Dispersion analysis of guided waves in the finned tube using the semi-analytical finite element method

Abstract

To increase heat exchange efficiency, finned tubes are widely used in petrochemical facilities. Recently, the application of guided wave testing to finned tube inspection has received attention. Since dispersion curves have not been obtained, the guided wave propagation process is still not clearly understood. Hence, the purpose of this paper is to calculate dispersion curves of the finned tube based on an accurate theoretical model, then features of guided waves propagating in finned tubes are further investigated. As fins are helicoidally welded around the outer surface of the tube with an equal interval, the semi-analytical finite element method is extended to this geometrically periodic waveguide. The shape of the discretized cross section is determined by geometric parameters of the finned tube. Numerical solutions show that group velocities of longitudinal modes in finned tubes are significantly slower than those in bare tubes and a special phenomenon of frequency pass bands and stop bands is presented. The changes of dispersion curves are also investigated with various geometric parameters of fins. Besides, torsional modes cannot propagate in finned tubes. By using an electromagnetic acoustic transducer, experimental results are in good agreement with numerical solutions, which indicates features of the guided wave propagation in finned tubes can be well predicted based on the proposed theoretical model.