The evolution of the welded joints structure at low cycle fatigue

Ekaterina Poyarkova,Iskander Kuzeev,S Bratan,S Roshchupkin,S Leonov,S Gorbatyuk

doi:10.1051/matecconf/201712902045

Abstract

The effect of cyclic damage on the structure evolution and the change in the micro stresses of the crystal cell in characteristic zones of dissimilar welded joints of steels strength classes X60 and X70 is estimated. It is shown, that with increase in the number of loading cycles in less strong metal of the welded joint, relaxation of internal stresses, realized by splitting individual ambits of ferrite grain or by the initiation of micro cracks, is observed. The results of fractographic analysis of a less reliable weld zone at different levels of samples fractures of accumulated damage are presented.

Highlights

Trends in the development of the modern oil and gas industry are due to the impressive volume of requirements growth for the survivability of structures as full-fledged constructions
With an increase in the number of loading cycles at the microscale level, microstresses accumulate in a less strong metal, which leads to the formation of discharge bands in the region adjoined to it
In the field of low-cycle fatigue, meso- and macro-scale levels are involved, when rotations play the main role, and processes do not associated with dislocations

Summary

Introduction

Trends in the development of the modern oil and gas industry are due to the impressive volume of requirements growth for the survivability of structures as full-fledged constructions. Since the process of development and accumulation of damages both of structures materials in general, and of their welded joints in particular, is localized; the resource of the entire construction, according to [1], is determined by the "resource of their critical zones". The issues of increasing the safety of operation of critical engineering facilities by preventing fragile destruction of their elements are becoming more urgent and acute every year This is true for oil and gas pipelines that have heterogeneous butt joints. One of the reasons for their destruction is internal structural and mechanical changes occurring in the metal

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Conclusion