Preliminary Exploration: Fault Diagnosis of theCirculating-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, ChinaEmail: {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 forefficient heat transfer from one medium to another, which isvery important to petrochemical enterprises. Since heat systemoften uses industrial circulating water as cooling water, the heatexchanger is prone to scale, clogging and leakage, resulting in sub-standard products and even serious economic losses. Therefore,how to monitor and find out heat exchangers scaling, cloggingand leaking timely is a very import subject for petrochemicalenterprises. When fluid flow through narrow pipes within heatexchangers, it will cause the pipes to vibrate and produce sound.If there exists congestion, the heat exchanger would producea different sound from that in normal. Thus, in this paper,we explore the probability of using sound sensors for largeheat exchanger fault diagnosis in petrochemical enterprises. Ourextensive experiments show that it is very difficult to use sounddetection technology for fault diagnosis of large circulating waterheat exchangers because environmental noise is too large. It isnecessary to continue to explore and improve the fault diagnosisof large circulating water heat exchanger using Non-destructivetesting technology of sound sensor.

Keywords—Circulating water heat exchanger, Leak, Soundsensor, Fault diagnosis

I. INTRODUCTION

Circulating water heat exchanger, which is indispensableto realize the heat exchanger and transfer. It is widely used inmany industries such as petroleum, chemical industry, nuclearenergy, especially in the petroleum refining and chemicalprocessing device. The working situation of circulating waterheat exchanger directly affect the smooth running of theentire unit, for safety, stability, long running, which plays animportant role.

To save costs, the industrial circulating water is often usedas cooling water in the Maoming ethylene factory. However,the quality of circulating water is unqualified and the circu-lating water heat exchanger’s pipeline does not belong to thespecial material. It easily leads to the heat exchanger pipessevere blockage, corrosion and leakage. As shown in Fig. 1,it results in significant security risks and economic losses.

At presented, domestic and international monitoring meth-ods for heat exchanger mainly based on regular testing. Thescope of testing is relatively fixed. For example, Maomingethylene factory detects the faults of heat exchanger by the

(a) (b)

Fig. 1. The inside situation of a heat exchanger in Maoming ethylene factory

change of some physical quantities between both ends ofexchangers, such as temperature, pressure and pH. Thesemethods have the following disadvantages:

• The main disadvantage is artificial reading, whoseaccuracy is not high and which consumes a largeamount of manpower.

• It cannot monitor the operation of the heat exchangerin real time, which causes a serious lag time, conse-quently affecting the effective failure detection of theheat exchanger.

Therefore, to solve this problem, we should study a newapproach to monitor the heat exchanger and detect the faults.When the fluid flowing through the narrow pipe of the heat ex-changer, it will cause pipes to vibrate and produce sound. Withfurther investigation in the process, we found that sometimeswe can hear the internal noise of the heat exchanger whenthe heat exchanger is running, e.g., the acoustic resonance.Heat exchanger would produce abnormal noise1 when a faultoccurs. Based on the research in [1], which is proposed forthe boiler heat exchanger pipes leak detection and location. Itis found that for a heat exchanger, the sound of blockage orleakage is different from the normal pipelines. Therefore, weput forward the fault diagnosis of the circulating water heatexchanger based on sound sensor and Non-destructive testing2

(NDT) technique.

1http://bbs.hcbbs.com/thread-733167-1-1.html.2In 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-invasivelydetermine the integrity of a material, component or structure.

2013 8th International Conference on Communications and Networking in China (CHINACOM)

978-1-4799-1406-7 © 2013 IEEE488

In this paper, we study and analyze the sound signalof the heat exchanger in running. The noise from externalenvironment has a greater impact on the collected sound signal,so we first consider filtering the noise. However, any kindof filtering can generate signal distortion in varying degrees.Instead of simply filtering the noise, we try to improve theexperimental equipment. Then, the sound signal with highersignal-to-noise ratio can be obtained.

The research work has certain contributions:

• The sound signal of heat exchanger is different whenit is in different conditions. Therefore, real-time mon-itoring the heat exchanger sound signal in its run-timecan efficiently detect the faults of the heat exchanger,e.g., blockage and leakage.

• The novel method is simple: it is a breakthroughto sensor networks applications which uses a largenumber of low-cost sound sensors to detect the heatexchanger in running.

• Attempted to combine theory and practice: accordingto researches on sound signals of running heat ex-changers at home and abroad, we find that it is feasiblethat sound detection can be used in the field of faultdiagnosis of heat exchangers.

Fault diagnosis of the circulating water heat exchangersbased on sound sensor and NDT technique, as a new detectiontechnology, there would be better prospects.

