Alkaline intergranular corrosion and stress corrosion cracking of Alloy 600
- Sumitomo Metal Industries Ltd., Amagasaki, Hyogo (Japan). Corporate Research and Development Labs.
Intergranular corrosion (IGC), often termed IGA, and intergranular stress corrosion cracking (IGSCC) have continued to occur on mill-annealed (MA) Alloy 600 tubing in the secondary side of steam generators, which are still serious corrosion instances in operating pressurized water reactors. The IGC and IGSCC phenomena have occurred on MA Alloy 600 at the crevice between the tube and tube support plate, in which a high concentration of caustic solution is formed under dry and wet conditions at high temperature. A review of technical articles has been performed concerning environmental and metallurgical factors affecting the IGC and IGSCC, and their mechanistic aspects. A combination of IGC and IGSCC, one of the most common modes of corrosion on the secondary side of steam generators, occurs in a specific potential region, at the active-passive transition potential, in a concentrated caustic solution at elevated temperature. The anodic dissolution of Alloy 600 increases as the temperature of caustic solutions is increased. The corrosion rate for each constituent of Alloy 600 such as nickel, chromium, iron or chromium carbide is influenced differently by temperature, resulting in various effects on the characteristics of corrosion protective surface films. Increase in chromium content and thermal treatment at 700 C are beneficial for IGC and IGSCC resistance. IGC is intergranular corrosion, and IGSCC is initiated above a critical applied stress. Grain boundary chromium carbides such as Cr{sub 7}C{sub 3} and Cr{sub 23}C{sub 6} have been formed to increase resistance to IGC and IGSCC. Several theories have been proposed concerning the roles of chromium carbides at grain boundaries. Some specific theories are focused on in this paper with supporting data.
- OSTI ID:
- 409738
- Report Number(s):
- CONF-9510292-; ISBN 1-57570-008-4; TRN: 97:000740
- Resource Relation:
- Conference: Improving the understanding and control of corrosion on the secondary side of steam generators, Airlie, VA (United States), 9-13 Oct 1995; Other Information: PBD: 1996; Related Information: Is Part Of Control of corrosion on the secondary side of steam generators. Proceedings; Staehle, R.W. [ed.] [Univ. of Minnesota, Minneapolis, MN (United States)]; Gorman, J.A. [ed.] [Dominion Engineering, McLean, VA (United States)]; McIlree, A.R. [ed.] [Electric Power Research Inst., Palo Alto, CA (United States)]; PB: 814 p.
- Country of Publication:
- United States
- Language:
- English
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