Characterization of wear scars on fretted U-bend steam generator tubes

The fretting scar geometry at the contact between the steam generator (SG) U-bend tube and the offset scallop bar support is analyzed to establish the relationship between the scar geometric characteristics and the operating conditions; namely, the tube orbital motion, alignment, axial motion, scar depth and scar volume. The fretting wear scars of two U-bend SG tubes removed from an operating CANDU nuclear steam generator were examined to determine various operating conditions at the tube/tube support interface. This information, which cannot be measured in-situ, is needed to justify assumptions used in numerical modelling of the tube/support dynamic interaction. To relate field measurements to laboratory-generated data base and code predictions, the relationship between the maximum wear depth and volumetric wear losses is investigated. The wide scatter in the variation of the average wear depth with the scar volume is significantly reduced by using a proposed weighted-average. 7 refs., 8 figs., 1 tab