Failure analysis of the 150 MW gas turbine blades

A 150 MW gas turbine experienced a forced break down because of extremely high vibrations and subsequent output power reduction down to almost zero. Before the break down, the turbine was operated by approximately 1800 hours in intermittent mode, with a record of 65 start-ups in total. When the turbine casing was opened it was found that all blades, stationary and moving ones, were in damaged status. Especially destroyed was the first row moving blades, with four missing blades. In contrast, no damage or excessive wearing out was found neither in the combustion chamber nor in the transition pieces; even nor at the region of entry to the nozzles. The first author was present during disassembly of the turbine to watch the status. The aim of the diagnostic work was to find out the main cause of the blades failure. The results of further investigation lead to establish that the former cause of the blade failure was low cycle fatigue that originated a crack in the securing pin hole (stress raiser) located at the root of the blade and propagated.