Luzhetskyy V. Strength and durability assessment of long-term exploited pipes of oil-and-gas pipelines with taking into account of corrosive-aggressive environments action

Object of research: fracture process of elements of pipelines for different purposes, which realizes by propagation of initial crack-like defects under action of operating factors. Aim of work: development of engineering methods for assessment of strength and durability of elements of the pipelines systems of long-term exploitation with taking into account of subcritical growth of the corrosive-mechanical crack-like defects. Methods of research: experimental methods for determining of the cyclic corrosion crack growth resistance diagrams of metal of pipelines for different purposes with taking into account of the operating factors; calculation methods for determining of the kinetics of the crack-like defects growth in the wall of pipelines; evaluation of admissible size of defects and failure pressure for pipelines with corrosive-mechanical crack-like defects. The method for numerical assessment of kinetics and shape evolution of crack-like defects during their propagation in the wall of pipe was developed for conditions of fatigue and corrosion fatigue mechanisms of fracture. The regularities of fatigue crack growth in the walls of trunk oil-and-gas pipelines were determined in dependence of crack's initial shape and depth and also with taking into account the influence of operating time and composition of corrosive environment on corrosion fatigue fracture behaviour of materials of pipelines. The rapid method for forecasting of strength and serviceability of defected pipeline system was proposed and verified. It has been proved that the multiply corrosion-mechanical defects of length up to 100 mm cannot contain the threat of fracture for oil pipeline "Druzhba". The calculations of depth of potentially critical defects were made for trunk oil pipeline "Druzhba" in dependence of their location on the pipeline route. Results of work are implemented the NGVU "Boryslavnaftogaz" (JSC Ukrnafta).