Small- and Full-Scale Fatigue Testing of Lead Cable Sheathing
- Audun Johanson (Nexans Norway Oslo) | Luigi Mario Viespol (Norwegian University of Science and Technology) | Antonio Alvaro (Sintef Industry Trondheim) | Filippo Berto (Norwegian University of Science and Technology)
- Document ID
- International Society of Offshore and Polar Engineers
- The 29th International Ocean and Polar Engineering Conference, 16-21 June, Honolulu, Hawaii, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. International Society of Offshore and Polar Engineers
- Subsea Power Cables, Creep, Lead Sheath, Fatigue
- 3 in the last 30 days
- 21 since 2007
- Show more detail
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.
High voltage subsea power cables operating require an impermeable water barrier to prevent humidity in the isolation system. In the case of Mass-Impregnated (MI) or Cross-Linked High-Density Polyethylene (XLPE) insulation systems as normally used for high voltage submarine power cables, humidity can compromise the systems electrical integrity. Lead-based alloys are normally used as a water barrier due to ease of extrudability and ductility. Lead-based alloys are also associated with favorable low-cycle fatigue properties when compared to higher strength materials such as copper or aluminum. However, due to its combination of very poor high cycle fatigue properties and low creep resistance, multiple cyclic scenarios can challenge the fatigue-creep life of the sheathing. Critical scenarios include cable installation and offshore jointing. These operations imply a temporary dynamic suspension between the seabed and a floating vessel where the cable will be subjected to bending due to wave motion on the cable and vessel. Additional bending fatigue damage can be introduced from vortex-induced vibrations (VIV) in the temporary catenary or free-spans along the cable route. Another case arises from the insulation temperature fluctuations during operation. Thermal expansion and contraction of the oil in MI insulation or the XLPE will cyclically strain the lead sheath in radial direction. The high relative temperature for lead-alloys at room temperature (∼0.5 Tm) and low creep resistance for typical cable sheathing alloys cause a significant strain rate dependency under loading. These properties also depend on the alloying elements and the microstructure.
|File Size||723 KB||Number of Pages||6|