APPLICABILITY INSTRUMENTAL INDENTATION METHOD FOR DETERMINING MECHANICAL PROPERTIES OF IN-SERVICE EQUIPMENT BY HADNESS EVALUATION

摘要

Long term operation of nuclear power plants imply increased requirements to in-service inspection of degree of ageing (degradation) of mechanical properties of welded connections of the most loaded zones of equipment and pipelines of nuclear power plants. Fullest information on strength properties of metal provide diagram of uniaxial tension deformation. Our researches, have shown that it is possible to estimate such diagram with a high degree of accuracy using nondestructive instrumental indentation test method (ISO-14577), which can be used, when it is necessary, for in service inspection of material of equipment. The instrumental indentation test method describes procedure of recording of indentation diagram in coordinates 《loading - indentation depth》. Such diagram represents itself the result of mechanical elastic - plastic deformation test. However, most effectively this diagram can be used for reconstruction of uniaxial tension diagram with subsequent estimation of standard mechanical properties of material. Our completed version of indentation diagrams interpretation technique was taken as a basis of the new Russian standard GOST-R 56232-2014 《Determination of 《stress - strain》 diagram in the course of ball instrumental indentation. General requirements》. For development and adaptation of the reconstructing methodology the extensive database of results of tests of steels in various conditions of artificial and real ageing in conditions of NPP vessels long operation was collected. Also, the methodology of non-destructive estimation of fracture toughness characteristics of pressure vessel materials on the basis of instrumental indentation test method was elaborated. Development of the reconstructing methodology was carried out along with modernization of test equipment and of software. Together with the MUBATEC company (Germany) it was developed the device, allowing currying out tests in full agreement with standards ISO-14577 and GOST-R 56232-2014. Device was designed for both in laboratory and field application. The field applicable version typically assumes portable computer controlled indentation system mounted on the pipe with straps or on the surface of vessel with magnetic shoes. The instrumental indentation test method was widely used for testing the equipment and pipelines of the first contour of nuclear power plants after 30-years term of operation. This method is especially effective as applied to inspection of metal of non-cladded vessels of reactors such as VVER-440. With this purpose the special equipment for realization of this work was manufactured, and also the special full-scale stand for certification of this equipment was prepared. The use of instrumental indentation procedure for testing the results of regenerative heat treatment (annealing) enables to estimate operatively the degree of restoration of properties of metal on height and perimeter of the vessel in terms of statistically representative files of experimental data.