The removal of the Fulmar Single Anchor Leg Mooring (SALM) Buoy was carried out by Stolt Comex Seaway Ltd within a ten day period during July 1994. The removal of the SALM was achieved by cold cutting the buoy from its base utilising underwater Jet Abrasive Cutting (JAC) equipment. The cutting was achieved by mixing a water/grit slurry on the surface and pumping it through a hose to a nozzle positioned within certain parameters from the face of the steel being cut. The nozzle was manipulated to achieve the required cutting line by utilising a number of track systems developed specifically for the project.
The objective was to remove the SALM in a safe and controlled manner. The buoy had In excess of 2000T upward buoyancy when attached to the seabed so once a certain amount of cutting was completed the buoy broke free Safe access and prediction of breakaway were all considered when deciding on the cutting sequence A safety case was prepared by Shell UK Exploration and Production for the work.
A total of 24 metres of 65mm to 75mm thick steel plate was cut using this cold cutting method. The result of the cutting process was the ultimate breakaway of the Fulmar SALM Buoy from its fixed seabed base Once the SALM was released and was free floating it was towed to a storage site In a Norwegian Fjord.
In November of 1993, Shell Expro contracted Stolt Comex Seaway Ltd to remove the Fulmar SALM Buoy from its anchored position in the Fulmar field. This work formed part of the overall decommissioning of the Fulmar floating storage and offloading facility The Fulmar SALM Buoy itself consisted of a rigid buoy structure connected to a base on the seabed by a universal joint arrangement. When the SALM Buoy was operational, a topside articulated rigid arm permanently moored a Tanker Storage.
Vessel Prior to the removal of the SALM Buoy by Stolt Comex Seaway the rigid arm and tanker were removed by others, leaving only the top structure of the SALM Buoy visible above the surface (See Fig 1).
This paper describes the application of Jet Abrasive Cutting for the SALM Removal Works.
During the pre-engineering phase it was established by Shell Expro that following upon the removal of the rigid arm assembly, a net upward buoyancy of around 2000 tonnes would be acting on the SALM Buoy Base. This meant that during the process of removal of the Buoy these forces would at some point cause the buoy to ‘break free’ from its seabed base. The design for removal had to take this into consideration and it was imperative that the possibility of the SALM Buoy only being partly removed and therefore greatly weakened to the elements was eliminated by a safe, reliable and predicable system of removal.
During the conceptual engineering phase for the removal of the Fulmar SALM Shell Expro considered various approaches for release of the buoy from the buoy base