METALLURGICAL STUDY OF A LAST STAGE NUCLEAR TURBINE BLADE FAILURE

摘要

A 236 MW capacity nuclear turbine which had logged about 17,000 hrs of operation suffered a catastrophic failure causing extensive damage to steam turbine, generator, bus duct, civil structures etc. The Low pressure (LP) turbine, on being opened, revealed that 16 blades of the last stage (stage 5) were broken. Out of these, two blades adjacent to one another, failed at the first serration of the blade root. All the other blades had failed in the profile portion of the blade. The aim of the metallurgical investigation was mainly, to ascertain whether the fatigue of the two blades in the root portion was consequential or not. The metallurgical observations coupled with other relevant data were thoroughly examined and the conclusions were arrived at. The initial cracking in the root portion of the blades was similar so those observed in blades of the same design in other parts of the world. These cracks were arresting type and cannot lead so failure. It was opined that the failure of the blades was consequential and would not have occurred otherwsie.