An analysis of the results of periodic testing of hardness of metal of pipelines bends of power unit No. 2 of Pivdennoukrainsk Nuclear Power Plant (PNPP) after ~100,000 and ~200,000 h of operation was carried out. It is shown that during the operation of feedwater and “hot” steam pipelines during the second 100,000 h of operation, the aging of the metal is observed, which is manifested in a partial, at least in their surface layers, uneven decrease in the strength of the metal. An increased rate of aging of the metal of pipeline bends is observed in areas where the metal was subjected to the greatest plastic deformation during the pipe manufacturing process (compressed and stretched sides of the bends). The critical parameter among the normalized mechanical properties of bending metal is the tensile strength, which is the first to reach a critical level when extrapolating the obtained data. While maintaining the rate of change in the mechanical properties of the metal at the level of the second 100,000 h of operation for post-project operation, the projected residual resource of metal bends of feedwater pipelines and "hot" steam is ~590,000 and ~380,000 h, respectively.

The analysis of operational damages of heat transfer tubes (HTT) in steam generators (SG) of WWER-1000 power units was carried out. The processes of contamination of the surfaces of HTT of SG PGV-1000M are considered. The processes of formation and growth of corrosion pits on the surface of heat transfer tubes are analyzed. The process for the initiation of corrosion pits and the development of cracks in the heat transfer tubes metal, which includes the combined action of a corrosive environment and non-metallic inclusions in heat transfer tubes, was proposed.

The comprehensive analysis of the results of research by direct methods of BM of MCP of the South-Ukraine NPP after 100,000 and 200,000 h of operation was carried out. In BM with a fine-grained initial structure, the first stage of the aging process, accompanied by metal strengthening, is completed during the first 100,000 h of MCP operation; then the second stage begins, accompanied by decreasing of metal strength. In BM with a coarsegrained initial structure, the first stage of the aging process lasts more than 200,000 h of operation. The predicted residual resource of MCP is determined by the resource of BM with a fine-grained initial structure. The critical regulatory property at the first stage of the aging process of BM is relative elongation, at the second stage – the strength limit.

A comprehensive analysis of the damaged heat exchange surface of the PGV-1000 steam generator during long-term operation, their relationship with hydrodynamic, water-chemical regimes and surface properties was conducted. The methods of minimization of damages during the operation of Ukraine's NPP are considered.

The base metal (BM) of the main circulation pipeline (MCP) of the unit 3 of the South Ukraine NPP, which has been in operation for 200 thousand hours, was investigated by direct methods. It is shown that the mechanical properties and structure of BM of the MCP after 200 thousand hours of operation satisfy the requirements of regulatory documentation for metal. A comparison of the test results of the BM in the initial state and after 100 and 200 thousand hours of operation was carried out. It is shown that in the process of operation there is a decrease in the rate of changes in the mechanical properties of BM, in particular, during the last 100 thousand hours of operation in comparison with the previous ones.

In this work, we studied the properties of samples from steel 15Cr12WNiMoV after vacuum activated chromium plating at temperatures of 1070 and 1100 °C for 4 and 10 h. It was found that after chemical-thermal treatment on the samples a diffusion layer with a thickness of 50 to 130 µm is formed, consisting of 56…82 wt.% of chromium, the rest is iron. Metallographic studies were carried out on the samples and tests for heat resistance were carried out at a temperature of T = 900 °C. It was found that chrome-plated samples significantly exceed the initial samples and nitrided ones in terms of heat resistance. Tests of samples for tensile strength after chromium plating showed a significant increase in strength indicators for ultimate strength and yield strength. The plasticity characteristics of these samples are reduced.

Mechanical properties of the metal from drums of boilers at the Starobeshevskaya and the Lugansk thermal power plants (TPPs) were investigated. According to the results of the standard technical diagnostics and a strength analysis, both drums comply with the applicable regulatory requirements. At the Starobeshevskaya TPP, the drum was ruptured during a hydraulic test. It was found that this was caused by the low impact strength of the metal at room temperature. The objects of the investigation were fragments of the ruptured drum and a “plug” cut out of the shell during a scheduled inspection. An attempt is made in this paper to assess the state of equipment metal based on the results of tests on subsize Charpy specimens. It has been demonstrated that when standard Charpy specimens (10 × 10 × 55 mm) cannot be made but impact bend tests have to be performed, the brittle-to-ductile transition temperatures for standard Charpy specimens may be obtained in testing 2 × 8 × 55 mm specimens. The correlation developed to relate the test results from subsize specimens to standard Charpy specimen enables us to assess in the first approximation the fitness for service of the metal to prolong the equipment’s service life. The rupture surface of subsize Charpy specimens has almost the same appearance as that of standard specimens. The temperature dependence of ductile component of subsize specimens agrees well with the corresponding dependence for standard Charpy specimens. To integrate the test data into a single database, it is desirable to derive a correlation to relate the critical brittleness temperature from a subsize specimen test to the critical brittle temperature from standard Charpy specimens.

