Development Of Non-Contact Guided Wave Transducer Based On Wiedemann Effect

Steel pipes are widely used in the oil and gas transportation industry.Defects in the steel pipe will reduce the safety performance and even cause loss of life and property.Therefore,steel pipes must be regularly inspected for defects.The magnetostrictive guided wave technology has been widely used for inspecting steel pipes because of the advantages of longdistance inspection from a single probe position,non-contact inspection,etc.Currently,there are many researches on non-contact magnetostrictive longitudinal guided waves,and there are few studies on torsional and flexural guided waves,while the latter are beneficial to detection signal processing,defect location,etc.Based on Wiedemann effect,this thesis develops a noncontact magnetostrictive guided wave transducer which can generate and receive torsional or flexural guided waves to detect the steel pipe,which provides support for defects inspection of steel pipes.Firstly,an excitation source analysis method which can be used to design guided wave transducers for pipes is proposed based on time and spatial Fourier transform.This method converts the excitation source distribution functions from time and space domains to frequency,circumferential order and wavenumber domains by time and spatial Fourier transform to obtain the guided wave excitation capability of transducers.The guided wave excitation capability of the transducer array on the outer surface of the pipe are analyzed by this method.The circumferential amplitude parameters,axial amplitude parameters and circumferential delay parameters are obtained,and the excitation source distribution forms of the axisymmetric and non-axisymmetric mode guided waves are presented.The effectiveness of this method is verified by simulations and experiments.Secondly,the sensing mechanisms of non-contact torsional and flexural guided waves in the steel pipe are presented on the basis of Wiedemann effect.Based on the analysis of the Wiedemann effect and its inverse effect,the non-contact torsional and flexural guided wave sensing methods for the steel pipe are proposed by considering the excitation source distribution forms of the axisymmetric and non-axisymmetric mode guided waves and the wave structures corresponding to the torsional and flexural guided waves.The mode verification,frequency characteristic verification and defect detection feasibility verification of the two types of guided wave sensing methods are carried out by experiments.Finally,the non-contact torsional and flexural guided wave transducers based on Wiedemann effect are designed and manufactured.The influences of the key structural parameters of the transducer on the guided wave signals are studied by experiments.And based on this,the guided wave transducers composed of magnetization modules and coil modules are designed and manufactured.The transducers are used to build an experimental platform for defect inspection experiments.The experimental results show that the designed mechanical structure can facilitate the disassembly,installation and movement of the transducer,and the transducers can perform non-contact defects inspection on the steel pipe.