Establishing the causes of premature damage of steam turbine rotor blades of TPP

Abstract

The technical condition of the metal of the steam turbine blade was analyzed and the reasons for its fracture were established. It was shown that the relative elongation δ of the blade metal varied from 7.4 to 11.5%, and was lower than the regulated level. The low values of δ and the obtained values of the ratio between yield strength and ultimate tensile strength σYS / σUTS, which varied from 0.8 to 0.89, indicate a low margin of plasticity of the blade metal, which contributed to its cracking under the action of working loads. Metallographic analysis revealed pores in the surface-hardened layer of the blade. They caused low adhesion of the layer with the base metal of the blade, and also of crack initiation. The high stress concentration and the contact of the blade metal with the working medium contributed to the growth of a subcritical corrosion-fatigue crack in the cross-section up to its complete destruction.