Direct electrical heating (DEH) has shown to be a very promising method to prevent wax and hydrate formation in subsea pipelines in the North Sea. Up to now the system has been installed on flowlines of lengths up to 15 km. In this system the heated pipeline is an active conductor in a single-phase AC electric circuit, together with a single core high voltage extruded cable strapped to the heated flowline. This paper presents results from measurements of mechanical and electrical properties of different candidate semi-conductive cable outer sheath materials aged in relevant service conditions, and measurements of electrical resistivity and water content of clay samples taken from relevant oil fields. The results are very promising and indicate good mechanical and electrical properties as well as long endurance of the candidate semi-conductive outer sheath materials. The tests also show that approximately the same resistivity was measured for the semiconductive outer sheath and clay making continuously transferring of AC currents to ground possible. The main mechanisms for reducing the lifetime of the outer sheath materials can be thermal oxidation in combination with increased desorption of stabilizers due to seawater. In order to reveal if a cable design with a semiconductive outer sheath can be used in high temperature seawater conditions, an accelerated ageing program was accomplished.
HV XLPE cable design for direct electrical heating of very long flowlines
2005
5 Seiten, 4 Bilder, 4 Tabellen, 10 Quellen
Aufsatz (Konferenz)
Englisch
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