【作者】 杨平；

【导师】 杨理践； 于洋；

【作者基本信息】 沈阳工业大学 ， 测试计量技术及仪器， 2014， 博士

【摘要】 随着国家石油化工行业发展，中国已经成为世界第二大石油消费国。在不久的将来有可能超过美国，成为世界第一石油消费国。为应对国际油价的波动及地区局势对我国原油安全的影响，中国从1993年开始着手原油储备计划。随着原油储备计划三期工程的完工，届时我国原油储备将达8000万立方米以上。再加上与国家储备规模相当甚至超过国家原油储备的商业用油储备，我国将拥有庞大的石油储备系统。在石油储备系统中储罐是核心设备，而腐蚀给储罐安全带来了严重威胁。因此原油储罐腐蚀的有效检测，尤其是原油储罐腐蚀在线检测具有重要意义。声发射检测技术是一种在线无损检测技术，只需在储罐外壁或在被检测对象表面放置若干传感器，就可以检测罐底或被检测对象的腐蚀状况。但目前腐蚀声发射检测技术还存在以下问题：过度地依靠经验和专家系统，对腐蚀声发射的产生机理及腐蚀声发射信号本身的认识不够充分；声发射信号的特征提取、识别及检测过程中关键参数的选择缺乏理论依据，检测结果的可靠性及实际可用性都有待提高；没有建立起声发射信号与腐蚀过程的具体对应关系，难以给检测到的信号赋予实际的物理意义，对检测结果难以给出准确的评价。本文针对腐蚀声发射机理、有效性、声发射信号与腐蚀过程之间的关系、声发射信号特征提取与识别、声发射源的鉴别等关键问题展开理论与实验研究。本文的主要研究内容有：（1）从腐蚀过程基本原理出发，通过对钢板腐蚀过程中阴极和阳极发生的化学反应、腐蚀反应及反应产物与声发射之间的可能关系、腐蚀过程中可能产生的应力变化的研究。提出了腐蚀过程中，氢气泡成长的原因。得出大气压、液体液位和气泡表面张力为气泡破裂声发射应力脉冲来源；大气压、液体液位和残余应力为腐蚀裂纹声发射可能的应力脉冲来源。根据Knopoff点应力脉冲理论，考虑到大气压、液位高度、气泡表面张力等参数对应力脉冲位移的影响及声发射传感器对薄板振动位移的响应，建立了腐蚀过程与声发射信号之间的理论关系，经过数值计算直接从理论上证明了腐蚀声发射检测技术的有效性，一定程度上揭示了腐蚀声发射的检测机理。（2）针对腐蚀过程中产生的气泡、金属开裂及金属腐蚀产物开裂、腐蚀电位波动现象，分别从理论上研究了气泡尺度、腐蚀开裂尺寸与开裂速度及腐蚀电位与声发射信号时频特征之间的关系。从理论上推导出腐蚀声发射信号特性，即声发射信号的幅值与气泡半径的平方、液位的高度成正相关；声发射信号的频率与气泡的半径成反比。腐蚀开裂产生的声发射信号强度与开裂面积、液位高度及局部应力强度成正比；声发射信号的频率与裂纹扩展的长度成正比，与裂纹扩展的速度成反比；揭示了腐蚀声发射信号特征，为腐蚀声发射检测过程中，液位加载高度、传感器带宽的选择、声发射信号特征提取、检测结果的评价提供一定的参考。（3）设计密封条件下钢板在不同腐蚀液中的等面积腐蚀实验，并通过高频、低频全带宽声发射系统在距腐蚀位置相同的条件下对腐蚀过程进行长时间全程监测。分析声发射信号各种参数特征及声发射信号与腐蚀过程、腐蚀类别之间的区别与联系，通过理论推导和实验证明气泡破裂和腐蚀开裂所产生的声发射信号频谱特征不同。气泡破裂产生的声发射信号频率主要集中在10～80KHz之间，金属开裂的声发射信号分布在80～1000KHz之间，可以通过声发射信号的频谱分布区分与识别气泡破裂与裂纹开裂产生的声发射信号。（4）研究声发射信号降噪与声发射信号特征提取方法，给出小波处理声发射信号过程中小波基函数及噪声处理过程中门槛值的选择依据；并且应用谱分析法、小波变换、S变换法研究声发射信号噪声处理及时频分布特征。指出db8小波是常见小波中最佳的声发射信号噪声处理及特征提取的小波之一，S变换能有效地提取声发射信号的时频局部特征。更多还原

