Method and system for laying a submarine pipeline

A system for laying an off-shore pipe, the system comprising:

• a fixed receiving structure installed in a target position on a seabed, said fixed receiving structure having a redirecting device for a damping cable,
• a pipeline end termination device mounted to an initial end length of a pipe,
• an underwater suspension buoy which is removably connectable to the pipeline end termination device so as to apply a vertically upwards directed suspension force to the pipeline end termination device,
• an underwater damping buoy having a buoyancy force,
• wherein the damping cable is removably connectable to the damping buoy and to the pipeline end termination device and extends through the redirecting device, so that the damping cable is slidingly supported and redirected by the redirecting device and tensioned by the buoyancy force of the damping buoy, so as to form a damping provisional anchoring of the pipeline end termination device to the fixed receiving structure,
• wherein:
• the suspension force of the suspension buoy counterbalances at least part of a weight of the pipeline end termination device,
• the buoyancy force of the damping buoy counterbalances a pulling force of the initial end length of the pipe, and
• a sliding support of the redirected damping cable allows relative compensation movements between the pipeline end termination device and the fixed receiving structure;
• wherein the fixed receiving structure forms a landing ramp with guiding surfaces which form a guide and an abutment support from below for the pipeline end termination device, said guiding surfaces extending on two opposite sides with respect to the redirecting device and in the same direction so that the damping cable drags the pipeline end termination device along the guiding surfaces.

A method of laying an off-shore pipe comprising:

• installing in a target position on a seabed a fixed receiving structure having a redirecting device for a damping cable,
• on a laying vessel, providing the pipe with an initial end length to which a pipeline end termination device is mounted,
• connecting an underwater suspension buoy to the pipeline end termination device, the underwater suspension buoy applying to the pipeline end termination device a suspension force which is directed vertically upwards,
• paying-out a first length of the pipe with the pipeline end termination device from the laying vessel vertically towards the seabed to a provisional anchoring position, in which the initial end length has an approximately vertical orientation with a vertical safety distance between the pipeline end termination device and the seabed,
• extending the damping cable from the pipeline end termination device through the redirecting device to an underwater damping buoy, so that the damping cable, slidingly supported and redirected by the redirecting device and tensioned by a buoyancy force of the damping buoy, forms a damping provisional anchoring of the pipeline end termination device to the fixed receiving structure,
• moving the laying vessel horizontally away from the fixed receiving structure and paying-out, from the laying vessel, a further length of the pipe so as to incline the initial end length progressively from the vertical orientation towards a horizontal orientation up to a lowered position,
• with the initial end length in the lowered position, moving the laying vessel to position the initial end length in the horizontal direction in a final abutment position with respect to said target position, then abutting the pipeline end termination device in the final abutment position,
• during the steps of inclining to the lowered position and of horizontally positioning the initial end length:
• using the suspension force of the suspension buoy to counterbalance at least part of a weight of the pipeline end termination device,
• using the buoyancy force of the damping buoy to counterbalance a pulling force of the initial end length of the pipe and to damp movements of the initial end length of the pipe,
• using a sliding support of the redirected damping cable to allow relative compensation movements between the pipeline end termination device and the fixed receiving structure;
• the method further comprising, during the step of abutting the pipeline end termination device:
• abutting and sliding front sliding bars of the pipeline end termination device on a landing ramp of the fixed receiving structure until abutting the front sliding bars against stop portions of the fixed receiving structure,
• checking positioning of the pipeline end termination device using marks applied on the front sliding bars and corresponding marks applied on the stop portions.

