For detecting fine, tight cracks oriented perpendicular to the X-ray beam in a thick weld, why might radiographic testing be less effective than ultrasonic testing?

Radiographic testing (RT) relies on the principle that X-rays pass through an object, and variations in material thickness or density cause different amounts of X-ray absorption, creating an image (radiograph). To detect a discontinuity like a crack using RT, there must be a significant change in the material’s effective thickness or density along the path of the X-ray beam. When a fine, tight crack is oriented perpendicular to the X-ray beam, the X-rays primarily encounter the crack along its minimal thickness. Because the crack is “fine” and “tight,” meaning there is very little material separation, the actual path length difference through the material with the crack versus without it is extremely small. This negligible difference in X-ray absorption results in very poor contrast on the radi....