Tape winding angle influence on subsea cable sheathing fatigue performance

A fundamental component of subsea power cables is the thin galvanized steel tape winded around the dielectric and sheathing layer in order to prevent permanent thermal cycling induced deformation. The pressure state induced by the resistance offered by such tapes against radial reformation reduces the triaxiality ratio of the stress state of the lead sheathing layer. It is known that a reduced triaxiality has a beneficial effect on ductility and fatigue life of metals. In the present work a series of finite element simulations are performed in presence of galvanized steel tapes at three different winding angles and without such reinforcement at all, obtaining a qualitative indication of its effect on the stress state induced in the sheathing layer. Loading conditions as internal pressure related to thermal dielectric expansion and cable bending are modelled. The numerical qualitative results are discussed in connection to a series of full-scale fatigue tests performed on subsea power cables with and without the support of steel tapes. 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/

Effect of Vanadium on Grain Refinement of Aluminium

Today, grain refinement of aluminium is effectively achieved by inoculation. The performance of the inoculants, as well as further growth restriction in the liquid metal, can be affected by alloy- elements and impurities. A trend towards increasing amounts of some specific impurities in the coke- anode bring forth increasing amount of these elements in the final metal. One such element is vanadium. The effect of limited amounts of vanadium on the grain refinement is in this thesis assessed. Both the impact on inoculation properties and continued growth restriction is investigated. Levels ranging from 0 to 500 parts- per- million (PPM) is evaluated in a commercial 6060- aluminium alloy and highly pure 5N (99.999 $\%$ Al)- alloy. Thermal analysis and optical microscopy are used to investigate the solidification and final microstructure. Edge- to Edge Mismatch (E2EM)- model, Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB) and Transmission Electron Microscopy (TEM) are applied to investigate the inoculants with respect to vanadium. Both theoretical and experimental evaluations indicate that vanadium has little or no effect on the grain refinement of aluminium at the investigated levels. Investigations of the inoculation particles also show that their composition and properties are unchanged. These results are consistent with the most recent literature

Effect of Vanadium on Grain Refinement of Aluminium

Today, grain refinement of aluminium is effectively achieved by inoculation. The performance of the inoculants, as well as further growth restriction in the liquid metal, can be affected by alloy- elements and impurities. A trend towards increasing amounts of some specific impurities in the coke- anode bring forth increasing amount of these elements in the final metal. One such element is vanadium. The effect of limited amounts of vanadium on the grain refinement is in this thesis assessed. Both the impact on inoculation properties and continued growth restriction is investigated. Levels ranging from 0 to 500 parts- per- million (PPM) is evaluated in a commercial 6060- aluminium alloy and highly pure 5N (99.999 $\%$ Al)- alloy. Thermal analysis and optical microscopy are used to investigate the solidification and final microstructure. Edge- to Edge Mismatch (E2EM)- model, Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB) and Transmission Electron Microscopy (TEM) are applied to investigate the inoculants with respect to vanadium. Both theoretical and experimental evaluations indicate that vanadium has little or no effect on the grain refinement of aluminium at the investigated levels. Investigations of the inoculation particles also show that their composition and properties are unchanged. These results are consistent with the most recent literature

Room temperature creep mechanism of a Pb-Sn-Sb lead alloy

Lead alloys are the most common materials adopted for the production of subsea power cable sheathing. The sheathing is a layer of stable and watertight metal, which serves to prevent the electrical failure of the cable. During the predicted operational life of the cables of several decades, these experience strains due to the installation process, the oceanic currents and the thermal expansion of the cable. The low melting temperature of such alloys, around 600 K, imply that creep deformation will occur when subjected to loading even at room temperature. The goal of the present study is to investigate the tensile behavior of the Pb-Sb-Sn alloy of interest in order to predict the correlation between strain rate and stress level. A mechanical characterization was performed through tensile testing at different strain rates of specimens cut from power cable sheathing. Due to the extreme ductility of the material, the use of digital image correlation was necessary to compute an acceptable approximation of the in-plane strain field on the surface of the specimens. The results were implemented in finite element method environment using Abaqus and Isight to calibrate a creep model able to reproduce at best the behavior of the material. Such model was also positively tested in the case of a relaxation test. In addition, a tensile test of several steps at different loads was executed with the aim of extrapolating and interpreting the steady state creep exponents at different creep regimes and the indications that these can provide on the deformation mechanisms of the alloy.publishedVersio

