Investigation On Propagation Characteristic Of Ultrasonic Guided Wave And Defect Detection In Helical And Corrugated Structures

In our country, more than83%of the electricity is supplied by the thermal powerplants. High pressure heater and condenser in power plant mostly use brass, carbonsteel or stainless steel tube as the heat exchange tube. Except hidden defects in theproduction and installation of these pipes and continuing to expand in the runningprocess, the use of the process can produce a variety of new defects in the pipelinewhich will be resulting to leakage, such as sediment induced corrosion, chemical gasinduced tube outer annular groove corrosion pits and pipe water impact abrasion.Nondestructive testing and evaluation in industrial pipeline using ultrasonicguided wave is becoming more and more mature. Ultrasonic sensor has been appliedin engineering practice and achieved good results. While contraposing boiler pipenetwork in large thermal power station which is the special detection object, thenondestructive testing technology for corrugated pipe which has complex structure ofthe heat exchange tube outer wall damage detection is relatively small. The influenceof ultrasonic guided wave propagation characteristics in the corrugated structure hasbeen researched based on theoretical analysis, numerical simulation and experiments.The main research contents are as follows.(1) Based on the classical wave dispersion equation in the free plate, corrugatedparameters in the corrugated plate has been imported into the dispersion equation, andthen the SH wave and Lamb wave dispersion equation of corrugated plate can beobtained. The dispersion equation is solving using the method of dichotomy, and thephase velocity and group velocity dispersion curves of guided wave propagationcharacteristics in flat and corrugated plate has been compared. The variation rules ofguided wave group velocity with corrugated parameters has been researched.(2) Derivation of free hollow cylindrical guided wave dispersion equation isobtained based on the classic, the bellows of torsional mode and longitudinal modeguided wave dispersion equation has been ratiocinated, and the sensitivity of theguided wave modes of wave parameters are compared. At the same time, the finiteelement simulation of propagation characteristics in corrugated structure has beenresearched on the platform of Abaqus software, and the actual changes of guidedwave propagation distance in corrugated structure are analyzed.(3) Analysis of ultrasonic guided wave phase velocity and group velocity dispersion curves when the material of longitudinal velocity and shear wave velocitiesare changed. For the change of wave parameters to the same degree, compareddifferent sensitivity to changes in corrugated board and corrugated pipe.(4) Through the analysis of relevant concepts of the magnetostrictive effect andultrasonic guided wave characteristics, magnetostrictive sensor are putting forwardoptimization scheme by multi-layer winding coil sensor on the basis of the existing.The longitudinal modes of ultrasonic guided wave excitation and reception, andcompared with past experimental results. Through the special design of the solenoidstructure of magnetostrictive sensors, the high order modes of ultrasonic guided waveexcitation and reception can be realized, and the artificial defects were detected.(5) Constructing the calculation model of spiral corrugated pipe in the Abaqussimulation software, and the simulation of guided wave propagation characteristics inspiral corrugated pipe with a crack has been shown. Then the electromagnetic acoustictransducer is developed in the spiral corrugated tube. The identification and locationof the artificial crack defects in spiral corrugated pipe by excitation and receivinglongitudinal mode guided waves. Analysis software for finite element simulation ofmagnetic field distribution of pipe selection multi-physics coupling, and the workingefficiency of sensor has been improved by coated with a layer of nickel alloy ribbons.(6) Changing temperature will inflect some material parameters, and then thepropagation characteristics of ultrasonic guided waves will affect in the waveguidestructure. The variation curve of guided wave phase velocity and group velocity withcorrugated parameters has been calculated from the temperature coefficient, and thenthe influence of environmental temperature on the propagation characteristics ofultrasonic guided wave has been researched by using the method of finite elementsimulation and experiments.