Pipes and tubular conduits – Flexible – Spirally wound material
Patent
1999-11-17
2000-11-14
Brinson, Patrick
Pipes and tubular conduits
Flexible
Spirally wound material
138135, 138131, 138134, 138129, F16L 1116
Patent
active
061455466
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a flexible pipe capable of being used for transporting fluids such as hydrocarbons for example.
Several types of flexible pipe are used. Some flexible pipes comprise, from the inside outwards, an internal sealing sheath made of plastic, elastomer or some other relatively flexible appropriate material; an unsealed flexible metal tube which has to withstand the loads developed by the pressure of the fluid flowing along the pipe; one or more plies of armours and at least one external sealing sheath made of a polymeric material. This type of flexible pipe is often termed a "smooth-bore" by specialists in this subject.
Other flexible pipes termed "rough-bore" comprise, from the inside outwards, an unsealed metal tube known as the carcass, consisting of a section wound into interlocked turns such as, for example, an interlocked metal strip or wire of an interlocking shape such as a wire in the shape of a T, U, S or Z, an internal sealing sheath made of a polymeric material, one or more plies of armours capable of withstanding the forces developed by the pressure of the fluid flowing through the pipe and the external forces to which the flexible pipe is subjected, and at least one external protective sheath of the polymeric type.
In the latter type of flexible pipe, the internal sealing sheath is directly extruded, continuously, over the carcass which, between the wound turns, has spaces or gaps.
To ensure good contact between the internal sealing sheath and the metal carcass, it is necessary for the inside diameter of the internal sealing sheath to be as close as possible and even equal to the outside diameter of the flexible metal carcass.
When manufacturing a flexible pipe of the "rough-bore" type, the internal sealing sheath which is extruded over the metal carcass shrinks onto the latter as it cools. Depending on the materials used to produce the internal sealing sheath, deformations known as "shrinkage cavities" appearing on the internal face of the said internal sealing sheath and particularly on each side of the gaps between the turns of the metal carcass can be observed after cooling. Such shrinkage cavities are due, it would seem, to the differential shrinkage of the material used for the internal sealing sheath, because of the variation in cooling gradient through the thickness of the internal sealing sheath, combined with the effect of the gaps between the turns of the metal carcass. What actually happens is that since the extruded plastic sealing sheath is in contact via its internal face with the metal carcass which is at ambient temperature, the cooling of the said internal face is very quick, and this causes surface irregularities or shrinkage cavities; this phenomenon is amplified at the gaps between the turns of the metal carcass, the differential shrinkage at these points leading to local variations in the thickness of the internal sealing sheath. When the sealing sheath is made of semicrystalline polymer, sensitive to the presence of surface defects leading to a deterioration in the sheath which may go so far as to rupture it, such as for example PVDF, this very often, in operation, leads to degradation of the sealing sheath (rupture) so that it then no longer fulfils its sealing function.
In order to remedy a drawback of this nature and to solve the problem which arises through the appearance of shrinkage cavities, the solution of depositing a thin sacrificial sublayer of an appropriate material such as PVDF between the metal carcass and the internal sealing layer was found and adopted. The internal sealing sheath is then extruded over the said sacrificial sublayer but making sure that there is no "welding" or intimate bonding between the sealing sheath and the "sacrificial" sublayer, so that cracks propagating from the internal face of the sublayer outwards are stopped at the interface between the sealing sheath and the sacrificial sublayer. This is what is described in WO 95/24578.
The major disadvantage of this solution is the s
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Hardy Jean
Morand Michel Paul
Brinson Patrick
Coflexip
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