Inelastic behavior and creep-fatigue damage evaluation of intermediate heat exchanger for HTGR

In the structural design of intermediate heat exchanger (IHX) of high temperature gas-cooled reactor (HTGR) for hydrogen production, creep-fatigue damage evaluation at high temperature up to 950 ℃ is important. In this paper, inelastic behavior and creep-fatigue damage of IHX components such as heat-transfer helical tubes and manifold perforated pipe made of Alloy Ni-22Cr-9Mo-18Fe-B, was clarified by detailed inelastic analysis. A simplified creep-fatigue damage evaluation method on the basis of elastic analysis was proposed, which is suitable for parametric study in an initial stage of structural design. This method considers the characteristics of inelastic behavior as follows; stresses are in elastic range; elastic follow-up coefficient during stress relaxation in a steady state is below 3; and a post relaxation stress is a primary stress of structures. The simplified method was applied to both heat-transfer helical tubes and manifold perforated pipe subjected to primary stress and thermal stress. Predicted creep damages were conservative within a factor of 3 compared with the results of detailed inelastic analysis. Influence of temperature, initial stress and post relaxation stress on creep damage was also discussed.