Seabed-to-surface link for a deep underwater pipeline resting on seabed has base anchoring unit holding connection between underwater pipeline and riser

摘要

A riser (5) and an underwater pipeline (11) are linked using an anchoring system. This is a base comprising a curved flexible pipe (12), a platform (151) on the seabed and an upper structure (152) fixed to the platform and holding the ends of the pipes in position. The bottom of the riser is fixed relative to the base and the two ends are in the same perpendicular plane as the platform There is a vertical riser from the underwater pipeline to at least one float, and a flexible linking pipe between a floating support and the top of the riser. Fixings hold the end of the flexible pipe connected to the underwater pipeline to the base, or guides (rollers or skates) (19) allow only longitudinal movement along the axis of the pipeline and prevent rotation above the axis. Stabilizers including dead weights (18) and/or suction anchors (17) are fixed to the seabed. The flexible linking pipe includes a flexible element between the bottom face of the float and the top of the riser, connected to the top of the riser via a swan neck and extended to pass through the float in a rigid tube. This allows the inside of the riser to be cleaned or scraped. The base can also provide a connection for two underwater pipelines to two risers. The underwater pipelines and/or risers can be bundled within an insulating envelope containing paraffin or a gelled component. The connections for multiple pipes are as described for a single pipe, with a flexible linkage and movement along the axis of the underwater pipe only. An Independent claim is also is included for assembling the above devices by pre-assembling the underwater pipe, the flexible pipe, the riser and the flexible linking pipe, installing the base at the appropriate point, lowering the assembly into the sea and positioning the base before stabilizing and fixing it to the seabed.