基于聚类分析的罐底声发射检测信号融合方法

采用声发射技术进行罐底腐蚀与泄漏检测过程中,需要对多个传感器的检测到的声发射信号进行融合处理,将属于同一声发射源的声发射信号判定为一个声发射事件。但是在现场检测过程中,由于噪声的存在,使得在声发射信号融合处理时容易对声发射源产生误判。针对该问题,提出了一种基于聚类分析的罐底声发射信号融合方法,其基本原理是先根据事件定义时间进行初始声发射事件判定,然后采用聚类分析方法对初始声发射事件中的信号进行分类,将每一类信号分别判定为一个声发射源。现场实验表明采用该方法抗噪声干扰能力强、误判概率低,能准确反应罐底腐蚀的实际情况。     

储油罐声发射在线检测技术研究与应用

由于传统储罐检修中的定周期、盲目开罐可能造成巨大财力物力损失、“坏”罐漏检等问题,近年来国内外出现了睹罐在线检测技术。而声发射技术是目前国内外应用比较多的储油罐底板腐蚀在线检测定性评价技术。本文在声发射在线检测原理基础上,探索出一种实用的储罐声发射信号采集流程。在神经网络的声发射信号模式识别方法的基础上,提出了一种混合式的声发射信号处理方法。本文的研究成果成功应用于储油罐声发射在线检测的现场数据采集和分析处理,对储油罐在线检测技术研究具有一定的指导作用。     

基于小波聚类的罐底声发射源聚集区域自动识别

利用声发射(AE)技术进行储罐罐底腐蚀检测过程中,不仅要获得声发射信号,还要根据声发射源分布的疏密了解罐底各处的腐蚀情况.传统方法一般采用人工方式进行腐蚀区域划分和识别,效率和准确率都低.为解决该问题,提出了一种基于小波聚类的罐底声发射源聚集区域自动识别方法.算法过程主要包括:划分网格、二维离散小波变换、区域查找和标记、确定声发射源所属区域等步骤.现场实验数据表明,该方法能够对任意分布形状的声发射源聚集区域进行自动识别,特别是能够将因加热盘管腐蚀产生的声发射源划分到同一区域,有效提高了对罐底腐蚀评估的效率和准确性.此外,以声发射源分布信息熵作为区域识别有效性的评价指标,选择信息熵最大的识别结果作为最终声发射源聚集区域识别结果最为有效.     

基于相关分析的声发射储罐罐底检测降噪方法

基于声发射原理的大型储罐罐底腐蚀和泄漏检测方法近些年被业界普遍认同。作为一种高效率、低成本的先进方法取得了越来越多的应用。然而由于该方法本身的特点,在检测过程中不可避免地会采集到大量的噪声信号。如不能有效地消除这些噪声信号,就会严重影响对罐底评估的准确性。因此,人们提出了多种去噪方法,然而这些方法却不能很好地消除“虚定位”事件。针对该问题,提出了一种基于相关分析的声发射罐底检测降噪方法以消除“虚定位”事件。通过对现场实际检测数据的处理表明,该方法能够有效消除“虚定位”事件,使得罐底评估的结果与开罐实测的结果更加相符。     

立式圆筒储油罐底板焊接变形原因分析及控制

储油罐是存储液态石油的重要设备,罐底板的检修是储罐施工的重要环节,对罐底检测、几何形体检测、腐蚀检测、罐底技术评定等问题进行分析讨论,提出如何制定合理的检修方案及罐底板变形控制措施,从而有效地控制底板的变形。     

储罐罐底板外壁腐蚀及防护

罐底板的腐蚀一直严重威胁着储油罐的安全生产，本文阐述了罐底板外壁的腐蚀现状，分析了腐蚀原因，提出了合理的罐底板及外边缘板防腐方案；并对罐底外壁常用阴极保护法进行比较，提出了网状阳极是目前最常用且有效的阴极保护方式，并对罐底阴极保护系统的绝缘问题提出了建议。     

