Evaluation of the operating conditions of gas turbine blades and vanes after long term service

The combination of structural and materials performance together with the actual service conditions will determine the ideal timing for maintenance and the technical lifetime of gas turbine blades. While the designer aims to fit the process, structural and materials solutions together according to the foreseen service, some deviation is likely both in the manufactured components and in the actual service conditions. These deviations do not need to be large, as in particular a relatively small shift in local temperature can translate into large differences in life. The interest on the actual service temperatures often extends beyond the original supplier, but then the assumptions of design or original test data may not be available. Sacrificing one blade of a set for detailed inspection provides an opportunity to estimate the distributions of the effective service temperatures. In this paper, the principles of doing this are reviewed in brief, and few examples are given of evaluated blades. Although it is naturally possible that blades suffer from higher than expected thermal loads, quite often the evaluation will result in allowed life extension with or without refurbishment. The limitations of the approach are also discussed in brief.