Dolinska I. Materials fracture diagnostics and residual resource of structural elements determination under local creep

The dissertation is devoted to the methods development of slow fracture estimation of materials and structural elements with creep cracks under the actions of long-term mechanical (static and cyclic) loading, maneuvering regime of loading change and physicochemical exploitation factors, as well as to the methods of the elements diagnostics using method of acoustic emission (AE). The methods development is based on the general energy approach formulated in the dissertation, which makes it possible to establish the kinetics of cracks growth and determine the period of their subcritical growth under various exploitation factors effect on the structural element. Based on the energy approach and the basic concepts of the acoustic emission method the calculation models in the parameters of the AE signals for the analytical description of the materials and structural elements slow fracture under exploitation conditions have been developed. New calculation models for estimation of hydrogen, corrosive environments and neutron irradiation influence on life-time (residual life-time) of structural elements under long-term static and time-varying loading action, as well as elevated temperatures, have been developed. Calculation models for investigation of the cracks growth kinetics (fatigue and high temperature creep) in double-layer plates and determination their residual life-time on this basis have been constructed. The obtained equation of the hydrogen crack growth with parameters of accompanying AE signals and ultrahigh hydrogen concentration has been applied to the investigation of separation between the base and welded metals of the oil hydrocracking reactor wall. Based on the energy approach the methods of residual life-time estimation of the energy equipment elements under maneuvering regime exploitation have been created. As an example the disk of steam turbine rotor has been calculated and the ranges of the load changes (start-stop) number have been found for the case when the maneuvering regime is allowed to be modelled by stationary or low cycle fatigue and for the case when it is not allowed because of fracture risk. The results of the calculation of admissible corrosion defects have been used during the development of the Recommendations for repairing the problem areas of the pipe of the “Kalush-Western border” ethylene pipeline. These Recommendations are implemented in the work and activities of KARPATNAFTOKHIM LLC. The received results are included in the standard of organization of Ukraine (SOU 49.531570412-027: 2015) in the form of a method of calculation of the residual life of oil transport equipment in the presence of creep cracks. The results of research have been used for the residual life diagnosing and evaluating of locomotives power units at Lviv Locomotive Repair Plant PJSC.