In-situ tensile and fatigue behavior of electrical grade Cu alloy for subsea cables

Di Wan,Anette Brocks Hagen,Luigi Mario Viespoli,Audun Johanson,Filippo Berto,Antonio Alvaro

doi:10.1016/j.msea.2022.142654

Abstract

Distribution of electrical energy through subsea power cables has an increasingly important role in the renewable power generation. The majority of the subsea cables uses copper (Cu) as a conductor material. Cables suspended from sea level to sea floor are subjected to both static and cyclic loads that can introduce microstructural damage due to fatigue, creep and their interaction. In addition, since the manufacturing process of the stranded conductor results in Cu-materials with superficial irregularities and metallurgical anisotropy, the material performances need to be carefully addressed in order to reliably assess the wires life. In order to provide a deeper insight into the occurring damage mechanisms, monotonic and cyclic tests of micro-sized Cu tensile specimens were carried out using in-situ micromechanical testing, inside a scanning electron microscopy (SEM) equipped with an electron backscatter diffraction. Tensile and cyclic loading behavior are discussed in correlation with the damage mechanisms observed directly and post-mortem. The twin boundary fraction in the microstructure is found to be linked to the deformation status, and thus can potentially be used as an indicator for predicting the remaining life of the material under service conditions.

Highlights

At the present day, a vast network of subsea cables is installed for high voltage power transfer, across stretches of water, often several hundreds of kilometers long, to neighboring landmasses and islands, effectively interconnecting different national grids to balance energy supply and demand
The deformation structure – boundary interaction is of great interest as the boundaries can work as active barriers for dislocation slip and strengthening the material. When it comes to copper, the twin boundaries, especially the coherent twin boundaries, are appreciated due to the strengthening effect to the ma terial’s mechanical performance without significantly increasing the electrical resistivity due to their coherent characteristics to the matrix [19]
As the current work is aimed at exploring the deformation and damage behavior of Electrolytic Tough Pitch (ETP) Cu, especially regarding the creep-related phenomena, uniaxial tensile tests with different strain rates were per formed

Summary

Introduction

A vast network of subsea cables is installed for high voltage power transfer, across stretches of water, often several hundreds of kilometers long, to neighboring landmasses and islands, effectively interconnecting different national grids to balance energy supply and demand. In the recent years, floating wind farms have become an important solution with respect to renewable energy. This includes dynamic power cables, hanging from/connected to the floating units, that will be subjected to fatigue loading from waves, current and motion from the floating structure [1]. The material can be subjected to creep deformation even at temper atures at and slightly above room temperature, if the stress level is sufficiently high to activate relevant mechanisms [5]. Creep deforma tion has a detrimental impact on the ultimate load, and on the ability to withstand fatigue loading [6,7,8], which is of paramount importance for the reliability of floating systems [9,10]

Results

Discussion

Conclusion