Sheathing for Subsea Cables

Enabling deep-sea power cables to operate at higher voltages and greater depths than ever before

High voltage subsea cables carry power to offshore oil and gas production platforms, wind farms and power grid applications.  The sheathing around the cable must withstand mechanical movements caused by ocean waves and currents and ust have reliable fatigue resistance.

Current cable sheathing is mostly made of lead.  However, there is industry pressure to move to 420 kV XLPE insulated power cable systems, at depths up to more than 1,000 metres and spanning up to 200 km.  Lead sheathing cannot be used for this application as it does not meet the 40-year lifetime requirement.

Electrical insulation

Higher voltages require thicker electrical insulation, and this insulation expands and contracts with temperature changes created by variations in the cable loading and the enormous external pressure of water at hundreds of meters beneath the sea.

As the insulation heats and expands, it creates large mechanical stresses on the surrounding watertight metal sheath. When the cable cools, the insulation contracts and the external pressure compresses the sheath. The sheath will eventually crack as a result of fatigue and allow water to migrate into the insulation causing the cable to fail. These problems are intensified as the diameter of the cable and the depth of operation increase.


Copper - the perfect solution

Engineers and scientists have developed fatigue-resistant, compliant copper sheathing.  It decreases the weight and diameter of the cable, producing lighter cables, with higher voltage and higher power transmission capacity.

The copper sheathing is designed to keep water out of the insulation, as well as withstand many expansion/contraction cycles and mechanical movements.  It is hoped that the newly developed copper sheathing will be brought to market very shortly.