Dissimilar metal weld joints and their performance in nuclear power plant and oil refinery conditions

Hannu Hänninen, Pertti Aaltonen, Anssi Brederholm, Ulla Ehrnstén, Hans Gripenberg, Aki Toivonen, Pitkänen Jorma, Iikka Virkkunen

    Research output: Book/ReportReport

    12 Citations (Scopus)

    Abstract

    The operating experience of major nuclear power plant (NPP) pressure boundary components has recently shown that dissimilar metal weld joints can jeopardize the plant availability and safety because of increased incidences of environment-assisted cracking (EAC, PWSCC) of Alloy 600 and corresponding weld metals (Alloys 182/82). Alloy 690 and associated weld metals (Alloys 152/52) are widely used for repair and replacement of the affected thick-section components. The selection of new materials relies mainly on excellent laboratory results and short-term service experience. The long-term behavior of these materials and their performance in the plant has still to be demonstrated. Weldability of the studied nickel-base materials is evaluated based on the results obtained with weld metals of different chromium contents. The susceptibility to hot cracking is examined as well as the PWSCC susceptibility in the reactor primary water based on the metallurgical properties of the nickel-base alloys. The microstructure and microchemistry in the multi-pass nickel-base alloy welds is very different than in the wrought and recrystallized nickel-base materials. Additionally, the thermal ageing experience of various nickel-base weld metals is discussed. Weld residual stresses and their role in PWSCC as well as surface stress improvement techniques for PWSCC mitigation are also reviewed. Finally the application, improvements and qualification of NDE for nickel-base weld locations are evaluated concerning the probes, techniques and scanning devices. The need for representative mock-ups for technique development and qualification is discussed. The technical basis for development of inspection requirements for dissimilar metal welds and efforts to qualify inspection procedures and personnel are also emphasized. Maintaining the structural integrity of the NPP and oil refinery main components throughout the service life in spite of the several possible ageing mechanisms related to the dissimilar metal welds is essential for plant safety and availability.
    Original languageEnglish
    Place of PublicationEspoo
    PublisherVTT Technical Research Centre of Finland
    Number of pages212
    ISBN (Electronic)951-38-6806-0
    ISBN (Print)951-38-6805-2
    Publication statusPublished - 2006
    MoE publication typeNot Eligible

    Publication series

    SeriesVTT Tiedotteita - Meddelanden - Research Notes
    Number2347
    ISSN1235-0605

    Keywords

    • nuclear power plants
    • refineries
    • steel structures
    • welded joints
    • dissimilar metals
    • welding
    • Ni-base alloys
    • residual stress
    • environment-assisted cracking
    • hot cracking
    • non-destructive testing

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