Stress Distribution and Crack Development in Welds of Metal Structures of Main Gas Pipelines

The change in the stress state in the main gas pipelines in the zone of butt welds of pipe edges, which is the most stressed element of pipelines, is considered. It is indicated that in thin-walled pipes, a plane stress state mainly acts and the stresses acting normally to the circumferential weld is selected as the calculated one. The features of the course of fatigue processes in these structural elements are presented, depending on the stress level, and zones with different fracture gradients are marked. It is shown that a one-sided cyclic bending occurs in the walls of aboveground pipelines, which determines the shape and geometric parameters of the fatigue dolom in the form of an ellipse. The calculation schemes of crack resistance of structural elements, in which the equation for determining the intensity Paris’ coefficient is the main one, are studied. This function gives a reliable value for static and low-cycle loads. In case of multi-cycle fatigue, which leads to variations in the parameters, shapes and locations of the dolom area, the use of this coefficient leads to a two-stage adjustment of the parameters and the determination of the maximum equivalent stress, applying the Mises strength theory. As a result, the maximum equivalent values of stress and cyclic durability are obtained for a reliable assessment of the service life of the pipeline.