The rest of the paper is organized as follows: The secondsection describes the related work. The section III presentsthe problem statement. The section IV is the introductionof the experimental apparatus. The section V introduces theheat exchanger sound signal acquisition experimental and dataprocessing. Part VI is the analysis of the experimental dataand draw conclusions. Part VII is future working.

II. RELATED WORK

At present, NDT technology at home and abroad mainlyinclude magnetic particle, penetrate, ultrasound technology(UT) [2], radiographic inspection [3], acoustic pulse detection,magnetic memory method [4] and potential analysis [5] onthe heat exchanger. The detection of the heat exchanger in theinstallation site, it is usage of NDT instruments that is suitablefor on-site testing of portable equipment [6]. However, inpractical, most of the enterprises still collect and analyze partof the main parameters of the heat exchanger (E.g, water flowrate, inlet temperature, outlet temperature, steam temperature,etc.), and based on these problems to determine the statusof the heat exchanger. What is more, these parameters areextracted by the instruments automatically.

For the online monitoring of the heat exchanger, re-searcher’s had put forward some methods, e.g., Fluorimetryand Potentiometry. These methods have large limitations (E.g.,they are only applicable when the heat exchanger leaks.). Ifthe defaults were not detected and cleared in time, it is easyto result in the production of unqualified products.

To find the fatigue crack or welding defects, as for usingsound as a way of detection, the focus of this study is

mainly to utilize ultrasound to carry out spot checks or acomprehensive inspection of the heat exchanger. Moreover,the ultrasonic instrument has been widely used, due to itssmall size, lightweight, and harmlessness to the human body.Existing methods of ultrasonic detection include Time of FlightDiffraction (TOFD) , Phased Arrays and Holographic Imagingetc. For example, the idea proposed by Dr. Noam Amir saidthat acoustic pulse reflectometry can be used to fully inspectthe heat transfer tubes and identify contamination, leakage,corrosion, and other key drawbacks [7].

The detection technology of tubes is not just limited to oneway. In many studies, researchers have tried to put a varietyof methods together. For example, ultrasonic and eddy currentNDT techniques for composite [8].

At present, the heat exchanger sound online testing hasgradually aroused researchers’ attention. And the researchon the heat exchanger sound signal has already had a solidfoundation of theory [9-24]. Therefore, we try to use the faultdiagnosis of the circulating water heat exchanger based onsound sensor and NDT technique.

III. PROBLEM STATEMENT

From the section I and section II, we know that the heatexchanger can generate sound when it is running. In this paper,we try to evaluate a new method to detect faults of heatexchangers: sound sensor fault diagnosis of the heat exchangerwhen it is running.

The first sub-problem of this paper is to verify that environ-ment influence is so large that the method of heat exchanger’ssound detection is difficult to realize.

As the fluid state in the heat exchanger’s different positionsis different, we need to detect sound signals in differentpositions. The second sub-problem of this paper is to detectsound signals in different positions.

We design an experiment to research and discuss this issueafter we went to the Maoming Petrochemical Company fieldtrips. Related issues will be discussed in detail in the followingsections.

IV. THE DESIGN OF SOUND SIGNAL COLLECTION SYSTEM

When using sound sensor to collect sound signal of heatexchangers, environmental noises have an impact on the re-sults. Because it is very easy to couple environmental noises.Therefore, in this paper, we try to reduce noise by improvingthe hardware.

To reduce environmental noise, we make enclosures ac-cording 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 diminishthe influence of reasonance and coincidence effect. 3© usesthe hollow sound insulation sealing strip to avoid rigid contactbetween enclosures and sound source equipments, which canreduce the influence of outside noise and improve the signal-to-noise ratio greatly. Meanwhile, the noise enclosure is easyto operate, install and remove.

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Fig. 2. The sound sensor with noise enclosure

Fig. 3. Schematic diagram of sound signal collection system

The circulating water heat exchanger is large. The damagepositions varied. To collect sound signals of different positionsfor comparison, we have designed a multipoint synchronoussound signal acquisition device. The device is shown in Fig.3.

V. SOUND DETECTION OF THE CIRCULATING-WATERHEAT EXCHANGER EXPERIMENT

The ambient noise intensity is very high in the industrialsite. The measured data of the noise around the circulatingwater heat exchanger in the Maoming petrochemical companyis collected higher than 90 dB.

In Maoming petrochemical company, we collect soundsignals in the same positions of two running heat exchangersand one stopping running simultaneously. We also collectedambient noise and sound signals of the heat exchanger inletpipe. As shown in Fig. 4-5. Nodes layout diagram is shown inFig 6. he purpose is to detect whether environmental noise havea significant impact on heat exchanger’s sound monitoring.

