Intergranular corrosion mechanisms of alloy 600: Final report
Some sections of alloy 600 steam generator tubes were cut in order to perform various analyses on samples that had undergone Intergranular Attack (IGA) or Intergranular Stress Corrosion Cracking (IGSCC). Micrographs of polished cross sections were taken showing in some cases intergranular penetrations of more than 200 micrometers (16% of wall thickness). Electron microprobe analyses on these samples indicated a decrease in chromium, nickel and iron concentration at the corroded grain boundaries as well as the presence of oxygen, sulfur and sodium in the same areas. Direct examinations and analyses of corroded grain surfaces were also carried out by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The SEM examination of these intergranular surfaces showed the presence of a thin layer partially covering the IGA and IGSCC grains. This layer has not been fully characterized but AES analyses indicated the presence of oxygen, silicon and sulfur. Autoclave tests were also carried out on alloy 600 heats in pure NaOH and in NaOH + Na/sub 2/SO/sub 4/ solutions at 350/sup 0/C with an overpressure of hydrogen. The aim of these experiments was to clarify the influence of impurities (in the alloy and in the solution) on IGA processes. These experiments were performed using tube sections and coupons of commercial grade alloy 600, both stressed and unstressed, and U-bend for the high purity specimen. Chromium sesquioxide was also added to the testing solution in some cases. The results of these tests showed that in pure caustic solution IGA had occured only on the stressed samples, and was enhanced by the presence of sodium sulfate and chromium sesquioxide.
- 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
- OSTI ID:
- 6144256
- Report Number(s):
- EPRI-NP-5396; ON: TI87920577
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
220200* -- Nuclear Reactor Technology-- Components & Accessories
36 MATERIALS SCIENCE
360103 -- Metals & Alloys-- Mechanical Properties
360105 -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
AUGER ELECTRON SPECTROSCOPY
BOILERS
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISTRY
CHROMIUM ALLOYS
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
CORROSION
CORROSION INHIBITORS
CRACK PROPAGATION
CRACKS
ELECTRON MICROSCOPY
ELECTRON SPECTROSCOPY
INCONEL 600
INCONEL ALLOYS
INTERGRANULAR CORROSION
IRON ALLOYS
MICROSCOPY
NICKEL ALLOYS
NICKEL BASE ALLOYS
NIOBIUM ALLOYS
NUCLEAR FACILITIES
NUCLEAR POWER PLANTS
OXIDES
OXYGEN COMPOUNDS
PHOTOGRAPHY
PHOTOMICROGRAPHY
POWER PLANTS
SCANNING ELECTRON MICROSCOPY
SPECTROSCOPY
STEAM GENERATORS
STRESS CORROSION
THERMAL POWER PLANTS
TRANSITION ELEMENT COMPOUNDS
TUBES
VAPOR GENERATORS
WATER CHEMISTRY