Unravelling subsea cable failure in offshore wind

According to a report by GCube Insurance in 2021, the average insurance claim nearly doubled from £1.7 million (€2 million) in 2010-2015 to £3.1 million (€3.6 million) in 2020. In total, claims for offshore wind grew from around £124 million (€145 million) in 2010-2015 to around £500 million (€585 million) in 2020.

Of these, around 50% were down to damage to subsea cables, with other insurers estimating that damaged subsea cables represent between 70% and 80% of their claims. 

It is clear to me that if we are to meet the huge ambitions placed on Offshore Wind by nations around the globe and meet Net Zero targets, we will need to find new – and better – ways of working.

A recurring problem for the Offshore Wind industry is damage caused to the submarine power cables during the installation process – nine out of ten insurance claims on cables are due to installation damage, and the Offshore Renewable Energy Catapult in the UK estimates that damage incurred during installation contributed to 46% of all power cable failures. 

At the point at which cables leave the laying vessel and meet the seabed, they are frequently subject to damage caused by over-bending, cable-pulling, and inadequate design of lead into the monopile. While installation contractors can use Sonar or ROV monitoring to observe the cable as it leaves the vessel, this is an expensive approach which will not work if stirred-up sediment is affecting visibility. Finding a way to detect installation damage should be an essential priority for the industry. 

In a study carried out in 2019 by the University of Strathclyde, the average rate of power cable failure is approximately 0.003 failures/km/year for European wind farms. This means that a wind farm with 100km of power cable has a 30% chance of cable failure in any given year. The average downtime for an inter-array cable repair is around 40 days, and 60 days for an export cable. On average, inter-array cable damage costs between $1.8 million to $12 million, and export cable damage costs between $10 million to $30 million. 

Faced with this technical challenge, the industry has now responded through the International Marine Contractors Association (IMCA) with a new Code of Practice (IMCA M264) which applies to all vessels that lay cables in an offshore environment and which sets a new baseline for successful cable installation. 

It defines minimum requirements for safely laying offshore submarine power cables within the renewable energy industry covering topics such as laying spread (the combined systems including cable lay operation centre, Linear Cable Engine, main cable turntable, drums/tensioners, clamps, support, rollers, etc..), the cable lay vessel or barge on which it is installed, the interface between the vessel and the spread, and the safest ways for over boarding, trenching and cable pulling.

Building on the technical expertise of IMCA and its Members, the new document sets the standard of acceptable practice for everyone in the industry, including energy companies. As a Code of Practice, it will be used to formulate technical specifications within contracts, which means it can potentially have a huge and positive impact on an industry looking for practical solutions and tangible improvements to how we work. 

The product of positive and proactive industry collaboration, the Code of Practice not only recognises the experience of major contractors who have a wealth of experience in the design, testing, operation, and maintenance of cable lay equipment and its interface with supporting vessels, but also recent analytical techniques and innovation based on now readily accessible technology.  

All of this means that our Code of Practice will enable the industry to overcome the challenges for subsea cable laying safely and efficiently and help our sector to continue to play its part in meeting huge expectations. 

This article originally appeared in Offshore Support Journal.