| Summary: | 碩士 === 國立中山大學 === 機械與機電工程學系研究所 === 103 === The storage tank is a general equipment in petrochemical industry, power plant and gas industry. Long-term usage of storage tank, the artificial and natural defect will cause structural damage. Recently, Acoustic Emission (AE) Testing was introduced to tank bottom corrosion inspection. The advantage of using Acoustic Emission Testing is a large range inspection of tank bottom without opening the tank. However, positioning of acoustic source is always be the problem of AE testing. The reason is that corrosion, crack growth and plastic deformation will produce numerous mode of wave making trouble for positioning of the defects.
This study analyzed corrosion on the tank bottom will generate mode and behaviors of zeroth Lamb wave, and utilized Finite element method for analyzing wave propagation which judged position of the source with AE parameters. Furthermore, the theoretical velocity of Lamb wave with different viscous fluid boundary was calculated and wave propagation of Leaky Lamb wave was simulated. Finally, Lamb wave and Leaky Lamb wave effect on positioning the AE source using Wavelet Transform analysis result of the small tank filled with different viscous fluids.
The study confirmed corrosion producing AE signal which is A0 mode by experiment and simulation. And using rise time, average frequency and amplitude will help to recognize position the AE source. The results showed that Leaky Lamb wave propagated in the low viscous fluid for positioning the AE source. On the country, A0 Lamb wave propagated on the bottom plate with high viscous fluid for positioning the AE source. The Wavelet analysis was used successfully to define the wave mode in the first arrival wave packet. Interpret the wave modes and wave propagation behavior as positioning the AE source of corrosion, and improve the ability of corrosion inspection on tank bottom.
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