Regularities of welded joint surface relief morphology change of oil and gas equipment under operating conditions

Abstract

Methods that are used to study the fine structure of constructional materials are becoming more popular. Interdisciplinary approaches are important for explaining the relation between macrolevel processes and higher levels of metal destruction mechanisms research. Synergetics properly reflects the essence of natural processes, in particular the plastic deformation of metals. It is known when energy is supplied from outside, the open system organizes itself, striving to produce minimum of entropy. In this case when the accommodative mechanism is exhausted, the system passes to another dissipative structure with a dramatic change in properties. The authors studied deformation processes of outer layers and internal subsurface volumes of a metal when welded joints are deformed. It is shown that the zone of thermal influence in a welded joint is the area of discharge of the supplied energy and the zone of accommodation of the plastic deformation of the welded joint. The deformations of a new and embrittled metal after theoperation run in different ways. This difference is taken as the basis for the assumption about the welded joint continuity preservation mechanisms under deformation. The microrelief of the welded joint on the surface and in the internal subsurface volumes zones has been investigated: welded seam, zone of influence, base metal. The relief parameters on micro-, nanolevel have been quantitatively evaluated: dispersion Rа and asymmetry Rsk according to GOST R ISO 4287-2014. It is shown that all parameters increase in the zone of thermal influence and are sensitive to discontinuities in the form of microcracks. One should note that the deformation relief is self-similar at various hierarchical levels. Fractal analysis of welded joint zones has been performed. It is shown that under deformation fractality increases in the zone of thermal influence.

Keywords

• welded joint
• surface deformation relief
• etching topography