Development of Thermo-Mechanical Service-Like Testing for Supercritical CO2 Expanders

The detailed prediction of the actual life expenditure of expanders operating in power plants has become a common topic of investigation. In the current energy market axial expanders are subjected to frequent load change and to the exposure to higher temperatures. The proper prediction of their life expenditure determines operability and availability improvements through faster start-ups and longer maintenance intervals. A common strategy to achieve this objective has led in the last years towards the development of progressively more and more detailed “service-like” tests aimed at recreating the actual loading conditions in terms of strain and temperature profiles. Recently the need to face the challenge of energy transition through the introduction of advanced cycle employing supercritical carbon dioxide is requiring to further improve this kind of tests by including the effect of environmental attack through corrosion and carburization. This work addresses this topic by presenting the development of customized specimens and of a testing campaign able to evaluate the degradation of creep and fatigue capabilities when high temperature carbon dioxide exposure occurs. After a short introduction on the state of the art, the specimen design will be detailed with FE simulation evaluating stress and temperature distribution in specimens and key insights will be given regarding the design of a proper test matrix and the essential theoretical framework for the interpretation of the results of a testing campaign.