Mathematical Modeling of Aging Processes of Pipeline Materials and Estimation of their Residual Lifetime

Mathematical models for evaluation of the residual life of pipelines, taking into account the simultaneous processes of local destruction (development of the cracks in the pipe wall) and the aging of pipe material during of the long-term operation have been developed. The aging of the pipeline material is described by the change in time of the strength, mechanical and fatigue parameters of the material (degradation parameters) under the interaction with hydrogen-containing and corrosive media (so-called soil-origin corrosion). Experimental studies of changes in the material of oil and gas pipelines due to their long-term (up to 30 years) operation are analyzed. Models of material degradation as some dependences on change of parameters of material degradation in time are constructed. Applying the first law of thermodynamics and models of material degradation, differential equations are constructed, which simulate the growth of the surface cracks in the walls of pipelines under the interaction with corrosive environments and because of hydrogenation of pipe walls. The growth of a fatigue crack in the wall of the oil pipeline with the turbulent flow of oil inside, taking into account the aging of the pipe material during operation time mathematically simulated. It is established that the aging of the material during operation reduces the life time of the pipeline. The parameters of material degradation are calculated and the residual life of the gas pipeline with the corrosion-mechanical crack on its external surface is estimated. Developed mathematical models create the basis for the engineering methods for estimating of the residual life of constructions with long-term loading, taking into account the conditions of their operation.