This paper presents a case study highlighting the use of the elastic-plastic fatigue methods in ASME Section VIII, Division 2 in the design fatigue evaluation of a heavy wall nozzle. The nozzle is expected to undergo a variety of thermal cycles during its design life, some of which include a rapid heatup or cooldown. The elastic fatigue approach is used for the initial evaluation; however, the thermal stresses induced by the rapid transients result in the application of a significant fatigue penalty factor (Ke,k).
An elastic-plastic stress analysis is therefore used to provide a more appropriate evaluation of the fatigue penalty factor for this case. Both the Twice-Yield and cycle-by-cycle methods are used to calculate the fatigue penalty factor, and give very similar results.
