Influence of metal structural heterogeneity in a sheet tube billet on forming mechanical properties and crack resistance of steel pipes for operation in the Arctic climate conditions

Oil and gas main pipelines, which provide delivery of gaseous and liquid raw materials from the Russian distant Arctic and Sub-Arctic regions for processing at the production facilities in the central RF areas, remain the base of the transportation system for energy carriers. New pipeline systems are expanding far and far to the north and north-east mostly uninhabited territories with weakly developed transport infrastructure and extremal operating conditions – low climatic temperatures and increased corrosion activity of mined raw materials. Analysis of operation of pipeline systems in such conditions displayed enormous rise of the number of accidents and rejects at pipelines in comparison with operation of such pipelines in the central RF regions. Thus, metal structural heterogeneity in a sheet tube billet, presented by its increased banding and difference of grain size as well as presence of large non-metallic inclusions, are considered as one of the key causes of rise of the number of accidents. The results of investigation of the effect of non-metallic inclusions and heterogeneity of the structural state of a sheet billet on mechanical properties, crack resistance and corrosion resistance of the basic metal and heat-affected zones are presented in this research. The examined tubes are used for transportation of energy carriers at the minimal possible climatic temperatures. The research was carried out within the State assignment of the RF Ministry of Science and Higher Education (theme No. FSEG-2024-0009 “Development of models for degradation of service properties of metallic and composite materials for building in the conditions of permafrost soils”).