Marine pipeline installation system and methods

摘要

A method for installing an accessory onto a pipeline to be laid on the seabed, includes launching the pipeline from a first position of a tower in which the tower is at an angle α with respect to the vertical; stopping the launch of the pipeline, and hanging off the launched pipeline in a hang off module; positioning an accessory in a tower firing line; attaching the accessory to the launched pipeline in the hang off module and to at least one A&R cable; suspending the accessory and the launched pipeline from an A&R system; disengaging the hang off module from the launched pipeline; pivoting the pipeline launch tower to an accessory launch position in which the tower is at an angle γ that differs substantially from angle α, such that a pipeline launch trajectory is created which is large enough to launch the accessory and the launched pipeline with the A&R system.

主权项

1. A marine pipeline installation system for laying an offshore pipeline, wherein the system comprises:
a vessel, a pipeline launch tower comprising pipe laying equipment defining a tower firing line, which tower is mounted pivotably about a tower pivot axis on said vessel and which is adapted for launching the pipeline in the tower firing line into the sea in a first position of the tower in which the tower is at an angle α with respect to the vertical, an abandonment and recovery (A&R) system comprising at least one A&R cable and a sheave arrangement with a plurality of sheaves supported by the pipeline launch tower, a hang off module supported in the lower part of the tower firing line for clamping and supporting the weight of previously launched pipeline, wherein two of the plurality of sheaves used to guide the at least one A&R cable having a sheave pivot axis substantially parallel to the tower pivot axis are supported by a support frame, the support frame is skiddable along a support frame guide provided in a lower part of the pipeline launch tower, the support frame guide is provided substantially perpendicular to the tower pivot axis and substantially perpendicular to the tower firing line, such that the two of the plurality of sheaves supported by the support frame are skiddable into and out of the tower firing line, and wherein the two of the plurality of sheaves are supported by the support frame through respective mechanisms, allowing a movement with respect to the tower pivot axis between a one cable guide position and a double fall A&R position.