Pyrig T. Impact of preoperational loads in the process of laying on resource of safe operation of subsea pipelines

The dissertation is devoted to studying the influence of the preoperational loads in the process of laying on resource of safe operation and load-carrying capacity of subsea pipelines. For the first time it was fatigue curves and areas of corrosion fatigue curves constructed for specimens of the base metal and welded joint of subsea pipeline with taking into account preload by S-lay and J-lay methods of installing that allow to determine the durability of the material of subsea pipelines with intact and damaged insulation coating during its operation depending on the method of construction and the level of mechanical stresses during its laying. It was established the main regularities of the influence of stresses on the stage of laying on the deformational behavior of subsea pipelines material during its operation. Based on a pooled analysis of durability and deformational behavior indicators of the pipeline material it was proposed a method for determining the resource of safe operation and introduced the notion of "relative resource of safe operation" of subsea pipelines, the use of which allows leveling influence of specimens durability scattering and the associated calculation errors within the same stress level. It was shown an increase in the non-homogeneity and the appearance of defects in the structure of the pipeline material due to the preoperational loads, which leads to a substantial decrease of durability and resistance to deformation as compared with the initial state. For the first time it was disclosed the influence of the preoperational loads on the electrochemical behavior of the pipeline material and constructed kinetic curves of the electrode potential, which can be used for scientifically substantiated selection of parameters of active and means of passive protection of pipeline material from corrosion.