Humidity Effects on Corrosion-Assisted Fatigue Fracture of Heavy-Duty Gas Turbine Compressor Blades

Statistically, there has been an increased rate of common fracture failure in compressor blades of heavy-duty gas turbines installed at a seaside power plant. Investigations show that corrosion and pitting on the surface of the blades are sources of initial cracks. Therefore, reasons for the corrosion pit initiation are investigated in this paper. In this respect, experimental and numerical analyses are dedicated. Chemical analysis reveals that the blade material is the AISI Custom 450 grade martensitic stainless steel (C450), which has low pitting resistance due to small corresponding pitting resistance equivalent number. Energy dispersive analysis by X-ray shows a high amount of halide elements in the pit zones. To determine the source of water droplets that assist the pitting corrosion, moisture variations in the compressor are studied. Results show that air moisture is condensed in the prior stages of the compressor, especially on the pressure side of the first stage rotating blades. Regarding the results of investigations, it is concluded that the source of pit initiations are condensate water and halide deposition on blade surfaces during compressor operation.