Effect of sulfur bearing residues from chemical cleaning on alloy 600

This paper summarizes the results of EPRI Project S305-9, a side-effects evaluation dealing with the sulfur residue that remains on steam generator surfaces after chemical cleaning and its potential for causing tube damage. This investigation was directed toward assessing the residue effects of the generic process for cleaning steam generators. To accomplish this effort, a wide range of faulted and nonfaulted conditions of Alloy 600 tubing were exposed to the generic cleaning process in order to establish representative residues on representative specimens. Metallurgical analysis techniques were then used to characterize the residue (with emphasis on sulfur) as to its chemical state and morphology. Select specimens were assessed for the effects of unremoved residue during extended secondary-side Steam Generator Owners Group (SGOG) guideline and worst-case layup conditions, followed by SGOG guidelines and worst-case operational conditions. The worst-case layup condition consisted mainly of extended air exposure with otherwise guideline chemistry. The worst-case operational condition consisted of higher contaminant levels of chloride and sulfate than guideline chemistry