Structural health monitoring of high-temperature pipelines using piezoelectric ultrasonic guided wave transducers

Abstract

This thesis focusses on the development of high temperature piezoelectric transducers for monitoring of pipes using fundamental torsional guided waves in the 20-100 kHz frequency range, with the ability to operate at temperatures up to 600°C. A combined numerical and experimental approach is employed to design, optimise, and characterise non-resonant transducers for high-temperature torsional operation. Additionally, the guided wave monitoring capabilities of an existing transducer system are demonstrated at temperatures up to 150°C. Thermal stability is evaluated through long-term experiments with simulated defects and field conditions in a power plant, achieving a defect sensitivity of 1% cross-sectional change with the proposed temperature compensation and defect detection approach. Multiphysics finite element models of the transducer are developed and verified, and the approach is applied to optimise the transducer design by eliminating undesired mode coupling. The findings are initially applied to a guided wave monitoring system for ambient temperatures. The modified bismuth titanate and gallium phosphate piezoelectric materials are then used to develop high-temperature transducers, which are characterised and verified for continuous operation at 350°C and 600°C. The results show promising ultrasonic performance, defect sensitivity, and stability for guided wave monitoring applications, enhancing confidence in the technique for use at higher operating temperatures.