The mode conversion of the guided wave by a welded pipe shoe

• Main Authors: Jie-horn Lee, 李傑弘
• Other Authors: Shiuh-kuang Yang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/49409770980977292874

碩士 === 國立中山大學 === 機械與機電工程學系研究所 === 94 === The detection of corrosion in pipes is of major importance to the oil and chemical industries. Current methods involving point-by-point inspection are available for the detection of general wall loss associated with corrosion, but unfortunately the current methods tend to be very slow, limited to single positions, thus make the inspection of the kilometers of pipeline typically found in industrial plants virtually impossible. Ultrasonic guided waves provide an attractive solution to this problem because they can be excited at one location on the pipe and will propagate many meters along the pipe, returning echoes indicating the presence of corrosion or other pipe features. Nevertheless such techniques still have many practical difficulties in application due to the complex characteristics of guided waves such as dispersion and mode conversion. This thesis studies guided waves influenced by the welded supports, a.k.a. pipe shoe. A research of the reflection of mode-converted guided waves from pipe shoes on pipes in the frequency range 18-32 kHz has been carried out. Measurements are made on a 6 inch bore diameter, 7.1mm wall thickness pipe. The axisymmetric symmetric T(0,1) mode is incident on the pipe shoes and the mode-converted guided waves are received in reflection. In parallel, a finite element model is used to simulate the experiments by using Ansys. Received signals are separated into single-mode with a mode extraction technique. This research reveals that when T(0,1) propagates through the pipe shoe, the energy of T(0,1) passes into the pipe shoe. The leakage phenomenon results in the complexity and misinterpretation of the echo.