An Automated System for Analysis of the Surface Topography of Fretted U-Bend Steam Generator Tubes

Abstract

Physical measurement and analysis of the fretting scar geometry on tubes removed from operating steam generators provide valuable information regarding the tube orbital motion, and other in-service conditions, namely, misalignment, and eccentricity. This type of information is required to justify the assumptions made in the finite element impact simulation analysis and to qualify NDT techniques. An automated surface scanning and analysis system has been developed at the Fretting Laboratory, Ontario Hydro Technologies, to determine the maximum depth and volume of the fretting scars on steam generator tubes. To define the true shape and topography of the fret mark, the analysis accounts for the unknown curvature of the U-bend section, and the ovality of the tube cross section. A description of the measurement system and the formulation of the analysis are presented in this paper. An error analysis for the effect of the measurement uncertainties is also given. Examples of the three-dimensional maps of the topography of fretted samples are presented to demonstrate the accuracy of de-trending the curvilinear surface of the U-bend tube.