A method of laying an off-shore pipe comprising:

• installing in a target position on a seabed a fixed receiving structure having a redirecting device for a damping cable,
• on a laying vessel, providing the pipe with an initial end length to which a pipeline end termination device is mounted,
• connecting an underwater suspension buoy to the pipeline end termination device, the underwater suspension buoy applying to the pipeline end termination device a suspension force which is directed vertically upwards,
• paying-out a first length of the pipe with the pipeline end termination device from the laying vessel vertically towards the seabed to a provisional anchoring position, in which the initial end length has an approximately vertical orientation with a vertical safety distance between the pipeline end termination device and the seabed,
• extending the damping cable from the pipeline end termination device through the redirecting device to an underwater damping buoy, so that the damping cable, slidingly supported and redirected by the redirecting device and tensioned by a buoyancy force of the damping buoy, forms a damping provisional anchoring of the pipeline end termination device to the fixed receiving structure,
• moving the laying vessel horizontally away from the fixed receiving structure and paying-out, from the laying vessel, a further length of the pipe so as to incline the initial end length progressively from the vertical orientation towards a horizontal orientation up to a lowered position,
• with the initial end length in the lowered position, moving the laying vessel to position the initial end length in the horizontal direction in a final abutment position with respect to said target position, then abutting the pipeline end termination device in the final abutment position,
• during the steps of inclining to the lowered position and of horizontally positioning the initial end length:
• using the suspension force of the suspension buoy to counterbalance at least part of a weight of the pipeline end termination device,
• using the buoyancy force of the damping buoy to counterbalance a pulling force of the initial end length of the pipe and to damp movements of the initial end length of the pipe,
• using a sliding support of the redirected damping cable to allow relative compensation movements between the pipeline end termination device and the fixed receiving structure;
• wherein the step of anchoring the pipeline end termination device in the final abutting position comprises:
• overturning a locking yoke of the pipeline end termination device from a raised disengaged position to a lowered position of engagement with a stop pole of the fixed receiving structure,
• subsequently separating a connection between the damping buoy and the pipeline end termination device.

A system for laying an off-shore pipe, the system comprising:

• a fixed receiving structure installed in a target position on a seabed, said fixed receiving structure having a redirecting device for a damping cable,
• a pipeline end termination device mounted to an initial end length of a pipe,
• an underwater suspension buoy which is removably connectable to the pipeline end termination device so as to apply a vertically upwards directed suspension force to the pipeline end termination device,
• an underwater damping buoy having a buoyancy force,
• wherein the damping cable is removably connectable to the damping buoy and to the pipeline end termination device and extends through the redirecting device, so that the damping cable is slidingly supported and redirected by the redirecting device and tensioned by the buoyancy force of the damping buoy, so as to form a damping provisional anchoring of the pipeline end termination device to the fixed receiving structure,
• wherein:
• the suspension force of the suspension buoy counterbalances at least part of a weight of the pipeline end termination device,
• the buoyancy force of the damping buoy counterbalances a pulling force of the initial end length of the pipe, and
• a sliding support of the redirected damping cable allows relative compensation movements between the pipeline end termination device and the fixed receiving structure, wherein, stop portions can form or be formed by portions of a vent hatch for a suction piles foundation on which the fixed receiving structure is installed.

A system for laying an off-shore pipe, the system comprising:

• a fixed receiving structure installed in a target position on a seabed, said fixed receiving structure having a redirecting device for a damping cable,
• a pipeline end termination device mounted to an initial end length of a pipe,
• an underwater suspension buoy which is removably connectable to the pipeline end termination device so as to apply a vertically upwards directed suspension force to the pipeline end termination device,
• an underwater damping buoy having a buoyancy force,
• wherein the damping cable is removably connectable to the damping buoy and to the pipeline end termination device and extends through the redirecting device, so that the damping cable is slidingly supported and redirected by the redirecting device and tensioned by the buoyancy force of the damping buoy, so as to form a damping provisional anchoring of the pipeline end termination device to the fixed receiving structure,
• wherein:
• the suspension force of the suspension buoy counterbalances at least part of a weight of the pipeline end termination device,
• the buoyancy force of the damping buoy counterbalances a pulling force of the initial end length of the pipe, and
• a sliding support of the redirected damping cable allows relative compensation movements between the pipeline end termination device and the fixed receiving structure,
• wherein the fixed receiving structure comprises a locking pole which can be engaged from above by a corresponding locking yoke of the pipeline end termination device.