Pipes and tubular conduits – Flexible – Spirally wound material
Patent
1998-07-22
2000-07-11
Brinson, Patrick
Pipes and tubular conduits
Flexible
Spirally wound material
138133, 138134, 138130, F16L 1108
Patent
active
060857994
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to flexible pipelines used for transporting fluids, such as, for example, live crude oil, along the seabed between sub-sea operating installations or between sub-sea or surface operating installations and coastal operating installations. Such flexible pipelines are of the type known as flow lines.
Flexible pipelines of the flow line type may, in certain cases, be protected when used on seabed by being covered with a certain depth of sediment or of a filling material, known as depth of cover, so as to be protected from any damage due to shipping or to the environment or for the purpose of not being subjected to the action of the current and/or the swell.
This protection may typically be achieved by digging a trench or furrow in the seabed, placing the flexible pipeline in this trench, then allowing the trench to fill naturally or, preferably, by filling the trench. This is then known as burying.
There are also other ways of protecting a flexible pipeline, for example covering the flexible pipeline, laid on the seabed, with rocks or any other filling material then known as rock dumping or gravel dumping, or with bags filled with gravel or cement as described in patent FR 2,602,300. This is then known as sand bagging.
In all cases, the problem of a variation in the length of the flexible pipeline thus protected, under the effect of the internal pressure or of expansions of thermal origin (as temperature variations may reach 100.degree. C. and more) arises, because the buried or covered flexible pipeline is not free to deform laterally or downwards, and its extension, localized to individual regions where the depth of cover is less or there is fluidized sediment, may then lead to the formation of one or more buckling loops of a significant height and to the emergence of all or part of the flexible pipeline, something which is of course unacceptable.
Reference will usefully be made to the publication by the French Petroleum Institute entitled "Flambage vertical des conduites ensouillees [vertical buckling in buried pipelines]", published in the magazine of the French Petroleum Institute, volume 37, No. 1, January/February 1982, which examines from the theoretical and the experimental point of view the risk of buckling in flexible pipelines and of the formation of at least one buckling loop, as a function of the pressure inside the flexible pipeline and of the stiffness of this pipeline.
Since 1980, the Applicant Company has manufactured and laid several hundreds of kilometers of buried or covered flexible pipeline. These pipelines all have a reinforcing layer for withstanding circumferential components of the internal pressure, called a pressure arch, and reinforcing layers for mainly withstanding tension, known as tension reinforcing layers, and tend to lengthen under the effect of an increase in internal pressure. The tension reinforcing layers are overspecified in order to give the pipeline a significant stiffness and benefit from the fact that the stiffer the pipeline, the higher the critical pressure, that is to say the internal pressure to which the flexible pipeline must be subjected in order to cause a buckling loop to appear.
Despite their special design, these known flexible pipelines have to be buried under a significant depth of cover, to avoid any risk of one or more buckling loops emerging.
By way of indication, for a pipeline inside diameter of between 2 and 18 inches, and a service pressure of between 100 and 400 bar, the depth of cover is usually between 1 m 50 and 2 m 50 and the pipelines are therefore considerably time-consuming and expensive to lay.
To avoid the appearance of buckling loops, efforts have been made to design flexible pipelines that are dimensionally stable in terms of length, specially intended for burying.
Thus, publication U.S. Pat. No. 5,024,252 proposes a flexible pipeline especially intended for burying, of the rough bore type, comprising, from the center outwards: carcass, typically consisting of a helical windi
REFERENCES:
patent: 4693281 (1987-09-01), Creedon
patent: 4860798 (1989-08-01), Kovacs et al.
patent: 4867205 (1989-09-01), Bournazel et al.
patent: 4903735 (1990-02-01), Delacour et al.
patent: 5024252 (1991-06-01), Ochsner
patent: 5176179 (1993-01-01), Bournazel et al.
patent: 5813439 (1998-09-01), Herrero et al.
C. Bournazel, Revue De L'Institut Francais du Petrole, Vertical Des Conduites Ensouillees, vol. 37, No. 1, Jan.-Feb. 1982, pp. 113-117.
Estrier Pascal
Kodaissi Elie
Brinson Patrick
Coflexip
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