Turbulent mixing of hot and cold flows can lead to thermal fatigue of piping systems. Especially in primary pipework of nuclear power plants this is an important, safety related issue. Because the frequencies of the involved temperature fluctuations are generally too high to be detected well by common plant instrumentation, accurate numerical simulations are indispensable for a proper fatigue assessment. In this paper, fatigue crack growth analyses are presented for turbulent mixing in a T-junction. The temperatures in the fluid and the pipe were calculated by large eddy simulations with conjugate heat transfer, and the resulting stresses in the pipe by the finite element method. The stresses in the pipe wall have subsequently been used as input for crack growth analyses, which were performed according to ASME Boiler and Pressure Vessel Code, Section XI (2017). The time to a through-wall crack has been calculated for different temperature differences between the hot and cold flows. The analyses presented in this paper have been performed in preparation for the analyses of the EU project ATLAS+. In that project similar analyses will be performed on a different configuration.