Effects of welding defects on reducing lifetimes of first stage nozzles of a 123 MW gas turbine made of FSX-414 alloy

In this paper, premature failure of one set of first stage nozzles (stationary blades) in a 123 MW gas turbine has been analyzed. Metallurgical and mechanical experiments showed that the main mechanism for such unexpected cracks is thermal fatigue phenomenon accelerated by presence of welding defects in nozzles. Based on the results, it is recommended that repaired nozzles be thoroughly checked before being re-installed in turbines. Moreover, it is recommended; based on the results; to coat nozzles by corrosion/oxidation resistant coatings after their welding by low chromium filler metals such as L-605.