Measurements of the Extension of the Magnetite Piles on Steam Generator Tubing with Eddy Current Techniques

Eddy current method is the main method in the nuclear power plant in-service inspections to inspect the integrity of the steam generator tubing. The method has high inspection speed and it is sensitive to both inner surface and outer surface defects. The applied inspection techniques are based on the use of bobbing probes. During operation of the pressurized water reactor magnetite deposits precipitate on the outer surfaces of the steam generator tubing. After deposits have grown thick enough, the deposits peel as flakes from the surface of the tubes. These magnetite flakes can form magnetite piles. In this study experiments were conducted to detect the extension of the magnetite piles. For this purpose a simple mock-up simulating the horizontal steam generator tubing with parallel horizontal tubes was constructed. Piles of magnetite flakes were heaped up between the tubes. In the tests a single bobbin probe and a novel two-probe technique was used. The goal of the experiment was to study the eddy current signal on different piles of magnetite in order to map the existence and location of the magnetite piles within the steam generator tubing. The conducted experiments showed that the existence of the magnetic piles can be detected with the applied techniques. The results of the experiments are presented.