2013 8th International Conference on Communications and Networking in China (CHINACOM) Preliminary Exploration: Fault Diagnosis of the Circulating-water Heat Exchangers based on Sound Sensor and Non-destructive Testing Technique Xufeng Zhu, Lei Shu, Haiming Zhang, Anxiong Zheng, Guangjie Han Guangdong Petrochemical Equipment Fault Diagnosis Key Laboratory Guangdong University of Petrochemical Technology, China Department of Information & Communication Engineering, Hohai University and Changzhou Key Laboratory of Sensor Networks and Environmental Sensing, Changzhou, China Email: {xufeng.zhu, lei.shu, haiming.zhang, anxiong.zheng}@lab.gdupt.edu.cn; hanguangjie@gmail.com Abstract A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another, which is very important to petrochemical enterprises. Since heat system often uses industrial circulating water as cooling water, the heat exchanger is prone to scale, clogging and leakage, resulting in substandard products and even serious economic losses. Therefore, how to monitor and find out heat exchangers scaling, clogging and leaking timely is a very import subject for petrochemical enterprises. When fluid flow through narrow pipes within heat exchangers, it will cause the pipes to vibrate and produce sound. If there exists congestion, the heat exchanger would produce a different sound from that in normal. Thus, in this paper, we explore the probability of using sound sensors for large heat exchanger fault diagnosis in petrochemical enterprises. Our extensive experiments show that it is very difficult to use sound detection technology for fault diagnosis of large circulating water heat exchangers because environmental noise is too large. It is necessary to continue to explore and improve the fault diagnosis of large circulating water heat exchanger using Non-destructive testing technology of sound sensor. Keywords Circulating water heat exchanger, Leak, Sound sensor, Fault diagnosis I. INTRODUCTION Circulating water heat exchanger, which is indispensable to realize the heat exchanger and transfer. It is widely used in many industries such as petroleum, chemical industry, nuclear energy, especially in the petroleum refining and chemical processing device. The working situation of circulating water heat exchanger directly affect the smooth running of the entire unit, for safety, stability, long running, which plays an important role. To save costs, the industrial circulating water is often used as cooling water in the Maoming ethylene factory. However, the quality of circulating water is unqualified and the circulating water heat exchanger s pipeline does not belong to the special material. It easily leads to the heat exchanger pipes severe blockage, corrosion and leakage. As shown in Fig. 1, it results in significant security risks and economic losses. At presented, domestic and international monitoring methods for heat exchanger mainly based on regular testing. The scope of testing is relatively fixed. For example, Maoming ethylene factory detects the faults of heat exchanger by the Fig. 1. (a) The inside situation of a heat exchanger in Maoming ethylene factory change of some physical quantities between both ends of exchangers, such as temperature, pressure and ph. These methods have the following disadvantages: The main disadvantage is artificial reading, whose accuracy is not high and which consumes a large amount of manpower. It cannot monitor the operation of the heat exchanger in real time, which causes a serious lag time, consequently affecting the effective failure detection of the heat exchanger. Therefore, to solve this problem, we should study a new approach to monitor the heat exchanger and detect the faults. When the fluid flowing through the narrow pipe of the heat exchanger, it will cause pipes to vibrate and produce sound. With further investigation in the process, we found that sometimes we can hear the internal noise of the heat exchanger when the heat exchanger is running, e.g., the acoustic resonance. Heat exchanger would produce abnormal noise 1 when a fault occurs. Based on the research in [1], which is proposed for the boiler heat exchanger pipes leak detection and location. It is found that for a heat exchanger, the sound of blockage or leakage is different from the normal pipelines. Therefore, we put forward the fault diagnosis of the circulating water heat exchanger based on sound sensor and Non-destructive testing 2 (NDT) technique. 1 http://bbs.hcbbs.com/thread-733167-1-1.html. 2 In general terms, non-destructive testing (NDT) is the inspection or measurement of a material without damage to the item. Technically defined, non-destructive testing is the use of an interrogative medium to non-invasively determine the integrity of a material, component or structure. (b) 488 978-1-4799-1406-7 2013 IEEE
