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[References: p. 186 (20 tit.)]

The effect of the long-term operation on changes in the parameters of fracture toughness and a tendency for a delayed fracture of the steel of main gas pipelines is investigated. Based on the method of the full strain diagrams the general regularities of operational degradation influence onto the static fracture toughness and microscale failure mechanisms of 17MnSi steel after long term operation have been established. Generalization of results on the influence of absorbed hydrogen onto the pipeline steel structure and fracture pattern made possible to systemize the data on dispersed damage accumulation. The schematization of fracture mechanisms of 17MnSi steel is offered. The proposed approaches to the study of static fracture toughness of the steel of the main gas pipelines can be used in the evaluation of their technical conditions and planning of their overhaul.