Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Submerging – raising – or manipulating line of pipe or cable...
Patent
1996-11-26
1999-10-26
Taylor, Dennis L.
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Submerging, raising, or manipulating line of pipe or cable...
405158, 405166, 405169, F16L 112
Patent
active
059716665
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the laying of submarine pipelines.
Known methods of submarine pipelaying fall into two broad classes.
First, there are methods in which pipe lengths are shipped on a vessel such as a lay barge and are welded end to end as laying proceeds. These can be divided into "S lay" where the pipe is welded up in a horizontal path and laid over a stinger, and "J lay" where the pipe is launched from the vessel in a substantially vertical direction and each succeeding pipe length must be erected into a substantially vertical position for welding to the last section.
Each of these has problems and limitations. S lay requires a cumbersome and expensive stinger and can operate only in relatively shallow water. J lay can cope with deeper water, but handling pipe lengths into the vertical and welding them in that position is difficult and time consuming.
The second broad category of known method is reel pipelaying. This has the great benefit of allowing the bulk of the welding to be carried out in factory conditions ashore. However, a complex, specialised lay vessel is required for larger diameter pipelines. Reel pipelaying using existing arrangements is generally preferable on economic grounds for pipelines having an o.d. of 16" or less. However, this is not an absolute limit and may vary depending upon detailed operational requirements.
It should be noted that in the first of the foregoing categories, persons in the art have always considered it important to avoid plastic deformation of the pipe, seeking to control the double bends of S lay and the single bend of J lay such that the elastic limit of the pipe material is not exceeded. In reel pipelaying, the act of reeling solid pipe requires plastic deformation which is subsequently reversed by a straightener assembly.
An object of the present invention is to provide methods of, and vessels for, laying underwater pipelines which do not fall into the foregoing categories. The invention is particularly, but not exclusively, applicable to the laying of large diameter pipe which it is not practicable to coil on a reel and which must therefore be welded on the lay vessel.
In accordance with a first aspect of the invention, there is provided a method of laying an underwater pipeline, comprising assembling pipe sections together along a substantially horizontal axis on the deck of a vessel to form a pipeline and laying the pipeline onto the sea bed as pipeline assembly progresses, the pipeline being bent as it is laid from the vessel.
Preferably, the pipeline is plastically bent about a substantially arcuate path in a substantially vertical plane.
In preferred embodiments of the invention, the pipeline is bent through an angle greater than 90.degree..
Preferably also, the pipeline is launched at a substantial angle to the horizontal and tension is applied to the pipeline, said angle being selected to allow the pipeline to form a catenary curve between the launch point and the sea bed for a given applied tension. The tension is preferably also controlled to ensure that the bending of the pipeline at the point where it meets the sea bed is within the elastic yield limit of the pipe material.
Also in the preferred embodiments of the invention, bending of the pipeline is followed by straightening thereof.
In certain embodiments, the bending of the pipeline includes diverting the pipeline upwardly along a substantially arcuate path and subsequently diverting the pipeline downwardly and launching the pipeline via an adjustable-angle ramp. Preferably, said pipeline is straightened by straightening means mounted on said variable angle ramp after being diverted downwardly to its final launch angle. Preferably also, tension is applied to said pipeline by tensioning means prior to being diverted upwardly.
In certain particular embodiments, said upward bending of the pipeline diverts the pipeline about a horizontal axis through substantially 180.degree. prior to being launched via said ramp. In these cases the pipeline is preferably bent about a circular sheave def
REFERENCES:
patent: 3681927 (1972-08-01), Duc et al.
patent: 3685305 (1972-08-01), Lloyd
patent: 3685306 (1972-08-01), Mott
patent: 3822559 (1974-07-01), Matthews et al.
patent: 5011333 (1991-04-01), Lanan
Carmichael Donald
Martin Robert George
Roberts Stephen John
Coflexip Stena Offshore Limited
Taylor Dennis L.
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