【Abstract】 With the developments of the National Petroleum and chemical industry, China hasbecome the second largest oil consumer in the world at present. It will be exceeding Americaand becoming the first oil consuming country in the future. The crude oil reserve plan hadbeen started from1993in order to cope with the international oil price fluctuation and the statesafety. With the third stage of the project complete, China oil reserves will reach eightymillion cubic meters. Taking into account the business reserves, the reserve scale is evenmore than the National Petroleum reserve. China has a huge oil reserve system. The storagetank is the key equipment in the petroleum reserve system. Corrosion is a serious threat to thestorage tank. Therefore, an effective storage tank corrosion detection technology is essential,especially on-line detection technology.Acoustic emission detection technology is an online testing technology. It detects the tankbottom corrosion with several sensors that are placed on the tank wall. It is quite differentfrom other tank bottom corrosion detection technology which needs open the tank to detect thetank bottom corrosion. But acoustic emission corrosion testing technology has the followingproblem: First, the engineer’s experience and the experiment system is essential and muchmore needed; second, the mechanism of corrosion acoustic emission and the characteristic ofacoustic emission signal is not understood to people; third, the theory is lack when theengineers extract the characteristic of acoustic emission signal and select the key parameters ofacoustic emission signal, so the reliability and availability of acoustic emission detectionshould be improved; forth, the relationship between acoustic emission and corrosion processhas been not found, so the physical meaning of corrosion acoustic emission signal can’t beunderstood and the accurate test results are hard to be made by engineers. To resolve theseproblems, the mechanism of corrosion acoustic emission, the validity of corrosion acousticemission detection technology, the relationship between acoustic emission signal and thecorrosion process, the extraction of acoustic emission signal characters and the identificationof acoustic emission sources were studied in theory and experiment. The following contentshave been studied:(1) Based on the foundation of corrosion, the reaction of cathode and anode in steelcorrosion process, the possible relationship between the reaction of steel corrosion and acoustic emission signal, the possible relationship between the reaction products of steelcorrosion and acoustic emission signal and the change of stress in corrosion process werestudied. The cause of hydrogen gas bubble growth is presented. The atmospheric pressure,liquid level, and bubble surface tension are the sources of bubble burst acoustic emission stresspulse. And atmospheric pressure, liquid level, and residual stress may be the potential sourcesof steel crack acoustic emission stress pulse. Based on the theory of knopoff point stress pulse,the parameters of atmospheric pressure, liquid level and bubble surface tension weresubstituted the relationship between the response of elastic sheet displacement and the pointforce pulse, and then the displacement was substituted the relationship between the responseof acoustic emission sensor and the elastic sheet displacement. The relation between acousticemission signal and corrosion process is constructed in theory. Based on the numberconclusion and the steel corrosion acoustic emission detection experiment, the effectiveness ofcorrosion acoustic emission detection techniques is directly provided by theory andexperiment. To some extent, the mechanism of corrosion acoustic emission detection wasrevealed.(2) Considering the phenomenon of bubble burst, the crack of steel, the crack of steelcorrosion product and the fluctuation of corrosion potential in corrosion process, therelationship between the gas bubble scales, corrosion cracking scale, cracking speed andcorrosion potential fluctuation with AE signal time-frequency characteristics were studied intheory. The characteristics of acoustic emission of corrosion and the relationship betweencorrosion acoustic emission and the bubble diameter and the liquid level were directly derivedin theory. It is that the amplitude of AE signal is proportional to the bubble radius square andthe liquid level，and its frequency is inversely proportional to the bubble diameter. The AEsignal strength of steel corrosion cracking is proportional to the local stress strength and theAE signal frequency is proportional to the crack propagation distance and inverselyproportional to the crack propagation velocity. The characteristics of corrosion acousticemission were revealed. That is helpful to the engineers who detect the corrosion with acousticemission technology to determine the height of liquid level, select the sensor bandwidth,extract the feature of the acoustic emission signal and evaluate the detection conclusion.(3) The steel corrosion experiment with the same area immersed in the etchant solutionwas designed under sealed condition. The AE systems with high frequency and low frequency were used to detect AE signal during the whole corrosion process at the same distance. TheAE signal parameters were studied. The difference and relationship between AE signal andcorrosion process, corrosion types were studied. The spectrum of bubble breaking out acousticemission signal and corrosion cracking acoustic emission signal that is different was proofedin theoretical and experimental. The frequency range of bubble burst acoustic emission is from10～80kHz. The frequency range of steel cracking acoustic emission is between the80～1000KHz. These two styles acoustic emission signals could be distinguished by thedistribution of power spectrum.(4) The acoustic emission signal characteristics extraction and noise reduction methodswere studied and the rule of choosing the best wavelet function for acoustic emission signalprocessing and noise threshold were proposed The AE signal in time and frequency domaincharacteristics was studied by power spectrum and the S transform spectrum. Thecharacteristic of corrosion acoustic emission signal and the noise was analyzed db8wavelet isone of the best wavelet for the acoustic emission signals noise processing and featureextraction. S transform method can effectively extract the local features of acoustic emissionsignals.更多还原