Sizing of cracks embedded in sub-cladding using the ultrasonic synthetic aperture focusing technique (SAFT)

This paper deals with the experimental work carried out to demonstrate the feasibility of the ultrasonic Synthetic Aperture Focusing Technique (SAFT) to obtain improved detection and sizing of vertical/inclined (10ϒ and 15ϒ simulated cracks underneath different claddings. Crack heights ranging from 1.68 mm to 19.04 mm underneath stainless steel, Inconel and ferritic steel cladding were sized with an accuracy of ±0.1 to ±0.3 mm. The problems encountered in TOFD with regard to sizing of near-surface cracks was successfully overcome by SAFT. Mis-oriented (inclined) defects embedded below the cladding suffer added disadvantage for ultrasonic detection due to loss of reflected energy due to mis-orientation. Using SAFT even these defects could be sized accurately.