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[References: 34 tit.]

Relevance of the studies is brought up by the necessity to provide a highly reliable operation and diagnostics of welded assemblies and steel tubes at hazardous production facilities. The main purpose of the paper is to suggest a new approach to integrated engineering diagnostics for heat treatment of welded structures and generator surface tubes, based on the X-ray microdilatometry. Key findings of the study are the following: cyclic heating of specimens without preliminary heat treatment does not result in changes of solid solution composition, but demonstrates the structural stability at a wide range of temperatures; structural stability during cyclic heating is explained by the hypothesis about specimen surface chemisorption of atmospheric nitrogen; the preliminary thermal cycling process within the range of 100–500 ?°C is shown to bring to the effective reduction of solid solution composition of failed steel tubes, and maintaining the structural stability later during cyclic mechanical deformation testing within a wide range of external loads; temperature of preliminary cyclic heat treatment is selected in the region of anomalous jump of lattice thermal deformations, as it indicates the first-order phase transition, associated with changing of atomic structure of the amorphous component; based on the X-ray microdilatometry, a microscopic sign of solid solution structure stabilization is found in failed steel tubes.