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CASE STUDY
12” Split Sealing Clamp for Subsea7
In the summer of 2022, Subsea7 sent out a request for the provision of a repair clamp for a 12” pipeline located in the UK sector, and to be delivered as part of a larger scope for a big E&P company with activities focused on the North Sea. Challenging design specifications included sour service under high pressure and a large sealing area.
We promptly responded with engineering concepts and drawings, and we were selected to manufacture the dual barrier repair system with lifting and installation tooling.
During a visual inspection, a crater in the seabed was observed, and both the 12” Water Injection line and the 4” piggybacked gas lift were exposed. Divers were able to observe coating damage and an extensive rupture on the WI pipeline (approximately 900 mm).
To regain pipeline sealing integrity, we designed and manufactured a split sealing clamp (with an installation frame), taking into account the requirement to also include cradles to support the existing piggyback system. With forgings from Italy and packers from the UK, the assembly and testing took place in Norway.
Challenges
Sour service
200 bar design pressure
Size and weight for diver installation
Ongoing pipeline erosion
Outcome
Custom tooling for safe installation
Cradle supports for piggyback line
Two revisions due to ongoing pipeline erosion
Delivered in time on a tight schedule
Successfully installed
However, after further survey and pressure analysis, the client realized that the pipeline’s integrity was worse than originally deemed. The wall was under ongoing erosion, and there were sections with a wall thickness of just 8 mm (close to 60% loss in comparison to the original 19 mm).
We quickly revised our original design and engineered an alternative version of the split sealing clamp, featuring reduced squeeze pressure from the packers to compensate for the reduced wall thickness.
