S. Basu, I. German, R. Rhodes, G.C. Stevens, J. Thomas
Gnosys Global Ltd,
Keywords: self-healing, self-repair, asset management, polymer, advanced material
Summary:Recently, there have been significant advancements in the development of self-healing materials. When damaged, these materials are capable of autonomously repairing the damage, restoring the pre-damage characteristics of the material and preserving asset integrity. This latter quality is of great value for assets for which access is either extremely difficult or prohibitively expensive. In these cases, the inability to carry out preventative maintenance means that minor damage can, over the course of many years, progress to the point that asset integrity is compromised. Repairing or replacing a damaged asset is a time-consuming and expensive task particularly for power cables, and further penalties may be imposed due to loss of service or environmental contamination. As part of a number of materials self-healing and asset self-repair projects, Gnosys has investigated the potential of different materials to provide self-repair functionality for both solid and fluid-filled cables. In both instances, this has yielded a number of highly promising systems that are now being taken forward for large-scale trials prior to full deployment. In solid polymeric cables, it has been found that the most significant long-term threat is water ingress, which can attack the insulation and cause premature degradation. Although cable manufacturers use water blocking tapes to prevent this, it has been found that these provide only limited protection to the cable. As alternatives, Gnosys proposes the use of hydrophilic TPEs, which swell in a similar fashion to water blocking tapes, but which contain a polymeric constituent that provides structural stability to the layer. This allows the material to resist water ingress at high pressures and even when challenged with seawater (which typically elicits a minimal swell response). This also allows the material to be processed using common cable extrusion techniques as opposed to tape-winding (as with water-blocking tapes) resulting in significant savings and increased cable production speeds. For fluid filled cables (FFCs), the aim is to limit the loss of insulation oil through defects in aging cable sheaths. As FFCs are being steadily decommissioned, it is necessary to develop solutions that can be deployed without altering the cable itself. Here, Gnosys has developed a number of reactive oils that cure upon exposure to oxygen; if the oil leaks through a defect, the oxygen in the surrounding soil will cause it to react and cure, forming a solid plug that prevents further leaks. These oils can also provide a secondary ‘containment’ function, which limits the propagation of already leaked oil and prevents watercourse contamination. This allows the operator of the cable additional time in which to act without risking further costs associated with environmental contamination and remediation.