基于极限学习机和b值法的罐底声发射检测腐蚀信号识别方法

声发射储罐罐底腐蚀检测过程中,采集到的腐蚀信号里不可避免地混有干扰。针对该问题,提出了基于极限学习机(ELM)的石油储罐罐底腐蚀信号识别方法。为验证该方法的有效性,在秦皇岛输油站的消防水罐里,进行模拟罐底腐蚀检测实验,并应用ELM对采集到的声发射信号进行分类识别,用b值法对ELM的分类效果进行评估。实验结果表明:ELM识别正确率高于90%。ELM识别出的腐蚀信号的b值变化规律与实验室条件下腐蚀信号的b值变化规律一致,并能够反映磷酸腐蚀碳钢板的过程。     

时间反转在列车转向架声发射源定位中的应用

针对高速列车转向架的动态检测提出一种新的损伤声源定位方法,采用声发射检测技术对转向架易损伤的焊接部位进行时间反转定位方法研究。首先利用有限元软件建立转向架焊接部位结构有限元模型;然后在模型上模拟发出一个声发射损伤信号,通过预置的声发射传感器接收声发射源信号;最后根据时间反转聚焦原理对接收信号进行处理,并通过检测区域成像,确定损伤声发射源的准确位置。数值仿真实验结果表明:该定位方法能够准确定位声源位置,定位结果比常规四点圆弧法更精确。     

容量比较法解决储油罐罐底变形引起的差量

储油罐罐底变形引起的计量误差,是目前全国从事油品储存加工企业急需解决的一个问题.以容量比较法为测试验证方法.采用罗斯蒙特0.1级质量流量计,测试储油罐罐底基础沉降与罐底板形成间隙引起的夹层(暗舱)而造成的差量.将测得的差量结果来重新修正容量表,解决了储油罐因罐底变形造成计量误差的问题,大大提高了罐容使用的准确度.     

油罐底板腐蚀漏穿分析及底板更换

根据124#罐底板漏磁检测数据报告，总结出罐底漏穿的特征，分析了罐底板腐蚀漏穿的原因为电化学腐蚀，论述了更换罐底板的施工措施，总结了更换底板旌工中的经验。     

Cluster analysis of acoustic emission signals in pitting corrosion of low carbon steel

The pitting corrosion characteristics of low carbon steel specimens are studied by acoustic emission (AE) and electrochemical techniques, in a 3.0 wt.% NaCl solution acidified to pH 2.0. The acoustic emission signals generated by pitting corrosion are classified based on multiple acoustic emission parameters using K‐means clustering algorithm, then each classified signals are analyzed by acoustic emission parameters correlation plot and distribution with time. Furthermore, each acoustic source characteristics is extracted using Gabor wavelet transform (WT) in the time and frequency domain. An error back propagation (BP) artificial neural network (ANN) is trained according to the classified signals, so as to successfully identify the acoustic emission signals from parallel experiments. Experimental results show that the hydrogen bubble activation, oxidized film rupture and pit growth are typical acoustic emission sources in pitting corrosion process, which can be effectively classified by cluster analysis and recognized by back propagation neural network. The data gathered from laboratory tests combined with the real data from acoustic emission on‐line storage tank floor inspection can help to evaluate the bottom corrosion severity and interpreter the corrosion source, further to make the on‐site testing more reliable and reduce the risk.     

基于小波变换与统计分析的转子碰摩声发射特性研究

为解决转子碰摩损伤声发射信号分类及解释难题,应用PCI-2声发射系统和WS-ZHT1型多功能转子实验台组成转子碰摩声发射检测系统,采集转子局部碰摩声发射信号,通过理论分析声发射信号特征和小波基函数性质,dB8小波适合提取声发射信号特征;碰摩产生大量声发射信号,大量声发射信号的统计特性蕴涵较多碰摩信息。对不同转速条件下不同检测位置碰摩声发射信号的统计分析表明,声发射信号的功率谱密度集中在100～400 kHz。声发射信号平均幅值、平均能量可作为区分转子碰摩程度特征参数;功率谱主频可作为区分声发射相对位置特征参数,结论与碰摩类型无关。     

