Various mechanical and structural characteristics of individual sections of the welded joint, formed under the influence of the thermodeformation cycle of fusion welding, have different fracture resistance. The difference in the mechanical characteristics of the welded joint zones is due to structural changes at the micro and macro levels. Changes at the micro level due influenced by the temperature gradient have a hierarchical relationship with changes at the macro level. A large number of studies have been devoted to these issues, including for welded joints made of ferrite-pearlite steels. However, the assessment of the cyclic durability of a pipe welded assembly with technological or operational stress concentrators located in various zones of the welded joint is still an urgent task. In addition, the effect of cyclic loads on the structure and resistance of individual sections of welded joints, as well as on the interaction of adjacent sections of zones of mechanical heterogeneity of welded joints requires additional study. The mutual influence of neighboring zones of mechanical heterogeneity of welded joints leads to localization and development of plastic deformations in the loading cycle. The local zone of plastic deformation is a concentrator, which in the presence of a technological defect of the welded joint has an additional effect on the stress-strain state and on the transition in the concentration zone to the active formation and growth of secondary cracks. Identification of the most dangerous zones of mechanical heterogeneity of welded joints under cyclic loading conditions will improve the assessment of the danger of defects of welded joints detected during diagnostic work. Taking into account the influence of zones of mechanical heterogeneity will make it possible to more accurately predict the places of crack formation.
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