Analysis of the welded pipe joints state and the methods for increasing the bearing capacity of gas transmission systems‘ pipelines

Abstract

Abstract The changes in the structural state of the weld material of gas pipes at different seam cross-sections are considered. The classification of external and internal weld defects caused by different types of factors carried out, the stress concentration in the transition zone of the weld to the pipe metal is the most significant factor. The analysis of atmospheric effects on the welded seams of pipelines, that initiate adsorption and electrochemical processes of the metal microstructure, which cause corrosion on the external surface of the weld, is given. Taking into account the non-stationary loading mode of pipes due to fluctuations in the internal gas pressure, corrosion and fatigue damages are also added to these defects, which cause the development of fatigue cracks, leading to a violation of the system’s tightness and even to the welds destruction. The method for increasing the bearing capacity of pipelines is proposed by applying a technological operation of the external surface plastic deformation of the weld and of the transition zone to the pipe metal, which creates residual compressive stresses that relieve working tensile stresses in the stress concentration zone.