||The guided wave has been used to detect the corrosion on pipes for the petrochemical industry in Taiwan for a long time. This technology is usually utilized to overhead pipes, coated pipes, buried pipes and pipes in culvert. It costs a lot to set support, remove coating, and excavate when uses others non-destructive techniques. Therefore, the guided wave technology has to be more progressive. Using guided wave to detect the general corrosive pipelines causing the energy of guided wave attenuated, and the background noise increased. It is likely to let the serious corrosion signal be covered leading to the much serious corrosive signal could not be detected. 3D laser scanning is an emerging technique used to assess the corrosive situation on the pipe being portable, fast detecting and reproducible. If we could make use of the image scanning with 3D laser to build model, it is close to reality undoubtedly. Then, taking advantage of this model to use finite element method to simulate the propagation of wave in order to let the results of simulation is similar to guided wave detect.|
This research uses 3D laser construct the external part of pipe model, and import this model to finite element method software to do numerical simulation. Then, we should compare with the simulated results and measurement data, and using ECL, called Estimated Cross Sectional Loss, to analyze. We want to investigate that the propagation of guided wave when guided wave incidents from the clear pipe/general corrosive pipe, and there is corrosion around the pipe support. Also, we have to consider the influence of different detecting frequency. According to the modeling simulation analysis of corrosive support, the reflective signal is disorder because of the different geometries of supports. For example, if the support has a medium partial corrosion, which ECL is 7.25 %, the back signal is easy to be covered by the back signal of support since the wavelength of 20 kHz is longer than 50 kHz. So as to choose 50 kHz to detect, we can distinguish the corrosive signal easily. As we set the transducer on general corrosion pipe, it is easy to let the noise level and call level raised. For example, we can easy to detect the partial corrosion, which ECL is 5.45 %, if there is a general corrosion, which ECL is 3.46 %, under the transducer. However, if the ECL of general corrosion is 7.94 %, the percentage is much more than the partial corrosion. It causes the non-axisymmetric and symmetric ratio of back signal decreasing greatly. These situations lead to the corrosive signal of support be ignored. This moment, we should choose the new location for setting the transducer or clearing the pipe to reduce the influence of general corrosion on pipe. From the analytical and numerical results, in the same corrosive case, the signal in a high frequency regime is much easier to be detected than the signal in a low frequency regime. Hence, we exploit the guided wave in a higher frequency regime and the rate between symmetric and antisymmetric coherent signal to differentiate the corrosive level of pipe support.