Development of Eddy-Current Probes for the Evaluation of Magnetite in the Support-Plate Crevices of Nuclear Steam Generators

Eddy current technique has played an important role in the understanding of the corrosion behavior of steam generator components. Until recently, its role has been primarily in the evaluation of the condition of the heat exchanger tubes. Recent developments have led to the use of this technique for detecting corrosion of the carbon steel plates supporting the tubes. The detection and quantification of possible accumulation of corrosion products such as magnetite in the crevices between tubes and supports may often be a desired objective of such inspections since the presence of such deposits is of interest with respect to tube denting and other corrosion phenomena. This paper discusses the difficulty of an unambiguous determination of the presence of magnetite in the tube support crevices and points to the difficulty of obtaining a quantitative estimate for the amount of magnetite which may be present. This paper further discusses the development of new probes which provide improved discrimination between magnetite and a steel support thqs providing for a better estimate of the amount of magnetite in tube support crevices.