Intergranular attack of alloy 600: Simulation and remedial action tests: Final report
The intergranular attack (IGA) that affects alloy 600 tubes in the tube sheet crevices of PWR steam generators is hard to simulate in laboratory studies. For this study, a special apparatus was designed with a range of representative materials, mechanical conditions and geometry. The design also took account of sludge piles, thermal fluxes and water chemistry. During a first series of seven model boiler tests, chemical parameters and test procedures were adjusted to finally obtain a field prototypical degradation of tubing over a significant length within the tube sheet crevice for the case of caustic pollution. IGA was not produced for the river water in-leakage case. A second series of model boiler tests also showed the possibility of producing a representative IGA by initially filling the tube sheet crevices with concentrated caustic solutions. A third series of five model boiler tests aimed at studying in the effectiveness of remedial actions on either virgin of IGA affected tubing. Tube sheet crevice flushing operations using the natural circulation procedure showed a poor efficiency for moving concentrated contaminants, but they succeeded in forcing chemicals additives (acetic acid or boric acid) within the non-occluded portions of crevices. This off-line treatment resulted in a reduction in the progression rate of the pre-existing IGA by a factor of 2 to 3. Simulation of this treatment on virgin material showed that this result was obtained because acetate or borate shifted the cation-to-anion equivalent ratio to well under one. However this off-line treatment could not prevent the occurrence of intergranular stress corrosion cracking (IGSCC) near the top of crevices, since caustic continued to hideout under full power operation. The best remedial action consisted of a combination of off-line and on-line boric acid treatment. IGSCC was prevented both on virgin and IGA affected tubes. 3 figs., 3 tabs.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (USA); CEA Centre d'Etudes Nucleaires de Fontenay-aux-Roses, 92 (France). Section d'Etude de la Corrosion Aqueuse; Framatome, 92 - Paris La Defense (France)
- OSTI ID:
- 6162879
- Report Number(s):
- EPRI-NP-6115-M
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
INCONEL 600
CORROSION
PWR TYPE REACTORS
STEAM GENERATORS
BORIC ACID
CORROSION INHIBITORS
CREVICE CORROSION
ELECTROCHEMISTRY
INTERGRANULAR CORROSION
PROGRESS REPORT
SLUDGES
STRESS CORROSION
ALLOY-NI76CR15FE8
ALLOYS
ALUMINIUM ADDITIONS
ALUMINIUM ALLOYS
BOILERS
CHEMICAL REACTIONS
CHEMISTRY
CHROMIUM ALLOYS
CORROSION RESISTANT ALLOYS
DOCUMENT TYPES
HEAT RESISTANT MATERIALS
HEAT RESISTING ALLOYS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
IRON ALLOYS
MATERIALS
NICKEL ALLOYS
NICKEL BASE ALLOYS
NIMONIC
NIOBIUM ALLOYS
REACTORS
TITANIUM ADDITIONS
TITANIUM ALLOYS
VAPOR GENERATORS
WATER COOLED REACTORS
WATER MODERATED REACTORS
210200* - Power Reactors
Nonbreeding
Light-Water Moderated
Nonboiling Water Cooled
360105 - Metals & Alloys- Corrosion & Erosion