Effect of non-metallic inclusions in steel structure on premature failure of steam turbine rotor disk

The causes for the premature operational damage of a number of elements of the steam turbine rotor were analyzed. All mechanical characteristics of the steels, even after operation, met regulatory requirements; however, this did not prevent the destruction of the rotor elements. At the same time, a large number of corrosion-active non-metallic inclusions (CANI) were found in the structure of 30KhN3M1FA steel of the damaged rotor disk, which significantly intensified local corrosion in their vicinity, contributed to the formation of pits on all surfaces of the disks, as well as became sites of initiation of corrosion-fatigue cracks. The conducted studies show the importance (both for manufacturers of steam turbine rotors and for operators) of improving the requirements for monitoring the structure of steel in terms of the number of small CANIs and the density of their location as factors accelerating premature (within the design life) corrosion-mechanical fracture of rotor disks.