Guided wave propagation in pipes with viscoelastic coatings

This work studies the propagation of ultrasonic guided waves in multi-layer structures, including pipe and tubing coated with viscoelastic materials. The principal motivation of the work is to achieve the ultimate goal of using guided waves for performing a non-destructive inspection of pipe and tubing. The viscoelastic coatings that are often used for corrosion control on these structures severely attenuate the propagation of guided waves, making inspection difficult or impossible in some cases. A theoretical boundary value problem is developed that describes the guided wave propagation in multi-layer plate and hollow cylinder structures for the purpose of finding guided wave modes that propagate in these coated structures with little or no attenuation. The model uses a matrix technique for generating the dispersion equation that solves the boundary value problem for a system of an arbitrary number of plates or hollow cylinders. A numerical solution technique using functional minimization is developed for producing the phase velocity, group velocity and attenuation dispersion curves that describe the guided wave propagation. The attenuation dispersion curves show some guided wave modes that propagate with little or no attenuation in a coated structure. A number of numerical results are displayed to verify the accuracy of the numerical solution and to evaluate the effect of different coating materials and thickness. Experimental results are produced to evaluate the accuracy of the numerical solution in both multi-layer plate and hollow cylinder structures. Recommendations are made for selecting the proper low attenuation modes for carrying out an inspection of coated pipe and tubing.