Failure of Inconel 600 Thin-Walled Tubes Due to Nitriding
The self-powered flux detectors used in some nuclear reactors are Pt or V-cored co-axial cables with MgO as an insulator and Inconel 600 as the outer sheath material. The detectors are designed to operate in a He atmosphere; to maximize the conduction of heat (generated from the interaction with gamma radiation) and to prevent corrosion. A number of failures have occurred over the years because of a loss of the He cover gas in the assembly. This has resulted in either acid attack on the Inconel 600 sheath in a wet environment or gaseous corrosion in a dry environment. In the latter case, nitriding and embrittlement occurred at temperatures as low as 300 to 400 deg C (determined from an examination of the oxidation of the Zircaloy-2 carrier rod on which the detectors were mounted). Recent results are described and discussed in terms of the oxidation and nitriding kinetics of Zircaloy-2 and Inconel 600, respectively.
M. Griffiths, J. P. Slade, A. M. McDonald, Failure of Inconel 600 Thin-Walled Tubes Due to Nitriding, ASM Failure Analysis Case Histories: Power Generating Equipment, ASM International, 2019, https://doi.org/10.31399/asm.fach.power.c9001676
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