We use 4 transducers and inspect a dovetail using pulse-echo method from 4 directions at the same time, furthermore we can take 2 ways of pitch-catch method. We turn the rotor after setting the scanner on it and we can inspect a stage 360 degrees continuously. We evaluate the result using a B-scope, the indication patterns from a crack and rust or pitting are different.

We made some artificial cracks at dovetail and carried out the experiment using the new UT instrument. The main result is shown as follows:

(1) The detectable minimum size is getting much smaller than usual method.

(2) We can discriminate between the indication from a crack and that from rust or pitting.

(3) We can know if the detected crack is equal or bigger than the first hook or not.

(4) We can make the testing time short.