Defect Detection Studies On Time-reversal Theory In Pipes Using Ultrasonic Guided Wave

Corrosion and pitting defects in pipe work are major problems in the oil, chemical,and other industries. These defects can occur at the outer or inner surface of the pipeand can lead to a serious loss of pipe wall thickness. Traditional Ultrasonicnondestructive testing techniques are single position measurements, therefore theytend to be so slow that making long distance pipe inspection is almost impossible. Analternative to traditional pipe detection method is to excite stress waves, which canpropagate along the pipe, and to monitor the response of the pipe for changes in thereceived signal at some remote position. An ultrasonic inspection technique usingguided waves was applied to detect and determine the exact location of flaw in longsteel pipes. Since many modes of guide waves are generated due to guided waves’multi-modes characteristic in the inspected pipe, to select and excite only single modeto detect the pipe can obviously simplify the analysis complexity.The project just do research on using piezoelectric transducer to set up and receivecertain ultrasonic guided wave modes to detect the pipe flaw. First, the developmentin this field was introduced. And the relative theories and basis of guide waves andpiezoelectric transducer were explained. Finally, using distributed PZT transducers,different modes are repressed and given ultrasonic guided wave are generated andreceived in a pipe. The experimental results greatly agreed with the theoretical ones.On this basis, the flaw of the pipe with single or double fracture can be detected andlocated by analyzing the data from the receiving waves. The analysis of the reflectioncoefficient-circumferential extent percentage curve show that the crack length can bedetermined when its wall thickness reduction, axial width and circumference of thepipe are constant and the reflection coefficient is measured.When the time reversal method for ultrasonic guided wave was used fornondestructive testing of the pipeline defect, the temporal-spatial focusingcharacteristics for ultrasonic guided waves on pipeline based on the time reversal theory can focus the energy on the defect. But the sensitive degree for defects indifferent directions need to be further studied. Because a time reverse numericalsimulation method can visualize on guided waves propagation in pipes. The pipelinedefect model has been established for the validation of time reversal focusing method,the propagation of time reversal guided wave was visualized. Finally, the crack atdifferent circumferential size was detected based on the time reversal focusing method,the varying of reflection coefficient was studied and explained from the energydistribution perspective. The results show that, the echo amplitude of different crackcan effectively be enhanced after time reverse numerical simulation, the ratio ofamplitude of the defect echo is more bigger when circumferential size is more smaller.