It is well known that fatigue damage accumulates around T-junctions of piping system where two kinds of fluid with different temperatures are mixed. This phenomenon is called thermal striping, and simple method for evaluating the fatigue damage derived from this phenomenon is greatly important for both design and maintenance stages. However, the evaluation of the thermal stress derived from the thermal striping is rather difficult since the evaluation requires complicated analyses such as fluid mixing, heat transfer, and heat conduction. In addition, the closed-form solution to describe the stress-range distribution under random loading has not been established yet since the rainflow cycle-counting method is not suitable to the analytical treatment. Though numerical calculation may be available for the evaluation, it requires time-consuming work and is not practical for design stage. For this reason, an analytical method for evaluating the fatigue damage directly from stress power spectrum density (PSD) is desired. In this paper, the feasibility study to apply analytical methods to the evaluation of thermal-striping damage is examined. The analytical methods are applied to the fatigue damage evaluation from the stress PSD that was obtained by the thermal striping experiment. Finally, the applicability and problem of each method will be discussed. In order to apply the envelope PSD to design, the property of safety margin associated with the PSD is investigated too.
