Research On Pipeline Connection Structure Damage Monitoring By Using Time Reversal Method

Since last century,because the pipeline transportation has the advantages of low cost,large capacity,high efficiency,less pollution etc.,many countries are actively promoting the construction of the pipeline.Pipeline operating mileage in China has surpassed the railway and become one of the important means of transport in the process of economic construction and industrial development.In our country,the pipeline system is often used in long-distance transportation of oil and gas mainly.However,due to long-term work in complex condition,the pipeline structure will be affected by many factors,producing a variety of defects damage.Eventually,it may lead to pipeline leakage accident,which can bring unexpected economic losses and unrecoverable environmental pollution,and even casualties.Analysis of pipeline accidents show that the pipeline leakage accidents are often related to connection structure of pipeline and connection structure is the most important and weak link in the pipeline system.This shows that constantly damage detection of connection structure is essential,and ultrasonic guided wave propagate in there is complex.In the routine detection of long distance pipeline,the guided wave is inevitable to pass through the connection structure,so the piezoelectric wave method based on time reversal has aroused wide attentions from all over the world.In the routine health monitoring of long distance pipeline,the guided wave is inevitable to pass through the connecting structure,at present,there are few researches on the pipe connection structure.There are many problems to be solved urgently.Based on the combining method of the theoretical analysis,numerical simulation and experimental verification,this paper researches on the thread connection structure and flange connection structure of the pipe in common use are studied.First of all,propagation characteristics of ultrasonic wave in composite layer and the pipeline structure have been studied based on the theoretical analysis.The dispersion equation of cylindrical guide wave and circumferential guided wave are deduced.The guided wave dispersion equation by Matlab software is solved.Moreover,the needed pipe group velocity and phase velocity dispersion curves are drawn out.The modal analysis of guided waves is used to select the optimal mode and the central frequency of ultrasonic guided wave in the pipeline structure.The selection principle is making the small dispersion to minimize the complexity of the pipeline analysis of the signal,and providing a theoretical basis for the signal selection in the damage detection of pipe connection structure.The damage degree was evaluated by D value.Second,a test platform is set up,and a 5 cycle superimposed sinusoidal signal modulated by the Hanning window is applied for the experimental excitation signal.Piezoelectric ceramic patches are used as transducers for the signal excitation and reception.The damage identification tests were carried out on the flange connection structure and the threaded connection structure respectively.It shows that:when the torque of the threaded connection is decreased,the energy of the received ultrasonic pulse signal is gradually reduced to the minimum value;when the bolt torque of flange falls below a fixed value,the damage is produced,the ultrasonic pulse signal energy received is gradually reduced to a minimum;Finally,the propagation characteristics of ultrasonic wave in the composite layer of flange connection structure are studied,ABAQUS software was used to validate the model through numerical simulation.In addition,the health monitoring process of the flange structure is simulated.The energy attenuation law of ultrasonic wave in flange connection structure is obtained,and the influence of the change of bolt torque on the damage degree of flange is analyzed.The results show that the received ultrasonic signal energy decreases with the decrease of the bolt torque.Through the simulation results compared with the test results,it is concluded that their results are consistent and verified the feasibility and accuracy of numerical simulation and experimental method.