Ultrasonic guided waves and wave scattering in viscoelastic coated hollow cylinders

Over a million miles of piping is used in the USA in almost every industry that calls for a large scale transportation and distribution of energy or product. To preserve the integrity of these pipelines, viscoelastic coatings are widely used on the pipes. However, pipe aging and exposure to a variety of changing environmental conditions reduces the protection effectiveness consequently leading to the occurrence of defects, calling for an effective non-destructive evaluation (NDE) method.;Ultrasonic guided waves, with a long range propagation capability, are becoming useful in new solutions for pipeline inspection. However, guided wave inspection potential in coated pipe has not yet been studied in detail. Many important questions need answers, like focusing feasibility in coated pipes, wave scattering possibilities study for effective inspection of 3-D defects, and quantitative evaluation of inspection distances under various coating conditions.;In this work, guided wave propagation, scattering and focusing in coated pipes are studied comprehensively for the first time with numerical, analytical and experimental methods. A three-dimensional finite element tool utilizing ABAQUS/Explicit was developed for quantitatively and systematically modeling guided wave behavior in pipes with different viscoelastic materials. It is very exciting to find that guided waves can still be focused very well in a coated pipe for the frequency studied, although there is an amplitude loss due to the viscoelastic nature of the coating materials. Wave scattering from planar and corrosion like defects were investigated and it was found that axisymmetric waves had a small possibility of finding small corrosion like defects while focusing had a much higher chance. Defect sizing potential was also studied based on an observation of the wave interaction with defects and the mode conversion that occurred thereafter.;Moreover, in order to minimize the attenuative effect from the coatings, a parametric study of coating property effects on wave attenuation was conducted with a recommendation of appropriate coating properties, frequency range, and wave type for future work in the pipeline industry. In addition, an experimental method of property measurement for field coating materials was developed as a means of providing inputs to computer models. Finally, a detailed criterion to improve the inspection potential of coated pipes is recommended.