Research On Inner Detection Method Of Pipeline Coating Peeling Defect Based On Ultrasonic Energy Density

It is an important method to ensure the safe operation of pipeline which detect the running state of the coating inpipeline.At present, the pipeline coating detection method mainly uses the outside detection technology, Such methods can not meet the requirements of integrity management in oil and gas pipelines.At the same time, this method is difficult to realize quantitative description of coating defects. The intelligent pipeline internal detector can collect the data of pipeline operation status well and meet the requirements of the integrity management.Therefore, the pipeline Internalinspection technology is used to analyze the operation state of the pipeline and meet the comprehensive analysis of pipeline detection data. It realizes the quantitative detection of pipeline coating.In order to solve the above problems, this paper mainly studies the inner detection method of pipeline coating peeling defect based on nonlinear ultrasonic guided wave.The pipeline coating can be idealized as a double-layer structure which is combined with the elastic medium and the viscoelastic medium.In this paper, they are analyzed about the dispersion characteristics and energy propagation characteristics of ultrasonic guided wave in pipeline coating.In terms of theoretical modeling, simulation analysis and experimental verification, this paper studies the detection method of anti corrosion layer based on the energy density.The main research work and contributions are as follows:(1) Because the ultrasonic guided wave propagation mechanism is very complex in the pipeline coating, it is difficult to obtain the effective information to detect the defects of coating only through the analysis of the guided wave multimode dispersion characteristics.Therefore, starting from the elastic properties of monolayer plate structure, this paper studies the visco elastic double-layer structure in energy transmission characteristics and analyzes the influencing factors of ultrasonic guided wave propagation process of double-layer structure medium energy transmission.lt established a test platform was studied for the energy propagation characteristics with double-layer structure.Research shows that:when the double layer structure of the media produce defects such as peeling, it is obviously changed that the group velocity, phase velocity and energy density of each mode of ultrasonic guided wave.When the coating peeling defect size is large, the echo signal amplitude increases and the medium cut-off point vibration speed slow. Therefore, the energy attenuation becomes smaller.(2) Due to the complexity of the ultrasonic guided wave propagation mechanism and multi modal characteristics, it is difficult to identify the echo signal.In Lamb wave as the research object, by using the first law of thermodynamics to establish the element plate bodies in energy density distribution model, this paper studies the relationship between the vibration displacement and force density and energy density distribution by theoretical analysis and numerical calculation of micro element "V". At the same time, it puts forward the energy density distribution of multi-mode Lamb wave method in known excitation frequency in steel plate.Finally, it uses the transceiving separated electromagnetic ultrasonic Lamb wave transducer on the theoretical analysis and simulation calculation process of preliminary experimental study was carried out.Research shows that:the function of micro element vibration displacement and Lorentz force and magnetostriction forces reflect electromagnetic ultrasonic Lamb wave energy transfer in trend.Energy is constantly converted between kinetic energy and potential energy.Through the characteristic analysis of different modes of Lamb wave energy density distribution, this study obtained the modal energy intensity and the velocity of energy propagation. This conclusion is based on the energy density of the ultrasonic guided wave detection provides a theoretical basis.Under different excitation frequencies, the energy density distribution of the wave group is obtained, which can greatly simplify the recognition process of the echo signal.(3) Aiming at the defects such as holes and peeling in the pipeline coating, the SH guided wave energy density detection method is proposed.In this paper, it is established about energy balance unit V double wave structure modelby the dynamic viscoelastic theory, the element V in thedispersion characteristics, energy density and guided wave attenuation carry out the theoretical analysis and numerical calculation; the theoretical analysis and numerical calculation. Then it is designed SH-EMAT transducer on axial coating delamination defects of simulation and experimental research.Research shows that:in a certain frequency range,When the thickness of the anticorrosion layer is larger, the phase velocity and group velocity of SH guided wave modes are larger and there is a significant difference. When the frequency tends to infinity, it has the good linearity that SH guided wave phase velocity and coating peeling defect.Because the different stripping degree of coating, it can be caused the change of the modal SHo dispersion curve, thus it realizesto detect the coating peeling defect in pipeline by SHo mode group velocity detection.In this paper, it obtains the axial length and location information about the coating delamination defects through the study of SH guided wave attenuation. The energy density factor in unit V can be used in the research of the inner detection of the pipeline coating defects such an peeling and hole and so on, and provides the theoretical basis for quantitative research.(4)In this paper, in order to make a quantitative research on the pipeline coating peeling defects,it is obtained that the nonlinear characteristic parameters of the junction of the peeling defect by the time frequency analysis of the defect detection signal.The nonlinear characteristic parameters are used as the quantitative standard for the grade of the defect detection of the coating, which provides a quantitative research basis for the evaluation of the defect degree of the anticorrosive coating.To sum up, this paper has mainly carried out the pipeline coating defect detection researchthrough the using ultrasonic guided wave detection technology.It establishes the energy density propagation model to obtain the propagation characteristics of guided wave energy and analysis of the defect information. At the same time, the method of time frequency analysis is used to quantify the grade of the axial dimension of the coating in pipeline. Finally, the goal of detecting the defect information of pipeline coating is realized.