Abstract Scope |
Steam turbine and boiler materials for Advanced Ultra-Supercritical (A-USC) coal-fired power plants are required to withstand steam conditions up to 760˚C and 35MPa for a typical service life of over 100,000 hours. Long-term creep evaluation of these materials is challenging and relies on extrapolation of data from accelerated tests under steady-state conditions and increased temperatures and/or stresses. This study is focused on improving accuracy of creep property predictions by using a microstructurally informed constitutive creep model. The model was recently developed within the framework of continuum damage mechanics (CDM) for ã' precipitation strengthened alloys Haynes 282, Inconel 740H, and Nimonic 105 at stresses between 100 and 400MPa, and temperatures between 700 and 850ºC. The model incorporated physical mechanisms including (1) growth of micro-voids and cracks to macroscopic cavities, (2) accumulation of dislocations toward excessive inelastic deformations, (3) microstructural changes (e.g., ã' coarsening). The model was validated by comparing creep strain evolution in time and rupture times to data from uniaxial creep tests. As damage mechanisms are captured by specific damage variables, the model aims at making predictions beyond the secondary creep regime, well into the tertiary regime by tracking evolution of the damage variables, eliminating the typical need of linear extrapolation. |