Endesa has managed to successfully implement and design a programme that allows the useful life of gas power plant turbines to be extended by 60%. This system, based on a newly-developed turbine inspection method, was recognised as one of the nine most innovative projects worldwide by the US-based Electric Power Research Institute (EPRI), the top international certification agency in the power sector, in its annual Technology Transfer Award 2014.
This award from EPRI recognises the leaders and innovators in the electricity sector who have transferred research and technological development to practical applications in order to help create a more reliable, efficient, competitive and environmentally friendly power generation.
Endesa’s programme enables the extension of life and field inspection (at the installation) of gas turbine rotors. It extends the useful life of turbines to 8,000 starts from the 5,000 starts envisaged by manufacturers, while maintaining all safety guarantees.
The inspection method, on which the company has worked for two years, has already been applied to the 18 turbines operating in Endesa’s six gas-fired power plants supporting the Canary Islands network (Jinamar, Barranco de Tirajana, Candelaria, Granadilla, Punta Grande and Salinas) and in the three gas-fired plants supporting the Balearic islands network (Alcudia, Son Reus and Mahón). In line with such method, from the useful life studies, carried out on the different components of gas turbine rotors under different operating conditions, life-limiting damage mechanisms can be identified. These analyses allow to define and develop inspection techniques aimed at detecting, at an early stage, the deterioration of components that need to be replaced. It must not be forgotten that gas turbine power plants are key as backup electricity systems to guarantee the continuity of supply in remote electricity systems, like those on the islands. The inspection method can be applied to other types of turbines carrying out the same service.
This non-destructive trial method, which can be carried out in the field with no need to dismantle the rotor, allows cracks in interior areas to be detected without sending them to the manufacturer's workshop to be dismantled and inspected, which would leave gas turbines out of use for at least six months and would mean an average cost of 2.2 million euros per turbine. Thus, the system implemented in the 18 turbines has allowed savings of 39.6 million euros.
During the two years of work needed to define and develop this life extension system, a rotor was fully dismantled and all its components went under dimensional scanning as well as thermal-mechanical analysis under different operating conditions that cause the strain such components are normally subject to. Subsequently, the critical areas and damage methods that limit the life of each component were identified via mechanical trials in a laboratory to determine the properties of the material in service compared to the new material. With additional mechanical studies on fracturing the formation and progress of cracks can be identified, and finally, leveraging on all this information, an inspection method was defined and developed.
Traditionally, gas turbines functioning as backups have to perform many start-stop cycles which put components under maximum strain. Inspection practices and the withdrawal of turbines identified by manufacturers led to a review of the 5,000 starts, which required the installation to be stopped, the turbine to be dismantled and the rotors (the key components which deteriorate the most) to be transferred for analysis by the manufacturer.
With this new inspection system, the review is carried out in the power plant and intervention takes place only when real faults are detected. The analysis method provides a technical base from which to objectively evaluate the real situation of rotors and plan technical interventions that guarantee continuous and secure operation at any moment.
The method identified by Endesa, in which companies such as Navantia, Tecnatom and Aimen (Northwest Association of Metallurgical Investigation) have participated, has been developed under the direct supervision of EPRI. It provides gas turbine users with specific and objective model criteria to determine the useful life of the rotor in order to guide and plan their inspection and withdrawal decisions.