Corrosion Behavior of Sodium-Exposed Stainless Steel in Chloride-Containing Aqueous Solutions

Technical Report · Thu Dec 01 04:00:00 EST 1977

DOI:https://doi.org/10.2172/1846522· OSTI ID:1846522

Wu, Paul C. S. ^[1]

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1. Westinghouse Electric Corp., Madison, PA (United States). Advanced Reactors Div.

Corrosion behavior of sodium-exposed stainless steels in typical water pool conditions was investigated. The main purpose of this study was to assess the feasibility of water storage concepts for the LMFBR spent fuels. This report covers phase l of this program which was a screening study of sodium-corroded, 20% cold-worked Type 316 stainless steel (prototypic LMFBR cladding alloy) with the sodium removed by alcohol or water vapor/argon and/or steam/argon process. The results show that no observable material deterioration or failure occurred among specimens manufactured from this material and tested under pressurized condition (350 psi) at 82°C for periods up to five months in various water baths with chloride content above 500 ppm. This satisfactory performance was mainly due to two factors: l) massive intragranular carbide precipitation due to the cold-working which prevented the alloy from sensitizing during high temperature sodium exposure, which in turn reduced the susceptibility of the alloy to intergranular attack, and 2) the presence of a ferrite layer with high molybdenum which enhanced the alloy's resistance to localized pitting corrosion. Deposit-bearing Type 304 stainless steel specimens manufactured from an economizer (liquid sodium heat exchanger) were also studied under the same conditions. Rusting developed on most of the specimens in all four water baths; however, failure occurred mainly in the high chloride and neutral water bath. It was concluded that the failures were initiated by severe localized pitting and subsequently accelerated by intergranular attack. These failures were attributed to the presence of mass transfer deposits particularly iron and its compounds and to the sensitized structure of the base alloy. It was also found that high pH tends to enhance the corrosion resistance of this alloy. In addition, the failure was apparently independent of the sodium cleaning procedures employed for the removal of sodium from the test specimens.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-00OR22725; W-7405-ENG-26
• OSTI ID: 1846522
• Report Number(s): ORNL/TM-6068
• Country of Publication: United States
• Language: English

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