阀门内漏声发射检测实验研究

发布时间：2018-04-18 04:11

本文选题：声发射 + 阀门内漏　；参考：《东北石油大学》2015年硕士论文

【摘要】：在石油化工系统的装置中,阀门是不可或缺的部分,在此系统中,一直对阀门保持较高的使用率。由于在该系统生产过程中阀门内的介质多数具有腐蚀性、有毒、易燃、易爆等特点,阀门可靠性和安全性一直是人们关注的焦点,而在实际使用中,阀门内漏事故时常发生,而且绝大部分阀门内漏是难以发现的,这不但会导致原材料及产品的大量浪费,并且也会对周边的环境造成不可逆转的破坏,更严重的是会产生灾难性的安全大事故。因此,研究有效、准确的阀门内漏检测技术具有重要应用前景。本文将声发射技术应用于检验阀门内漏故障检测方面,采用理论和实验研究相结合的方法对阀门内漏声发射特性进行研究。首先,以阀门内漏发声机理理论为基础,得知阀门发生内漏时,阀体内介质在泄漏孔前后压力差的作用下从泄漏孔处高速喷射而出,在泄漏孔处产生波动压力场形成湍射流,从而产生声发射信号。并针对闸阀的截流原理及其内部结构,对闸阀内部泄漏的流道进行了简化处理,采用FLUENT针对闸阀在不同开度下泄漏的流场进行仿真模拟,分析了进口压力和开度对泄漏口处的流体的影响。在阀门开度固定的情况下,随着进口压力的增加,在泄漏口处及泄漏流道的边角处压力分布较高,并逐渐向中心处递减,但压力梯度变化不明显。在进口压力固定的情况下,随阀门开度的增大,压力分布较高的区域同样是在泄漏口处及泄漏流道的边角处,并逐渐向中心处递减,但压力梯度的变化明显,层次清晰。其次,以蝶阀和闸阀为研究对象,分别设计搭建了气体、液体介质阀门内漏故障模拟实验台和相应的声发射检测系统;通过不同压力,开度和泄漏率下声发射检测实验,得到内漏声发射信号幅值、能量、振铃计数、有效值电压随阀门进口压力和开度的变化规律,并根据以上声发射参数变化规律确定传感器的最佳布置位置。同时得出进口压力、阀门开度会对内漏声发射信号的强度、频谱分布情况产生影响的结论。将不同泄漏率下的声发射信号有效值电压按双对数关系通过MATLAB加以拟合,可得到不同进口压力下声发射信号有效值电压与泄漏率的定量关系。最后,采用谱分析和波形分析对采集到的声发射信号进行处理。通过谱分析确定阀门内漏声发射信号频率所集中的范围以及开度变化对阀门内漏声发射信号频率的影响。通过小波包分解得到的在各频段的信号能量分布情况得出声发射信号能量主要集中的频带。得出了FFT功率谱、FFT功率谱密度以及经小波包分解得到的在各频段的信号能量分布特点都与阀门内漏有一定的关系,可以用于表征阀门内漏的状态。根据在实验室条件下获取的不同工况下的闸阀内漏声发射信号的特点和检测条件,总结了一套适用于现场闸阀内漏声发射检测的方案,为现场检测提供有效的指导。
[Abstract]:Valve is an indispensable part of petrochemical system, in which the high utilization rate of valves has been maintained.Due to the corrosive, toxic, flammable and explosive characteristics of the media in the valve during the production of the system, the valve reliability and safety have been the focus of attention, but in practical use, the valve internal leakage accidents often occur.And most of the valve leakage is difficult to find, which will not only lead to a large amount of waste of raw materials and products, but also will cause irreversible damage to the surrounding environment, more serious is will produce catastrophic safety accidents.Therefore, the study of effective and accurate valve leak detection technology has an important application prospect.In this paper, acoustic emission technology is applied to the detection of valve internal leakage fault, and the characteristics of valve internal leakage acoustic emission are studied by combining theoretical and experimental research.First of all, based on the theory of sound mechanism of valve internal leakage, it is known that when the valve has internal leakage, the medium in the valve body ejects from the leak hole at high speed under the action of the pressure difference before and after the leakage hole, and the turbulent jet is formed by the fluctuating pressure field at the leak hole.Thus, acoustic emission signals are generated.According to the closure principle of gate valve and its internal structure, the flow channel of gate valve internal leakage is simplified, and the flow field of gate valve leakage under different opening degree is simulated by FLUENT.The influence of inlet pressure and opening on the fluid at the leak is analyzed.With the increase of inlet pressure, the pressure distribution is higher at the leakage outlet and the edge corner of the leakage channel, and gradually decreases to the center, but the pressure gradient is not obvious.In the case of fixed inlet pressure, with the increase of valve opening, the area with higher pressure distribution is also at the leakage mouth and the edge corner of the leakage passage, and gradually decreases to the center, but the pressure gradient changes obviously and the level is clear.Secondly, taking butterfly valve and gate valve as research objects, the simulation test bench of gas and liquid medium valve internal leakage and the corresponding acoustic emission detection system are designed and built, and the acoustic emission detection experiment is carried out under different pressure, opening and leakage rate.The amplitude, energy, ringing count and effective value voltage of the internal leakage acoustic emission signal are obtained with the valve inlet pressure and opening degree. The optimum position of the sensor is determined according to the above changes of acoustic emission parameters.At the same time, it is concluded that the inlet pressure and valve opening will affect the intensity and spectrum distribution of the internal leakage acoustic emission signal.The quantitative relationship between the effective value voltage and leakage rate of AE signal under different inlet pressure can be obtained by fitting the RMS voltage of AE signal with double logarithmic relation by MATLAB under different leakage rate.Finally, spectral analysis and waveform analysis are used to process the collected acoustic emission signals.Through spectrum analysis, the concentration range of acoustic emission signal frequency in valve and the influence of the change of opening degree on the frequency of leakage acoustic emission signal in valve are determined.The distribution of signal energy in each frequency band is obtained by wavelet packet decomposition, and the frequency band in which acoustic emission signal energy is mainly concentrated is obtained.It is concluded that the power spectral density of FFT power spectrum and the characteristics of the signal energy distribution in each frequency band obtained by wavelet packet decomposition are related to the leakage in the valve, which can be used to characterize the state of the leakage in the valve.According to the characteristics and detection conditions of acoustic emission signals in gate valves under different operating conditions obtained in laboratory, a set of schemes suitable for the detection of leakage acoustic emissions in gate valves are summarized, which can provide effective guidance for field detection.
【学位授予单位】：东北石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ055.81;TE65

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