Wear Prediction of Steam Generator Tubes due to Shell Side Foreign Objects

A method to evaluate tube wear due to foreign objects on a steam generator tube sheet is introduced. In order to produce the database for the evaluation, a simplified vibration model based on the zonal approach concept and dissected tube model is introduced in this paper. The entire tube sheet region of the steam generator is divided into 30 zones. The data of a representative tube is used in a zone that includes hundreds of tubes. Therefore, the number of tubes analyzed to produce the database is dramatically reduced by the zonal approach concept. The dissected tube model simplifies the mode analysis by adopting a single-span beam instead of a multispan beam idealizing the full-length U-tube of a steam generator. It is shown that the natural frequencies obtained from the dissected model are about 4 to 5% lower than those of the dominant modes between the tube sheet and the first tube support structure obtained from the analysis of the full-length U-tubes. If the concerned region is between the tube sheet and the first tube support structure of the steam generator, using the zonal approach concept and the dissected tube model is very effective to save time and efforts to calculate the vibration data. In this paper, a method to predict the wear depth of the tubes due to the fixed foreign objects on the tube sheet in the secondary side of a steam generator with the simplified vibration model is introduced.