Little use has so far been made of motion-compensated walkways in Norway’s petroleum sector. Tambar is the only producing facility on the Norwegian continental shelf (NCS) where an attempt has been made to land a walkway from a ship.
The PSA is devoting attention to the utilisation of vessels and motion-compensated walkways, both through supervision and in terms of regulations. Its investigation on Tambar illuminates an area which could be relevant for many players in the industry.
The Tambar field lies in the southern part of Norway’s North Sea sector. Operated by Aker BP, it came on stream in 2001.
Production from Tambar utilises a normally unmanned wellhead facility controlled from Ula. In normal operation, this facility is manned once a week for maintenance with personnel transferred to/from Ula by helicopter.
In connection with modification work on Tambar, Aker BP decided to use a ship with a motion-compensated walkway – known as a walk-to-work (W2W) vessel – to transfer personnel to the facility. This was intended to reduce the number of helicopter flights and speed up completion of the modification.
Aker BP chartered W2W vessel Island Diligence in June 2018 from Norwegian shipping company Island Offshore. Landing platforms to receive the walkway were installed on three sides of the Tambar facility.
The undesirable incident occurred in connection with a test landing of the walkway on 28 July 2018.
During this process, the walkway missed the landing platform and hit the edge of the latter before sliding off. It then attempted automatically, in line with its design, to find a fixed point to engage with on the receiving side.
The consequence of the incident was damage to railings and cable trays on the facility. Nobody was injured during the incident.
The PSA’s investigation has established that this incident, under slightly different circumstance, couldhave resulted in a major accident with the release of large quantities of hydrocarbons, substantial material damage and possible loss of life. This is because the incident could equally well have happened when using the landing platform at the southern end of the facility, where hydrocarbon pipelines and equipment could have been hit.
On 26 May 2018, the PSA ordered Aker BP to secure consent before using the W2W vessel to accommodate personnel on Tambar.
Following the incident, Aker BP decided to cancel its planned use of a ship with a motion-compensated walkway on Tambar, and the consent application was withdrawn. The PSA therefore did not complete its consideration of the application.
Breaches of the regulations
The PSA’s investigation has identified several breaches of the regulations, all with their background in Aker BP’s planning process for utilising the walkway solution.
The principal observations apply to the following areas:
- dimensioning accidental loads
- documentation of structural integrity
- decision base and planning
- organisation and coordination of roles, responsibilities and information exchange.
The PSA has asked Aker BP to provide it by 13 February with an explanation of how it intends to deal with the nonconformities, and will verify that these are corrected.
In the time to come, the PSA will follow up Aker BP through supervisory activities. These include verifying how the company is using the lessons learnt on Tambar when planning the use of a walkway solution on Valhall west flank.