Determination of the residual life of oil pipeline pipe taking into account material degradation

A method for estimating the residual life of X70 steel pipe of an oil pipeline with an external surface semi-elliptical crack, in which there is a laminar flow of oil under a pressure of 12 MPa, and a soil corrosive medium penetrates the crack, is proposed. The residual life of such a pipe after 33 years of operation, when corrosion-hydrogen degradation of its material takes place, was studied. Based on the experimental data on the degradation of X70 steel, known in the literature, an approximate basic diagram of the corrosion-mechanical crack growth in such a material was constructed. The energy approach previously formulated by the authors for determining the residual life of an oil pipeline pipe with a corrosion crack is applied to the new problem obtained in this way, when the basic diagram of such crack growth includes the simultaneous degradation of X70 steel. Graphical dependences of the residual life of the pipe on the initial size of the crack based on the simultaneous degradation of its material as well as for the cases of the reserve pipe and the pipe operated for 33 years are constructed and results are compared.