带包覆层管道脉冲涡流检测中干扰因素的影响研究（南航）
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带包覆层管道脉冲涡流检测中干扰因素的影响研究（南航）,覆层,管道,脉冲,涡流,检测,干扰,因素,影响,研究,南航
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Pulsed remote field technique used for nondestructive inspection offerromagnetic tubeBinfeng Yanga,?, Xuechao LibaInstitute of Telecommunication Engineering, Air Force Engineering University, Xian 710077, ChinabSchool of Electronics & Information Engineering, Xian Jiaotong University, Xian 710049, Chinaa r t i c l e i n f oArticle history:Received 4 November 2008Received in revised form12 January 2009Accepted 22 January 2009Available online 20 February 2009Keywords:Pulsed remote fieldFerromagnetic tubesNondestructive testinga b s t r a c tRemote field eddy current (RFEC) technique is an effective method for measurement of ferromagnetictube. However, traditional RFEC is unable to differentiate the internal and external defect and the probehas a long length. Pulsed eddy current techniques excite the induction coil with a pulsed waveform andhave the richness of frequency harmonics. The wideband excitation is thought to be a potential inproviding more information about the flaw. In this paper, pulsed RFEC technique is used to inspectferromagnetic tube. The finite element analysis and experiment method is used to give a thoroughanalysis of the influence effect with the variations of the system parameters. Results show that thistechnique effectively combines the advantages of RFEC and pulsed excitation, which not only acquiresmore inspection information, including measurements of inner diameter of tubes, internal and externaldefects, but also reduces the length of probe and power consumption. The agreement betweensimulation and experiment shows that the present method is correct.& 2012 Elsevier Ltd. All rights reserved.1. IntroductionNondestructive testing is highly important in down-holeinspection of oil-well casings because of harsh operating environ-ment and ecological and economic risks associated with oil-wellbreakdown 1. Remote field eddy current (RFEC) technique is aneffective method for measurement of ferromagnetic tube, con-ventional RFEC technique uses sinusoidal excitation and coilsseparated 23 tube diameters, which has the same detectingsensitivity for internal and external defects. However, sinusoidalRFEC has some inherent drawbacks, for example, it cannotdifferentiate whether the wall thickness is changed by an internalor an external defect, and relatively high power consumption andlong length of probe.The pulsed eddy current (PEC) nondestructive testing methodis a new technology developed in recent years, which has beendemonstrated to be capable of quantifying corrosion in themultilayer aircraft structure 24. In this paper, the advantagesof PEC and RFEC are combined together to form the pulsedremote field eddy technique (PRFEC). The effect of inner dia-meter, wall thickness, internal and external defect and thedesign of the magnetic route are analyzed with the finiteelement method.2. The principle of PRFECThe probe structure of PRFEC is similar with the conventionalsinusoidal RFEC, as shown in Fig. 1, which consists of an excitingcoil and a pick-up coil, PRFEC techniques excite the probesdriving coil with a repetitive broadband pulse, usually a squarewave. The resulting transient current through the coil inducestransient eddy currents in the tube wall, which are associatedwith highly attenuated magnetic pulses propagating through thetube wall 5. Because the eddy currents flow through the tubewall, by which are influenced the electromagnetic properties ofthe tube material (permeability and conductivity).3. Finite element analysisIn order to investigate the relationship between the systemparameter (the thickness and inner diameter of tube, the length ofprobe, etc.) and the resulting response signal, the method of finiteelement analysis is used, simulation is performed using FEMMfreeware package 6.In the simulation model, tube inner diameter is 120mm, tubewall thickness is 5mm, the length of tube is 550mm, the tubematerial has relative permeabilitymr100 and conductivitys5MSm?1. The inner diameter of exciting coil is 24mm, thethickness is 8mm, the length is 80mm, and the number of turnsis 1000. The inner diameter of pick-up coil is 104mm, thethickness is 3mm, the length is 2.4mm, and the number of turnsContents lists available at SciVerse ScienceDirectjournal homepage: /locate/ndteintNDT&E International0963-8695/$-see front matter & 2012 Elsevier Ltd. All rights reserved./10.1016/j.ndteint.2009.01.015?Corresponding author. Tel.: 8602984798479; fax: 867314573385.E-mail address: bf_ (B. Yang).NDT&E International 53 (2013) 4752is 2000. The amplitude of exciting pulse is 48V, the repetition rateof excitation is 20Hz, and the pulse duration is 5ms.Voltage induced in the pick-up coil consists of two compo-nents, one (coupling component) is induced directly by theexciter magnetic field and the other (eddy current component)is induced by the magnetic field of the eddy currents 7. In thecase of pulse excitation, the