| 摘要 |
<p>An improved method for defect detectability for inspection of liquid filled pipes using magnetostrictive sensors. The improved method comprises first recognizing liquid-induced changes in the dispersion properties of the second longitudinal wave mode, L(0,2). These liquid-induced changes include a severe dispersion (42) at periodic branching frequencies that result in a pulse-like characteristic in the extended received signal (80). A trailing portion (52) of a received signal component (48) associated with a geometric irregularity, is shown to comprise the branching frequency components. The trailing portion of the extended signal may therefore be removed in order to improve defect detection. The removal process comprises one of three alternative methods. A first method includes creating a short pulse free of the frequencies that comprise the trailing signals. A second method comprises transmitting a broadband signal and processing the detected signal (10) through a filter that eliminates those frequencies known to comprise the trailing signals. A third method involves using a signal whose bandwidth lies in the region between two adjacent branching frequencies in the dispersion curve (40). The result is a detected signal within which components representative of irregularities are less extended and therefore less likely to override subsequent defect components in the detected signal.</p> |
