流噪声标准偏差Si在亚稳蚀和稳态点蚀阶段发生明显的升高,噪声电阻(R_n)、点蚀指标(PI)在对应时间点表现出相应的降低或升高。小波分析表明,随着反应的进行,能量积累开始逐步增大;亚稳态点蚀期能量开始向d4~d6处累积,当进一步发展为稳态点蚀时d5~d8出现极大值。     

基于Hilbert-Huang变换的振动信号特征提取

采用Hilbert-Huang变换,提取高压齿轮泵泵壳振动信号故障特征.该方法先对信号进行EMD分析和Hilbert变换,再提取信号Hilbert谱及谱熵.Hilbert谱刻画了信号的能量随时间和频率的变化规律,而谱熵刻画了信号能量分布的复杂性.分析结果表明,提取的特征有效地刻画了故障信号,为故障模式的识别奠定了基础.     

非平稳运动能量Hilbert-Huang变换及其应用

大型旋转机械的故障在发生或发展时,其运行过程具有明显非平稳特性的瞬态过程.结合Hilbert-Huang变换的特点,本文提出了运动能量Hilbert-Huang变换分析方法,它融合了转子同截面两通道的振动分量,能准确地反映转子发生故障时的瞬态过程运动能量的变化.工程实践应用表明:运动能量Hilbert-Huang变换分析对于旋转机械故障诊断是一种新的、较为实用的信息融合方法.     

孔蚀过程中的电化学噪声特征

研究了几种钝态金属在合有活性离子的中性缓蚀剂体系及硫酸体系中发生局部腐蚀时的电化学噪声行为。结果表明:在研究的所有腐蚀体系中,饨态表面孔蚀过程中腐蚀电位波动噪声的功率密度谱(SPD)曲线都具有相同特征,即在极低频率下为白噪声,随频率升高,逐渐转变为1/f~n 噪声。视金属材料不同,测得的表观 n 值在2.2—3.4之间。SPD 曲线上最高频率 f_c 与溶液中 Cl~-浓度关系呈现三种类型。提出了一个解释实验结果的 SPD 的数学模型.     

两种船体钢耐点蚀性能的电化学噪声评估

运用电化学噪声(EN)测量技术和极化曲线技术检测两种船体钢A和B在0.5mol/L NaHCO3+3%NaCl溶液中的腐蚀状况,结果表明,两种钢的噪声图谱都表现出了明显的点蚀特征;在点蚀诱导期,B钢电位噪声波动的幅度和暂态峰的密集程度均比A钢大,而且诱导期持续时间较短;对噪声电阻的分析也表明,在该试验体系中A钢表面状态更稳定。极化曲线的分析结果表明A钢的点蚀电位较高、极化电阻较大、腐蚀电流较小,耐点蚀性能更好,这与电化学噪声分析的结论一致。     

测量不锈钢电化学噪声的非对称表面方法

提出一种基于同种材料不同表面处理的电极配对模式，采集非对称EN时域信号，主要反映单个电极的局部腐蚀扩展动态，从而拓展EN测量在不锈钢点蚀传播过程中的应用。结合EN与各个电极腐蚀电位的交替测量，提供各电极表面状态随浸泡时间的不同发展趋势的证据。研究结果有望提供一种EN测量局部腐蚀扩展过程的新模式，并建立EN信号与单电极上电化学腐蚀过程对应的电化学暂态模型，为测量、分析及预测钝性工程合金在海水中的局部腐蚀行为提供新的思路。     

316L不锈钢在FeCl3溶液中点蚀行为的电化学噪声检测

利用电化学噪声技术检测了316L不锈钢在6％FeCl3溶液中点蚀的电化学噪声谱,观测腐蚀形貌,分析电化学噪声谱特征参数。结果表明,在浸泡初期,电流噪声波动较小,有暂态峰出现,电流功率谱密度（PSD1）的斜率变化不大,表明电极表面出现亚稳态蚀点,钝化膜溶解与修复交替进行。在腐蚀后期,PSD1出现高频白噪声水平,电流噪声波...     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。     

X70钢及其焊缝在含Cl-高pH值溶液中电化学噪声行为研究

研究了不同外加电位下X70钢母材及其焊缝在含Cl-的高pH溶液中电化学噪声行为,并针对电化学噪声数据进行统计分析,得到表征点蚀萌生和发展的特征图谱.结果 表明,电化学噪声技术可以有效监测X70钢的腐蚀过程,电流噪声幅值大小一定程度上反映了局部腐蚀萌生和发展过程.当X70钢处于阳极极化时,电化学噪声的能量密度谱(EDP)...     

