The Inspection of Defect in Pipelines Using Guided Waves
This thesis is study about the capability of guided waves in the inspection of cracks in pipelines, and studying about the guided waves of mode conversion phenomenon caused by cracks. The generally used inspection methods in industry are all localized area inspection. It will cost expensively and spend lots of human resource and time consuming, if we want to inspect the whole area in pipelines in factory. Thus, guided waves are used to improve these shortcomings of traditional inspection methods. Guided Waves can propagate fast and long range along the pipelines without decay. With the ability that guided waves can incident at a single location then inspect the whole region of pipelines under efficiently propagating distance.
In this thesis, with using laboratory equipment, 3 Toneburst Cycles, 400¡B500¡B600 kHz, and L(0,1)¡BL(0,2) incident mode set up for crack detective sensitivity experiment. By calculating the group velocity of the signals of crack, it is known that there are three separated modes L(0,1)¡BL(0,2) and F(1,2) from reflected waves by cracks. These modes are exactly mode converted by cracks. The results show that in the same crack circumferential length or crack depth, the longer length or the deeper depth cause the higher reflection coefficient. It means they are more sensitive on the inspection of cracks. Also the reflection coefficient increases with the raising cross section area loss of cracks. In two dimensional fast Fourier transform experiment (2-D FFT), with 3 Toneburst Cycles, 400¡B500¡B600 kHz, L(0,1)¡BL(0,2) incident mode, and 0.5 cm interval set up to gather 40-point signals for proceeding the experiment. It can separate signals with different group velocity which are mixing together in time domain. From results, there are three different modes L(0,1)¡BL(0,2) and F(1,2) mode separated at three-dimensional picture.
Finally, using the guided waves inspection system with 3 toneburst, 90 kHz and T(0,1) incident mode set up to proceed the experiment as before. In inspecting crack sensitive experiment, the use of this system has the similar result with the use of laboratory equipment. It proves that the excellent capability of guided waves in inspection of cracks in pipelines. While in mode identification, this system can identify there is only T(0,1) and F(1,2) mode with the same group velocity exist. Then the same result is verified by 2-D FFT experiment. It shows that this system generate or receive the specific mode in detection cracks by phase construction or phase destruction of phase interference.
Advisor:Shiuh-Kuang Yang; Bor-Tsuen Wang; Shao-Yi Hsia
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:guided waves mode conversion
Date of Publication:02/12/2004