The ET-data collected provide opportunity to search for dynamical behavior of degradation mechanisms and defect themselves to conduct corresponding calculations and to estimate the terms of reliable and non-accidental operation.

Since 1997 in the frames of Lisbon Initiative and BMU Programme (Germany) the up-to-date equipment and technologies have been supplied for Ukrainian NPPs to conduct the ET of steam generators. The Intercontrole and INETEC companies provided training and certification of Ukrainian NPP specialists.

This articles deals with the analysis of trends in degradation mechanism of SG tubing depending on water-chemical regime of secondary circuit. The data collected and presented are based at results of SG tubes testing for 11 Ukrainian NPP units during the 1998 - 1999 years.