Production of eddy-current standards for caustic intergranular corrosion: Final report

Technical Report · Wed Apr 01 04:00:00 EST 1987

OSTI ID:6771727

Miglin, B P

A laboratory test was conducted to produce caustic intergranular attack (IGA) on the outside diameter (OD) surfaces of Alloy 600 and Alloy 690 nuclear steam generator sized tubing. Twelve 3-meter long tubes - eleven tubes of Alloy 600 and one of Alloy 690 - were exposed for up to 6045 hours in a solution of 50% caustic + 12% Na/sub 2/CO/sub 3/ at 343/sup 0/C. Most of the tubing was in the mill-annealed condition although tubes in the thermally-treated and stress-relieved conditions were also included. Depth of IGA penetration was determined by destructive metallurgical examination on several representative cross sections per tube. Other tasks within this project were aimed at both accelerating and retarding the rate of IGA. Surface modifications such as grit blasting the OD surface with magnetite, alumina, or steel shot did not accelerate IGA. Data were obtained which showed that 15% boric acid added to 10% NaOH retarded the rate of stress corrosion cracking (SCC) of Alloy 600 at 288/sup 0/C. Forty-day IGA tests of Alloy 600 in 10% NaOH at 343/sup 0/C with and without 15% boric acid were inconclusive. The IGA rate of mill-annealed Alloy 600 was found to be best described by a power law with a time to the 0.60 to 0.63 power dependence. The rate of attack for thermally-treated Alloy 690 was about the same as that of thermally-treated Alloy 600, but slower than the mill-annealed condition of Alloy 600. Alloy 600 suffered volumetric IGA while the corrosion morphology of Alloy 690 was a mixture of volumetric IGA and general attack.

• Research Organization: Babcock and Wilcox Co., Alliance, OH (USA). Research and Development Div.; Electric Power Research Inst., Palo Alto, CA (USA)
• OSTI ID: 6771727
• Report Number(s): EPRI-NP-5109; ON: TI87920409
• Country of Publication: United States
• Language: English

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