A method and apparatus are provided for laying pipelines. The apparatus is attached to a portion of a pipeline and includes a tensioning member and a buoyancy element attached to a mid-portion of the tensioning member. When the buoyancy element is submerged, the buoyancy force tensions the tensioning member, and the pipeline will take the intended deflected shape to follow seabed depressions.

A method of installing a subsea riser comprises placing an elongate negatively-buoyant support on the seabed and, when laying the riser on the seabed, guiding a riser portion onto the support to extend along and be cradled by the support. A hogbend region of 5 the riser is then formed by conferring positive buoyancy on the support to lift the support and the riser portion away from the seabed. An element of the support comprises a riser support disposed in a longitudinally-extending open-ended gap between buoyancy volumes disposed on opposite sides of 0 the gap. Coupling formations such as hinge portions can couple the element to a like element. When so coupled, the gaps of those elements align to define an upwardly-opening, longitudinally-extending groove to receive the riser.

A supporting device configured to support a pipeline on the bed of a body of water having a frame connectable in a sliding manner to a pipeline extending along a longitudinal axis between a laying vessel and the bed of a body of water; at least one floating body connected to the frame; and at least one connecting mechanism connecting the frame to the floating body and configured to define a distance between the axis of the pipeline and the floating body, so as to apply a torque to the portion of pipeline at the frame.

An apparatus for positioning an underwater pipe includes a plurality of fixing members for disposing on an outer circumferential surface of the underwater pipe in a spaced apart manner, a submersible unit connected to one of the fixing members, and a counterweight unit. The submersible unit is configured to float the underwater pipe on a water surface and submerge the underwater pipe. The counterweight unit is connected to the other one of the fixing members when the underwater pipe is submerged for positioning the underwater pipe on a bottom of a body of water.

A method for governing the elevation, attitude and structural integrity of a pressure-containing vessel in a body of liquid counterbalances flotation and incompressible ballast mediums against each other in separate serial compartments. Varying the quantity of incompressible ballast medium allows control of the elevation and attitude of the vessel. If the flotation medium is compressible, varying the quantity of flotation medium allows control of the ambient pressure of the vessel. The method facilitates floating and towing and laying of an undersea pipeline on, to and at a deep water site.

A system for laying an underwater pipeline on a bed of a body of water has a construction site to form a string of an underwater pipeline, the string being defined by a curved portion shaped substantially like a portion of the bed of the body of water characterized by an abrupt change in slope; at least two vessels to transfer, in the body of water, the string from the construction site to a laying site in the body of water and substantially on the vertical of a path along which to lay the string; and a plurality of floating devices configured to be coupled to the string and so as to selectively support and sink the string in the body of water, and progressively lay the string along the path on the bed of the body of water.

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 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 method of providing buoyancy to a subsea structure such as a pipeline bundle includes attaching to the structure a rigid elongate buoyancy tube that defines a floodable envelope. The envelope is arranged to contain a mass of buoyant macrospheres. Multiple openings penetrate a tubular wall of the buoyancy tube, in fluid communication with a void that extends between the macrospheres inside the tube. The void floods via the openings when the buoyancy tube is submerged, whereupon the macrospheres apply buoyant upthrust to the surrounding buoyancy tube and hence to the subsea structure to which the tube is rigidly attached.

A method of installing a subsea riser includes placing an elongate negatively-buoyant support on the seabed and, when laying the riser on the seabed, guiding a riser portion onto the support to extend along and be cradled by the support. A hogbend region of the riser is then formed by conferring positive buoyancy on the support to lift the support and the riser portion away from the seabed. An element of the support includes a riser support disposed in a longitudinally extending open-ended gap between buoyancy volumes disposed on opposite sides of the gap. Coupling formations such as hinge portions can couple the element to a like element. When so coupled, the gaps of those elements align to define an upwardly opening, longitudinally extending groove to receive the riser.