Abstract: A pipeline including an accessory such as a flowline end termination or an in-line tee is lowered to the seabed and a mudmat foundation is subsequently lowered toward the seabed for subsea docking with the accessory to provide a permanent foundation support for the accessory. Once docked and with a mudmat of the foundation landed on the seabed, weight loads of the accessory structure and the attached pipe are transferred to the mudmat to provide a permanent foundation for the accessory structure. Before and during installation of the mudmat foundation, the pipe may be allowed to become embedded in the seabed. Temporary interim support such as buoyancy may be provided to the accessory to limit embedment into the seabed.

Abstract: A method of transporting a rigid tie-in connection across a body of water for installation underwater is disclosed. The method includes the step of supporting the tie-in connection in the water by buoyancy acting on a frame that supports the tie-in connection until installation. The buoyancy-supported frame is lowered and the tie-in connection into a sub-surface transit configuration. The method further includes in the transit configuration, towing the buoyancy-supported frame and the tie-in connection behind a towing vessel toward an installation site. Also disclosed is a system for implementing the method. The system includes a towable frame arranged to support the tie-in connection until installation and an external buoyancy attached to the frame by an extensible suspension link arranged to suspend the frame from the buoyancy in water in use. The link is extensible to lower the frame from a raised surface-tow configuration into a lowered sub-surface transit configuration.

Abstract: A flowline branch structure (10) has at least one inner branch assembly with an inner flowline branch and at least one inner flowline pipe attached to and communicating with the inner flowline branch. At least one outer branch assembly (12) of the flowline branch structure has an outer branch housing disposed around the inner flowline branch and at least one outer pipe (14) disposed around the inner flowline pipe and attached to the outer branch housing. A generally annular space is defined between the inner and outer branch assemblies. At least one wiring element including an electrical heating element is disposed in the sealed space on an outer side of the inner branch assembly. The, or each, wiring element extends in one continuous length across an interface between the inner flowline pipe and the inner flowline branch. This reduces the number of connections necessary to create the flowline branch structure.

Abstract: A flowline branch structure (10) has at least one inner branch assembly with an inner flowline branch and at least one inner flowline pipe attached to and communicating with the inner flowline branch. At least one outer branch assembly (12) of the flowline branch structure has an outer branch housing disposed around the inner flowline branch and at least one outer pipe (14) disposed around the inner flowline pipe and attached to the outer branch housing. A generally annular space is defined between the inner and outer branch assemblies. At least one wiring element including an electrical heating element is disposed in the sealed space on an outer side of the inner branch assembly. The, or each, wiring element extends in one continuous length across an interface between the inner flowline pipe and the inner flowline branch. This reduces the number of connections necessary to create the flowline branch structure.

Abstract: A method of transporting a rigid tie-in connection across a body of water for installation underwater is disclosed. The method includes the step of supporting the tie-in connection in the water by buoyancy acting on a frame that supports the tie-in connection until installation. The buoyancy-supported frame is lowered and the tie-in connection into a sub-surface transit configuration. The method further includes in the transit configuration, towing the buoyancy-supported frame and the tie-in connection behind a towing vessel toward an installation site. Also disclosed is a system for implementing the method. The system includes a towable frame arranged to support the tie-in connection until installation and an external buoyancy attached to the frame by an extensible suspension link arranged to suspend the frame from the buoyancy in water in use. The link is extensible to lower the frame from a raised surface-tow configuration into a lowered sub-surface transit configuration.

Abstract: A coated or sleeved pipe for a hybrid riser tower is disclosed. The pipe has at least one stop formation that is integral with or attached to an external coating or sleeve of the pipe. The stop formation is arranged to restrain movement along the pipe of a structure attached to the pipe, such as a guide frame.

Abstract: A pipeline including an accessory such as a flowline end termination or an in-line tee is lowered to the seabed and a mudmat foundation is subsequently lowered toward the seabed for subsea docking with the accessory to provide a permanent foundation support for the accessory. Once docked and with a mudmat of the foundation landed on the seabed, weight loads of the accessory structure and the attached pipe are transferred to the mudmat to provide a permanent foundation for the accessory structure. Before and during installation of the mudmat foundation, the pipe may be allowed to become embedded in the seabed. Temporary interim support such as buoyancy may be provided to the accessory to limit embedment into the seabed.

Abstract: A coated or sleeved pipe for a hybrid riser tower is disclosed. The pipe has at least one stop formation that is integral with or attached to an external coating or sleeve of the pipe. The stop formation is arranged to restrain movement along the pipe of a structure attached to the pipe, such as a guide frame.