Investigation of turbine blade failure in a thermal power plant

• We found traces of chlorides on the fracture surface in the blade.
• The blade material shows an increased hardness compared to standard values. The high hardness values indicate a high sensitivity to stress corrosion creating.
• The investigation of the cross sections shows a typical crack structure as caused by stress corrosion cracking.

The failure of a LP (low pressure) turbine blade of a 310 MW thermal power plant is presented. The fracture took place at the aerofoil region, 150 mm from the root. Several pits were found on the edges of the blades and chloride was detected in these pits. They were responsible for the crevice type corrosion. The failure mode was intergranular type. The blade material matches the composition of X20Cr13 steel; however, the hardness shows high values (between 450 and 480 BHN) compared to standard values of 270–300 BHN.