Abstract
In this paper, the thickness extension mode gallium orthophosphate single crystal elements were characterised using the impedance analyser. Impedance characteristics of piezoelectric elements were investigated at temperatures from 25°C up to 580°C at first and then at a constant temperature of 580°C for a period of 25 days. The resonant and anti-resonant frequencies extracted from the impedance characteristics, capacitance (measured at 1 kHz), density and dimensions of the gallium orthophosphate elements were used to calculate electromechanical, piezoelectric and elastic properties of these elements at high temperatures as a function of time. The tested gallium orthophosphate elements proved to possess very stable efficiency and sensing capability when subjected to high temperature. The results are very encouraging for proceeding with development of phased array probes using gallium orthophosphate, for inspection and condition monitoring of high temperature pipelines in power plants at a temperature up to 580°C.
Highlights
Today, a number of power plants (PP) are operating beyond their designed life
The dimensions at 25°C were determined using a digital caliper to an accuracy of 0.01 mm, and for high temperatures (HT) the dimensions were calculated using temperature dependent coefficients of thermal expansion (CTEs) provided in the material datasheet
Same as with the kt factor, the value of d11 = 4.2 pC/N when compared with PZT-5A which shows d11 ≈ 370 pC/N is quite low; the GaPO4 elements showed very stable piezoelectric response far above the upper limitation temperature of PZT piezoelectrics
Summary
A number of power plants (PP) are operating beyond their designed life. Rigorous standards, regulations and codes are in place by regulatory bodies to ensure structural health inspection is carried out periodically during planned outages. Since the inspections are performed during outages, the inspection techniques and technologies used are effective at room temperature. High temperatures (HT) and pressures experienced in these pipelines, can lead to creep, fatigue and corrosion type defects, which if undetected may have catastrophic consequences. For this reason, in situ condition monitoring techniques should be developed to retain reliability and extend the lifetime of aging PP. Advanced ultrasonic techniques, such as Phased Array (PA) can be used to detect defects at room temperature. The key challenge is to develop HT PA probes for continuous monitoring of defect growth over time, so that when the defect reaches a critical size the PP can be shut down and maintenance can take place before failure
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: IOP Conference Series: Materials Science and Engineering
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
