A new pipeline system to export gas across the Black Sea involving:
With a rocky substrate that was too hard for trenching, the Turkstream pipeline was laid directly onto the seabed when transitioning over the continental shelf from 300m to 1100m water depth. Due to this, there were 2 touchdown locations that induced overstressing in the pipeline during MEG swabbing.
To reduce the pipeline stresses, 4 grouted supports (2 at each touchdown point, on either side of the shoulder) were installed. The grouted supports at the upslope locations were standard Subcon fabric formworks. However, due to the sloping seabed, both downslope locations required a complex solution to install the grouted support.
To provide temporary stability of the support, the fabric formwork was integrated into a custom Bag Support Frame (BSF). For contingency stability, the BSFs were attached to a Friction Locking Clamp (FLC) using an A-Frame. The FLC locked onto the pipeline during placement of the first layers of grout poured before being removed.
IntecSea with Allseas designed the A-Frame and FLC respectively. To ensure seamless offshore installation, a full-scale SIT was performed at Subcon’s headquarters in Perth, Australia.
The FLC and BSF were fitted with an inclinometer and bullseye to ensure that installation tolerances (4°) were respected during installation and inflation of the formwork.
The legs of the BSF were hydraulically actuated by ROV to accommodate any seabed differences from the Digital Terrain Model (DTM). Once the legs were at the correct length, the formworks integrated in the BSF were deployed ready for grouting.
