Optimization of a Lorentz forces EMAT for the reconstruction of the circumferential thickness profile of a steel pipe using high order shear horizontal modes

Abstract

Corrosion is a chemical reaction affecting a wide range of materials. Safety-critical structures in the oil, gas, petrochemical, and many other industries need a fast, reliable screening technique that can be performed without operational disruption. Partially accessible structures such as pipes at supports or under a layer of insulation are particularly challenging. In this respect, high-order shear horizontal (SH) guided wave modes can be used in medium-to long-range thickness gauging thanks to their cutoff frequency-thickness product. As the wave propagates, a reduction in the thickness behaves like a low-pass filter for high-order modes. It has been demonstrated that periodic and permanent magnet electromagnetic acoustic transducers (PPM EMAT) can be used for transmission and reception. This paper presents a comparative study between different PPM EMAT configurations on a 323.8 mm diameter, 10.2 mm thick steel pipe. Finite element (FE) simulations and experimental measurements are used to compare the effectiveness of the different configurations to measure the thickness in four intervals: less than 5.4 mm, between 5.4 and 7 mm, between 7 and 8 mm, and between 8 mm and 10.2 mm, thus allowing to detect thickness losses of up to 50% of the nominal thickness of the waveguide.