The current state of the main gas pipelines diagnostics is analyzed in this paper. It is noted that the gas extraction and gas transportation complex now plays an important role in the structure of the Ukrainian economy and is considered to be an industry which should ensure the implementation of important projects aimed to reduce the energy crisis in the country. Some aspects of implementation of the main gas pipelines open and hidden areas diagnostics are considered. The methodological principles of the construction of the scientifically grounded method of formulation of the predictive estimation of the gas pipelines residual life under the conditions of long-term operation are described. The peculiarities of the implementation of such approach is that the basic calculations of the criteria are carried out within the framework of theories reflecting the main mechanisms of the bearing capacity exhaustion of the gas pipelines pipe material, in particular, according to the criterion of static strength, taking into account the corrosion and deterioration of the material, estimation of the residual life according to the criterion of low cycle fatigue allowing to predict the residual life of the pipeline, taking into account the processes of the origin of fatigue cracks near constructive stress concentrators, estimating the residual resources according to the criterion of crack resistance. On the basis of the data obtained during the diagnosis, and the results of calculations the recommendations for the repair, replacement and strengthening of dangerous parts of main gas pipelines are developed; their regular diagnostics makes it possible to determine effectively the technical condition and allows to establish the expediency of further operation and recommendations for the elimination of detected defects.