Abstract
Laboratory tests and supporting finite element predictions of the interaction of Lamb waves with typical features found in chemical plant pipework are reported. The L(0, 2) mode is an attractive mode to use for long-range (> 15 m) propagation in 2–12 inch (51–305 mm) nominal bore pipes and the behaviour of this mode has been studied using a bonded piezoelectric transducer system. The amplitude of the reflection from butt welds and welded supports was found to be between 5 and 20 per cent of the incident amplitude, while flanges gave almost 100 per cent reflection. It is therefore not possible to test past a flange. It has been shown that wet or dry insulation has little effect on the propagation of the L(0, 2) mode, so inspection under insulation is feasible. Initial work on the reflections from defects is also reported. It has been shown that when the axial extent of the defect is significantly less than a wavelength of the L(0, 2) mode (about 80 mm at 70 kHz), the reflectivity is largely a function of the depth and circumferential extent of the defect. The reflections from notches, troughs and corrosion patches have been detected successfully.
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