A method of installing at sea a double-walled preheated undersea pipe for transporting fluids, wherein for each new pipe section to be assembled to a pipe that is already installed at sea: the method involves preheating the inner wall unit element inside the outer wall unit element of the new pipe section; assembling the inner wall unit elements of the new pipe section to the inner wall of the pipe that is already installed at sea; assembling the outer wall unit element of the new pipe section to the outer wall of the pipe that is already installed at sea; lowering the new pipe section into the sea; and repeating the above for other new pipe sections to be assembled so as to prestress the pipe while it is being installed at sea.

A subsea pipeline coated with a thermally insulating coating has a radially outer surface shaped to define external hold-back formations. In a J-lay operation, the weight load of a pipeline catenary is held back using a complementary bushing or clamp of an installation vessel engaged with the hold-back formations. The weight load is transferred from the catenary to the bushing or clamp by shear forces acting through the coating. The coating extends continuously along the pipe and is interposed between the hold-back formations and the underlying pipe. The hold-back formations may be integral with the coating.

A subsea pipeline coated with a thermally insulating coating has a radially outer surface shaped to define external hold-back formations. In a J-lay operation, the weight load of a pipeline catenary is held back using a complementary bushing or clamp of an installation vessel engaged with the hold-back formations. The weight load is transferred from the catenary to the bushing or clamp by shear forces acting through the coating. The coating extends continuously along the pipe and is interposed between the hold-back formations and the underlying pipe. The hold-back formations may be integral with the coating.

System for use in building and deployment of an elongate element (202) in a J-lay operation. The system includes an upright structure (206); a winching element (204) retractable along an axis within the upright structure (206); a coupling element (210) connected to the winching element (204), for coupling the winching element (204) to an elongate element (202); and a catcher element (212) configured to retain the coupling element (210) in alignment with a predetermined axis within the upright structure (206) during retraction or extension of the winching element (204).

System for use in building and deployment of an elongate element (202) in a J-lay operation. The system includes an upright structure (206); a winching element (204) retractable along an axis within the upright structure (206); a coupling element (210) connected to the winching element (204), for coupling the winching element (204) to an elongate element (202); and a catcher element (212) configured to retain the coupling element (210) in alignment with a predetermined axis within the upright structure (206) during retraction or extension of the winching element (204).

A method of installing a subsea pipeline for tie-in to a subsea structure includes laying, using a pipe laying vessel, an intermediate section of the pipeline on to a pipe restraint device, wherein the pipe restraint device is at or near the subsea structure, or is at or near a location at which a subsea structure will be installed, and the pipe restraint device restricts transverse movement of the pipeline. The intermediate section of the pipeline is configured to be tapped at or near the pipe restraint device for providing fluid communication between the pipeline and the subsea structure.

A method of installing a subsea pipeline for tie-in to a subsea structure includes laying, using a pipe laying vessel, an intermediate section of the pipeline on to a pipe restraint device, wherein the pipe restraint device is at or near the subsea structure, or is at or near a location at which a subsea structure will be installed, and the pipe restraint device restricts transverse movement of the pipeline. The intermediate section of the pipeline is configured to be tapped at or near the pipe restraint device for providing fluid communication between the pipeline and the subsea structure.

A method of providing motion compensation of a subsea package with a synthetic rope comprising attaching the synthetic rope to the subsea package, supporting a first gripper with a wire rope from a winch capable of motion compensation control characteristics and gripping the synthetic rope with the first gripper, supporting a second gripper with a second wire rope, and repeating the following sequence: lowering the first gripper, the synthetic rope, and the subsea package a first distance, gripping the synthetic rope with the second gripper, releasing the first gripper from the synthetic rope, raising the first gripper the first distance, gripping the synthetic rope with the first gripper, releasing the second gripper from the synthetic rope, such that when the subsea package is lowered proximate the subsea landing location the winch capable of operating with motion compensation characteristics can operate to compensate for the vessel motion and smoothly lower the subsea package to the subsea landing location.

A method of providing motion compensation of a subsea package with a synthetic rope comprising attaching the synthetic rope to the subsea package, supporting a first gripper with a wire rope from a winch capable of motion compensation control characteristics and gripping the synthetic rope with the first gripper, supporting a second gripper with a second wire rope, and repeating the following sequence: lowering the first gripper, the synthetic rope, and the subsea package a first distance, gripping the synthetic rope with the second gripper, releasing the first gripper from the synthetic rope, raising the first gripper the first distance, gripping the synthetic rope with the first gripper, releasing the second gripper from the synthetic rope, such that when the subsea package is lowered proximate the subsea landing location the winch capable of operating with motion compensation characteristics can operate to compensate for the vessel motion and smoothly lower the subsea package to the subsea landing location.

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.