1、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
2、 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
3、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
4、 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
5、.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 agreemen
6、t 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
7、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
8、,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 develope
9、d 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
10、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 probe
11、sdriving 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 t
12、he 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 respo
13、nse 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 di
14、ameter 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: International0963-8695/
15、$-see front matter&2012 Elsevier Ltd.All rights reserved.http:/dx.doi.org/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
16、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,decouplin