The paper reviews damages to metal pipelines in WWER-1000 cooling systems, initiated by nonmetallic inclusions. The nature of damage in steels of different classes is shown. The ways to improve the reliability of metal structures are identified.

This study was aimed at investigating the chromium coating effect on the mechanical properties of Zr1Nb fuel claddings in the case of a tensile fracture in longitudinal and transverse directions at temperatures of 20 and 350 °С. Tests were carried out using the samples of a similar shape, namely, with an equal test portion length that is important for comparison of results. The obtained results have shown that at a test temperature of 20 °С the mechanical properties of initial samples are higher in the longitudinal direction than in the transverse direction. The ductility is slightly higher at T = 350 °С in the longitudinal direction, and σ0.2 and σв are practically equal. The preliminary deformation of ring samples increases their ductility from 23 to 34% independently on the test temperature. Deposition of the chromium coatings on the samples leads to the slight increase of mechanical properties in the transverse direction and decrease of σ0.2 with unchanged σв and δ% in the longitudinal direction at the room test temperature, and at 350 °С it practically do not change the properties of coated samples in both the directions except the ring sample ductility decrease.

By metallography and scanning electron microscopy the effect of titanium carbonitride and silicon carbide on degradation of steel 08X18H10T was revealed on heat exchanging tubes (HET) of steam generators of powergenerating units of WWER-1000. The role of structural features of steam generators on nucleation and growth of operational defects of HET is shown.

С помощью металлографии и растровой электронной микроскопии установлено воздействие включений карбонитридов титана и карбида кремния на деградацию стали 08Х18Н10Т в теплообменных трубах (ТОТ) парогенераторов энергоблоков ВВЭР-1000. Показана также роль конструкционных особенностей парогенераторов в зарождении и росте эксплуатационных дефектов ТОТ.

The microstructure and mechanical properties of 10MnNi2MoV (high-quality) steel of the main circulation pipeline (MCP) of the WWER-1000 NPP after 200 thousand hours of operation were investigated. Metallographic methods, electron microscopy, mechanical static and impact tests were used. The obtained results are compared with those obtained for the metal samples of the MCP after 100 thousand hours of operation. The signs of metal aging are revealed. The probable cause of metal aging may be operational factors and processes occurring at the microstructural level. The example of MCP shows that small-scale metal cuttings are sufficiently informative in terms of controlling the structure and mechanical properties of metal in equipment and pipelines of NPP.

Defect formation into the heat exchangers of WWER-1000 steam generators at the South-Ukraine nuclear power plants (SU NPP) was considered using the data of multi-year eddy current control (ECC), taking into account the results of new metallographic investigations. The features of the defect distribution according to the control characteristics (amplitude of the signal, "lack of metal") are established. It has been shown that the damage germs formed in the metal can be non-metallic inclusions, which initiate the processes of local corrosion and corrosion fatigue. The analysis can be used to improve the regulations and plans for the next control at the NPP.

The results are presented of the development of methods and appropriate equipment for determining the temperature of ductile-to-brittle transition of metal using small metal samples cut from the investigated equipment. The method is based on registration of acoustic emission pulses generated in the process of destruction of specimens in the proper temperature range. The form of specimens for research and equipment for manual and automatic determination of temperature ductile-to-brittle transition are also described.

Results of the development of optical-mechanical module for measuring the residual stress in metal of the surface of the reactor vessel WWER-1000 are described. The methodology for determining the residual stresses in metal is described. The developed equipment is adapted for use on the surface of the reactor vessel.

The article presents the results of developed method of electroerosion cutting of low-sized templets for the reactor vessel metal composition and structure control in laboratory environment. The article describes the equipment for the remote electroerosive cutting of templets from WWER-1000 type reactor vessel by rigid electrode. The testing results are also shown.

Features of application of electroerosive methods are considered during the process of direct definition of properties of metal of the equipment of power units of the atomic power station. Results of development of a complex of the equipment for wire electric discharge machining of metal templet and its use are presented at the control of the basic metal of the main circulating pipelines over blocks of the atomic power station of Ukraine over long terms of operation.

Mechanical properties of metal of pipelines of reactor and turbine separation of Sonth-Ukrainian NPP-3 are certain by direct methods on standard specimens, on cross-correlation dependences of basic descriptions with hardness, and also on microspecimens of main circulation pipeline. Microstructure research of exhausted during 100.000 hours metal was carried out. Surface fractography of tension tested specimens and Charpy impact was studied by means of a raster microscope.