coupling component exists onlyduring the rise or fall of the excitation current. In the other times,the eddy current component attenuates slowly and dominates theresponse signal. As a result, decoupling in time is achieved. Inthe simulation analysis, the coupling component and the eddycurrent are analyzed to quantify the parameter of tube.4. The results of simulationThe changes of tube wall thickness and inner diameter, thelength and the magnetic route of the probe, the depth of flaw willinfluence the propagation of PRFEC, thus the features of responsesignal are changed, the influence effects of these factors areanalyzed with the simulation method.4.1. The influence effect of tube parametersThe information of inner diameter and wall thickness of tubeare important for the tube NDT, the influence effects of these twoparameters to the transient response signals are analyzed firstly.The results of response signals with the wall thicknesses of 5,7, and 9mm are shown in Fig. 2, the distance between theexciting coil and pick-up coil is 1.75 tube inner diameter. It canbe seen that the peak of response signal shows very little change,but the zero-crossing time has a linear relationship with tube wallthickness, which increases with increasing wall thickness. Thisindicates that the zero-crossing time can be used as the feature toquantify the thickness of tube wall.Fig. 3 suggests how peak of response signal can be used formeasurement of the tube inner diameter, the results of responsesignals with the inner diameters of 120, 130, and 140mm areshown in Fig. 3, the wall thickness is 5mm, the distance betweenthe exciting coil and pick-up coil is 1.75 tube inner diameter. Itcan be seen that the peak of response signal increases withincreasing inner diameter, but the change of zero-crossing timeis negligible. This indicates that the peak can be used as thefeature to quantify the inner diameter of tube.4.2. The influence effect of probe lengthFig. 4 shows the response signals when the distances betweenthe exciting coil and pick-up coil separately are 1.50, 1.75, and2.00 tube inner diameter. It can be seen that the couplingFig. 1. The principle of pulsed remote field eddy current.Fig. 2. The influence of response signal with the variation of wall thickness.Fig. 3. The influence of response signal with the variation of inner diameter oftube.Fig. 4. The influence of response signal with the variation of distance betweencoils.B. Yang, X. Li / NDT&E International 53 (2013) 475248component attenuates faster than the eddy current component,which indicates that the high frequency component is sensitive tothe change of coil distance, which nearly does not influence theeddy current component. Then, a shorter length probe can bedesigned.Figs. 5 and 6 show the current of exciting coil and responsesignals of pick-up coil when the inner diameters of exciting coilseparately are 24, 44, and 64mm, the tube inner diameter is200mm, the wall thickness is 5mm. It can be seen that theamplitude of response signal increases with increasing innerdiameter of exciting coil. However, it can also be seen fromFig. 5 that the rate of change of the rising edge is lower as theincreasing of inner diameter. The rate of change of the rising edgeof the current pulse is crucial as it determines the frequencycomponents contained in the excitation. The higher the rate ofchange, the more high frequency components generated andhence, more diagnostic information can be expected 8. As aresult, in order to get a strong response signal while does notreduce the detecting sensitivity, a large exciting voltage isnecessary.4.3. The influence effect of magnetic routeIt can be seen from Fig. 2 that eddy current componentweakens with increasing wall thickness of tube, which showsthat eddy current attenuates seriously while propagating throughthe thick wall, as a result, the amplitude of response signal isreduced. In order to overcome this problem, a new exciting coil isdesigned using the ferrite yoke, as shown in Fig. 7, thanks to thefeature that ferrite core has a high permeability, more excitingFig. 5. The influence of exciting current with the variation of inner diameter ofprobe.Fig. 6. The influence of response signal with the variation of inner diameter ofprobe.Fig. 7. The new exciting coil using the ferrite yoke.Fig. 8. The influence of response signal with the variation of thickness of ferritecore.Fig. 9. The influence of response signal with the variation of height of ferrite core.B. Yang, X. Li / NDT&E International 53 (2013) 475249magnetic field will be collected to propagate in the tube wall. As aresult, the coupling component decreases and the eddy currentcomponent increases at the same time, thus, the amplitude ofresponse signal is enhanced.In Fig. 7, T and H separately represent the thickness and theheight of ferrite core. Fig. 8 shows the response signals with the Tof 5, 15, and 30mm, it can be found that the amplitude ofresponse signal increases with increasing thickness of ferrite core.Fig. 9 shows the response signals with the H of 40, 45, and 50mm,it can also