Facts and views on the role of anionic impurities, crack tip chemistry and oxide films in environmentally assisted cracking

Pertti Aaltonen, Martin Bojinov, Mika Helin, Petri Kinnunen, Timo Laitinen, Erkki Muttilainen, Kari Mäkelä, Anneli Reinvall, Timo Saario, Aki Toivonen

    Research output: Book/ReportReport

    Abstract

    The aim of this literature study has been to evaluate the level of understanding of the role of anionic impurities in environmentally assisted cracking (EAC) of iron- and nickel-based alloys in the coolant conditions of a boiling water reactor (BWR) - type nuclear power plant, mainly under normal water chemistry (NWC). The study has been motivated by a need to find the most relevant experimental approaches that can be applied when looking for correlations between crack growth rate and measurable electrochemical and chemical parameters. Special crack tip chemistry conditions are established, when trace amounts are present in the BWR coolant and become enriched within a crack. Anions may influence both the conductivity and the pH of the coolant within the crack. In addition, they may influence the composition, structure and properties of the oxide films formed on crack walls either directly via adsorption or incorporation or indirectly via the effect of changes in pH within the crack. Based on the proposed mechanisms for EAC, oxide films formed on crack wall surfaces are likely to play a key role in determing the crack growth rate of structural materials. The prediction of the influence of anionic impurities is thus likely to be facilitated by means of understanding their effect on the films on crack walls. One of the most promising approaches to experimentally clarify this influence is based on investigating the electrochemical behaviour of oxide films Fe- and Ni-based materials in high-temperature conditions simulating the special chemistry within a stress corrosion crack. Results from such studies should be compared and combined with ex situ analytical results obtained using modern electron microscopic techniques. In addition to crack growth, currently available electro-chemical techniques should also be applied to find out whether crack initiation can be explained and modelled on the basis of the electrochmical behaviour of oxide films.
    Original languageEnglish
    Place of PublicationEspoo
    PublisherVTT Technical Research Centre of Finland
    Number of pages92
    ISBN (Electronic)951-38-6052-3
    ISBN (Print)951-38-6051-5
    Publication statusPublished - 2002
    MoE publication typeNot Eligible

    Publication series

    SeriesVTT Tiedotteita - Research Notes
    Number2148
    ISSN1235-0605

    Keywords

    • nuclear power plants
    • water chemistry
    • material properties
    • reliability
    • service life
    • management
    • environmentally assisted cracking
    • surface properties
    • oxide films
    • stress corrosion cracking

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  • Cite this

    Aaltonen, P., Bojinov, M., Helin, M., Kinnunen, P., Laitinen, T., Muttilainen, E., Mäkelä, K., Reinvall, A., Saario, T., & Toivonen, A. (2002). Facts and views on the role of anionic impurities, crack tip chemistry and oxide films in environmentally assisted cracking. VTT Technical Research Centre of Finland. VTT Tiedotteita - Research Notes, No. 2148 http://www.vtt.fi/inf/pdf/tiedotteet/2002/T2148.pdf