Estimation of the resource of pipes of the main circulation pipeline of a NPP by the criterion of crack resistance with account of operational degradation of properties

The results of an experimental determination of the characteristics of cyclic crack growth resistance of specimens made of stainless steel 08Kh18N12T are given. Compact samples 20 mm thick cut from Du 550–30 pipes of the primary circuit of the main circulation pipeline (MCР) were studied under eccentric tension in the initial state and after 100 thousand hours of operation in the conditions of the Novo-Voronezh NPP. Using a new engineering approach based on measuring the specimen tightening and constructing a cyclic elastoplastic fracture diagram for a specimen with a crack in the coordinates “tightening – the stress intensity factor, calculated taking into account the plasticity correction”, a calculated life estimation is given for the pipe of Du 550–30 MCР NPP, made of 08Kh18N12T steel, according to the criterion of cyclic crack growth resistance, taking into account operational degradation of properties caused by the running time of 100 thousand hours. The life (survivability), expressed in a number of cycles of change in internal pressure, for a pipe with the most dangerous defects (surface semi-elliptical crack and combined defect “pitting + crack”) is determined. An analysis of the influence of the level of initial damage and the type of hazardous defect on the survivability of the pipes is made. The results can be used to analyze damage and predict the life of pipes made of ductile metals and alloys, in cooling systems of reactors, as well as main pipelines of hydrocarbon transport.