SubseaCutter - 100 & 80mm chains
Subsea Ghana - 25 cuts on anchor chains done safely above active pipeline
Scope of Work
Control Cutter was contacted by major vessel owner to conduct multiple cuts on the Jubilee FPSO anchor chains off the coast of Ghana. The Jubilee FPSO had to be repositioned in order to reduce wear and tear on turret's bearing system. The plan was to move the mooring from the turrent to the FPSO
As a result of the continuous unfavorable wear on the turret the operation was pulled forward, giving limited time for preparations.
A live pipeline was running below some of the anchor chains and the client was concerned about dropping the cut anchor chain links on pipeline and potentailly damage the pipeline, worst case rupture.
Due to the size of the chain and the risk of dropping half chain links after the cut, custom made inserts had to be designed, manufactured and tested. Within 5 weeks the equipment had been tested onshore and was ready for mobilization.
The first phase of the operation consisted of cutting the FPSO free from existing anchor chains from the turret. The existing 80mm anchor chains were cut successfully in under 10 minutes.
For the second phase the new anchor chains were laid and tightened individually. After each tightening process the excess chain was cut to eliminate any "tail" on chain. The chains were tightened multiple times in order to get correct tension and a total of 20 cuts completed on the new 100mm anchor chains. All the cuts were successfully completed within 10 minutes.
All cuts were completed on the first attempt of engaging the SubseaCutter onto the chain. With conventional band saw there is high probability of the saw blade breaking, especially when chains are in tension. Each time a saw blade breaks, significant time has to be spent on resurfacing, redressing and redeploying the equipment.
A major risk for the operation was dropping cut chain links onto the live pipeline. But, as a result of the custom made insert and the cutting method, the chain links were squeezed together after the cuts were completed. The deformation to the chain made it impossible for the cut chain links to fall down and thus eliminated the risk of damage o the pipeline.
The efficient cutting time saved the client at least 25 hours of cutting time and eliminated the risk of damaging a live pipeline. Therefore reducing the overall environmental risk of an oil leak and the associated safety of the personnel onboard the vessel and the FPSO.