Pitting of steam-generator tubing alloys in solutions containing thiosulfate and sulfate or chloride

The pitting of nuclear steam generator tubing alloys 600, 690 and 800 was studied at 60 °C using dilute thiosulfate solutions containing excess sulfate or (for Alloy 600) chloride. A potentiostatic scratch method was used. In sulfate solutions, all alloys pitted at low potentials, reflecting their l...

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Bibliographic Details
Published in:Faraday discussions 2015-01, Vol.18, p.233-249
Main Authors: Zhang, William, Carcea, Anatolie G, Newman, Roger C
Format: Article
Language:English
Subjects:
Alloys
Anions
Charging
Chlorides
Electromigration
Molybdenum base alloys
Nuclei
Sulfates
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Summary:The pitting of nuclear steam generator tubing alloys 600, 690 and 800 was studied at 60 °C using dilute thiosulfate solutions containing excess sulfate or (for Alloy 600) chloride. A potentiostatic scratch method was used. In sulfate solutions, all alloys pitted at low potentials, reflecting their lack of protective Mo. The alloys demonstrated the most severe pitting at a sulfate : thiosulfate concentration ratio of ∼40. Alloy 600 pitted worst at a chloride : thiosulfate ratio of ∼2000. The results are interpreted through the mutual electromigration of differently charged anions into a pit nucleus, and differences in the major alloy component.
ISSN:1359-6640
1364-5498
DOI:10.1039/c5fd00008d