Développement d’un transducteur ultrasonore pour les environnements à haute température

Abstract

Petrochemical and nuclear facilities convert corrosive and eroding products using pressurized (up to ≥ 150 bar) and high-temperature (up to ≥ 650 °C) equipment. These two parameters accelerate erosion and corrosion, which reduces the thickness of the components such as pipes and vessels; pipe elbows are the among the most susceptible locations to this reduction in thickness. The related consequences are the generation of structural defects, such as cracks, and the risk of catastrophic equipment failures. Usually, inspections are performed at room temperature and during calendar-based plant maintenance shutdowns, as conventional ultrasonic techniques, which can measure remnant thickness nondestructively, do not withstand in-service inspections in this kind of harsh environment. Conventional piezoelectric and EMAT transducers technologies are limited by their Curie temperatures (≈ 300 °C). As for laser-based technologies, they do not allow multiple measurement points at different locations with a low footprint and in tight geometries. Therefore, the design of an ultrasonic transducer is required for in-service monitoring of the remnant thickness of pressurized equipment in a high-temperature environment, allowing integrity monitoring of equipment in real-time. This would avoid the economic losses due to costly shutdowns and long restart periods, and ensure the timely replacement of worn parts to avoid leaks of potentially harmful chemicals. Additionally, it enhances the safety and security of employees and the environment. In this thesis, the design of a contact single-element piezoelectric ultrasonic transducer is presented. The selection of the different materials constituting the main elements of an ultrasonic transducer is discussed : the piezoelectric material, the electrodes, the absorbing layer, the acoustic matching layer, and the bonding layers. This selection of materials relies on the consideration of the thermal expansion coefficients, acoustic impedances, acoustic coupling between each layer, absorbing or transmitting characteristics of materials, and thermal stability. Only the bulk longitudinal waves produced by the retained piezoelectric element, lithium niobate (LiNbO3), are considered for the presented single-element transducer. The transducer that was built and tested experimentally can reach operating temperatures of up to 775 °C for at least 72 hours. It is characterized by a center frequency of 3 MHz. Continuous operation in a high-temperature environment, from 20 to 550 °C, for at least two consecutive months was also demonstrated. Finally, the developed single-element transducer paves the way for the development of a high-temperature phased-array transducer.

Date	27 Apr 2023
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Pierre Bélanger (Supervisor) & Ricardo J. Zednik (Co-supervisor)