Residual Life Assessment of Steam Generators With Alloy 600TT Tubing: Methods and Application

The aim of the paper is to introduce methods to estimate the residual life of steam generators with alloy 600TT (thermally treated) tubing, taking into account PWSCC as the main contributor damage. The methods take into account both initiation and propagation of PWSCC cracks in the expansion transition zone of SG tubes, as well as the state of damage (cracking and plugging) of the tube bundle, at a given time, known from inspection results. A probabilistic model is used to treat initiation, while propagation stage is treated in a deterministic way based on inspection data. After introducing the methods used to assess the residual life, a brief parametric study will be shown, to illustrate the effects of initiation versus propagation. Eventually, the cases of a few actual steam generators with tubing made of alloy 600TT, showing different situations of present damage and damage evolution rates will be presented.