Abstract: Longitudinal ultrasonic guide wave dispersion equation of inviscid liquid-filled pipe is analyzed theoretically. Propagation characteristics of longitudinal modes in water- filled steel pipe and water cylinder with rigid boundary are studied. Except α mode, other modes in wall-filled steel pipe are the coupling of the modes of steel pipe in vacuum and of water cylinder with rigid boundary. To the same mode in water-filled steel pipe, its propagation characteristics vary greatly with frequency range. Furthermore, longitudinal modes are excited and received in steel pipes filled with and without water experimentally. Results show that propagation character- istics, such as mode branching and group velocity decrease, occur in water-filled steel pipe. When frequency band of longit- udinal mode in water-filled steel pipe is in the range of one unperturbed L(0, 2) mode branching of steel pipe in vacuum, the mode has the ability of long distance propagation, and the signal shape and amplitude are retained as it travels long distances for its low dispersion. As a result, the kind of longitu- dinal mode is suitable to defect detection of long distance water- filled pipe.

Key words: Liquid cylinder Longitudinal mode, Dispersion, Liquid-filled pipe, Mode branching, BCC lattice, BCT lattice, Cellular material, Lattice structure, Selective laser melting