Pipeline Circumferential Defect Detection Based On Time-reversal Guided Waves

In the long-term service of pipelines, corrosion, fatigue damage, pipeline internal potential defects and processing defects may cause crack to pipelines, and failure of pipelines may lead to huge economic losses and serious consequences on the society and the environment. Therefore, research and development of pipeline defect detection technology is particularly important. The excitated direct guided wave has modal conversion at defects, and the amplitude of the reflected defect echo decreases, which makes detection of defects difficult. However, the time-reversal guided wave focus on the defects, and improve its capability for detecting and locating defects. Based on the focusing theory of time-reversal guided wave field, the direct guided wave and time-reversal guided wave are applied to the detection of different types of defects in pipelines, to locate the circumferential defects in pipelines through theoretical analysis, numerical simulation, experimental verification. The specific works of this paper are in the following:The properties of space focusing and time focusing of the time-reversal guided wave on the defect are introduced. It shows that the energy of the time-reversal guided wave focus on the defect, which improves the amplitude of defect echo. Therefore, time-reversal method can improve the detection, localization and recognition capability of defects.Finite element software ABAQUS is used to simulate the direct guided wave and time-reversal guided wave method respectively, considering cases of different circumferential angle single defect, coaxial but different circumferential double defects, different axial and different circumferential double defects, different radial positions to single defect and different aperture circular defects, by setting appropriate simulation parameters. It is shown that the time reversal guided wave is more capable for the detection of small defects and long distance defects compared with the direct guided wave method. Time-reversal guided wave effectively improves the amplitude of the defect echo and the amplitude at the circumferential position of the defect. The larger amplitude and sharp position in the picture of the circumferential distribution of the amplitude of the reflected defect echo correspond to the location of the defects in the circumferential direction.Steel pipes are processed with different circumferential angle single defect, coaxial but different circumferential doub le defects, different axial and different circumferential double defects and different aperture circular defects respectively. Through parallel connection of piezoelectric patches by using terminal b lock, and improvement of the LabVIEW front panel and programming block diagram, a muti-channel data acquisition system that emits ultrasonic guided wave signal and receive defect echo signal at several PZTs is realized.The muti-channel data acquisition system is applied for defect detection with different circumferential angle single defect, coaxial but different circumferential double defects, different axial and different circumferential double defects and different aperture circular defects by the direct guided wave method and time-reversal guided wave method respectively. The echo signal is collected and the picture of the circumferential distribution of the amplitude of the reflected defect echo is drawn. Experimental results are in agreement with the numerical simulation results, which verifies that the time-reversal guided wave is more capable for the detection of small defects and long distance defects.Damage index is caculated for different circumferential angle single defect, different radial positions to single defect and different aperture circular defects by root mean square deviation(RMSD). It is shown that the damage index(RMSD) is linear with the size of the circumferential defect. Therefore the size of circumferential defect can be quantitatively analyzed using RMSD.