Applying a three-dimensional submersible VT unit in inspecting pool lining

The liner for a site bunker pool for storing solid wastes has been used in a relatively favorable environment. Since it is intended for use over a long period of time, however, the liner has been inspected mainly on the surface of weld beads for the purpose of protective maintenance. In the conventional inspection with a submersible TV camera, it was difficult to quantitatively determine whether a doubtful portion, if any, could be deemed as a defect. Using a three-dimensional submersible VT unit capable of quantitatively measuring the shape of a weldment on the surface, including the conventional inspection technique, the authors actually inspected the liner. In addition, an ECT (Eddy Current flow-detection Test) unit was also jointly employed, which was capable of taking measurements depthwise. This report deals with the principles and configuration of the three-dimensional submersible VT unit, including the findings respecting its on-equipment application. (author)