Glushko A. Increase of the life time of welded steam pipe joints from heatresistant pearlitic steels.

The dissertation is devoted to the research of structural changes occurring in the metal of welded steam pipelines joints, operated for a long time under the conditions of creeping. Structural changes lead to a decrease of mechanical properties and lead to damage and destruction of metal welded joints. Definition of features of structural changes allowed to reduce the intensity of their passages thus increasing lifetime of welded joints. Welded steam pipe joints of power plants are damaged more often than steam pipes themselves. Damage of welded steam pipe joints occurs more frequently than damage of the parental metal. This process happens because of structural, chemical and mechanical inhomogeneity of the metal of welded joints, which is the result of welding heat. The features of structural changes were studied by researching the physical and chemical processes occurring in the metal of welded joints and providing structural changes. The research used the theory of dislocations. The connection between the initial structural heterogeneity and the intensity of structural changes was found, and this allowed to optimize the structure of welded joints. It is important to determine a connection between the physical and chemical processes, the stability of the welded joint structures and metal damageability of welded joints to increase welded joints lifetime. Practical use of research results makes it possible to increase the lifetime of welded joints of steam pipelines, which have worked out their fleet life.