Assessment of materials properties variation of NPP equipment and piping after prolonged operation time

The methods of nondestructive testing of reactor components and pipelines are reviewed. It is shown that hardness measurements can be successfully used to determine the changes in such properties as ultimate strength, yield strength, ductility and material hardening exponent during long-term operation. For the practical implementation of the hardness measurement method a special code package is developed on the basis of the experimental curve of indentation. Experimental data are obtained for steel 20 and 22K reactor vessel walls (base metal and welds) at Kola, Bohunice and Kozloduy NPPs. For testing austenitic 08Kh18N10T and 12Kh18N10T steel resistance to intercrystalline stress corrosion cracking the following techniques are applied: potentiodynamic reactivity, corrosion potential and potentiostatic etching. For this purpose a specially designed transducer is fixed to the surface of the component investigated. A limitation of these techniques is that the degradation of internal surfaces contacting with the coolant cannot be evaluated