High Temperature Life Prediction of Monolithic Silicon Carbide Heat Exchanger Tubes

The need for improved performance in high temperature environments is prompting industry to consider the use of structural ceramic materials in heat exchanger tubes and other high temperature components. In recognition of this need, the U. S. Department of Energy has supported work for the development of nondestructive methods for evaluating flaws in monolithic ceramic components, and the associated establishment of criteria for the acceptance of flawed components. Under this development of flaw assessment criteria, DOE supported the work being presented in this paper.

The approach to developing the life prediction model combines finite element predictions, considering creep behavior, with continuum damage mechanics and Weibull reliability statistics. ABAQUS is used to predict time dependent creep response of the component based on experimental creep data. A continuity parameter is then calculated at each time step following continuum damage mechanics methods. Finally, Weibull statistics are used with the resulting continuity parameter to predict the reliability at each time step, through the use of the NASA-Lewis computer program CARES, interfaced to ABAQUS with ABACARES.

There is very limited data available to characterize the creep, continuum damage and reliability behavior of the material. For the life prediction model reported, it is assumed that the material damages isotropically. Directional effects of the damage can be added as material databases improve.