High cycle thermal fatigue crack initiation and growth behavior in a simulated BWR environment

At a tee junction point in a piping system, hot and cold water are mixed with each other in a whirl. The vibrating mixing boundary between the hot and cold water causes a temperature fluctuation on an inside surface of the pipe just after the connection point. The temperature fluctuation yields a cyclic thermal stress near the pipe surface and results in the crack initiation. In this study the thermal fatigue tests using disk-like specimens in simulated BWR environment were performed and the thermal fatigue crack initiation strength was compared with the mechanical fatigue strength. Furthermore, the thermal fatigue crack arrest depth was analyzed using linear elastic fracture mechanics. The arrest depth was found to be in proportion to the reciprocal root of the frequency of temperature fluctuation, and the experimental results agreed well with the analysis. (author)