Non-destructive Testing In Pressure Pipes Based On Ultrasonic Guided Waves

Non-destructive testing of pressure pipes is an important method to maintain the safe operation of the pipeline. At present, many examination methods have their limitation, for example, low efficiency, tedious process, complex instruments, difficult operation and so on. But the use of ultrasonic guided waves method can solve most of the difficult problems effectively. It only needs remove a little cladding from pipes all covered with cladding, thus it is easily operated;it breaks through the point-examination limitation completely, which makes the line-examination come true. The principle of guided waves examination is that the ultrasonic transducer is used to excite ultrasonic guided waves at one of the pipe's end, then the guided waves spreads along the pipe, finally the echo is received by ultrasonic transducer at the same end (or another end). Whether the pipe has defects as well as the defects position and size is determined through the analysis of the stress echo change. However, the inherent characteristic of frequency dispersion makes the modes convert in the examination, which makes the testing become complex. Therefore, the choice of single mode in the examination and the frequency-thick band of mode has been given a particular illumination separately in the paper, following a relative numerical simulation. And a multi-cyclical sine signal modulated by Hanning window is used to simulate the excitation wave, and then an inspected ring of nodes is established to receive the echo, finally how the length of the circumferential cracks, the width of the axial cracks and the degree of the thickness-reduce effect the result is explained through the analysis of the result, further more, the reflection factor in the defect has been calculated. Following, a experiment has been carried out, the incident waves with a frequency band of 200kHz-3 50kHz are used to the experiment, and a series of peak value-time curves are drawn each 10kHz, corresponding time are found through fitting peak value, thus the position of the defect is calculated accurately. The application of awl-shaped sensor head in the heat change water pipe experiment indicates that the ultrasonic guided waves may transmit nearly 50 meters in the pipe, which is not influenced by the elbows and makes it possible to test defects in long distance and large-scale. The water-load pipe experiment indicates that the displace and energy maybe leakage at the near-surface, which is significant for the further research.Through the numerical simulation and the experiment, the accurate position of defects is calculated successfully, and the discussion of the result has been carried on. It is explainedthat the ultrasonic guided waves method is an effective and fast testing method, whose prospect of application is extremely broad.