Research On Detecting Delamination Defect Of Inner Anti-Corrosion Pipe Based On Ultrasonic Guide Wave

Inner anti-corrosion pipes are compounded by the inner plastic pipe and the outer steel pipe.Because of its excellent transmission performance,great corrosion resistance and high mechanical strength,it is widely used in all kinds of industrial facilities including petrochemical industry,fluid transport system and so on.Under normal operational conditions,the inner plastic pipe can prevent the pipeline from corrosion thus avoiding the happening of the accident,while delamination defects might appear during the manufactural and use process.If not detected in time,it will develop and lead to crack of the pipe.Presently,there are no effective non-destructive means for such defect.Ultrasonic guided wave and its nonlinear ultrasonic method are the new nondestructive testing technology which has been developed in recent years and has the advantages of large detection range and high detection efficiency.By the title of “Research on Detecting Delamination Defect of Inner Anti-corrosion Pipe based on Ultrasonic Guide Wave”,this paper studied the transmission characteristics of the guide wave in the inner anti-corrosion pipe and conducted theoretical and simulation analysis.Delamination detecting methods were proposed and experiments were conducted to verify its effectiveness.This paper provided a novel thinking and method for effectively detecting the delamination defects,which is essential to the safe operation of the pipeline and is of high academic and engineering values.The main works of this paper are illustrated as follows:(1)The detection requirements were determined according to the manufactural and use process.Based on the transmission characteristics of the guided wave,the theoretical analysis of the propagation rules was conducted.Through the establishment of the simulation model,the propagation of the single mode guided wave in the interface of single layer and double layer was explored.Furthermore,the reaction of the guided wave to the delamination was investigated under superficial excitement.(2)Based on the reflection of the ultrasonic guided wave transmission signal to the delamination defect,a method of assessing the delamination based on reflection signal is proposed.By exciting Hanning window modulated sine signal in pipeline surface and acquiring signals in proper positions,the extracted amplitudes of the signal can be use to assess the delamination defect.(3)The simulation analysis of reflection signal was conducted.In comparison of the reflection signal under different damage states,a method based on EMD and matching pursuit was proposed to extract the reflection from the delamination defect.By this means,the location of the delamination can be realized according to the position of the extracted wave in time domain and the wave velocity.(4)Nonlinear ultrasonic technique was introduced into the delamination assessing.Firstly,the nonlinear phenomenon in inner anti-corrosion pipes was discussed.Secondly,according to the creation conditions of different nonlinear components,two nonlinear component extracting methods based on single harmonic wave and sideband component were proposed respectively.Ultimately,based on DFT and wavelet packet analysis,two nonlinear component assessing methods were proposed in detecting delamination.Wavelet energy method was proposed and introduced into nonlinear index to realize the delamination assessing.(5)Based on the constructed delamination detecting platform for inner anti-corrosion pipes,experiments utilizing the transmission signal and reflection signal of the ultrasonic guided wave were conducted,which proved the effectiveness of using the proposed method to assess delamination damage.Results also shows that by comparing the reflection signal under different damage states,the reflection signal can be extracted by matching pursuit and the defect can be well located with the error of less than 5 percent.On the other hand,delamination assessing experiments were conducted based on nonlinear components.By exciting single frequency wave and high-low frequency wave,the nonlinear components were extracted and processed using the proposed signal conditioning method.The results shows that the conditioned nonlinear components based on third harmonic wave and sum frequency decreased as the delamination defect grew bigger,thus these conditioned nonlinear components can effectively reflect the delamination damage of the pipe.