PZT-based Guided Wave Propagation Performances And Damage Detections For Layered Pipeline Structures

Pipeline structures are used in a wide range of applications such as long-distance liquid and gas transportation.In practical applications,the majority of the pipeline structures are made by multiple layers with multiple materials.These layered pipeline structures may be buried in deep underground,and it is highly difficult to find outdefects and damages right after they occur,which is of serious safety hazards.Pipeline structural health monitoring(PSHM)is an advanced technology that can detect hidden dangers in a timely manner and is of great significance for ensuring the safe and reliable operation of pipelines.Ultrasonic guided waves(UGWs)have become an important development direction for PSHM due to advantages of long-distance propagation,complete sound information,sound field vibration caused by particle vibration fulfilling the entire wall thickness and monitoring without peeling off the outer layer,etc.Based on the Navier wave equation this paper combines theoretical analysis,numerical calculation,experimental investigation and finite element analysis(FEA),with the usage of piezoceramics(Lead Zirconite Tatinate,PZT)UGWs,the UGW propagation mechanism,the boundary reflectance,the energy attenuation coefficient and the damage identification are respectively studied for single-layer pipeline structures,layered pipeline structures and overburden layered pipeline structures under both non-destructive and destructive conditions,which aims at proposing a basic theory and method for damage detection and structural health monitoring(SHM)of layered pipe structure,and improving the monitoring level of actual engineering pipeline structures.The main research consists of the following aspects:(1)Theoretical analysis on the wave performance of UGWs in pipeline structures was performed.Firstly,based on the Navier wave equation and the boundary conditions,the dispersion equations of a single-layer pipeline structure,a layered pipeline structure and the underground layered pipeline structure were established,respectively,and the numerical solution was carried out and the dispersion curves were drawn.Secondly,by analyzing the properties of the dispersion curves,the UGW mode and central frequency suitable for the pipe structure were selected.Then,the stress distribution law in the cross section of a pipeline structure was studied.Finally,the basic parameters of the UGW energy attenuation in the pipeline structure were proposed,including the boundary reflectivity and the energy attenuation coefficient,which laid a theoretical foundation for the analysis of UGW properties of subsequent pipeline structures in the furture.(2)A UGW propagation property test system for single-layer pipeline structurewas established and related tests were conducted.The experimental results showed that the error between experimental value and theoretical one of the UGW propagation velocities in the non-destructive/damage single-layer pipeline structure was small,which further verifiedthe correctness of the dispersion curves.(3)A UGW propagation property test system for layered pipe structures,damage layered pipeline structures and layered pipe structures covering soil was established and related tests were conducted.respectively.The test results of layered pipeline structure showed that the error between experimental value and theoretical one of the UGW propagation velocities in the layered pipeline structure was small.which further verified the correctness of the dispersion curves.In addiation,the energy attention of the guided wave was more serious than the single-layer pipeline structure.Then the test results of damage layered pipeline structure showed that the damage can be thought as a "secondary source" that conducted obviously damage inflection waves.The damage index of damage layered structure,as for the data foundation was obtained to establish the damage identification algorithm of layered pipe structures.Finally,the test results of layered pipeline structure covering soil showed that the theoretical velocity of the UGW propagation in the layered pipeline structure in covering soil was slightly different from the experimental velocity,but the error was small,which was basically consistent with the dispersion curve.(4)An FEA on damage identification of single-layer pipeline structures using PZT-based UGWs was carried out.The large-scale finite element software ABAQUS was used to establish the driving and sensing multi-physics model of the surface bonded piezoceramic(PZT)components.The PZT model was coupled with the pipeline structure model to establish an FEA platform for damage identification on pipeline structures,and the FEA under various working conditions was performed.The results showed that the calculated value of the propagation group velocity of the UGW in single-layer pipeline structure was basically equal to the theoretical value,which verified the correctness of the dispersion curve.In addition,the farther the signal receiving position was from the excitation position,the smaller the amplitude and the largerthe pulse width of the sensing signal.Compared with the test results,the correctness of the FEA results was verified.(5)The FEA on damage identification of layered pipeline structures using PZT-based UGWs was performed.The large-scale finite element software ABAQUS was also used to create a multi-physics entity finite element model and perform the FEA under various working conditions.Firstly,the numerical analysis on the guided wave frequency dispersive performance was carried out.The results showed that the calculated value of the propagation group velocity of the UGW in the layered pipeline structure was basically equal to the theoretical value,which was consistent with the dispersion curve.The axial propagation property of the layered pipeline structure was like that of the single-layer pipeline structure.However,the farther the sensing position was from the excitation position,the smaller the signal amplitude,the larger the pulse width,the smaller the end reflectance,and the greater the energy attenuation coefficient.The radial propagation in the layered pipe structure,especially in the insulation layer and the anti-corrosion layer,had obvious mode transmission and reflection,resulting in serious dispersion and energy attenuation.The waveform diagram showed that with the signal pulse width increasing,the signal was difficult to identify,while the amplitude was reduced,and the end reflection wave was not obvious,meanwhile the spectrogram showed that the main frequency was not concentrated and there was obvious bifurcation.Then,the FEA on the damage identification of the layered pipeline structure was carried out.The results showed that the damage position can be accurately localized.The greater the damage degree,the larger the energy of the damage reflection wave,which directly led to the smaller energy of the subsequent end reflection wave.Compared with the test results,the mode transformation waves,the end reflection waves and the damage reflection waves of the finite element simulation were consistent with the test results.The end reflectance in the simulation was greater than that in the test results,and the energy attenuation coefficient was smaller than the test results,which indicated that the energy attenuation of the experimental ultrasonic guided wave was more serious.Based on these inite element simulation results,the finite element models of layered pipe structures with different degrees of damage were established,and the quantitative relationship between damage degree and damage index was proposed,and the damage identification algorithm of layered pipe structures was established.According to the damage index,in the method the five damage levels of the layered pipeline structure were determined,and clearly proposes the degree of integrity of the layered pipeline structure from health to damage,but the recommended damage index for replacing the layered pipeline structure also was proposes.Finally,the FEA on the health monitoring of the underground layered pipeline structure was carried out.The results showed that the UGW had much modal transformation waves in the radial propagation direction of the pipeline structure,as the pulse width increased,the signal identification became much more difficult,and the UGW propagation property along axial direction was influenced by the covering soil,the energy attenuation of the axial propagating UGW in the pipeline structurewas serious,and the energy can leak from the structure to the covering soil,but it cannot propagate back from the covering soil to the pipeline structure again.