Serviced HGP Parts Assessment Using Microstructure-Based Models for New NovaLT™16 Gas Turbine Validation

Abstract

NovaLT™16 is a new high-efficiency gas turbine developed by Baker Hughes for mechanical drive and power generation applications in the 16MW market range. The Fleet Leader engine of this GT class underwent a planned stop which has been used to check the status of the most critical components and validate the engine design. Hot Gas Path (HGP) components specifically have been object of a detailed assessment of their post-service conditions which included NDT inspections, dimensional measurements, air and water flow checks of cooling circuits. Selected components have been also destructively examined to check their microstructure condition and assess the level of service-induced base material and coating alteration. The set of assessments carried out did not highlight any criticality in the engine overall condition or unexpected behavior with respect to design intent. For High Pressure (HP) buckets a quantitative assessment of the service temperature has been also obtained leveraging a microstructure-based model specifically developed by Baker Hughes for bucket base material René N4, a first-generation single crystal superalloy. This model takes into account the time-temperature dependent alterations of the γ/γ’ material structure and namely the growth of the periodicity width lambda (λ), measured along the [001] lattice direction of the single crystal structure.