Abstract: A technique based on shear horizontal(SH) wave for thickness measurement of surface attachment on plate is presented. This nondestructive method is implemented by using the relationship between SH wave dispersion variety and the thickness changing. Propagation of SH wave in bi-layer elastic structure is modeled and analyzed. Considering several conditions of surface attachment such as boiler scale, the dispersion curve of SH wave which varying with attachment thickness is tracked. A concrete implementation of the SH wave attachment thickness measurement is provided. The experimental study on boiler scale thickness detection is carried out with the Steel-CaCO3 bilayer specimen. The results show that the measurement of surface attachment thickness (including relative thick or thin attachment) with SH wave can be realized by measuring the group velocity of SH0 mode under low or high frequency.

Key words: Shear horizontal(SH) wave, Surface attachment, Thickness of boiler scale, Thickness of carbon deposition