Développement de transducteurs électromagnétiques acoustiques pour l’estimation d’épaisseur minimale sur des tuyaux corrodés en acier

Abstract

Guided waves nondestructive testing, NDT, includes various techniques to scan structures such as plates or pipes over medium to long distances. The results can range from the characterization of a defect, nature and size, to the estimation of the properties of the inspected material. A widely monitored phenomenon is corrosion. This chemical reaction degrades materials such as steel and can lead to an alteration of mechanical properties, the creation of stress concentrators or a local loss of thickness. This last case is particularly important in the petrochemical industry since an unmonitored corroded surface can lead to a pipe rupture and therefore to a leak of product potentially harmful to humans and the environment. Structural filtering is a method allowing this monitoring. It uses the high order guided wave mode dispersion relationships, or phase and group velocity relationships with the frequency and the waveguide thickness. Shear horizontal guided waves, SH waves, are favored for structural filtering inspections over Lamb waves because of the simplicity of interpretation of their dispersion curves, their low sensitivity to non-viscous surface loads, and the fact that they do not convert into Lamb modes when interacting with a defect parallel to the direction of polatization. However, SH waves are known to be difficult to excite and detect using conventional piezoelectric transducers. Electromagnetic acoustic transducers or EMAT make SH mode transduction relatively simple but existing concepts are mostly single-element probes, such as periodic and permanent magnets EMATs or PPM EMATs, limiting the excitation capabilities and data processing techniques that can be used with multi-element probes. The work presented in this thesis is based on results obtained by finite element simulations and experimental measurements and has demonstrated that : (1) a PPM EMAT when optimized for steel pipe inspection allows rapid reconstruction of the thickness profile of a corroded region; (2) a multi-element EMAT probe designed for SH wave transduction can allow the use of advanced excitation techniques and data processing algorithms such as two-dimensional Fourier transforms with similar performance to piezoelectric probes; (3) this probe when used on a steel pipe allowed the estimation of the minimum thickness at various positions with a maximum error of 0.4 mm and a positioning with an error of 10 mm for a total propagation distance of 600 mm.

Date	31 Jul 2023
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Pierre Bélanger (Supervisor)