EXPERIMENT RESEARCH ON PROPAGATION CHARACTERISTICS OF LOW FREQUENCY ULTRASONIC LONGITUDINAL GUIDED WAVES IN STEEL FLORAL PIPES

A steel floral pipe is a key load-carrying member of pipe supporting structures. It is important to apply ultrasonic guided wave technique to nondestructive testing of steel floral pipes. Firstly, the dimensions of PZT elements are optimized for the inspection of steel floral pipes and the excitation frequency of L(0,2) mode at 30kHz. In order to investigate the effects of the holes in steel floral pipes on the inspection ability of this low frequency ultrasonic longitudinal guided wave mode, the relation between the number of holes and the characteristics of received inspection signals are obtained from experimental research. Research results indicate that the holes in a steel floral pipe have almost little effect on the peak-to-peak amplitudes of L(0,2) mode at 30kHz. As a result, it is shown that low frequency longitudinal guided waves have potentials to inspect long range steel floral pipes nondestructively. Furthermore, group velocity of L(0,2) mode at 30kHz tends to decrease linearly with the increase of the holes on steel floral pipes. These research results provide a basis for nondestructive inspection of steel floral pipes based on ultrasonic guided waves in low frequency range.