NDT System for Metal Components in Concrete Structures

Improved NDT (non-destructive testing) techniques are needed for inspection of concrete structures in nuclear power plants. Steel reinforcements embedded within concrete can corrode and crack, leading to weakening of the structures, and existing NDT techniques do not provide the full picture. Condition assessment is critical in evaluating these structures in order to ensure safe, long-term operation of the plants. The objective of this research effort is to develop and analyze a novel electromagnetic method for the inspection of buried conductive material. This method is based on the eddy current technique but uses magnetic sensors to measure the low frequency electromagnetic field response of the material and flaws. This system will be able to quickly make a qualitative record of the presence and condition of the embedded metallic material. RMD has developed a unique coil-driven, magnetoresistive sensor based probe that can sense the presence of rebar at greater than six inches below the surface. This system has been modeled and optimized to improve the positioning and response of the sensors, and extensive testing has begun using a flexible, arbitrary surface scanner. The probe is capable of detecting breaks and material loss on buried steel in concrete. Our Phase IIA will expand on our Phase II research with several major efforts. We will improve the performance of the sensor and apply new techniques to extend the detection capability of the probe, utilizing the experience we have gained in Phase I and II. We will develop the needed algorithms and software for operating and interpreting the data in a user friendly fashion. Finally we will advance the design to a point where a fully embedded, more capable field deployable prototype that is representative of a commercially viable device can be built and tested. Other activities would include investigating new issues that have come up in Phase II, such as the difficulty in inspecting multiple layers of metal and interference from surrounding magnetic structures. Our technology will reduce the cost and time required for inspection at nuclear power plants by providing more reliable results and decreasing costly downtime for in-service inspections. Finally, our technology could provide an important new source of critical information to advance the science of remaining life prediction and predictive maintenance for concrete structures. In addition to safer nuclear power, the public will benefit from new NDT technology for safer roads, bridges, buildings and other concrete structures.