In this paper, we study and analyze the sound signal of the heat exchanger in running. The noise from external environment has a greater impact on the collected sound signal, so we first consider filtering the noise. However, any kind of filtering can generate signal distortion in varying degrees. Instead of simply filtering the noise, we try to improve the experimental equipment. Then, the sound signal with higher signal-to-noise ratio can be obtained. The research work has certain contributions: The sound signal of heat exchanger is different when it is in different conditions. Therefore, real-time monitoring the heat exchanger sound signal in its run-time can efficiently detect the faults of the heat exchanger, e.g., blockage and leakage. The novel method is simple: it is a breakthrough to sensor networks applications which uses a large number of low-cost sound sensors to detect the heat exchanger in running. Attempted to combine theory and practice: according to researches on sound signals of running heat exchangers at home and abroad, we find that it is feasible that sound detection can be used in the field of fault diagnosis of heat exchangers. Fault diagnosis of the circulating water heat exchangers based on sound sensor and NDT technique, as a new detection technology, there would be better prospects. The rest of the paper is organized as follows: The second section describes the related work. The section III presents the problem statement. The section IV is the introduction of the experimental apparatus. The section V introduces the heat exchanger sound signal acquisition experimental and data processing. Part VI is the analysis of the experimental data and draw conclusions. Part VII is future working. II. RELATED WORK At present, NDT technology at home and abroad mainly include magnetic particle, penetrate, ultrasound technology (UT) [2], radiographic inspection [3], acoustic pulse detection, magnetic memory method [4] and potential analysis [5] on the heat exchanger. The detection of the heat exchanger in the installation site, it is usage of NDT instruments that is suitable for on-site testing of portable equipment [6]. However, in practical, most of the enterprises still collect and analyze part of the main parameters of the heat exchanger (E.g, water flow rate, inlet temperature, outlet temperature, steam temperature, etc.), and based on these problems to determine the status of the heat exchanger. What is more, these parameters are extracted by the instruments automatically. For the online monitoring of the heat exchanger, researcher s had put forward some methods, e.g., Fluorimetry and Potentiometry. These methods have large limitations (E.g., they are only applicable when the heat exchanger leaks.). If the defaults were not detected and cleared in time, it is easy to result in the production of unqualified products. To find the fatigue crack or welding defects, as for using sound as a way of detection, the focus of this study is mainly to utilize ultrasound to carry out spot checks or a comprehensive inspection of the heat exchanger. Moreover, the ultrasonic instrument has been widely used, due to its small size, lightweight, and harmlessness to the human body. Existing methods of ultrasonic detection include Time of Flight Diffraction (TOFD), Phased Arrays and Holographic Imaging etc. For example, the idea proposed by Dr. Noam Amir said that acoustic pulse reflectometry can be used to fully inspect the heat transfer tubes and identify contamination, leakage, corrosion, and other key drawbacks [7]. The detection technology of tubes is not just limited to one way. In many studies, researchers have tried to put a variety of methods together. For example, ultrasonic and eddy current NDT techniques for composite [8]. At present, the heat exchanger sound online testing has gradually aroused researchers attention. And the research on the heat exchanger sound signal has already had a solid foundation of theory [9-24]. Therefore, we try to use the fault diagnosis of the circulating water heat exchanger based on sound sensor and NDT technique. III. PROBLEM STATEMENT From the section I and section II, we know that the heat exchanger can generate sound when it is running. In this paper, we try to evaluate a new method to detect faults of heat exchangers: sound sensor fault diagnosis of the heat exchanger when it is running. The first sub-problem of this paper is to verify that environment influence is so large that the method of heat exchanger s sound detection is difficult to realize. As the fluid state in the heat exchanger s different positions is different, we need to detect sound signals in different positions. The second sub-problem of this paper is to detect sound signals in different positions. We design an experiment to research and discuss this issue after we went to the Maoming Petrochemical Company field trips. Related issues will be discussed in detail in the following sections. IV. THE DESIGN OF SOUND SIGNAL COLLECTION SYSTEM When using sound sensor to collect sound signal of heat exchangers, environmental noises have an impact on the results. Because it is very easy to couple environmental noises. Therefore, in this paper, we try to reduce noise by improving the hardware. To reduce environmental noise, we make enclosures according to the research on material and enclosure designs [25-27]. The sound sensor with noise enclosure is shown in Fig. 2. In Fig. 2 (a), 1 is damping material which can diminish the influence of reasonance and coincidence effect. 3 uses the hollow sound insulation sealing strip to avoid rigid contact between enclosures and sound source equipments, which can reduce the influence of outside noise and improve the signalto-noise ratio greatly. Meanwhile, the noise enclosure is easy to operate, install and remove. 489
