Longitudinal mode L(0,4) used for the determination of the deposit width on the wall of a pipe

In this paper, the interaction of the longitudinal mode L(0,4) with a resin deposit coupled to the wall of a stainless steel pipe is studied. The considered deposit has the shape of an axisymmetric ring. The purpose of this work is to analyze the attenuation of mode L(0,4) as a function of deposit width. A finite element model is used for the computation of displacements at the pipe surface and a bistatic measurement method is employed to obtain time signals related to displacements at the same surface. A good agreement between the numerical predictions and the experimental results allows us to discuss the attenuation of mode L(0,4). An exponential law of the attenuation versus the deposit width is deduced from various results. To show that this loss of energy is mainly due to the scattering of mode L(0,4) in the deposit during its propagation along the pipe, an additional study on the scattering of mode L(0,4) is carried out for a stainless steel pipe embedded in a resin matrix.