Effect of boric acid on intergranular corrosion and on hideout return efficiency of sodium in the tube support plate crevices
- Electric Power Research Inst., Palo Alto, CA (United States)
- Commissariat a l`Energie Atomique, St. Paul Lez Durance (France)
- Electricite de France, St. Denis (France)
Sodium hydroxide is one of the main causes of intergranular attack/stress corrosion cracking (IGA/SCC) of alloy 600 steam generator (S.G.) tubes. Boric acid appears to be one of the possible remedies for intergranular corrosion process inhibition. In order to obtain data on boric acid injection efficiency, an experimental program was performed on previously corroded tubes. To prevent premature tube wall cracking, samples were sleeved on alloy 690 tubes. The objective of the tests was to evaluate, on a statistically valid number of samples, the effectiveness of boric acid and tube sleeving as possible remedies for IGA/SCC extension. Another independent experimental program was initiated to determine the hideout return efficiency in the tube support plate (TSP) and tubesheet (TS) crevices after a significant duration ({<=} 180 hours) of sodium hideout. The main objective of the first tests being a statistical evaluation of the efficiency of boric acid treatment, was not achieved. The tests did demonstrate that sleeving effectively reduces IGA/SCC growth. In an additional program, cracks were obtained on highly susceptible tubes when specimens were not sleeved. The companion tests performed in the same conditions but with an addition of boric acid did not show any IGA or cracks. These results seem to demonstrate the possible effect of boric acid in preventing the corrosion process. Results of the second tests did not demonstrate any difference in the amount of sodium piled up in the crevices before and after boric acid injection. They however showed an increase of the hideout return efficiency at the tube support plate level from 78 % without boric acid to 95 % when boric acid is present in the feed water.
- OSTI ID:
- 203816
- Report Number(s):
- CONF-950816--; ISBN 1-877914-95-9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
BORIC ACID
CORROSION INHIBITORS
CORROSION PROTECTION
CORROSIVE EFFECTS
CRACK PROPAGATION
EXPERIMENTAL DATA
INCONEL 600
INCONEL 690
INTERGRANULAR CORROSION
PERFORMANCE
PWR TYPE REACTORS
SECONDARY COOLANT CIRCUITS
SLEEVES
STEAM GENERATORS
STRESS CORROSION
TUBES