Prediction of Failures of Low-Pressure Steam Turbine Disks

Abstract

Localized corrosion phenomena, including pitting corrosion, stress corrosion cracking, and corrosion fatigue, are the principal causes of corrosion-induced damage in electric power-generating facilities and typically result in more than 50 percent of the unscheduled outages. In this paper, we describe a deterministic method for predicting localized corrosion damage in low-pressure steam turbine disks downstream of the Wilson line, where a condensed, thin electrolyte layer exists on the steel disk surfaces. Our calculations show that the initiation and propagation 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 operational) that the disk experiences in service.