Evaluating the Effectiveness of Magnetic-Pulse Treatment for Healing Continuity Defects in the Metal of Oil and Gas Pipelines

Abstract

This research paper addresses the issues in evaluating the effectiveness of magnetic-pulse treatment for healing continuity defects in the metal of oil and gas pipelines. A theoretical analysis of the magnetic-pulse action mechanism on continuity defects in the metal was carried out. The results of experimental studies of the effect of magnetic-pulse action on continuity defects of thick-walled samples, cut from used gas pipelines containing microcracks with different geometries, are also presented. The samples were processed under two different technological operating modes of the magnetic-pulse unit: the applied energy was 10 kJ for the first mode and 20 kJ for the second mode. The state of the cracks’ microstructure before and after the magnetic pulse treatment was studied using an optical microscope. As a result of the studies, it was found that magnetic-pulse treatment led to local heating of the crack tips, which was confirmed by the formation of a heat-affected zone in the vicinity of the crack tips. The temperature at the crack tips reached the metal’s melting point at the applied energy of 20 kJ, whereas at the energy of 10 kJ, signs of metal melting were not noted. In the course of the conducted experiments, it was found that the cracks were not completely eliminated after magnetic-pulse treatment; however, the edges of the crack tips melted, with subsequent filling by molten material. Magnetic-pulse treatment resulted in blunting of the crack tips, as their shape became smoother. It was established that the geometry and shape of the crack tip have significant influences on the effectiveness of this technology, as a narrow and sharp crack tip required less energy to reach the metal’s melting point compared to smoother one. The effect of magnetic pulse treatment on the microstructure of pipeline metal and its strength characteristics was also studied. It was found that this treatment leads to structural changes in the area of the crack tip in the form of grain refinement and subsequent strengthening of the pipeline metal.