DEVELOPMENT OF TECHNOLOGY OF COMBINED JOINING OF POSITION BUTTS OF THICK-WALLED PIPES OF HIGH-STRENGTH STEELS

摘要

The modern pipeline systems are designed for high operating pressures. During construction of such systems the pipes with wall thickness of up to 40 mm are applied. For joining of such pipes the new more effective methods are developed, including the combined ones. The combined technology envisages the welding of root and filling welds using different methods. To increase the rates of construction and quality of welding it is offered to weld the root using flash-butt welding (FBW), and the filling layers must be produced using automatic electric arc welding. The aim of this work is to study the features of formation of joints produced using FBW of root welds in pipes with thickness of more than 20 mm with different edge preparation and to investigate the quality of joints of root welds and combined joints. The influence of edge groove on the welding process and formation of joints under the conditions of increased heat removal from welding zone during flashing was investigated. The technology of FBW of root welds of the position butts of thick-walled pipes of high-strength steels, combined with electric arc welding, was developed. The optimum FBW parameters at different thickness of projections of root weld groove were determined. The level of influence of electric arc welding on the properties of root welds was established, including the improvement of ductile properties of welded joints. The comprehensive mechanical tests of joints of root welds produced using FBW and the combined arc-welded joints were carried out indicating their practical equal strength with the base metal. Such a combined process will allow a great simplification and acceleration of the process of assembly and welding of the root weld, which predetermines the productivity of the whole process of the position butt welding. This ensures the high reliability and quality of root welds of the joint.