It is described a method of laying a pipeline (1) on a seafloor (2), wherein the method comprises the steps of: —bringing the pipeline to an offshore location using a vessel, —laying the pipeline on the seafloor using the vessel, —defining a first zone (10) surrounding at least a first part length (1′) of the pipeline when laid subsea, wherein the first part length is uncovered, —defining a second zone (20) extending from the first zone, —monitoring the second zone for vessels approaching the first zone, —analysing vessels detected during said monitoring of the second zone, for the purpose of determining whether the vessels can cause harm to the first part length of the pipeline, —for each vessel monitored in the second zone and considered to be able to cause harm to the first part length of the pipeline, informing the vessel about the first zone and/or requesting the vessel not to enter into the first zone.

A method of installing a subsea pipeline supports at least one elongate pipe stalk at the surface of the sea at a first, relatively shallow-water location by virtue of buoyancy added to the pipe stalk. The pipe stalk is then towed at the surface to a second location that is in deeper water. There, with the pipe stalk supported between leading and trailing towing vessels, at least some of the added buoyancy is removed. This causes the pipe stalk to hang with catenary curvature beneath the surface between the vessels. The catenary-curved pipe stalk hanging between the vessels is then towed to a third location for subsea installation, which may involve upending the pipe stalk before landing a lower end portion of it on the seabed.

A subsea pipeline (14) has a friction-reducing outer coating, treatment or finish (30) that extends along discrete regions mutually spaced along the length of the pipeline. During laying, curvature is imparted to the pipeline (14) along its length, for example by the residual curvature method or by snake-lay, to create expansion loops (26) of increased curvature relative to intermediate portions (28) of the pipeline (14) that join those loops (26). Each of the loops (26) is coincident with a respective one of the regions that bear the friction-reducing outer coating, treatment or finish (30). This facilitates lateral movement of the loops (26) relative to the seabed (16) to mitigate and control buckling in use of the pipeline (14).

A subsea distribution equipment assembly includes a modular structure with a block having a metallic structure and panels that allow the configuration for several pieces of equipment, in such a way that both the hydraulic instrumentation and the electrical instrumentation are also modularized. A method of assembly a subsea distribution equipment assembly includes transporting a first block and a second block using a crane of a vessel, aligning and connecting eye joints installed on each of the first and second blocks, connecting a foundation to the first and second blocks using the crane and a trolley, and installing an umbilical termination assembly jumper between the first and second blocks.

A method for retrieving a pipeline from a seabed in the body of water to a vessel includes the steps of suspending at least a portion of the pipeline in the body of water between the seabed and the vessel, plastically deforming the portion of the pipeline to form a plastically deformed portion, and retrieving the plastically deformed portion to the vessel.

Lined pipelines with different inner diameters are spooled successively onto a reel while their constituent pipe stalks are cyclically pressurised internally to combat wrinkling of the liner. A first, variable diameter pig is advanced to a trailing end of a first pipeline. A transition joint is attached to the trailing end of the first pipeline to effect a transition from the inner diameter of the first pipeline to the different inner diameter of a second pipeline. A leading end of the second pipeline, containing a second pig, is attached to the transition joint. The first pig is driven through the transition joint into the second pipeline. The diameter of the first pig changes to match the inner diameter of the second pipeline. The first and second pigs are then driven along the second pipeline when assembling the second pipeline from a succession of pipe stalks.

An in-line accessory structure for a subsea pipeline has an elongate pipe section arranged to be integrated into the pipeline, hence defining a flow axis through the structure. A branch has a lower end in fluid communication with the pipe section and an upper end in fluid communication with a connector hub. The structure further has a subsea foundation such as a mudmat, arranged to support the structure installed orientation. When the structure is in that orientation, the branch inclines inwardly from its lower end toward its upper end in a transverse direction, toward an upright longitudinal plane containing the flow axis.

An in-line accessory structure for a subsea pipeline has an elongate pipe section arranged to be integrated into the pipeline, hence defining a flow axis through the structure. A branch has a lower end in fluid communication with the pipe section and an upper end in fluid communication with a connector hub. The structure further has a subsea foundation such as a mudmat, arranged to support the structure installed orientation. When the structure is in that orientation, the branch inclines inwardly from its lower end toward its upper end in a transverse direction, toward an upright longitudinal plane containing the flow axis.

A method of connecting a conduit to a subsea structure is provided. In the disclosed method, a tensioning member is provided on the conduit and attached to the conduit at two locations proximate a first end of the conduit. The tensioning member is used to maintain a curvature formed in the conduit between the two locations e.g. by deflecting a portion of the conduit. A first end of the conduit is engaged with a guide assembly provided adjacent to the subsea structure, and tension in the tensioning member is released to adjust the axial position of the first end of the conduit to enable direct connection between the conduit and the subsea structure. A method of disconnecting a conduit from a subsea structure, and a system for connecting a conduit to a subsea structure are also provided.

A method for controlling buckling in subsea pipelines involves identifying spaced-apart sections of a subsea pipeline suitable for controlled lateral buckling. Sets of inclined sleepers are installed at each spaced-apart section and are selected to support the spaced-apart sections of the subsea pipeline in an orientation that is perpendicular to the initial as-laid position. Any buckling caused by thermal expansion of the subsea pipeline is distributed to two or more of the spaced-apart sections, causing the two or more spaced-apart sections to deflect laterally along the inclined sleepers outwardly from an initial as-laid position.