SELECTION OF CORROSION-RESISTANT MATERIAL FOR THE CASING OF NPP PUMP UNITS UNDER CAVITATION DAMAGE CONDITIONS

The results of the surface condition assessment of a damaged pump unit casing are presented. It was found that the destruction of S355JR steel has a cavitational nature, with a corrosion rate of 15…20 mm/year. Fluid flow modeling indicated the possible formation of crevice cavitation in areas where intensive corrosion traces were detected during operation. The results of metallographic studies on the composition, structure, type, and nature of corrosion are provided, along with the characterization of the corrosion process in the metal of the casing. To select a suitable material for the pump unit casing of a nuclear power plant, the corrosion resistance of several chromium-nickel steels was investigated under conditions as close as possible to actual operating conditions. The highest corrosion resistance was demonstrated by steels containing molybdenum, such as 254 SMO, SAF-2507, and AISI 316Ti, as well as titanium. Steels like AISI 304 also exhibit high resistance to corrosion and erosion; however, under nuclear power plant operating conditions, they may be susceptible to pitting corrosion.