E - Fixed Constructions – 02 – D
Patent
E - Fixed Constructions
02
D
61/5.4
E02D 15/00 (2006.01)
Patent
CA 1177266
ABSTRACT OF THE DISCLOSURE A method of intermittently stopping and restarting the laying of pipe offshore from a reel pipelaying vessel having a reel for spooling relatively inflexible pipe thereon, pipe working and handling means for straightening the pipe as it is upspooled from the reel, vessel motive source means for imparting a forward thrust to the vessel, and a reel drive mechanism associated with the reel for imparting at least a dynamic braking force to the reel in an unspooling mode. The method comprises the steps of: (a) stopping the forward motion of the vessel in the direction of pipelaying by (1) gradually reducing the forward thrust imparted to the vessel by the vessel motive source, and (2) concurrently gradually increasing the dynamic braking force imparted to the reel by the reel drive mechanism, (3) to cause the reel to decrease its rotational rate toward zero while continuing to unspool pipe and to thereby maintain sufficient tension in the pipeline to hold the pipeline in a desired profile; (b) locking the reel against further rotation in the direction of unspooling when the vessel has stopped its forward motion; (c) thereafter controlling the forward thrust of the vessel motive source to maintain the vessel in a station keeping mode and to maintain the pipeline under said sufficient tension to hold the desired pipe profile while the vessel is in said station keeping mode; (d) performing any necessary operations on the pipe and/or coating while the vessel is in said station keeping mode; - a - (e) thereafter resuming forward motion of the vessel in the pipelaying direction by (1) disengaging the means locking the reel against the rotation in the unspooling direction, (2) concurrently substantially increasing the dynamic braking force imparted to the reel by the reel drive mechanism such that the dynamic braking force exceeds any increases in the forward thrust of the vessel's motive source at least up to the pipelaying thrust level required to move the vessel in the forward direction at a desired laying speed, (3) gradually increasing the forward thrust imparted to the vessel by the vessel motive source up to said pipelaying thrust level, and (4) thereafter gradually reducing the dynamic braking force of the reel drive mechanism at least until the forward thrust imparted to the vessel by the vessel motive source exceeds the dynamic braking force of the reel drive mechanism and the vessel begins to move forward. The step of performing necessary operations on the pipe and/or coating may for example comprise the step of applying one or more sacrifical anodes to the pipe at a designated work station located along the pipe path downstream of the straightening means in the unspooling direction. - b -
438176
Gowling Lafleur Henderson Llp
Santa Fe International Corporation
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