A subsea pipeline (10) of pipe-in-pipe configuration comprises an inner pipe (14), an outer pipe (16) spaced radially from the inner pipe and an annulus (20) defined by the radial spacing between the inner and outer pipes. A series of longitudinally-spaced outward projections (22) extend radially outwardly into the annulus from the inner pipe and are movable longitudinally relative to the outer pipe. A corresponding series of longitudinally-spaced inward projections (24) extend radially inwardly into the annulus from the outer pipe and are movable longitudinally relative to the inner pipe. When the inner pipe is subject to thermal elongation or contraction in use of the pipeline, the inner pipe is movable longitudinally relative to the outer pipe, hence moving the outward projections between and relative to the inward projections. The pipeline may be buried to restrain the outer pipe. The annulus may be flooded, in which case the inner pipe is covered with wet insulation.

An integrity monitoring system for a lined pipeline is provided for monitoring the integrity of a polymer liner in a host pipe. Methods and apparatus are described by which a lined pipeline is provided with such an integrity monitoring system sensor cable is able to bridge a joint between sections of lined pipe, for example by routing the sensor cable across the joint via a channel in an electrofusion fitting or by connecting successive lengths of sensor cable via pass-throughs in an electrofusion fitting. Advantageously, the sensor cable is disposed within a continuous annulus between linings and host pipes, and the continuous annulus is maintained across pipe joints using electrofusion fittings.

An integrity monitoring system for a lined pipeline is provided for monitoring the integrity of a polymer liner in a host pipe. Methods and apparatus are described by which a lined pipeline is provided with such an integrity monitoring system sensor cable is able to bridge a joint between sections of lined pipe, for example by routing the sensor cable across the joint via a channel in an electrofusion fitting or by connecting successive lengths of sensor cable via pass-throughs in an electrofusion fitting. Advantageously, the sensor cable is disposed within a continuous annulus between linings and host pipes, and the continuous annulus is maintained across pipe joints using electrofusion fittings.

A method of laying an off-shore pipeline (1) comprises: —installing on the seabed (3) a fixed receiving structure (4) having a redirecting device (5), —paying-out from a laying vessel (7) a pipeline (1) with the pipeline end termination device (9) vertically towards the seabed (3), —extending a damping cable (6) from the pipeline end termination device (9) through the redirecting device (5) to an underwater damping buoy (14), —connecting an underwater suspension buoy (15) to the pipeline end termination device (9), —inclining the pipeline (1) from a vertical orientation towards the horizontal orientation, using: —the suspension buoy (14) to counterbalance at least part of the weight of the pipeline end termination device (9), —the damping buoy (14) for damping the pipeline (1).

A method of laying an off-shore pipeline (1) comprises: —installing on the seabed (3) a fixed receiving structure (4) having a redirecting device (5), —paying-out from a laying vessel (7) a pipeline (1) with the pipeline end termination device (9) vertically towards the seabed (3), —extending a damping cable (6) from the pipeline end termination device (9) through the redirecting device (5) to an underwater damping buoy (14), —connecting an underwater suspension buoy (15) to the pipeline end termination device (9), —inclining the pipeline (1) from a vertical orientation towards the horizontal orientation, using: —the suspension buoy (14) to counterbalance at least part of the weight of the pipeline end termination device (9), —the damping buoy (14) for damping the pipeline (1).

A floating power-generation group comprises a floating hub such as a spar buoy that is anchored to subsea foundations by anchor lines. Floating power producer units such as wind turbines are connected electrically and mechanically to the hub. The power producer units are each moored by mooring lines. At least one mooring line extends inwardly toward the hub to effect mechanical connection to the hub and at least one other mooring line extends outwardly toward a subsea foundation. The groups are combined as a set whose hubs are connected electrically to each other via subsea energy storage units. Anchor lines of different groups can share subsea foundations. The storage units comprise pumping machinery to expel water from an elongate storage volume and generating machinery to generate electricity from a flow of water entering the storage volume. The pumping machinery may be in deeper water than the generating machinery.

In a method of joining a structure to a water-filled pipeline aboard a reel-lay vessel, a trailing end portion of the pipeline is suspended upright on a reel-lay tower. Water is drained from the trailing end portion while being retained in an inclined portion of the pipeline extending from the tower to a reel of the vessel and in a spooled portion of the pipeline coiled on the reel. The structure is joined to a trailing end of the pipeline after inserting a pig into the trailing end portion through the trailing end. Pumping additional water into a leading end of the pipeline on the reel propels the pig from the trailing end portion into a conduit of the structure while flooding the trailing end portion. This expels air through a port of the structure that was trapped in the trailing end portion between the pig and the structure.

A marine pipeline installation system for laying an offshore pipeline and/or installing a subsea riser includes a pipeline launch tower, a pipeline guide provided at an elevated position for guiding said pipeline to the pipeline launch trajectory along said tower, one or more tensioners, an abandonment and recovery (A&R) system including at least one A&R cable and associated A&R winch and a sheave arrangement with one or more sheaves supported by the pipeline launch tower at an upper position thereof. An auxiliary trolley is provided which is adapted to support the weight of the launched pipeline and which is movable along a rail in the pipeline launch trajectory when the one or more tensioner frames are in the retracted non-operable position, from a position above the uppermost tensioner to a position below the lowermost tensioner, the rail being supported by the pipeline launch tower.

A marine pipeline installation system for laying an offshore pipeline and/or installing a subsea riser includes a pipeline launch tower, a pipeline guide provided at an elevated position for guiding said pipeline to the pipeline launch trajectory along said tower, one or more tensioners, an abandonment and recovery (A&R) system including at least one A&R cable and associated A&R winch and a sheave arrangement with one or more sheaves supported by the pipeline launch tower at an upper position thereof. An auxiliary trolley is provided which is adapted to support the weight of the launched pipeline and which is movable along a rail in the pipeline launch trajectory when the one or more tensioner frames are in the retracted non-operable position, from a position above the uppermost tensioner to a position below the lowermost tensioner, the rail being supported by the pipeline launch tower.

The invention concerns a process and a device for laying a subsea pipeline according to the J-lay or S-lay method wherein straight sections are mounted onshore, dried and degassed then closed by plugs. The sections are loaded on a pipe-laying ship, are separated from their plugs before the welding. At the welding of each bulkhead a short pumping is operated to reduce the pressure in the part of the annulus located between the two last bulkheads and then the opening leading to the annulus are sealed.