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Microstructural Damage Due to Thermal Aging in Turbine Casings Observed with NDT: A Case Study

In many parts of the world, different types of electrical generation and compression gas turbines are used. The importance they have in the development of the population is very high, especially near thermal power plants, where the population and environment change but the turbines do not for long periods of time. Many thermal power plants have turbines that are changed out every 15 to 20 years, following the correct overhaul procedures; however, the casings of these turbines are not changed and remain intact throughout their life cycle. In some cases, the casings remain in service for more than 50 years. When the turbines are in operation, temperatures in the casings are very high, which means the casings undergo an aging thermal treatment for periods of over 20 years, increasing their fragility and risk of failure. Maintenance plans, which would include inspections observing microstructural changes over the casings’ operation cycles, would improve the reliability of the turbines and decrease the risk of failure. This study shows the microstructural damage that can occur in turbine casings. The study was undertaken using nondestructive techniques and metallography in situ, without affecting the component.

References

ASM, 2004, ASM Handbook Volume 9: Metallography and Microstructures, ed. George F. Vander Voort, ASM International, Materials Park, OH.

ASM, 2000, “Hardness Testing,” in ASM Handbook Volume 8: Mechanical Testing and Evaluation, eds. H. Kuhn and D. Medlin, ASM International, Materials Park, OH, pp. 195–288.

ASTM, 2013, ASTM E112-13: Standard Test Methods for Determining Average Grain Size, ASTM International, West Conshohocken, PA.

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