We developed a pitch-catch system based on electromagnetic acoustic transducers (EMATs) for pipe inspection, which moves inside the pipe in the axial direction. The first higher mode, T(0,2), of the torsional guided wave is transmitted and detected, and variations of amplitude and phase are measured while moving the EMATs. Several aluminum pipes containing dish-shaped defects are inspected, and the amplitude and phase show enough detection sensitivity. It is found that the phase measurement has better potential as a tool for quantitative inspection. The applicability of the technique for steel pipe is also confirmed.
A systematic study of the electron impact 3 2 D excitation of lithium, sodium and potassium from their ground states is considered in distorted-wave approximation theory. Results for differential and integrated cross sections, alignment, orientation and spin asymmetry parameters in the energy range 10-100 eV are calculated and presented. Our integrated cross section results show good agreement when compared with other theories and available experiments. Present differential cross section results for sodium are also compared with the only available recent differential cross section measurements. For the sake of further meaningful comparison and discussions, the first Born calculations for the cross sections are also performed and compared.
The group velocity of each higher torsional mode in a pipe depends on the wall thickness and it will convert to a lower mode when the thickness is smaller than a critical value, the so-called cut-off thickness. The fundamental torsional mode, T(0,1), and the first higher mode, T(0,2), are generated in pipes by an electromagnetic acoustic transducer (EMAT) and their mode conversion behaviors are investigated by changing the shape of a defect on the pipe. It is confirmed that the conversion behavior is sensitive to the shape of thickness transition and the total reflection of the T(0,2) mode occurs in a pipe with a tapered defect. On the basis of the mode conversion, defects with a cross-sectional loss larger than 35% are detectable.
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