There have been a radiographic inspection and an ultrasonic inspection as the volumetric inslection, however, the radiographic inspection method would be limited to utilize in the case of complicated structure and thick materials from the reasons that a sheet of film has to be set oppositely to radiation source sandwiching the portion to be examined and also because of its less detectability to defects than ultrasonic inspection for thick materials.

Accordingly, the ultrasonic inspection method can be expected to have a potential ability to inspection for small size diameter piping weldment and pipe branch connection. From the considerations mentioned above, we have set the objective of the investigation to developing a technique applicable to complicated structure such as weldments concerned here along the ultrasonic technique.

The sysytem developed is equiped with two transducers of 2.25MHz (longitudinal wave) arranged for ultrasonic beam to travel along V-path able to detect subsurface defects which can not be detected by conventional angle beam technique. We have utilized this system to inspect the mock-up specimens with seven drilled hole of 2.4 mm in diameter located at different depths and with different orientations and confirmed the potential detectability of defects concerned by detecting all these artificial defects.

In the course of this investigation, we have improved the scanner of the system with precise movement and developed an image processor to display the defects examined as image on a liquid-crystal screen simultaneously on testing. The ability of this system in field inspection has been verified also.