325The complex Program No. NPP PRG 550K07 on the erosion-corrosion problem is used in FGUP Kontsern Rosenergoatom for preventing the sudden damages and for improving the operational erosioncorrosion resistance of the pipeline and equipment components of nuclear power plant (NPP) power units. One of the important practical results of carry ing out the works mentioned in the Program has become a reduction of excess volumes and an enhancement of the efficiency of operational moni toring of metal for the circuit II equipment of power units in the Kalininskaya NPP (KLN NPP) and other NPPs [1].The analysis of the metal damageability database, created in the context of the Program, indicates that the cavitation erosion is responsible for many cases of intolerable thinning or damage of pipelines and equip ment of the condensate feed channel (CFC) of NPP power units. Components of the flow path of pipe lines, accessories, narrowing devices, and other equip ment (passed over by the one phase water flow where the cavitation effect takes place) are subject to the cav itation erosion. In two phase wet steam flows, there are no conditions for occurrence of cavitation effect and cavitation erosion [2].A view of the typical cavitation damage of the working surface of the flow path of a narrowing device is shown in Fig. 1. In this case, the throttling device is presented, which is arranged on the pipeline of recir culation of the auxiliary feeding electrical pump of the power unit of the NPP with VVER 1000 and operates at a temperature of 120°С with a substantial drop of pressure (p in = 9 MPa (90 atm), p max = 0.7 MPa (7 atm)) that contributes to the occurrence of the cav itation effect. It can be seen that the asymmetric cavi tation damage of the outlet edge of the orifice has resulted in the flow deflection and the inner surface degradation of the main channel downstream. The casing and the orifice plate of the throttling device were manufactured from the corrosion resistant steel 08Kh18N10T.The nature of the cavitation erosion phenomenon is unique and consists in the mechanical (impact) damage of the metal's surface layer during the collapse of bubbles formed upstream over the pressure range below the saturation pressure. Unlike the erosioncorrosion mechanism, to which only pearlitic and Abstract-The peculiarities of the cavitation effect are considered and some engineering criterion paramet ric methods are proposed for estimating the possibility of manifestation and the level of intensity of the cavi tation action on components of narrowing devices of circuit II of nuclear power plant (NPP) power units. Results of computational and experimental studies are presented which have shown that up to 30% of throt tling devices of the condensate feed channel of NPP power units are subject to the cavitation erosion. The possibilities of practical application of the developed methods were established for revealing the causes of wall thinning of narrowing devices in the NPP working channel and for preventing it.

628During the last decades, systematic and pro grammed works have been carried out in leading coun tries around the world for collecting and analyzing data on erosion-corrosion damages inflicted to the metal of equipment and pipelines at nuclear power stations (NPSs), studying the regularities pertinent to the mechanism of erosion-corrosion, developing software tools for estimating and predicting the ero sion-corrosion process, and optimizing measures for monitoring, revealing, and preventing erosion-corro sion thinning of the walls of power equipment and pipelines. In France, for example, works have been carried out for more than 15 years on revealing ele ments belonging to the risk group of intense wear and optimizing the operational monitoring (thickness measurements) of metal thinning in 58 power units at NPSs belonging to the EDF Company with the use of the BRT CICERO computation code [1]. The EDF database has been created using the results of these works, which included 99 534 elements, i.e., around 2000 elements per power unit as of April 2010. As the time for which NPPs have been in operation passed, cases involving inadmissible thinning and fail ures of the metal in welded connections are observed in more and more frequent occasions along with ero sion-corrosion failures of the main metal of pipeline and equipment elements. In 2002, the Electric Power Research Institute (the United States) published a report addressed to selective erosion-corrosion effect on welded connections. Since 2001, EDF has given the status of an individual problem to the wear of welded connections in a program on erosion-corro sion of the metal in NPS power units [1].Since 2007, the OAO Rosenergoatom Concern has been implementing a comprehensive program on the problem concerned with erosion-corrosion of the main metal of pipelines and equipment at Russian NPSs [2]. At present, sufficient grounds have ripen for drawing up a new version of this ongoing comprehen sive departmental program on the problem of damages inflicted to welded connections. The data on damage ability and the results from operational checks of metal that have been acquired and analyzed with due regard of the requirements specified in the above mentioned program made it possible to reveal numerous cases involving the occurrence of inadmissible thinning in welded connections and in near weld zones of NPS pipelines. Cases are also known in which loss of tight ness occurred in welded connections of NPS process loops as a result of their erosion-corrosion thinning.Such incident occurred in November 2004 in a power unit of the Balakovo NPS, at which a leak was found in the zone of welding the bypass pipeline bend (D nom = 108 × 6 mm) to a sleeve (D nom = 120 × 16 mm) of the feedwater pipeline (D nom = 426 × 24 mm). The working parameters of medium in the damaged part are 220°C and 8.0 MPa.Significant inadmissibly thinned places in welded connections of pipelines downstream of the feedwater control valves are observed in power units of Russian NPSs equipped with diffe...

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