A large and growing portion of electricity is produced by aging thermal power plants. Although excellent, high quality materials such as CrMoV steel and 12% Cr steel, etc. are used for the steam turbines, various forms of metallurgical degradation, due to creep and fatigue, etc. affect the parts and components during long-term operation at high temperature. Extending the life of steam turbines and ensuring high reliability requires life assessment technology, scheduled repairing, conversion, modification and upgrading of components in order to provide a stable power supply. As the high temperature parts and components of aged steam turbines are mainly metallurgically damaged by creep, fatigue and the interaction of both, life assessment combined with analytical and nondestructive methods is essential for realizing strategic plant life extension. We have developed a life assessment technology that takes material degradation into consideration, and have applied the procedure to more than 650 units and 2 500 components since 1983. A rotor bore replication device was developed in 1989 for the purpose of nondestructive observation of creep voids and supporting the validity of life prediction results. This paper describes the technical features and applied experience of recent life assessment technology for existing high temperature steam turbines.
Electricity generation utilities are increasingly looking for cost-effective solutions to maximise the value of aging steam turbine generator plant assets. To this end, retrofits of steam turbines after many years of operation have been carried out for the purpose of life extension of units, performance improvements, capacity up-rating, availability improvement, and improved environmental compliance. Major steam turbine manufacturers have continued to push forward the development of advanced technologies to satisfy demand from utilities by provided retrofit design that optimise the above criteria. This paper describes the advanced technologies adopted in the recent retrofits, including advanced steam path design and new last stage blades of improved efficiency, improved reliability, and of simplified or no maintenance. Retrofit case-studies of capacity up-rating and life extension are introduced to illustrate how these technologies have been applied and what has been the gain.
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