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Development of EMAT and piezoelectric transducers for high temperature ultrasonic thickness measurements
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Lunn, Natasha (2018) Development of EMAT and piezoelectric transducers for high temperature ultrasonic thickness measurements. PhD thesis, University of Warwick.
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WRAP_Theses_Lunn_2018.pdf - Submitted Version - Requires a PDF viewer. Download (22Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b3452877~S15
Abstract
Improving reliability of components operating at high temperature, such as pipelines, boilers and reactors, within a range of industries is of importance in the asset management process. This thesis concerns the development and testing of ultrasound transducers for use at elevated temperatures, up to 500 _C, without the use of active cooling. Ultrasound thickness measurement applications employing these high temperature transducers includes both portable-type non-destructive testing (NDT) inspections and permanent condition monitoring, primarily towards detection of corrosion and erosion.
The development and optimisation of an electromagnetic acoustic transducer (EMAT) design which generates and detects bulk radially polarised shear waves utilising a high temperature permanent magnet and a ceramic encapsulated spiral coil is discussed. This design was optimised for use on magnetite coated mild steel samples; it was shown that the magnetostriction mechanism tends to dominate, depending upon sample properties, producing large signals even at elevated temperatures. High temperature laboratory trials (up to 500 oC) demonstrated the non-linear change in signal amplitude with increasing temperature on magnetite coated mild steel samples, attributed to the complex non-linear relationship between magnetostrictive strains and applied external magnetic field. The EMAT provided good signal amplitude, even at relatively large sample-EMAT lift-off (up to 8.0 mm), demonstrating the applicability of this EMAT for high temperature scanning inspections. A longterm industrial field trial on a high temperature pipeline (≈ 350 oC) in a refinery exhibited the suitability of this design for high temperature continuous monitoring applications.
A piezoelectric transducer with a novel compression-type design was optimised for application at high temperature, with the use of a waveguide, high temperature piezoelectric element and high temperature backing material; the optimisation of these components is discussed. This transducer design incorporates compression applied via a central bolt, to achieve acoustic coupling between the components, avoiding the use of adhesive layers, to generate bulk longitudinal waves. With the application of a bismuth titanate piezoelectric element, the transducer was able to generate signals on stainless steel whilst withstanding high temperatures (up to 500 oC) continuously without cooling.
| Item Type: | Thesis (PhD) | ||||
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| Subjects: | Q Science > QE Geology T Technology > TJ Mechanical engineering and machinery T Technology > TK Electrical engineering. Electronics Nuclear engineering |
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| Library of Congress Subject Headings (LCSH): | Piezoelectric transducers, Transducers, Ultrasonics, Shear waves | ||||
| Official Date: | September 2018 | ||||
| Dates: |
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| Institution: | University of Warwick | ||||
| Theses Department: | Department of Physics | ||||
| Thesis Type: | PhD | ||||
| Publication Status: | Unpublished | ||||
| Format of File: | |||||
| Extent: | xxx, 227 leaves : illustrations, charts | ||||
| Language: | eng |
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