An Overview of Cable Burial Risk Assessment Methods

Since the 1850s, submarine cables have played an integral role in international data transmission and are now crucial to the growth of the offshore renewable sector. It is imperative to ensure the adequate protection of submarine cables so that they remain safe from threats such as fishing gear, shipping anchors, dredging and other dropped objects for the lifetime of the asset.  Cables are the root cause of 80 percent of the insurance claims against offshore wind development1. While understanding the threat to a cable is essential in assessing the lifetime risk to the system, understanding the whole life cost of the system including installation cost, insurance, cable repairs or loss of revenue is essential for development decisions.

Cable burial is generally regarded as the optimal protection technique, and first came into play in the 1970s (before which time most submarine cables were surface laid). The standard burial depth was ~0.6 meters for many years, mainly to provide protection against fishing gear. The Burial Protection Index (BPI), developed in the 1990s, became adopted as Best Practice guidance for submarine cables for over a decade. Originally developed for fiber optic communication cables, it became widely applied to the first and second generation offshore wind farms. However, the method had several limitations including its conservative approach to anchoring and fishing and ignoring the influence of water depth and sediment mobility. Some of these limitations were dealt with through the engineering judgement of the design team; however, this limited the standardization and repeatability of design and lead to significant over-conservatism from perceived threats.

Completing installation of power cables in a cost-effective manner is essential for future wind farm developments. The CBRA Guidance promotes a risk-based assessment method and enables the burial Depth of Lowering specification to be optimized. In addition, it provides a means to assess the residual risk to the cable after burial operations are complete to a specified depth. The Carbon Trust Cable Burial Risk Assessment Guidelines offer a standardized, repeatable and qualitative method to improve risk management of subsea cables for offshore wind farms, improve estimates of risk through reducing undue conservatism, and ultimately reduce the installation and insurance costs for subsea cables.

This new method has been driven chiefly by the offshore renewables sector, becoming an established standard in countries such as the UK, Denmark, Belgium, Netherlands, France and Australia. In addition, emerging markets are looking at the Carbon Trust method including U.S., Korea and Taiwan.

Cathie Associates were one of the lead authors of the Carbon Trust CBRA guidelines and were then retained by the Carbon Trust Offshore Wind Accelerator to act as technical advisers. Cathie Associates will be speaking and exhibiting at the International Offshore Wind Partnering Forum in Princeton, NJ from Apr 3-6. Ed Jones, Subsea Cable Lead, Cathie Associates, will be presenting a brief history of subsea cable protection, and will discuss developments in the CBRA methods and the current state of play. If you are attending the event, don’t forget to join our session on Apr 5, 2:00 – 3:15 PM, Session 6 – Subsea Cable Risk.