Detection of Inner Wall Circumferential Cracks in the Special-Shaped Pipes Using Surface Waves

This paper presents a detection method for the inner wall circumferential cracks in the special-shaped pipes with small diameter-depth ratio using surface waves by placing the transducer at the end face. The scattering characteristic of surface waves at the vertical edge that the maximum of transmission coefficient can be delivered only when the ratio of chamfer size to surface wavelength a/λ = 1, was obtained by finite element method (FEM) simulations and verified experimentally. Electromagnetic acoustic transducers (EMATs) with a center frequency of 1.5 MHz were used to generate and receive surface waves at the end face of the thick-walled pipe. In the pitch-catch mode, the propagation ability of the axial surface wave transmitted at the edge was tested and analyzed. Moreover, in pulse-echo mode, the circumferential grooves in the inner wall were efficiently detected by the surface wave EMAT placed at the end face of the pipe.