PREDICTION OF FAILURES OF LOW-PRESSURE STEAM-TURBINE DISKS

Localized corrosion phenomena, including pitting corrosion, stress cor rosion cracking, and corrosion fatigue, are the principal causes of co rrosion-induced damage in electric power-generating facilities and typ ically result in more than 50 percent of the unscheduled outages. In t his paper, lye describe a deterministic method for predicting localize d corrosion damage in low-pressure steam turbine disks downstream of t he Wilson line, where a condensed, thin electrolyte layer exists on th e steel disk surfaces. Our calculations show that the initiation and p ropagation of stress corrosion cracking (SCC) is not very sensitive to the oxygen content of the steam, but is sensitive to the conductivity of the condensed liquid layer and the stresses ( residual and operati onal) that the disk experiences in service.