Development And Application Of Guided Wave Inspection Device Based On Time Reversal Method

Ultrasonic guided wave possesses the characteristics of long propagationdistance and less attenuation along a long pipe-shape and rod-shape structure. Thesignal obtained includes internal and surface defects information. Such concern ismainly caused by small leakages induced from aging, corrosion, and poor workingconditions of the pipeline in service. In this research, a novel ultrasonic guided waveinspection method, based on time reversal theory, was proposed and applied for thedefects detection of long pipelines and rods. The temporal-spatial focusing inspectionsystem for ultrasonic guided waves based on the time reversal theory was alsopresented in this paper. This inspection system could be ultilized to pipe and rods withdifferent transducer or transducer array. The experimental work with this system waspresented on long pipelines and rods. The main research works were given as follows.(1)The temporal--spatial focusing characteristics for ultrasonic guided waves inpipeline based on the time reversal method were investigated. A time reversal guidedwave inspection method was numerically simulated using Finite Element Method(FEM), the partial thickness defects with the same and increased depth in differentradial location were analyzed with3D models, single and double through thicknessdefects fabricated in a pipeline were studied with2D models, the propagation of timereversal guided wave was visualized.(2)Base on the excitation and focusing characteristics of guided waves in thepipeline, two new methods for time reversal inspection were realized. If incidentangle and circumferential loading area of variable-angle wedge transducer is seteffectively, most of the generated modes will be L(n,2). An efficient new time reversalmethod based on the oblique incidence of local loading and easily realized wasimplemented. A piezoelectric wafer array worked in the way of all exciting at thesame time and receiving respectively. Then the received signals were dealt with timereversal process and the time reversal signals of different wafers were transmittedagain. All wafers were used to received the time reversal signal and the purity L(n,2)mode is achieved. The other efficient new time reversal method based on piezoelectricwafer array was implemented.(3)The key device for applications of the time reversal technology in the field ofguided wave is high-voltage arbitrary waveform excitation board which can generate time reversal wave. During the design of excitation board, Interacting FSM Modelwas used to synthesize the time reversal signal, amplifier circuit was used to drivehigh-voltage output stage, and differential structure was employed to realize thehigh-voltage output stage of exciting board, which ensure high-voltage time reversalwave could be quickly generated in the detection process. When the ultrasonic guidedwave testing system working in pulse-echo mode, an echo detection system withself-protection function was designed to detect the start time of the excitation pulseand the echo signal. The system includes self-protection circuit, preamplifier, filtercircuit, program-controlled amplifier, A/D converter circuit and so on. The detectionprocess of the system was controlled by DSP+FPGA.(4)When time reversal focusing method was used for defect detection on rod, asingle piezoelectric transducer installed in the end was excited to generate ultrasonicguided wave with narrow and broad frequency signal. Detection of single or dualdefects in the rods was inquired with experimentally using the time reversal method.(5)Multi-channel oblique probe array and piezoelectric wafer array wereimplemented for stimulating L(n,2) modal cluster. The sound field of array couldcover the entire pipeline circumferential direction. According to the requirement of fortime reversal method, an inspection system was developed. With this system, thefocusing effect was experimentally studied for different initial excitation signal types,center frequencies, time reversal window width and relationship between defectreflection ratio and section miss rate after time reversal.(6)The reflected acoustic field was recorded on different circumferentialpositions and decomposed into L(n,2) modal cluster, a numerical dispersioncompensation technique has been employed to implement time-space transform of thedecomposed signals, so that the defect imaging was achieved with the transformedsignals. In order to restrain circumferential guided waves, the selection of excitingsources was studied by FE. The configuration method of exciting and receivingpiezoelectric wafers was studied to achieve the imaging algorithm. The validation ofthe algorithm was experimentally verified with through thickness crack anddual-defects using time reversal guided waves. The results showed that the methodcould locate the axial and circumferential position of the defect.