Research On Curved Pipeline Damage Identification By Using PZT-based Ultrasonic Guided Waves

At present,pipeline transport has become the fifth largest transportation mode after highway,railway,aviation,and water transport,since it has a unique advantage of low cost,large volume,less land occupation and environmental pollution,etc.It occupies an important position in the national economic construction and industrial development.Pipeline system in our country is mainly used in oil and gas transportation,playing in an important role.However,since the pipeline structure may meet various factors in the process of long-term service,it produces the various defects such as cracks,corrosion damages etc.When these damages occur and cause leakage accidents,the ppeline structure will bring unpredictable economic loss and environmental pollution,and even casualties.Considering the above situations,evaluating the cracks in the pipeline system is very necessary.Today,compared with the traditional pipeline detection method,a new method called supersonic guided wave examination method based on PZT waves has aroused wide attentions from all over the world.So far,the results on damage detection of hollow straight pipe are relatively more,but less on curved pipe.There are a lot of problems to be solved.Based on the combining method of the theoretical analysis,numerical simulation and experimental verification,this paper researches on non-defective pipes,cracked pipes and water-filling pipes.First of all,the guided wave property in a hollow circular tube structure has been studied based on the theoretical analysis.It is for the cylindrical guide waves and circum ferential wave dispersion equation,respectively,using Matlab software to numerically solve of guided wave dispersion equation,then the group velocity and phase velocity dispersion curves given pipe for a dimension can be drawn.Through the modal analysis of pipe transmission determines the ultrasonic guided wave propagation in the selection of pipe modal and driving frequency.The selection principle is for making the tiny dispersion to minimize the complexity of the pipeline analysis of the echo signal,and providing a theoretical advantage for the signal selection in the damage detection of the pipeline.Second,the verification experiment of the pipeline structure is carried out in this paper.Based on the analysis of excitation signal,it shows that the narrower bandwidth and the greater number of signal cycles,the better control of the signal frequency.At the same time,because of long time signals in time domain,the waveforms are easily to be superimposed.Considering the above situations,a 7 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,and a set of effective and convenient testing system can be established for identification of,for nondestructive straight pipe,weld straight pipe,weld crack bend test,analysis of its rules and influences.Finally,based on pulse echo-method,using ABAQUS software,curved pipe with weld cracks are numerically simulated,and wave propagation process is also obtained.The guided wave detection sensitivity to parameters of crack changes are analyzed.The results shows that the relationship between damage degree of pipe and crack length,width and depth is linear.Through the simulation results compared with the test results,it is concluded that the two basic consistence verifies the feasibility and accuracy of numerical simulation and experimental method.