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High Accuracy Ultrasonic Corrosion Monitoring

Permanently installed transducers have improved the precision of ultrasonic inspection by orders of magnitude and provide an accurate non-invasive alternative to other corrosion monitoring methods.

Product Number: 51317--8990-SG
ISBN: 8990 2017 CP
Author: Fangxin Zou
Publication Date: 2017
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$20.00
$20.00

There exist many well-establishedtechniques for corrosion monitoring. These include but are not limited to weight measurements linear polarisation resistance (LPR) measurements and tactile measurements. However all of these approaches are not easy to apply to fluid conduits in the field since they require access to the interiors of components. Also weight measurements and LPR measurements are only capable of determining mass loss rates. The corresponding calculation of wall thickness losses requires integration and the assumption of several parameters such as the area over which the measurement is taking place. Ultrasonic measurements which can be carried out from the exteriors of components are much more field-deployable. It has been demonstrated that by using permanently installed transducers a precision in the order of micro-meters in wall thickness measurements can be achieved. This means that for corrosion rates of the order of 0.1 mm/year a change in wall thickness will only be detectable over the period of a few days. Much shorter response times could allow corrosion mitigation strategies to be implemented more effectively and are therefore desirable. In this paper an optimised ultrasonic setup for wall thickness monitoring will be introduced. Careful maximisation of the signal-to-noise ratio and accurate temperature compensation have allowed us to demonstrate that a repeatability of 40 nm in wall thickness measurements is achievable. This drastically shortens the response times of ultrasonic measurements and enables the detection of corrosion rates of the order of 0.1 mm/year in hours rather than days. The ultrasonic measurements presented in this paper have been verified by the results of optical surface metrology and where possible by predictions based on Faraday’s Law.

Key words: non-destructive evaluation, structural health monitoring, ultrasonic, corrosion

There exist many well-establishedtechniques for corrosion monitoring. These include but are not limited to weight measurements linear polarisation resistance (LPR) measurements and tactile measurements. However all of these approaches are not easy to apply to fluid conduits in the field since they require access to the interiors of components. Also weight measurements and LPR measurements are only capable of determining mass loss rates. The corresponding calculation of wall thickness losses requires integration and the assumption of several parameters such as the area over which the measurement is taking place. Ultrasonic measurements which can be carried out from the exteriors of components are much more field-deployable. It has been demonstrated that by using permanently installed transducers a precision in the order of micro-meters in wall thickness measurements can be achieved. This means that for corrosion rates of the order of 0.1 mm/year a change in wall thickness will only be detectable over the period of a few days. Much shorter response times could allow corrosion mitigation strategies to be implemented more effectively and are therefore desirable. In this paper an optimised ultrasonic setup for wall thickness monitoring will be introduced. Careful maximisation of the signal-to-noise ratio and accurate temperature compensation have allowed us to demonstrate that a repeatability of 40 nm in wall thickness measurements is achievable. This drastically shortens the response times of ultrasonic measurements and enables the detection of corrosion rates of the order of 0.1 mm/year in hours rather than days. The ultrasonic measurements presented in this paper have been verified by the results of optical surface metrology and where possible by predictions based on Faraday’s Law.

Key words: non-destructive evaluation, structural health monitoring, ultrasonic, corrosion

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