| The media transported through pipes in power plant has the character of high temperature, high pressure, or radioactivity. It will destroy the environment or injury people when a leakage happened. Many accidents occurred in history which was caused by leakage of power plant pipeline. Ultrasonic guided wave developed from the traditional ultrasonic inspection has the advantage of long distance, all pipewall, and no cover removal, thus making it very suitable for fast inspection of pipeline in power plant. Furthermore, it has the potential of on-line monitoring.Many investigation about the application of ultrasonic guided wave in power plant was performed in this paper, includes:The variation of disperse curve in pipe when material property altered which caused by temperature. The influence of elastic modulus, Poisson ratio, and density to disperse curve is discussed from room temperature to 500℃. And the weight of these three physical quantities is analyzed. The result shows that elastic modulus play important roal to the variation of disperse curve when temperature changed. The mode of L (0,1), L (0, 2) and T (0,1) at low frequency was affected little by material properties. The L (0,1) mode is chosen as detection wave for its easy excitation when load from the outer surface of pipe. Numerical simulation was carried out to prove the excitation of chosen mode using mono-cell sensor and comb sensor that based on wavelength matching principle.The propagation of ultrasonic guided wave in pipe with macro crack was studied by means of software ANSYS, so to validate the excitation of L (0,1) mode utilizing oblique incidence transducer on the basis of phase matching principle, and confirm the relation between reflection coefficient and crack dimension in axial, circumferential and ridial direction.Most of the conventional ultrasonic methods are quite sensitive to gross defects, but much less sensitive to evenly distributed microcracks.The thesis researched the feasibility of inspecting the micro crack using guided waves from two parts, data prosessing and nonlinear wave.Advantage and disadvantage of three signals, which is time domain signal, frequency domain signal and disperse curve, characterizing the wave mode are found. The frequency domain signal is got by Fourier transform, and the disperse curve is obtained by matrix pencil method. If observe the disperse curve alteration, the micro crack can be seek. This method has a high sensitivity than time-space transformation, and can locating the damage.Combining the guided wave with nonlinear detection, the high order harmonic longitudinal wave will be got, and this wave can be used to micro crack inspection. After calculating the mathematical solution to excite the second order harmonic in pipe, determinating the operating point, the relation between the relative amplitude of harmonic and micro crack size are drawn.The thesis proposed a feasible method to detect and quantitative evaluation the damage in hard contacting pipe.
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