A pliant link to mitigate fatigue-inducing motion of a subsea catenary riser has an articulated spine having a longitudinal series of interconnected rigid segments. The spine can be coupled to upper and lower sections of the riser to transmit loads along the riser through the link on a load path that extends through the segments. The link also has a pliant pipe terminating in end fittings that can be joined, respectively, to the upper and lower sections of the riser for fluid communication along the riser through the link.

A subsea tubular system comprises extended sections of a first material and interposed sections of a second, different material that aids in damping vibration resulting from subsea dynamic conditions such as current. The vibration damping sections may make up a portion of the overall system significantly less than the sections of the first material. The number, length, and positions of the vibration damping sections may be selected based on factors such as the diameter, overall length, profile, and so forth. The system may be used as a riser or other conduit for the production of minerals such as oil and gas.

A system for liquid surge protection of a subsea riser having a horizontal portion on the seabed and a sag bend portion includes: a flexible tubing having a top end and a bottom end; a plurality of autonomous valves configured to permit liquid to pass through into the flexible tubing, wherein the autonomous valves are arranged between the top end and the bottom end of the tubing; and an inlet device coupled to the bottom end of the flexible tubing, wherein said inlet device is biased against a bottom wall the riser.

A subsea riser is installed by lowering at least one riser conduit to the seabed when piggybacked to an elongate support that comprises at least one flowline. The elongate support may be a pipeline bundle, which may be attached to one or more towheads in a towable bundle unit. The riser conduit may be in fluid communication with the flowline. At the seabed, a free end portion of the riser conduit is detached from the elongate support by releasing subsea-releasable fastenings. Then, with the elongate support and a root end of the riser remaining at the seabed, the detached free end portion of the riser conduit is lifted away from the elongate support to a riser support, such as a platform, an FPSO (floating production, storage and offloading vessel), or a buoy.

A subsea catenary riser comprises a rigid riser pipe that is suspended from a floating support on the surface and extends through a sagbend to the seabed. A hang-off interface allows rotation or pivoting of the riser pipe relative to the support about mutually orthogonal horizontal axes. A subsea buoy is positioned on the riser pipe above the sagbend. The buoy applies buoyant upthrust force to the riser pipe via an attachment interface that allows rotation or pivoting of the riser pipe relative to the buoy about mutually orthogonal horizontal axes. In response to movement of the support, the riser pipe deflects with S-shaped curvature to vary the inclination, relative to the buoy, of the portion of the riser pipe to which the buoy is attached. The curvature comprises mutually opposed curves respectively above and below the buoy, joined by a region of inflection that coincides with the buoy.

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 subsea line clamp assembly (1) has a body (10) having an axis and a clamp member (50), assembled in segments around a subsea line (3), and tethered to a subsea anchor (5). The clamp member (50) is movably located within the body (10). The inner surface of the body (10) and the outer surface of the clamp member (50) have respective tapered portions as part of teeth (32, 72) arranged to inter-engage. Adjacent teeth (32, 72) may be separated by axis-parallel portions. The clamping force on the subsea line (30) can be maintained at a consistent clamping force throughout the service life of the subsea line (3), despite the actions of creep and compression acting to reduce the outer diameter of the line (3).

A method approximates and connects an off shore riser duct to a floating unit, includes installing a tubular coupling recipient on the floating unit at a riser coupling level, the coupling recipient having an annular side wall extending around a longitudinal axis. A pulling device is on the floating unit at a pulling device level above the riser coupling level. The pulling device pulls a line extended through the coupling recipient and connected to a pulling head at a riser duct upper end. The riser duct upper end is pulled into the coupling recipient, providing a locking mechanism to lock a coupling adapter against downward withdrawal. Extending the line along a curved deviating surface deviates the pulling direction. The curved deviating surface is formed by a deviating member connected to the coupling recipient at a distance from the longitudinal axis smaller than an annular side wall to longitudinal axis distance.

A subsea flexible riser installation has a seabed foundation and a steep-configuration flexible riser anchored to the seabed by the foundation. An attachment formation is fixed relative to the riser and a locating formation is fixed relative to the foundation, both at positions elevated above the seabed. The locating formation is engaged with the attachment formation on the riser. This holds the attachment formation and the riser against movement when engaged, protecting the base of the riser from over-bending and fatigue.

A flexible pipe body and method of producing a flexible pipe body, the flexible pipe body including a collapse resistant layer comprising a radially inner surface and a radially outer surface, the radially inner surface comprising a plurality of substantially regular protrusions and/or depressions extending in a direction perpendicular to a tangent of the radially inner surface, for breaking up a boundary layer of fluid flowing along the flexible pipe body in use.