Characterization of nonhomogeneity in the dispersive properties of the materials used in pipes

This article is focused on the characterization of the lack of homogeneity in the dispersive acoustic properties of polymeric materials used in industrial pipes. Usually, the parameter of interest associated to dispersion is the variation in the propagation velocity as a function of the frequency or the temperature. Nevertheless, this paper, studies the variation in the propagation velocity, as a function of the intensity of the acoustic signal. In these cases, pipes made of PVC, PP and PVDF, which are commonly used in industrial installations, have been characterized. For each type of pipe, high and low acoustic intensity signals have been applied in order to reproduce working conditions that typically appear in the pipe wall below the transducers in commercial Clamp-on ultrasonic flowmeters (UFMs). Under these conditions, acoustic velocity maps have been created for the three materials under test. These maps reveal two effects that are not usually taken into account. The first one is the variation of the propagation velocity with the power density of the ultrasonic signal and the second one is the nonhomogeneous behaviour along the pipe surface. Finally, the acoustic maps reflect how a stronger acoustic signal produces greater behaviour differences in the materials under test. The characterized phenomenon of lack of homogeneity in dispersive acoustic properties, produces a variation in the zero flow error in Clamp-on UFM caused, so as not to fulfil the reciprocity criterion.