An ultrasonic inspection apparatus is newly developed to detect internal flaws behind the surface of the actual marine propeller blade.

An ultrasonic transducer scans automatically on required area of a blade. If ultrasonic sound waves are bounced from internal flaws, echo signals are plotted on a X-Y recorder obtaining C-scope patterns. The system also has B-scope display to indicate the depth to the flaws.

Voids tears-cracks or clusters of these flaws having cross sections larger than 2mm2 are detectable. This nondestructive testing method is applicable to marine propellers made of Ni-Al bronze, but not to propellers made of Mn bronze because of extremely high attenuation of sound waves.

The report includes some detection examples of actual flaws showing fairly good agreement between actual size of flaw and that of detected results.

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