be found that the amplitude of response signalincreases with increasing height of ferrite core. When T30mmand H45mm, the amplitude of response signal is 30 times thanthe probe which does not has the ferrite core.Fig. 10 shows the response signals when the distancesbetween the exciting coil and pick-up coil separately are 0.90,1.10, and 1.30 tube inner diameter as the probe using the ferriteyoke. Simulation result shows that the distance between theexciting and pick-up coil can be shorten to the 1.10 innerdiameter of tube, which indicates that the design of a shorterlength of probe can be realized with using the ferrite yoke.4.4. The influence effect of internal and external defectsThree circumferential notch defects are simulated as externaland internal on the tube, Figs. 11 and 12 show the results for thepick-up coil is placed beneath the defect, the distance betweenthe exciting coil and pick-up coil is 1.75 tube inner diameter, theexciting coil using the ferrite yoke, the wall thickness is 5mm. Itshows that the depth of defect can be differentiated by using thefeature of zero-crossing time, which decreases with increasingdepth of defect. Fig. 13 shows the change in zero-crossing time forinternal and external defects. It can be found that the zero-crossing time has a fairly linear relationship with both kinds ofdefect depth, which can be extracted as the feature to quantifythe depth of defect.5. The results of experimentThe PRFEC instrumentation used in this work consists of apulser, power amplifier, data acquisition module and a probe.Fig. 10. The influence of response signal with the variation of distance betweencoils.Fig. 11. The influence of response signal with the variation of depth of innerdefect.Fig. 12. The influence of response signal with the variation of depth of externaldefect.Fig. 13. The relationship of zero-crossing time and the depth for internal andexternal defect.B. Yang, X. Li / NDT&E International 53 (2013) 475250Fig. 14 shows a schematic of the experimental setup. In thisexperimentalsystem,DirectDigitalSynthesizer(DDS)chipAD7008 is used to generate the exciting pulse. The amplitude ofexciting pulse is 10V, the repetition rate of excitation is 20Hz andthe pulse duration is 5ms. A power amplifier is employed toenhance the excited magnetic field. The transient signal of thepick-up coil is sampled at 1MHz sampling rate using dataacquisition module and is recorded for the purpose of off-linepost-processing.The inner diameter of exciting coil is 50mm, the thickness is2mm, the length is 80mm, and the number of turns is 800. Theinner diameter of pick-up coil is 90mm, the thickness is 3mm,the length is 2.5mm, and the number of turns of pick-up coil is2000.Fig. 15 shows the response signals with the tube innerdiameters of 98, 103, and 108mm, the wall thickness is 5mm.It can be seen that the peak of response signal increases withincreasing innerdiameter, however, thezero-crossing timealmost does not change.Fig. 16 shows the response signals with the wall thicknesses of5, 7, and 9mm, the inner diameter of the tube is 98mm. It can beseen that the zero-crossing time of response signal increases withincreasing wall thickness, however, the peak shows very littlechange.Figs. 17 and 18 show the results with internal and externaldefects on the tube, the wall thickness is 5mm, the innerExciting pulseOscillographData acquisitionSignal magnifyPower magnifyExcitingcoilPick-upcoilFig. 14. The schematic diagram of the PRFEC instrumentation.Fig. 15. The influence of response signal with the variation of inner diameter oftube.Fig. 16. The influence of response signal with the variation of wall thickness.Fig. 17. The influence of response signal with the variation of depth of innerdefect.Fig. 18. The influence of response signal with the variation of depth of externaldefect.B. Yang, X. Li / NDT&E International 53 (2013) 475251diameterofthetubeis98mm,thedefectsizesare(length?width?depth): 15mm?5mm?2mm, 15mm?5mm?3mm, and 15mm?5mm?4mm, the detector coil is placedbeneath the defect. It can be seen that the zero-crossing time ofresponse signal is linearly related to the depth of defect, for the tubewith the external defects, the change of the peak with the defectdepth is negligible comparing to the case of the tube with the internaldefects. The general shapes of experiment and simulation accord witheach other, this shows that the zero-crossing time can be used as thefeature to quantify the depth of defect, and the internal and externaldefect can be differentiated by the feature of peak.6. ConclusionTraditional sinusoidal RFEC inspection techniques have someinherent shortcomings, in order to overcome these problems, theRFEC probe is excited with the pulse waveform, PRFEC technique isapplied to inspect the ferromagnetic tube in this paper, and theinfluence effects of system parameters on the inspection results areanalyzed by the finite element and experiment method. Simulationand experiment results show that the PRFEC technique effectivelycombines the advantag
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