Author： Sargent J P
Publisher： The British Institute of Non-Destructive Testing
ISSN： 1354-2575
Source： Insight - Non-Destructive Testing and Condition Monitoring, Vol.52, Iss.11, 2010-11, pp. : 609-616
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Abstract
Measurements are described using a portable structural health monitoring (SHM) system for monitoring the weld, heat affected zone (HAZ) and surrounding plate for defects and corrosion in steel plates. This was based on the use of simple, inexpensive surface-mounted transducers and the use of S0 Lamb wave modes. Detection of weld/HAZ defects in beaded welds was performed using weld-guided modes, and a synthetic aperture array system was used for detection of defects both in the plate and in the weld/HAZ. Corrosion defects comprised both simulated machined examples and also real corroded defects introduced via an accelerated test using a salt spray chamber. Detection of simulated discrete areas of corrosion was via the detection of signals reflected directly from the defects and detection of distributed areas of real corrosion was via changes in either transmitted or reflected amplitude from existing reflectors, such as the plate end, or from backscattered signals. It was demonstrated that, with suitable protection, the transducers would survive a hostile accelerated salt spray environment; however, it was also found that measurements of arrival time, as might be used in velocity measurement, were unsuitable for corrosion monitoring because of the changes that occurred due to the protective sealant, transducer or bond line.
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