Effect of the structure and stress state on the magnetic properties of metal in different zones of welded pipes of large diameter

Abstract

The existence of an extensive network of main pipelines, both already operating and being constructed, which are exploited under complex climatic conditions, specifies the need for the development of methods of a nondestructive control for testing the current state of both the pipes themselves and the welded joints in the process of manufacture and subsequent service. In this work, we give the results of microstructural studies, as well as the mechanical and magnetic properties of different zones of welded joints (base metal, heat-affected zone, and the weld) of pipe steels of the strength classes X70 and X80 produced using the method of controlled rolling. The influence of different modes of loading on the magnetic characteristic of the metal of all three zones of welded joints has been investigated. The magnetic parameters that unambiguously characterize changes in the stress-strain state of the separate zones of the welded joint (weld, heat-affected zone, base metal) have been determined in certain ranges of the applied stresses.