Some Adverse Effects of Stress Corrosion in Steam Turbines

The performance and reliability of a steam turbine can be seriously impaired by the admission of steam of unacceptable quality. Of particular concern are contaminants such as caustic, chlorides, and sulfides which can promote the occurrence of corrosion attack and stress corrosion cracking. Critical flaw size growth from cracks initiated by the stress corrosion mechanism can result in brittle-type failure. The importance of stress corrosion as one of the failure mechanisms responsible for turbine outages indicates the need for some understanding of the essential aspects of this phenomenon. The metallurgical aspects of stress corrosion cracking, field experiences with turbine components in aggressive steam environments and results of a study of turbine-material behavior in caustic and sulfide environments are discussed. Field experiences discussed are limited to fossil-fueled industrial and small utility turbines. To further emphasize the serious consequences of stress corrosion failures, typical turbine outage times based on our experience are discussed.