Source: Petroleum Safety Authority Norway
Over the course of the last ten years, there have been 26 collisions between facilities and visiting vessels on the Norwegian shelf. Six of the incidents had a very large hazard potential. The Petroleum Safety Authority Norway (PSA) believes training and organisational factors should receive more attention, while at the same time, the technical failure rate must be reduced.
The PSA is concerned that incidents involving collisions with vessels on assignment to the relevant facilities – so-called visiting vessels - will cause major accidents.
Over the last ten years, there have been 26 collisions between visiting vessels and facilities on the Norwegian shelf. The incidents are caused by both deficient organisation of work and responsibilities, inadequate training of involved personnel and failures in the technical equipment. The responsibility for the incidents has rested both with the operating companies, shipping companies and the crew.
In other words, there is not one single cause, but several factors that form the background for the incidents in recent years.
There is a need for a significant improvement in how the vessels are operated and for assessing design loads for the facilities.
The PSA is of the opinion that training and organisational factors should receive more attention and the technical failure rate must be reduced. Improved quantification of the risk entailed by collisions is also necessary. The PSA has not identified a need for changes in the regulations.
Raising the bar on standards and responsibility
The equipment and training of crews on the vessels is the shipping company's responsibility, in accordance with the requirements in maritime legislation. The location-specific assessments of what takes place within the safety zone are, to a large extent, the operating companies' responsibility and must be followed up by them. The guidelines for safe management of offshore supply and facility movement could, if they were followed, have prevented several of the incidents.
The PSA wants to point out that many of the collisions have occurred in connection with operations where the facilities have been tied to wells. The facilities are designed to withstand collisions of a certain size, but several of the collisions have involved higher collision energy than what is used as a basis for the platform design.
Loads on, and the strength of, the facilities
According to the Facilities Regulations, facilities must be designed for a collision with an annual probability of 10-4 per year. It has been common for mobile facilities to be designed to withstand, as a minimum, a collision with a 5,000-tonne supply vessel with a speed of 2 m/s, corresponding to a collision energy of 14 MJ. These 14 MJ are also a guiding criterion in NORSOK for production facilities.
During the last decade, we have had about one thousand platform years on the Norwegian shelf. During the same period, we have had two collisions with supply vessels between 20 and 30 MJ, and one collision with energy exceeding 30 MJ. This indicates that the 14-MJ collision energy as a design load could be too low in relation to what is actually observed in terms of collision energies and collision frequencies.
In the 1980s and 1990s, tankers have had several collisions, but only one collision after the year 2000. Due to the small number of collisions, it is more difficult to predict the collision frequency, but the collision energy used in analyses can here also be too low.
The PSA expects there to be reasonable agreement between performed collision analyses and actual experienced collisions on the facilities on the Norwegian shelf. Good collision analyses will not increase safety if they become only an academic exercise. There is little detail in the assessed risk analyses of collisions with visiting vessels. Several failure modes have not been identified or analysed. The analyses are rarely used as a basis for reducing risk. Here, we see a need for improvement.
In the PSA's opinion, the incidents with the greatest possibility of resulting in major accidents in recent years have been:
18 January 2010 - collision between Far Grimshader and Songa Dee:
The supply vessel Far Grimshader was working on the lee side of the mobile drilling facility Songa Dee. The facility's crane malfunctioned, and the vessel had to be moved to the windward side to use another crane. During the move, the vessel's propeller was caught in a wire attached to the facility's anchoring. The vessel then lost control and laid for two hours, striking the Songa Dee.
Two of Songa Dee's columns were damaged. Far Grimshader suffered six holes in its hull and main deck, with water penetration to the engine room.
Far Grimshader was built in 1983 and is registered at 2,528 gross tonnes. The collision energy in each blow was low, but the number of collisions could have been several hundred.
6 June 2009 - collision between Big Orange XVIII and Ekofisk2/4-W:
The well stimulation vessel Big Orange XVIII was approaching the Ekofisk 2/4 X facility for an assignment. The captain of the vessel engaged the autopilot and later forgot to switch it off. This resulted in him not being able to override the autopilot, and the speed increased towards the Ekofisk 2/4 W facility. Big Orange XVIII struck Ekofisk 2/4 W at a speed of 9.5 knots.
The incident resulted in significant damage to the 2/4-W jacket, bridge, risers and to the Big Orange XVIII. The incident caused a lengthy shutdown of the 2/4 A facility and termination of water injection on 2/4 W.
Big Orange XVIII was built in 1984 and is 3,424 dead weight tonnes. The estimated collision energy was 39 MJ.
18 July 2007 - collision between Bourbon Surf and Grane:
The supply vessel Bourbon Surf had an assignment on the Grane field. After the vessel passed the Grane facility's safety zone, both the captain and the first officer left the bridge. When the bridge crew returned, it was too late to stop the vessel, but they succeeded in reducing its speed from 3 m/s to 1 m/s before it hit Grane.
Bourbon Surf was built in 2003, and is 3,117 dead weight tonnes. The collision energy was low, but with a large potential for a more serious incident.
13 November 2006 - collision between Navion Hispania and Njord B:
The incident occurred as the tanker Navion Hispania blacked out during connection to the storage ship Njord B on the Njord field. This resulted in most propellers stopping. The reason was polluted fuel, and a system malfunction caused the faults to spread. As the ship sailed towards Njord B, they tried to avoid collision, but, nevertheless, Navion Hispania struck Njord B at a speed of 1.2 m/s.
Navion Hispania sustained damage to the bow, while Njord B sustained damage to the stern.
Navion Hispania was built in 1999, and is 126,183 dead weight tonnes. The collision energy exceeded 100 MJ.
2 June 2005 - collision between Ocean Carrier and the Ekofisk 2/4 P bridge:
The first officer navigated Ocean Carrier towards Ekofisk in dense fog. The sea was calm, but there was poor visibility due to fog. The visibility was estimated at about 100-150 metres. The captain entered the bridge, and there were misunderstandings as to who was responsible for the navigation. The vessel had a speed of about 5.5 m/s as it passed into the facility's safety zone. When the captain saw the facility, he reduced the speed, but it was too late.
Ocean Carrier sustained considerable damage to the bridge area, as well as to the bow.
Ocean Carrier was built in 1996, and is 4,679 dead weight tonnes. The collision energy exceeded 20 MJ.
7 March 2004 - collision between Far Symphony and West Venture:
Far Symphony had a course towards the mobile drilling facility West Venture's safety zone, at the same time as the autopilot was engaged. The duty officer on the bridge did not discover that the autopilot was engaged, and could not navigate the vessel. This ended in a collision.
The facility sustained damage to a column and the vessel sustained damage to the bow.
Far Symphony was built in 2003 and is 4,929 dead weight tonnes. The collision energy exceeded 20 MJ.
Safety Check: NPD investigates risk of collisions between offshore facilities and visiting vessels
Source: Petroleum Safety Authority Norway