A. Experimental procedure

1. Step A: collecting the sound signal in the same modelof two using and one stopping heat exchangers in the middle.The sampling frequency is 44100Hz, the bit rate is 32bit. Everyheat exchangers collected the date 30 seconds. The collected

Fig. 4. Maoming petrochemicalcompany Fig. 5. Test of the heat exchanger

Fig. 6. The location of soundsensor

Fig. 7. The layout of sound-nodesof the different position in the sameheat exchanger

sound signal’s files are named Normal 1, Normal 2, Disabledrespectively.

2. Step B: collecting the heat exchanger outlet piping’ssound signal and the ambient noise. Do the experimental stepsA and B at the same time, which to ensure the simultaneityof the collected data. The step B collected sound signal’s filesare named Duct, Noise respectively.

3. Step C: collecting the sound signal at different positionsin heat exchanger, the node position is arranged as shown inFig. 7. Collecting the sound signal of the heat exchanger closeto the shell inlet and outlet water and middle position. Thesampling frequency, sampling time, sampling precision andcollect numbers are the same as step A, B. Collected soundsignal files are named Left (Fig. 7, left sound-node), Middle,Right respectively.

4. Step D: coursing of the experiment, we want to ensurethat the sound nodes appress the surface of the heat exchangerand no one is interference.

5. Step E: analysising and processing of the sound signalswe collected.

B. Experimental data processing

We analyze the collected data, with Matlab by time domainanalysis and frequency-domain analysis of sound signals asshown in the Fig. 8.

VI. THE ANALYSIS OF EXPERIMENTAL DATA ANDCONCLUSION

A. The analysis of experimental data

According to the experimental results of the section V, Bythe Fig.8, we can be seen:

1. From the spectrum we can know that the sound signalof almost all concentrated in the low frequency band, while athigh frequencies in 20000Hz-30000Hz and 55000Hz.

2. The stopping using heat exchanger only connect one endof the circulating water pipeline. Near the end of the pipelinecentrifugal pump is not connected. The sound signal is mainlyconcentrated in the low frequency band by the power spectrumof the figure. As shown in Fig. 8(c).

3. The spectrum at the different frequency segment mainlyconcentrated around 20000Hz, comparison of the spectrumand time domain analysis of the two heat exchangers usingin normal. The Fig like the Fig. 8(a), Fig. 8(b).

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(a) Normal 1 (b) Normal 2

(c) Disabled (d) Duct

(e) Noise (f) Left

(g) Middle (h) Right

Fig. 8. Time domain analysis and frequency-domain analysis of sound signals

4. The contrast setting group with the frequency spectrumof 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 thesame and the amplitude is slightly different.

5. In contrast with the data of the three groups in figuresshown as Fig. 8(f), Fig. 8(g), Fig. 8(h), we can see the leftand right one’s value is close. And the middle group has greatdifference in high frequency band. It is shown that the sound

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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 sensorsis used to detect the heat exchanger, it is affected heavilyby surrounding noise, which mainly result from the fact thatheat exchanger pipe is connected with a centrifugal pump, andthe sound signal emitted by the centrifugal pump when it isworking can be transmitted through the pipeline to the heatexchanger.

2. The sound signal of heat exchangers at the differentpositions is different. This estimate is related to the externalenvironment or changes of internal temperature and the heatexchanger fluid. Because the influence of temperature is differ-ent on the sound propagation, impact strength and heat transferfluid flow tube.

3. The collected sound signal is mainly in the low frequen-cy band, and the trend of the spectrum is similar, which showsthat the influence of the external environment plays a leadingrole, according to the technology, voice monitoring, using inthis study to the heat exchanger to the fault diagnosis.

VII. FUTURE WORKING

We had proved the feasibility of the detecting heat exchang-er of the sound in a certain extent by collecting the analysistheory of sound heat exchanger in operation during this study.However, the Maoming petrochemical field experiment foundthat environmental factors have a great interference of sounddetection. The sound detection’s failure of the heat exchangeralso need continuous improvement. Here, we propose somesuggestions.

A. To improve the experiment’s device and the signal’snoise ratio.

B. To achieve the sound signal demising, eliminating theinfluence of the external environment.

C. The heat exchanger should be detected by a long time,in which to improve the technology of sound detection duringthe exploration continuously.

ACKNOWLEDGMENT

Lei Shu is the corresponding author. This work is supportedby the Guangdong University of Petrochemical Technolo-gy’s Internal Project No. 2012RC0106, “the Applied BasicResearch Program of Changzhou Science and TechnologyBureau, NO. CJ20120028” and “the Scientific Research Foun-dation for the Returned Overseas Chinese Scholars, StateEducation Ministry”.

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