This paper describes the construction and installation of a 932m long bundled submarine pipeline system to make the connection between the onshore pipeline and the nearshore pipeline sections of the Angola LNG project. The bundle consisted of three separate heavy-walled, concrete coated pipes, 18??, 22??, and 24?? connected together which were pulled from on onshore stringing right-of-way, down an excavated slope and through a 12m wide excavated cofferdam and into the ocean. The pulling was done by a 300mT linear winch secured to a cargo barge located 1.2km offshore. All three pipelines are part of the Sonangol offshore pipeline network and will initially deliver feed gas to the Angola LNG plant located in Soyo, Angola. The pipeline network will be operated by Sociedade De Operações & Manutenção de Gasodutos S.A. (SOMG).

The construction of the bundle is discussed as well as the installation engineering challenges of pulling the bundle.


There are numerous options when it comes to installing pipelines at a landfall site. These options were made available during the FEED study, but careful consideration had to be given to the engineering and financial feasibility of these options. One of the main considerations for the Angola LNG project is how the tie-in would be performed offshore in very shallow water with a pipelay vessel inside a dredged channel. As such, it was decided that the pipelines would be built onshore on a right-of-way allocated by the company, and the pipelines would be pulled into the water using a 300mT linear winch secured to a cargo barge moored offshore.

Once a bundled pipeline philosophy was decided upon many installation challenges arose to install the heavy concrete coated pipelines. There was a large amount of excavation and earth work to be completed for the landfall, a cofferdam had to be built and excavated, and a dredged channel had to be constructed for the pipelines to be laid in and later backfilled. An enormous challenge was to build the pipeline strings long enough on the allocated right-of-way to allow a pipelay vessel to safely come as close as possible within the dredged trench to recover each individual line and be laid to its respective block offshore. Environmental conditions had to be mitigated as there were extreme amounts of erosion and sedimentation in the area as well as large bottom currents which threatened the on-bottom stability of the bundle. Finally, as the three pipelines belonged to three separate operators, there was a client requirement to have 3m separation between the pipelines, centerline to centerline, which made the bundle nearly 7m wide. To maintain the 3m separation, clamped spacers were positioned every 300m along the bundle.

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