Factors affecting low temperature crack propagation (LTCP)

Matias Ahonen, Ulla Ehrnstén, Tapio Saukkonen, Olga Todoshchenko, Hannu Hänninen

    Research output: Contribution to conferenceConference articleScientific

    Abstract

    The effect of hydrogenated PWR primary water on the Low Temperature Crack Propagation (LTCP) susceptibility of the nickel-based Alloy 182, 82, 152 and 52 weld metals was studied performing J-R tests for all-weld metal and dissimilar metal weld (DMW) mock-up specimens at a slow displacement rate in simulated low temperature PWR primary water. Single edge bend (SE(B)) specimens were tested in hydrogenated environments (100, 30 and 5 cm3 H2/kg H2O) with and without exposure to high-temperature hydrogenated PWR water prior to loading (24 h or 30 days at 300??C). Additionally, the effect of post-weld heat treatment on LTCP behaviour of Alloy 182 and 52 weld metals was studied. It was observed that Alloy 182 was the most susceptible material to LTCP, but also some specimens of Alloy 52 exhibited rather low JQ values, similar to those of Alloy 182, when tested with highest hydrogen content. Specimens of DMW Alloy 52 behaved in varying manner when tested with high hydrogen content, in both AW and PWHT conditions. PWHT seems to increase the tearing resistance of Alloy 182. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive Xray spectroscopy (EDS) were applied in order to examine the cracking path and to characterize the microstructural features affecting hydrogen trapping in Alloy 182 and 52 weld metals. A clear relation between high hydrogen content of the water, low fracture resistance values and intergranular/interdendritic type of fracture was observed, although also transgranular brittle-like fracture was observed in DMW Alloy 182 and all-weld metal Alloy 82 specimens tested in low temperature hydrogenated water. Hydrogen thermal desorption spectrometry (TDS) measurements were performed for Alloys 182 and 52 by using varying heating rates in order to study the effect of high temperature pre-exposure, different trapping sites and trapping activation energies. The high temperature pre-exposure was found to decrease the hydrogen content of Alloy 182 and 152 weld metals and consistently the fracture resistance values were increased. Different factors affecting the LTCP behaviour of nickel-based weld metals are discussed.
    Original languageEnglish
    Number of pages18
    Publication statusPublished - 2015
    Event17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, ENVDEG 2015 - Ottawa, Canada
    Duration: 9 Aug 201512 Aug 2015

    Conference

    Conference17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, ENVDEG 2015
    Abbreviated titleENVDEG 2015
    CountryCanada
    CityOttawa
    Period9/08/1512/08/15

    Keywords

    • nickel-based weld metal alloys
    • low temperature crack propagation
    • hydrogen trapping
    • fracture resistance

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  • Cite this

    Ahonen, M., Ehrnstén, U., Saukkonen, T., Todoshchenko, O., & Hänninen, H. (2015). Factors affecting low temperature crack propagation (LTCP). Paper presented at 17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, ENVDEG 2015, Ottawa, Canada.