darkbarly
x-ray is the least favorable method to detect damage in composite structure. It is OK to find water ingress in honeycomb sandwich, but useless to find delamination in more or less flat panels. You have to use x-ray in the same plane as the delamination to see it, but normally you are just able to apply x-ray perpendicular to the surface. As long as no contamination has filled the delaminated area, you will see nothing. If you are looking for delaminations close to metallic bushings, they will hide the damage due to the high x-ray absorption of metals compared to composite.
Ultrasonic is most effective for inspecting monolithic composite structure for delaminations.
To give a simple statement, you could say : If the damage is large enough to be harmful, it can be found by visual inspection and tap testing. If you need ultrasonic or x-ray to detect it, it is most probably not dangerous at the moment.