Abstract
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.
Highlights
The fatigue behaviour of subsea high voltage cable sheathing, pro duced by extrusion of lead alloys, is affected by the design of the cable and by time dependent deformation and damage mechanisms
The numerical quali tative 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
Full scale fatigue testing results in presence and absence of such tapes are available in the literature and show improved fatigue performances for cable designs which include the reinforcement tapes
Summary
The fatigue behaviour of subsea high voltage cable sheathing, pro duced by extrusion of lead alloys, is affected by the design of the cable and by time dependent deformation and damage mechanisms. An investigation on creep behaviour of cable sheathing lead alloys was published by the University of Illinois evidencing, at three different temperatures, time dependent deformation even for very low stresses and a marked effect of pulling speed on tensile resistance [1] and the effect of alloying elements, thermal treatments and cyclic loading [2]. The studies performed regarded the tensile behaviour and microstructure [7], influence of production defects on fatigue life [8,9], steady state creep [10] and fa tigue results of full-scale testing [11]. The present work utilizes the material properties obtained in the tensile testing and the creep model calibrated based on the test results from [7] to perform a qualitative numerical investigation on the. The full-scale fatigue results [11] are discussed focusing on the influence of stress triaxiality on the fatigue life of metallic alloys
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