Melnyk N. Development of the method of magnetoelastic acoustic emission for the state diagnostics of long-term exploitation of the ferromagnetic construction elements

The dissertation is aimed at solving the significant scientific and technical problem consists in the development of the method for diagnostic of the condition of the long-term exploited ferromagnetic elements of constructions on the parameters of the signal of magnetoelastic acoustic emission (MAE). This method is based on the analysis of the mechanism of generation of the MAE, selection and substantiation of the statistical model of the registered signal, development of effective algorithms for processing the result of the received signals as well as the method for diagnostic of ferromagnetic objects. Based on the energy approach, a mathematical model of motion of 90° domain wall during the ferromagnetic re-magnetization is developed. The relation ship between parameters of the jump of 90° domain wall and the parameters of the MAE signal and the tested ferromagnetic material is established. Distinct features of the MAE signal are found, in particular, the random occurrence of individual events in time, time boundedness, and amplitude randomness. The model of the MAE signal in the framework of statistical model of the random impulse flow is developed. The impulse, time and spectral characteristics of the pulse signal at the output of the primary piezoelectric converter are singled out. Informative parameters of the MAE signal and algorithms for their estimation together with an experimental verification have been proposed and substantiated. High sensitivity of these parameters to structural changes of ferromagnetic material, influence of physico-chemical and mechanical factors, parameters of the re-magnetizing field is revealed. Based on the proposed informative parameters of the MAE signal, the technique for diagnostic of the stress state of ferromagnetic materials is developed and its experimental testing on long-term exploited pipe steels is carried out. This technique makes it possible to identify areas of residual stresses and in practice provide an error less than 11%. The research results areintroduced for MAE-diagnostics of long-term exploitation facilities at “Main pipelines “Druzhba”, a branch of PJSC “Ukrtransnafta” and at “PRIKARPATTRANSGAS Gas Pipeline Management”.