Study of the mechanical properties of the gas pipeline metal after long-term operation in conditions of the North

Abstract

The residual strength and technical condition of the material of 530-mm steel pipe (14KhGS) of main gas pipeline are estimated to ensure the safety of long-term operation of pipelines in climatic conditions of the North. The mechanical properties are determined using standard methods of mechanical testing in laboratory conditions. A full-scale pressure test up to failure is used to determine the actual values of the fracture toughness and safety factor of the pipe. Full-scale tests were carried out on a test bench, a computer-measuring complex which displayed the reaction of the object to the load. A pipe fragment was cut from the linear part of the main gas pipeline and welded with spherical plugs. The outer surface of the pipe was notched along the pipe axis. The depth of the notch was calculated such that the breaking load on the ligament section at the notch site corresponded to the working pressure of the gas pipeline. No significant changes in the mechanical properties of the pipe metal were revealed in the absence of visible corrosion and deformation damage during long-term operation of the pipe in the North. Impact tests did not reveal embrittlement of the metal of the tested pipes. Full-scale tests of a pipe with an artificially applied defect made it possible to calculate the value of the critical stress intensity factor, which allowed us to estimate the residual strength of a pipe with a longitudinal crack. The value of the strength criterion of the fracture mechanics indicates the preservation of a sufficiently high viscosity of sheet metal pipes. Similar tests of the pipes (of other size and made of other materials) operating in the main gas pipelines should be continued taking into account temperature ranges and material degradation after long-term operation.