1. Wavelet transform-based approach for processing ultrasonic B-scan images.
- Author
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Sharma, G. K., Bhagi, S., Thirunavukkarasu, S., and Rao, B. P.
- Subjects
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STEEL pipe , *WAVELET transforms , *ULTRASONIC imaging , *CRYSTAL grain boundaries , *SIGNAL processing - Abstract
The attenuation of ultrasound beams in coarse-grained austenitic stainless steels due to grain boundary scattering influences flaw detection and sizing. This paper presents an approach for processing ultrasonic B-scan images of thick coarse-grained austenitic stainless steel parts using a discrete wavelet transform (DWT) technique. In this approach, DWT processing of A-scan signals obtained during B-scan imaging is performed to reduce the noise caused by grain boundary scattering. The Daubechies (db8) mother wavelet with decomposition level 5 is found to be optimum for this purpose. Experimental studies are carried out on coarse-grained stainless steel specimens having flaws machined at different depths. These studies reveal that the proposed approach results in an improvement of more than 13 dB in signalto-noise ratio, as compared to two-dimensional DWT processing of the original B-scan image using the same wavelet and decomposition level. Furthermore, the proposed approach produces a smaller number of artefacts than the twodimensional DWT technique. The studies reveal that by using the proposed approach it is possible to detect flat-bottomed holes located at 40 mm below the surface of a 50 mm-thick stainless steel part with a grain size of 200 µm at normal incidence. The proposed approach is fast and attractive for online implementation. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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