Comprehensive analysis of the performance of welding joints of gas pipelines with different viscosities

Abstract

Full-scale tests of gas pipelines with different viscosities were carried out in landfill conditions, which are as close as possible to the natural conditions of operation of gas pipelines. The kinetics of crack propagation along welded joints - their trajectory, the transition from the weld seam to the base metal of the pipe and vice versa, the speed of movement of cracks in viscous and brittle metal and defined zones of plastic deformation - were experimentally investigated. It is known that tests on Menaget, Charpy and other samples, which have thicknesses that do not correspond to the thickness of the pipe walls, do not reflect the real picture of visco-plastic and brittle fractures, which does not allow to develop a methodology or model for predicting the final resource (non-accident) of long-term gas pipelines period of operation. At the same time, theoretical and laboratory researches do not always adequately answer the questions directly related to ensuring the durability and trouble-free operation of pipelines. It is likely that in the laboratory conditions of enterprises or scientific institutions it is difficult to reproduce and take into account all the factors that characterize the growth and spread of destruction in a real operating gas pipeline. Therefore, the data of laboratory studies must be checked and necessarily clarified according to the results of pneumatic tests of long pipe sections, i.e., at present, the need to combine laboratory and field tests of pipes of the gas pipeline network is urgently needed. Such tests are not massive, but as a result of their performance, important information is obtained regarding the behavior and properties of the metal in the conditions of loading and operation, which are closest to operational conditions. In field tests, pipes with a diameter of 1000x18 mm were used, which underwent controlled rolling (steel class X70 - grade 06G2BA) at a working pressure of RR = 9.7 MPa (in the northern - low-temperature version). Tensile tests, studies of impact toughness, strength and plasticity of the weld metal were carried out according to standard methods described in works [2-5]. During the experiments, a large number of sensors of temperature, pressure, strain, stress, crack propagation speed, etc. were used. The obtained results regarding the kinetics of the destruction of natural pipes in landfill conditions lay the groundwork for the development of a mathematical model of the engineering forecast of the residual (non-accident) resource of pipelines operating in oil and gas fields.