Fedorovych I. Estimation of the danger of the main gas pipelines with detected surface crack-like defects destruction

The dissertation focuses on problems of the development of a method for assessing the conditions of long operating main gas pipelines destruction in accordance with the approaches of fracture mechanics and the results of their technical diagnostics, as well as the development of technology on the basis of continuing their performance on this basis. New experimental data on changes in the characteristics of the cyclic fracture resistance of gas-fired steels are obtained, depending on the combined effect of the duration of operating time and corrosion media. On the basis of the conducted researches, in the cross section of the pipe of the main gas pipeline “Kyiv - West Ukraine I thread” more accelerated development of fatigue and corrosion-fatigue cracks than in the axial (longitudinal) direction. The calculation method for predicting the development of crack-like defects of semi-elliptical shape in the pipeline wall is adapted, depending on the internal pressure of the gas, and on this basis the regularities of the further development and change of the shape of the diagnosed surface cracked defects in the pipe of the main gas pipeline “Kyiv - Western Ukraine I thread” are established. It is substantiated that extended semielliptical corrosion-fatigue cracks are more dangerous than “short” in the form of a corrosive ulcer. The dependence of the limiting sizes and the shape of the cracks from the threshold (initial) is proposed, which makes it possible to assess the danger of the diagnosed defects and interpret the results of the survey of long exploited gas pipelines. The method of repair of steel gas pipelines is proposed, which significantly impedes the formation of fatigue and corrosion-fatigue cracks on the treated surface of these pipes.