Detection of magnetite piles on steam generator tubing with eddy current method

The magnetite deposits and deposit piles on the secondary circuit of the steam generator tubing are detected with eddy current method in in-service inspections. The volume of the detected deposit pile is not evaluated. In many cases the growing defects are located at the same area as the magnetite deposit piles. For this reason it is important to locate and to size the piles of magnetite on the steam generator tubing. In this study experiments were conducted by using eddy current method using bobbin probe techniques and small mock-up simulating the horizontal steam generator tubing. The goal of the experiment was to size the thickness of magnetite piles under and around the test tubes. The results of low frequency tests showed that the thickness of magnetite layer under the steam generator tube can be measured up to 11 mm. The results of the tests showed also that in more general case, where the tube is embedded into unsymmetrical pile, the pile thickness cannot be measured using ordinary single probe technique.