The number of potentially dangerous equipment that has completed its established operational time, but is still being used, is permanently increasing. Therefore there is a problem of its further operations. A decision to continue to operate power-generating plants, when the initial resource of the equipment’s working time is ended, and its further operation without considerable expenditures on repair and the diagnostic of a metal state is possible only with the help of long-term research of metal in power-generating plants. Only a complex of research techniques can estimate the real state of a construction. In the article problems connected with the definition of operation reliability of steam pipeline elbows are investigated. Different areas of an elbow were researched. Results of a microstructure analysis, and mechanical characteristics (time history) research of an elbow metal are presented. Also results of calculation of an elbow on low - cyclic thermal fatigue are presented.