Estudio no destructivo de la integridad estructural de álabes de turbinas

Abstract

Los álabes rotatorios de una turbina de vapor son considerados componentes críticos en las centrales de generación eléctrica, no solo por la importancia económica que representan sino también por los riesgos existentes, como la ruptura catastrófica. Estos componentes de la turbina a menudo presentan problemas de fatiga, corrosión bajo tensión, corrosión por fatiga, erosión, vibraciones, debido a diversos factores como la química del agua, selección de materiales, condiciones de operación, entre otros. Se presenta un análisis modal de álabes de turbina de etapa de baja presión empleando distintas técnicas. La metodología contempla el levantamiento geométrico del álabe empleando un escaneo láser tridimensional, el posterior modelaje empleando elementos finitos y la aplicación de distintas condiciones de sujeción en la raíz con el programa COSMOS/M y la medición experimental de las frecuencias y modos de vibración empleando sensores de contacto y vibrómetro láser para validar el modelo matemático. Los resultados muestran que el comportamiento dinámico del álabe se ve influenciado por la condición de ajuste en la raíz. Dada la disponibilidad en el laboratorio de un álabe retirado de servicio y tres álabes nuevos se trató de encontrar diferencias en la frecuencia de vibración entre ellos, pero los resultados obtenidos no mostraron diferencias significativas contundentes para distinguirlos.|Rotating blades of steam turbines are critical components of electric power plants, not only because of their economic importance but also because of the risk of catastrophic failure. The blades may currently suffer fatigue, stress corrosion, fatigue corrosion, erosion, vibrations, due to various factors, such as water chemistry, material selection, operating conditions, among others. In what follows a modal analysis of the turbine blades in the low pressure stage is presented. Different techniques are used: shape scanning with a 3D laser scanner, finite element modelling with COSMOS/M under variable root fixing conditions, and the validation of the mathematical model through experimental measurements of the natural frequencies and the vibration modes with contact sensors and a laser vibrometer. The results show that the blade dynamic behaviour is affected by the root fixing condition. Vibration modes of three new blades and of a cracked one removed from service were studied, in the search for significant differences in their natural frequencies and vibration modes, which might provide a NDE method for blade characterization. The results so far did not show any such significant differences.

Rotating blades of steam turbines are critical components of electric power plants, not only because of their economic importance but also because of the risk of catastrophic failure. The blades may currently suffer fatigue, stress corrosion, fatigue corrosion, erosion, vibrations, due to various factors, such as water chemistry, material selection, operating conditions, among others. In what follows a modal analysis of the turbine blades in the low pressure stage is presented. Different techniques are used: shape scanning with a 3D laser scanner, finite element modelling with COSMOS/M under variable root fixing conditions, and the validation of the mathematical model through experimental measurements of the natural frequencies and the vibration modes with contact sensors and a laser vibrometer. The results show that the blade dynamic behaviour is affected by the root fixing condition. Vibration modes of three new blades and of a cracked one removed from service were studied, in the search for significant differences in their natural frequencies and vibration modes, which might provide a NDE method for blade characterization. The results so far did not show any such significant differences.