DEVELOPMENT OF TECHNOLOGIES OF REPAIR BY ARC WELDING OF OPERATING MAIN PIPELINES IN UKRAINE

摘要

In order to lower material-financial and ecological losses inherent to classical method of main pipeline repair, associated with their stopping, methods allowing main lines to be repaired without taking them out of service, are applied worldwide. The paper deals with the directions of development at PWI of technologies of restoring the load-carrying capacity of defective sections of the main pipelines under pressure with arc welding application. Analysis of the features of arc welding application on pipelines under pressure has been performed and ways to eliminate the unfavourable factors have been determined. Influence of welding heat on strength characteristics of pipe metal is shown, and safe conditions of welding-up corrosion defects are established, depending on thermophysical properties of the transported product and internal pressure magnitude. The paper presents an original design-technological approach to performance of repair operations with arc welding application, which is implemented on operating mail pipelines of Ukraine. Experimental-theoretical assessment of the advantages of application of overlap-butt welded joints over traditional joints with fillet welds is given. Results of investigations by polarization-optical method of stress concentration factors in the points of deposited metal transition to base metal are presented for various kinds of loading of simulation samples. Application of overlap-butt joints allows expansion of heat input range in arc welding; controlling the dimensions, structure and properties of HAZ metal; lowering concentration in the points of circumferential weld transition to the pipeline and thus improving the fatigue limit of welded joints of reinforcing structures at repeated static load. Normative-technical documents have been developed and introduced, which specify repair of the main pipelines under pressure with application of arc welding, and cases of practical application of the most effective design solutions are shown.