Tensile characterization of a lead alloy: creep induced strain rate sensitivity

acceptedVersio

Ormen Lange "tie-in" på Sleipner R

Gassen som produseres ved det nye Ormen lange feltet skal hovedsakelig eksporteres til England og en ny rørledning fra prosesseringsanlegget på Nyhamna i Aukra kommune til Easington i England skal bygges. Den nye rørledningen skal kobles opp mot det eksisterende gassrørledningsnettet i Nordsjøen. Denne oppkoblingen skal skje på Sleipner R plattformen og gjør det mulig å blande gassen fra Ormen lange med gass fra Sleipner og Troll. Misjonen med denne blandingen er å oppnå de spesifikasjonene kunden har satt for gasskomposisjonen. Ormen lange gassen har for høy ”sot-verdi” til å kunne eksporteres direkte, derfor blandes den med gass fra Troll og Sleipner. I oppgaven vår har vi etablert en reguleringsalgoritme for denne gassblandingsprosessen, samt prøvd å optimalisere denne med hjelp av en matematisk modell i datasimuleringsverktøyet Matlab. I den matematiske modellen er det rom for ytterlige forbedringer, det samme gjelder vurdering av risikomoment, da vi ikke har faglig grunnlag for videre sikkerhetsberegninger. Videre har vi sett på de komponentene ABB OS har valgt til reguleringen og prøvd å forklare disse valgene

Small and Full-Scale Fatigue Testing of Lead Cable Sheathing

The fatigue behavior of a PbSnSb alloy used in subsea power cable sheathing was studied using small- and full-scale experiments. The aim of the work was to understand the transferability between the scales and suitable testing methods. Creep phenomena are addressed by considering the cyclic strain rate as well as the small-scale loading mode. The fatigue test results show significant difference between different loading modes and scales. It is also evident that fatigue- creep interaction is highly important

Subsea power cable sheathing: an investigation of lead fatigue performance

The protection of subsea power cables against electrical failure is achieved by the use of a watertight layer. Due to its properties of chemical stability and ductility, lead has been the material of choice for this purpose for several decades. Due to the low melting temperatures of lead alloys, their behaviour is strongly influenced by time-dependent phenomena, such as creep and recrystallization, which become more prominent for lower strain rate deformations. In order to understand the performance of the alloys of interest under cyclic loading experienced during and after installation in combination with the different variables influencing its behaviour, extensive testing is necessary. This manuscript presents the results of fatigue tests at two different strain rates for an alloy of industrial interest. The tests are monitored with the aid of digital image correlation, which greatly reduces the uncertainty on the quantification of the real strain field. The post-mortem fracture surfaces are investigated through scanning electron microscopy and metallurgical characterization to help understanding the differences in the failure modes active in the different stress/strain regimes

Room temperature creep mechanism of a Pb-Sn-Sb lead alloy

Lead alloys are the most common materials adopted for the production of subsea power cable sheathing. The sheathing is a layer of stable and watertight metal, which serves to prevent the electrical failure of the cable. During the predicted operational life of the cables of several decades, these experience strains due to the installation process, the oceanic currents and the thermal expansion of the cable. The low melting temperature of such alloys, around 600 K, imply that creep deformation will occur when subjected to loading even at room temperature. The goal of the present study is to investigate the tensile behavior of the Pb-Sb-Sn alloy of interest in order to predict the correlation between strain rate and stress level. A mechanical characterization was performed through tensile testing at different strain rates of specimens cut from power cable sheathing. Due to the extreme ductility of the material, the use of digital image correlation was necessary to compute an acceptable approximation of the in-plane strain field on the surface of the specimens. The results were implemented in finite element method environment using Abaqus and Isight to calibrate a creep model able to reproduce at best the behavior of the material. Such model was also positively tested in the case of a relaxation test. In addition, a tensile test of several steps at different loads was executed with the aim of extrapolating and interpreting the steady state creep exponents at different creep regimes and the indications that these can provide on the deformation mechanisms of the alloy

Subsea power cable sheathing: an investigation of lead fatigue performance

The protection of subsea power cables against electrical failure is achieved by the use of a watertight layer. Due to its properties of chemical stability and ductility, lead has been the material of choice for this purpose for several decades. Due to the low melting temperatures of lead alloys, their behaviour is strongly influenced by time-dependent phenomena, such as creep and recrystallization, which become more prominent for lower strain rate deformations. In order to understand the performance of the alloys of interest under cyclic loading experienced during and after installation in combination with the different variables influencing its behaviour, extensive testing is necessary. This manuscript presents the results of fatigue tests at two different strain rates for an alloy of industrial interest. The tests are monitored with the aid of digital image correlation, which greatly reduces the uncertainty on the quantification of the real strain field. The post-mortem fracture surfaces are investigated through scanning electron microscopy and metallurgical characterization to help understanding the differences in the failure modes active in the different stress/strain regimes.publishedVersio