STP821

    Evaluation of SCC Test Methods for Inconel 600 in Low-Temperature Aqueous Solutions

    Published: Jan 1984


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    Abstract

    In late 1981, widespread leakage was encountered in Alloy 600 steam generator tubing at the Three Mile Island Unit 1 nuclear power plant. The phenomenon was identified as low-temperature intergranular stress-corrosion cracking (SCC) initiated from the inner surfaces of the tubes exposed to the primary coolant. A testing program was initiated to examine the material and environmental factors relevant to these failures, which were found to be associated with sensitization of the material and contamination of the coolant by air and sodium thiosulfate. The test solutions contained 1.3% boric acid with various additions of sulfur compounds and lithium hydroxide. Constant extension rate testing was used as the primary tool to examine environmental effects such as the inhibition of cracking by lithium hydroxide. Important effects of crack initiation frequency on the specimen potential (and therefore crack velocity) are demonstrated. In some of these tests, straining was interrupted following crack initiation, and the effects of further environmental additions were monitored by following the load decay at constant total strain. This procedure generally resulted in a different ranking of the environments. U-bend tests showed that the ranking of different sulfur-containing environments was also highly dependent on the metal heat treatment.

    Keywords:

    corrosion, stress corrosion cracking, nickel alloy, sensitization, steam generator corrosion, slow-strain-rate testing


    Author Information:

    Newman, RC
    Associate Metallurgist, Corrosion Science Group, Department of Nuclear Energy, Brookhaven National Laboratory, Upton, N.Y.

    Roberge, R
    Visiting Scientist, Brookhaven National LaboratoryInstitute de recherche d'Hydro-Quebec, UptonVarennes, N.Y.Quebec

    Bandy, R
    Associate Metallurgist, Corrosion Science Group, Department of Nuclear Energy, Brookhaven National Laboratory, Upton, N.Y.


    Paper ID: STP34440S

    Committee/Subcommittee: G01.06

    DOI: 10.1520/STP34440S


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