Investigation of Conformable Eddy Current Probes for Inspection of Complex Geometry Structures, 18-R8094

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Principal Investigators
Gary L. Burkhardt
Jay L. Fisher

Inclusive Dates:  08/01/09 – 12/01/09

Background - The reactor pressure vessel of a pressurized water nuclear reactor contains dozens of cylindrical penetrations for the control-rod drive mechanisms (CRDMs) and in-core monitoring mechanisms. The penetrations are welded at the intersection with the inside surface of the upper and lower heads with a dissimilar-metal J-groove weld. The Nuclear Regulatory Commission is now requiring nondestructive inspection of the J-groove weld and adjacent surfaces. To inspect the complex-geometry J-groove weld region, flexible eddy current probes based on printed circuit board (PCB) technology could provide a low-cost approach that is more attractive and effective than conventional wire-coil probes.

Approach - PCB coils were fabricated that could be configured so that different arrangements and modes could be evaluated to determine flaw detectability in the presence of inspection surface geometry variations. The probes evaluated included absolute and driver-pickup coil arrangements, as well as a new "orthogonal-axis" probe that simulates a previous SwRI design using conventional wire-wound coils with driver and pickup axes oriented orthogonal to each other. The probes were evaluated on samples containing geometry representative of the J-groove weld area, as well as on samples having simulated cracks.

Accomplishments - Project results demonstrated that flexible ECT probes can be readily manufactured using conventional flexible PCB technology, resulting in low manufacturing cost and consistent electromagnetic characteristics. The probes are adaptable to the variation in geometry expected in J-groove welds in CRDM penetrations and other applications such as header-to-tube welds in fossil power plants. Flaws are readily detected with minimal geometry response. The project provided data, know-how, and potentially patentable intellectual property that will be valuable in developing and manufacturing inspection systems and probes. A contract with the Electric Power Research Institute to develop a flexible probe array for header welds resulted from this project.

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