Crack Cause Analysis and Manufacturing Process Improvement of Impellers of Cooling Water Pumps in a Nuclear Power Plant

Cracks were found in the impellers of several cooling water pumps of the same type in a 1 000 MW nuclear power unit during maintenance. The reasons of impeller cracking were analyzed from the crack morphology, material properties, casting process and heat treatment process. The results show that the metallurgical defects such as pores and porosity in the casting process were the main reasons for the impeller blade cracks. The casting process and heat treatment process of the impeller were improved. The casting defects such as crack and perforation were eliminated in the impeller produced by the new process, and the quality and service performance of the impeller were improved.