Restoration of metal properties of circulation pump blades by the method of surface ultrasonic impact treatment

During the transition period to a market economy, the works producing equipment for the nuclear industry became lame duck companies. The market of heavy industry equipment reduced dramatically, and quality control requirements imposed to goods became lower. Deviations from regulations' requirements and technical specifications for equipment manufacture results in inevitable decrease of reliability during operation but also to failure during check tests. It is not always possible to replace promptly ill-conditioned equipment; in such cases, it is necessary to carry out compensatory measures for restoring working properties up to an acceptable level in order to ensure operational reliability due to the strength improvement of the components of machines and constructions during the whole service life or up to the scheduled date of equipment replacement. This paper is dedicated to development and practical implementation of restorative technology of strengthening ultrasonic treatment used for the metal of the blades of impellers of 16DPA10-28 circulation pumps of 10URS unit pump station located at Novovoronezh NPP-2. The dynamic surface treatment was implemented for compensating the technological defects of the metal of blades. It was revealed that the impact elastic-plastic deformation has a comprehensive compensation effect on the metal of blades in the initial state of delivery and creates the surface-strengthening layer with higher strength properties (strain hardening) of the depth up to 1.5 mm. The surface strain hardening increases the cyclic strength, re-distributes beneficially the residual technological and repair stresses, and heals small surface cracks improving the surface quality. The developed technology was used for treatment of 32 blades of impellers of 10PAC01AP001, 10PAC02AP001, 10PAC03AP001, 10PAC04AP001 circulation pumps. The implemented 100-h full-scale test of the pumps revealed the high efficiency of the developed technology and made it possible to recommend it for application at both the stage of blade manufacture and during the pump operation for prolongation of their service life.