An incident angle optimization method for transverse defects detection of pipes based on Zoeppritz's equation

Zoeppritz's equation is a set of equations that describe the relationship between the displacement amplitude of the reflection and refraction waves and the one of the incident plane wave at the interface of two media, from which the partitioning of wave energy at the interface can be inferred. The echo signal energy is directly affected by the value of the incident angle when oblique incidence of sound beam is applied in the detection of the pipes, therefore it is necessary to adjust the incident angle to the optimal range for an ideal flaw detection sensitivity. A method of echo signal energy estimation based on Zoeppritz's equation is put forward in this paper to seek out the optimal range of the incident wave, with which the echo signal energy-incident angle relation curve can be calculated. As a verification, an experiment of detecting the transverse defects on both the inner and the outer wall of a φ165.1mm pipe is conducted, using a 0.5inch/5MHz water immersion probe. The experimental results are in accordance with the calculated ones, proving that the method of incident angle optimization proposed is valid.