电化学噪声在接地网土壤腐蚀监控中的应用

采用电化学噪声测试技术对变电站接地网土壤腐蚀状况进行实时在线监测。结果表明:接地网环境发生改变时,对土壤腐蚀特性有较大影响,接地网腐蚀状态变化较大。电化学噪声监测系统对土壤腐蚀环境的变化反应灵敏,能够进行实时准确的监控预警,可用于变电站基建勘察以及运行维护阶段的腐蚀监控。     

Electrochemical noise monitoring of the atmospheric corrosion of steels: identifying corrosion form using wavelet analysis

The early stage atmospheric corrosion of T91 and Q235B steels exposed to Tianjin’s urban atmosphere over 20 days was studied using two electrochemical probes via an electrochemical noise (EN) technique. To identify the corrosion process and the corrosion form of the two steels, EN data were analysed by statistics and wavelet transform. The results revealed that the wavelet energy of decomposed EN mainly located at high-frequency level for Q235B steel, whereas it mainly located at the low-frequency level for T91 steel. Analyses of surface images confirmed that Q235B steel underwent uniform corrosion whereas T91 steel suffered from localised corrosion. The obtained noise resistance correlated well with weight loss data.     

Corrosion Behavior of 316LN and 316 Stainless Steels During Long-term Exposure to Aerated 0.5 M NaCl Using Electrochemical Noise Technique

In the present work 316LN as well as 316 stainless steel (SS) coupons each of dimensions (0.025 × 0.018 × 0.006 m³) in well-polished condition were used as two nominal electrodes which were immersed in the aerated solution of 0.5 M NaCl. Correlated current and potential electrochemical noise (EN) signals were collected at 1 Hz sampling frequency for 1 h daily over a period of 30 days. The detrended EN data were used to calculate the noise resistance (R _N) as well as the spectral noise resistance at zero frequency (R _SN^o) values and other statistical parameters. To study the nature of pits and distribution of their diameters as well as depths, extensive observations of the pitted and the blank specimens were carried out using Confocal Laser Scanning Microscopy (CLSM). The current and the potential records of the two alloys showed distinct differences in their corrosion behavior. It was observed that within less than 4 h of immersion, 316SS showed signals indicative of unstable pitting and onset of stable pitting was noticed after 48 h of exposure. However, until about 24 h, 316LN showed just the random signals and unstable pitting was observed after 28 h. The signals clearly indicated continuous growth of the stable pits in 316SS as against the repassivation of the unstable pits in 316LN after 7 days exposure. It was observed that R _N values showed a continuous decrease in the case of 316SS, but were quite stable in the case of 316LN over the exposure period. Concurrent to these observations it was observed that 316SS specimen was extensively pitted. The frequency distributions of pit diameters as well pit depths were observed to be highest at 10-20 μm and 5-10 μm, respectively. However, pits with as large as 70-80 μm diameter and as deep as 20-25 μm too were observed. No pits were observed in case of 316LN even after 30 days of exposure, an observation that corroborates well with the stable R _N values. Thus, in the present investigation, the long-term tests using EN technique coupled with CLSM studies conclusively prove that many unstable pits initiated in 316SS turn into stable ones resulting in insidious localized corrosion attack whereas the unstable pits initiated in 316LN get passivated in the simulated coastal environment.     

电化学噪声技术研究X80钢的点蚀过程

采用电化学噪声(Electrochemical Noise,EN)方法研究了X80管线钢在NaHCO3+NaCl溶液中亚稳态与稳态点蚀特征。结果表明:在含Cl-溶液中,当试样处于点蚀亚稳态,电位与电流噪声具有典型的快速下降或上升,缓慢恢复的暂态峰(Transient)特征,噪声电流峰平均宽约5~10s,而噪声电位峰宽为100s。随着腐蚀时间的延长,亚稳态点蚀噪声峰数量增多,亚稳态点蚀程度加剧;当点蚀由亚稳态发展到稳态初期,电流噪声峰恢复时间变长,与电位噪声峰寿命趋于一致;而随着稳态点蚀的发展,电位与电流峰出现的频率显著增加,电位与电流峰具有很好的相位同步性。