Abstract
Damages in pipes such as cracks and corrosions may threaten the integrity of pipeline. Using ultrasonic guided waves to detect these defects is efficient. The waves propagate in the pipe wall and carry information of the entire structure. The signal of damages is included in the reflections of guided wave. Ultrasonic guided waves are dispersive in waveguides, which means the speed of the wave is dependent on frequency. And under a certain frequency, there are multiple modes exist. The characteristic of dispersion and multi-mode make guided wave testing difficult to solve in analytical ways. Finite element method is an efficient way to investigate the problems. To assess damages in pipes, a 3-D pipeline finite element model was set up with artificial defects vary with depths and circular lengths. Taking the circular distribution of guided wave reflection into consideration, two series of defects changing in depth and circular length were introduced in numerical simulation. Circular energy distribution was put forward to assess the defect. Mode conversion will occur when the axisymmetric mode of guided wave meet nonaxisymmetric discontinuities in the pipe. The incident L (0, 2) converts into F(1,3) and enhances the energy on the opposite position of the defect. The circular energy distribution was proved feasible for damage assessment in pipes.
