A cracked, martensitic stainless steel, low-pressure turbine blade from a 623 MW turbine generator was found to exhibit fatigue cracks during a routine turbine inspection. The blade was cracked at the first notch of the fir tree and the cracks initiated at pits induced by chloride attack. Examination of the blade microstructure at the fracture origins revealed oxide-filled pits and transgranular cracks. The oxide filled cracks appeared to have originated at small surface pits and probably propagated in a fatigue or corrosion-fatigue fracture mode. It was recommended that the sources of the chlorides be eliminated and that the remaining blades be inspected at regular maintenance intervals for evidence of cracking.
J. Ciulik, Failure Analysis of a Cracked Low-Pressure Turbine Blade, Handbook of Case Histories in Failure Analysis, Vol 2, Edited By Khlefa A. Esaklul, ASM International, 1993, p 280–282, https://doi.org/10.31399/asm.fach.v02.c9001355
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