The Effect of Water Chemistry on the Reliability of Modern Large Steam Turbines

The results of a survey of 50 once-through steam generators and 60 drum boiler steam supplies for modern large steam turbines are presented in this paper. A questionnaire was circulated and the information gathered was used to assess current industry practices related to feedwater treatment, boilerwater chemistry and steam purity measurements. Further information was gained by visiting 28 of the surveyed power plants and developing more information concerning their water chemistry practices. The results of the survey and visitation information are then related to individual cases of major corrosion damage that have occurred in the turbines of the participating utilities: The once-through steam generators provide the best measure of steam purity because, in general, the steam purity is equal to the feedwater purity. Major corrosion damage, in many instances stress corrosion cracking, appears to be related to upset conditions of steam purity and water chemistry.