UT was carried out using shear waves of optimum frequency (4 MHz). During testing it was found that a much higher signal amplitude was obtained from the tight cracks on the shell compared to that found on a flat plate. An attempt was made to explain this higher amplitude in terms of change of reflection angle of the ultrasonic shear waves at the inside surface of the shell due to curvature, change of orientation of crack faces due to rolling, release of tightness of the crack, increase in crack size due to rolling etc.

A theoretical analysis was made to find the change in reflection angle of the ultrasonic shear waves at the inside surface taking the variables like refraction angle in the material, inside and outside diameter of the chamber etc. Effect of the change of orientation of the crack faces in the reflection amplitude was experimentally studied and the same was taken into account for finding the effect of change in reflection angle of the ultrasonic shear waves at the inside surface and the change in the orientation of the crack faces due to rolling on the reflected amplitude from the crack in the shell.

The major contribution to the increase in amplitude could be due to the release of tightness of the crack. The same was estimated by finding the size of a standard notch ultrasonically equivalent to the tight crack in terms of the amplitude response and taking the ratio of their actual areas.

To verify these theoretical estimates and also to find the occurrence of crack growth, if any, during rolling, a rectangular specimen with a tight crack was prepared, rolled to the same diameter and ultrasonic response was taken. The theoretical estimate of the ultrasonic response and the one observed was closely matching. After breaking open the specimen it was found that the crack size did not increase significantly to give rise to a measurable increase in ultrasonic response.

These theoretical estimates could be successfully applied to explain the higher response obtained from the tight crack on the shell of the subscale chamber.