Pipes and tubular conduits – Flexible – Braided – interlaced – knitted or woven
Patent
1998-08-03
2000-07-11
Hook, James
Pipes and tubular conduits
Flexible
Braided, interlaced, knitted or woven
138130, 138153, F16L 1110
Patent
active
060857986
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a flexible pipe for conveying over long distances a fluid at high pressure and the temperature of which may be high, such as a gas, crude oil, water or other fluids.
A flexible pipe generally comprises, from the inside outwards, the chemical action of the fluid to be transported, the fluid in the sealing internal sheath, the said first pressure armor layer generally also being known as the vault pressure, tension produced especially by the pressure of the fluid, when this pressure is high,
In some instances, the flexible pipe comprises an armor layer, arranged over the internal sheath and which simultaneously withstands both the effects of tension directed longitudinally along the axis of the flexible pipe and the circumferential component of the internal fluid-pressure.
The pressure armor layer consists of at least one winding with non-contiguous coils in order to give the flexible pipe a certain amount of flexibility. The expression non-contiguous coils is understood to mean coils between which a certain space is left.
Under the effect of the internal pressure and/or of the temperature developed by the fluid, the internal sheath, which is relatively flexible, is pressed against the pressure armor layer and tends to penetrate one or more of the spaces between coils. The tendency of the internal sheath to penetrate or creep increases with time and/or the severe service conditions of the flexible pipe, for example when the fluid to be conveyed flows at high pressure (several hundreds of bar) and high temperature (above 100.degree. C.), a high temperature generally reducing the rigidity of the internal sheath. When the internal sheath gradually penetrates the said spaces, either cracks are produced which thus affect the sealing function of the sheath, or one or more local ruptures of the sheath may even occur, the consequence of such incidents being that fluid passes out of the sheath which no longer provides the required sealing.
Several solutions have been proposed and/or adopted in order to limit or in an attempt to prevent the creeping of the sheath into the spaces between coils of the pressure arch.
One solution, the simplest, consists in choosing a material and a great thickness for the sheath, so that it has better mechanical performance and higher chemical resistance. The drawback of this solution is twofold: it is more difficult to produce the flexible pipe because of the large size of the sheath and the cost of manufacture is very high.
Another solution consists in using a more precious material in order to keep the sheath to an acceptable thickness. Thus, instead of using a polyethylene to make the sheath, use has been made of a polyamide, the cost of which is very markedly higher than that of polyethylene.
Other solutions which in some cases are not directly related to the subject-matter of this invention are proposed and described in WO-A-82/01159, U.S. Pat. No. 3,880,195, EP-A-0,166,385, EP-A-0,147,288, FR-A-2,465,416 and FR-A-2,417,707.
The prior art most closely related to the invention consists of documents U.S. Pat. No. 3,729,028 and FR-A-2,590,646.
In document U.S. Pat. No. 3,729,028, the sealing internal sheath comprises a wound strip but neither the structure nor the mechanical properties of the strip, apart from the fact that it is of rectangular section, are described or even suggested.
Document FR-A-2,590,646, like the present invention, uses an intermediate strip capable of restricting the creeping of the internal sheath between the coils of the pressure armor layer for resisting the internal pressure. According to that document, the intermediate strip, which may be wound around the internal sheath in the direction of winding of the coils of the pressure armor layer or in the opposite direction, needs to have a high elastic modulus in the direction of winding. For that, and with the purpose of obtaining satisfactory results, it is recommended that use be made, for producing the tape, of substantially uni-directional fibres
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Coflexip
Hook James
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