316L奥氏体不锈钢点蚀的原位声发射监测

为了研究316L不锈钢自然点蚀的生长规律,发展基于声发射技术的小孔腐蚀监测方法,利用声发射技术原位研究了316L奥氏体不锈钢在pH=1.0和中性(pH=6.7)的3.5%NaCl溶液中的自然点蚀状况,同时监测了开路电位E_(OCP);通过扫描电镜对试验后样品的表面形貌进行表征,并通过Matlab平台对声发射信号进行聚类分析。结果表明:316L奥氏体不锈钢的自然点蚀具有不同的孕育周期,声发射信号的获取跟E_(OCP)的变化具有较好的对应关系。在点蚀快速发展阶段,声发射信号具有较高的绝对能量。在Matlab平台上建立了一套信号处理程序,并对声发射信号进行重新定义,对处理后的信号进行声发射信号参数分析,得到了3类较好的声发射信号聚类,来源于不同腐蚀现象或阶段。其中,在点蚀的快速发展阶段主要以高持续时间高计数和高持续时间低计数2类谐振信号为主。     

Q235B钢原油储罐底板腐蚀穿孔原因

某Q235B钢储罐底板发生腐蚀穿孔泄漏事故。通过宏观分析、微观分析、化学成分分析、力学性能试验、金相检验等方法,对储罐底板腐蚀穿孔原因进行了分析。结果表明:储罐底板的涂层因质量较差发生鼓包后破损,在破损点发生了氧腐蚀,进而导致储罐底板腐蚀穿孔。     

Optimization of Positioning of an Acoustic Emission Sensor for Monitoring Hot Forging

Optimization of a sensor location for effective characterization of a hot forging process using acoustic emission (AE) signals is discussed in this paper. Acoustic emission signals generated during forging operations on an aluminium alloy were recorded using three sensors simultaneously by mounting them on the top bolster, bottom bolster, and bottom die of the press. The AE signals with maximum sensitivity could be detected with a sensor attached to the bottom die in preference to the other positions. Using AE parameters, the forging process could be differentiated into three regions, i.e., 1) yielding of the workpiece material, 2) intermediate deformation region, and 3) filling of the die. The results show that the optimum position of the AE sensor for monitoring hot forging is found to be the bottom die of the forging press.     

Acoustic emission from stress corrosion cracks in aligned GRP

Acoustic emission (AE) produced by the propagation of stress corrosion cracks in an aligned glass fibre/polyester resin composite material has been recorded. Tests have been carried out over a range of crack growth rates and the variation of AE with crack velocity/applied stress intensity has been examined. The main source of AE is fibre fracture and there is a one-to-one relationship between the number of fibre fractures and the number of high-amplitude AE signals. This enables crack growth to be monitored directly from acoustic emission. The amplitude of AE signals produced by fibre failure appears to be proportional to the fracture stress of the fibres, although further analysis requires a greater understanding of the generation, transmission and detection of AE signals. This work demonstrates that stress corrosion cracking is an ideal source for the study of AE produced by fibre fracture without complications caused by interface effects, such as fibre debonding or pullout.On leave from the Technical University of Wroclaw, Wroclaw, Poland.     

Corrosion and stress-corrosion cracking of exploited storage tank steel

We study the corrosion resistance of St3S steel under loading and its susceptibility to corrosion and hydrogen-induced cracking in bottom water. Sections of a tank are distinguished according to the character of the media interacting with the metal of the inner surface in the process of operation. It is shown that bottom water is characterized by high levels of corrosion activity and that the degrees of in-service degradation of different sections of the tank are different. The worst corrosion and stress-corrosion resistance are exhibited by steel operating in contact with bottom water. Significant levels of plastic strains intensify the process of corrosion in steel and make the rates of corrosion in different sections of the tank closer to each other. The in-service degradation of steel can not only intensify the process of corrosion of the inner surface of the tank but also promote the brittle fracture of the material characterized by the elevated susceptibility to hydrogen-induced cracking.Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 3, pp. 113–117, May–June, 2004.