A digital radiography study of the detectability of simulated cracks in 301 stainless steel

A series of simulated cracks in 301 stainless steel (SS), consisting of slits with depths from 12.8% to 40% of the plate thickness, is fabricated in this study. The examination includes a microfocus X-ray tube and a digital detector array (DDA) with 0.075 mm pixels at three angles of incidence (0°, 5° and 10°). The basis of the methodology for the minimum detectable slit width stems from the noise statistics in the images and a minimum detectable contrast-to-noise ratio (CNR) of 3. These minimum detectable widths range from 0.019 mm to 0.003 mm for 12.8%-deep and 40.0%-deep slits, respectively, for the 0° incidence condition. As the incident angle increases to 10°, the size of the minimum detectable slit width also increases, up to a factor of two for the shallower slits. It is noted that these simulated cracks, which have straight parallel sides and flat bottoms, do not accurately represent natural cracks that have irregular paths and taper at depth. Therefore, the results in this study represent the best scenario for detection, establishing some bounds of crack width detectability.