Fig. 6. sensor Fig. 2. The sound sensor with noise enclosure The location of sound Fig. 7. The layout of sound-nodes of the different position in the same heat exchanger sound signal s files are named Normal 1, Normal 2, Disabled respectively. 2. Step B: collecting the heat exchanger outlet piping s sound signal and the ambient noise. Do the experimental steps A and B at the same time, which to ensure the simultaneity of the collected data. The step B collected sound signal s files are named Duct, Noise respectively. Fig. 3. Schematic diagram of sound signal collection system The circulating water heat exchanger is large. The damage positions varied. To collect sound signals of different positions for comparison, we have designed a multipoint synchronous sound signal acquisition device. The device is shown in Fig. 3. V. 3. Step C: collecting the sound signal at different positions in heat exchanger, the node position is arranged as shown in Fig. 7. Collecting the sound signal of the heat exchanger close to the shell inlet and outlet water and middle position. The sampling frequency, sampling time, sampling precision and collect numbers are the same as step A, B. Collected sound signal files are named Left (Fig. 7, left sound-node), Middle, Right respectively. 4. Step D: coursing of the experiment, we want to ensure that the sound nodes appress the surface of the heat exchanger and no one is interference. S OUND DETECTION OF THE C IRCULATING - WATER H EAT E XCHANGER EXPERIMENT The ambient noise intensity is very high in the industrial site. The measured data of the noise around the circulating water heat exchanger in the Maoming petrochemical company is collected higher than 90 db. 5. Step E: analysising and processing of the sound signals we collected. In Maoming petrochemical company, we collect sound signals in the same positions of two running heat exchangers and one stopping running simultaneously. We also collected ambient noise and sound signals of the heat exchanger inlet pipe. As shown in Fig. 4-5. Nodes layout diagram is shown in Fig 6. he purpose is to detect whether environmental noise have a significant impact on heat exchanger s sound monitoring. We analyze the collected data, with Matlab by time domain analysis and frequency-domain analysis of sound signals as shown in the Fig. 8. B. Experimental data processing VI. T HE ANALYSIS OF EXPERIMENTAL DATA AND CONCLUSION A. The analysis of experimental data A. Experimental procedure 1. Step A: collecting the sound signal in the same model of two using and one stopping heat exchangers in the middle. The sampling frequency is 44100Hz, the bit rate is 32bit. Every heat exchangers collected the date 30 seconds. The collected According to the experimental results of the section V, By the Fig.8, we can be seen: 1. From the spectrum we can know that the sound signal of almost all concentrated in the low frequency band, while at high frequencies in 20000Hz-30000Hz and 55000Hz. 2. The stopping using heat exchanger only connect one end of the circulating water pipeline. Near the end of the pipeline centrifugal pump is not connected. The sound signal is mainly concentrated in the low frequency band by the power spectrum of the figure. As shown in Fig. 8(c). Fig. 4. Maoming petrochemical company Fig. 5. Test of the heat exchanger 490 3. The spectrum at the different frequency segment mainly concentrated around 20000Hz, comparison of the spectrum and time domain analysis of the two heat exchangers using in normal. The Fig like the Fig. 8(a), Fig. 8(b).
(a) Normal 1 (b) Normal 2 (c) Disabled (d) Duct (e) Noise (f) Left Fig. 8. (g) Middle Time domain analysis and frequency-domain analysis of sound signals (h) Right 4. The contrast setting group with the frequency spectrum of the normal use of the heat exchanger ( As shown in Fig. 8(a), Fig. 8(b), Fig. 8(e).), we can see the trend is almost the same and the amplitude is slightly different. 5. In contrast with the data of the three groups in figures shown as Fig. 8(f), Fig. 8(g), Fig. 8(h), we can see the left and right one s value is close. And the middle group has great difference in high frequency band. It is shown that the sound 491
signal in different places of the heat exchanger is different, which is estimated with the external environment. B. Conclusion 1. In this paper, it can be found that when sound sensors is used to detect the heat exchanger, it is affected heavily by surrounding noise, which mainly result from the fact that heat exchanger pipe is connected with a centrifugal pump, and the sound signal emitted by the centrifugal pump when it is working can be transmitted through the pipeline to the heat exchanger. 2. The sound signal of heat exchangers at the different positions is different. This estimate is related to the external environment or changes of internal temperature and the heat exchanger fluid. Because the influence of temperature is different on the sound propagation, impact strength and heat transfer fluid flow tube. 3. The collected sound signal is mainly in the low frequency band, and the trend of the spectrum is similar, which shows that the influence of the external environment plays a leading role, according to the technology, voice monitoring, using in this study to the heat exchanger to the fault diagnosis. VII. FUTURE WORKING We had proved the feasibility of the detecting heat exchanger of the sound in a certain extent by collecting the analysis theory of sound heat exchanger in operation during this study. However, the Maoming petrochemical field experiment found that environmental factors have a great interference of sound detection. The sound detection s failure of the heat exchanger also need continuous improvement. Here, we propose some suggestions. A. To improve the experiment s device and the signal s noise ratio. B. To achieve the sound signal demising, eliminating the influence of the external environment. C. 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