| Pressure pipeline is widely used in petrochemical,power stations,military industry,and other areas of the energy industry,because of its long-term work in harsh environments such as high temperature,great pressure,area easy to corrode,it is inevitable to cause crack by various external forces or itself reason during the manufacturing process,which will affect the safe operation of the pipeline.Therefore,pipeline crack detection is of great significance for pipeline safety evaluation.Cracks can be divided into longitudinal crack,circumferential crack and oblique crack according to the crack direction of pipeline.The crack detection includes ultrasonic wave,magnetic flux,elastic wave and other technical methods,including ultrasonic wave method,which is one of the main techniques of crack detection.At present,the ultrasonic wave method of pipe crack detection at home and abroad mainly uses the circumferential guide wave and the longitudinal guide wave to realize the longitudinal and circumferential crack detection respectively.During the detection of the oblique crack in the pipeline,the direction of the reflection ultrasonic acoustic beam is not propagated along the longitudinal and circumferential direction of the pipe,and the spiral direction of the pipe is propagated in the direction of the pipe helix.For the reason of ultrasonic wave direction,the traditional guided wave receiving probe can not receive the ultrasonic wave propagating in the direction of the main acoustic beam.Aiming at the problem of spiral guided wave technology in pipeline crack detection,a lot of research work has been carried out in theory,simulation,design and experiment,and some novel research results have been achieved.In this paper,the basic concept and mathematical description of helical guide wave are presented and the propagation equation of the spiral guide wave is derived.For the receiving technical difficulties of the helical guide wave,this paper studied the theory foundation of the ultrasonic guided wave in the spiral pipe.By analyzing stress and strain elements during the solid deformation,the author combined the elastic properties of solid medium and elastic coefficient,and described the isotropic solid medium of the acoustic wave equation.Based on the theoretical study of circumferential guided wave and longitudinal guided wave in pipeline and the theoretical basis of torsional wave,the mathematical description of helical guided wave in pipeline is given.Through the cylindrical coordinate system,the three-dimensional cylinder surface is expanded into two dimensional plane,analytical analysis of pipeline plane is carried out.The propagation equation of helical wave in plane for circumferential defect,longitudinal defect and general oblique defect detection is deduced,including the propagation equation of the main axis of the helical wave beam,such as transmitting wave and reflecting wave.A method of spiral guided wave analysis for ultrasonic guided wave multimodal analysis is proposed in this paper.In this paper,the analysis of guided wave propagation direction of electromagnetic ultrasonic transducer and the control theory of guided wave propagation direction of electromagnetic ultrasonic helical wave in three-dimensional pipeline are studied.Based on the theoretical study of helical guided wave in pipeline,this paper elaborates the principle of non-contact electromagnetic ultrasonic energy transfer,and expounds the electromagnetic and mechanical theoretical basis of electromagnetic ultrasonic transducer.The magnetic field,eddy current field and Lorentz force of the electromagnetic ultrasonic transducer are analyzed by establishing the simulation model of the analytic plane electromagnetic ultrasonic transducer.In non-ferromagnetic materials,the mechanism of electromagnetic ultrasonic energy transfer is Lorentz force mechanism,in ferromagnetic materials,the mechanism of electromagnetic ultrasonic energy transfer are magnetization force mechanism,magnetostrictive force mechanism and Lorentz force mechanism.Based on Biot-Savar's law,the magnetic field distribution theory of current elements in space in magnetostatics is proposed,the analysis model of guided wave propagation direction of electromagnetic ultrasonic transducer is proposed.Through the mathematical calculation and analysis of the magnetic field distribution generated by the instantaneous equivalent energization closing coil,it is found that the magnetic field distribution is the largest in the direction perpendicular to the working wire.When the vertical distance is equal,the magnetic field distribution is the largest in the direction of the vertical line of the working wire.A control model of the propagation direction of electromagnetic-ultrasonic helical guided wave in three-dimensional pipeline is established.It is concluded that the transmission direction of the main beam of helical guided wave can be controlled by changing the helical angle of the transducer coil.In this paper,the simulation of electromagnetic ultrasonic transducer in analytical plane is studied.The magnetic field,eddy current field and Lorentz force of electromagnetic ultrasonic transducer are analyzed.The structure of oblique winding coil is designed,and the electromagnetic ultrasonic spiral guided wave transducer used in pipeline detection isdesigned and manufactured by using flexible FPC coil.Based on the theoretical analysis and simulation analysis of the electromagnetic ultrasonic transducer,this paper presents and designs an electromagnetic ultrasonic spiral guided wave transducer,and studies the relationship between the coil angle of the transducer and the spiral guided wave elevation angle.According to Faraday's law of electromagnetic induction,when the electromagnetic ultrasonic spiral guided wave transducer works,the coil of the transducer with high frequency and high power exciting current induces alternating magnetic field along the spiral direction inside the steel pipe.Under the static bias magnetic field of permanent magnet,the surface and near surface of steel pipe will undergo periodic contraction and tension changes,thus driving the particles in the pipe to form high-frequency vibration.The high frequency vibration propagates in the form of ultrasonic along the spiral direction of the pipeline,forming electromagnetic ultrasonic spiral guided wave.In this paper,four kinds of electromagnetic ultrasonic spiral guided wave transducers for pipeline detection are designed according to the internal and external detection methods of spiral guided wave and the radial and longitudinal biased magnetic fields.Aiming at the design of electromagnetic ultrasonic transducer which generates and receives spiral guided waves,the experiment of verifying the propagation function of spiral guided waves and the experiment of directivity of the sound field of spiral waves are carried out,the propagation mechanism of spiral guided waves in electromagnetic ultrasonic pipeline is experimentally studied.In this paper,the comparison test is carried out for circumferential groove defects on sample pipe.The receiving time of the spiral guided wave with different elevation angles is different when the slope of the excitation coil of the electromagnetic ultrasonic spiral guided wave transducer changes.The echoes can be received by the circumferential grooves distributed at different clock positions in the circumferential direction,which verifies the correctness of the spiral guided wave electromagnetic ultrasonic transducer.The results show that the spiral guided wave can be used for pipeline crack detection,the spiral guided waves with different elevation angles can be generated and received by the coils of the electromagnetic ultrasonic spiral guided wave transducer,the greater the helix angle of the spiral guided wave,the faster the propagation velocity of the guided wave along the longitudinal direction,the smaller the spiral angle of helical guided wave is,the slower the velocity of helical guided wave propagates along the longitudinal direction,and the clearer the separation of multi-mode guided wave is,the helixguided wave with small angle angle parameters has the function of echo multimodal analysis.In this paper,the calculation methods of longitudinal location and oblique angle of defects in electromagnetic ultrasonic spiral guided wave pipeline inspection are studied.Aiming at the design target of pipeline circumferential,longitudinal and oblique defect detection,two schemes of electromagnetic ultrasonic pipeline detection system are proposed in this paper.Based on the dynamic and static echo time parameters,amplitude parameters,receiving and receiving parameters,spiral angle parameters of transducer coil and pipeline parameters of echo signal,the calculation equation of pipeline longitudinal positioning coordinates is deduced.The dynamic and static echo time value and amplitude of echo signal are the key parameters for longitudinal location of defect detection.Through theoretical calculation of spiral guided wave,modeling and Simulation of electromagnetic ultrasonic transducer and experiment,the feasibility of spiral guided wave propagation and pipeline circumferential and longitudinal defect detection is verified,and a new pipeline defect detection technology is explored. |
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