GB2284819A - Flexible sheath and its application to flexible metal pipes and cables - Google Patents

Description

L 2284819 FLEXIBLE SHEATH AND ITS APPLICATION TO FLEXIBLE METAL PIPES AND

CABLES The present invention relates to a flexible sheath made of trif luoroethylene polymer (PVF3) and its application to flexible metal pipes or cables.

it is well known to use flexible pipes in maritime oil and gas exploitation. These flexible pipes comprise of an inner flexible steel pipe, a plastics sheath, the function of which is to render the pipe leakproof to oils and gases, and metal armouring. Such flexible pipes are, for example, described in European Patent EP 166,385.

Polyamides, which are suitable when the temperature of exploitation of the fluids does not is exceed 80 to 1000C, are used as leakproof thermoplastic sheaths.

For higher temperatures, for example up to 130 or 1400C, poly(vinylidene fluoride) (PVW) is used. However, as this polymer is semicrystalline and is highly rigid, its use is not suitable when the structure is intended to be coiled and uncoiled, sometimes at very low temperature, unless internally or externally plasticized. An example of internal plasticization is 25 described in European Patent EP 166,385 mentioned above: vinylidene fluoride is copolymerized with a fluorinated monomer. The flexibility of the sheath is thus increased but its temperature of use is generally 2 decreased, its permeability to gases is increased and there is an increased sensitivity (with respect to the homopolymer) to bursting under sudden decompression, making its use dangerous for some high temperature and 5 pressure operations.

The use of external plasticizers is mentioned in French Patents 2,560,884, 2,592,655 and 2,618,791. Some plasticizers make PVDP homopolymer sufficiently supple for use on flexible pipes. However, in use, it is observed that the sheath slowly returns to its original rigidity due to loss of the, generally highly PVW compatible, plasticizer. Not only does the rigidity increase but the polymer becomes embrittled as a result of the creation of internal stresses due to is loss of the plasticizer and the tendency of the sheath to shrink being impeded.

It has now surprisingly been found that the disadvantages resulting from the use of internally or externally plasticized PVDP may be avoided by the use of a polymer comprising trifluoroethylene units. In particular it has been found that particularly flexible sheaths (or pipes) may be made by using a polymer comprising trifluoroethylene units.

According to the present invention, there is provided a flexible sheath based on a polymer comprising trifluoroethylene units.

The sheaths according to the present invention have temperatures of use much greater than 3 those produced from PVW. Moreover, the sheath is much more flexible.

In addition to trif luoroethylene (VF3) F the sheath polymer can also comprise residues of chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropene, vinylidene fluoride or ethylene units.

It would not be departing from the scope of the invention by adding to the sheath polymer fillers, pigments or even a small amount of plasticizers e.g. of ester or sulphonamide type. The present invention also provides a flexible metal pipe bearing a sheath according to the present invention. is The flexible pipe according to the invention is particularly useful for transporting liquid or gaseous hydrocarbons at high temperature. The flexible pipe can also carry a protective layer such as of rubber, metal or textile cloth, and the like. 20 For gas transportation, it is preferable that the polymer of the sheath is essentially trifluoroethylene homopolymer. The sheaths according to the invention may also be used to protect cables. 25 The invention also provides a cable bearing a sheath according to the present invention. The cable can be a metal wire or a strand or a number of strands forming a metal cable.

4 Whether cables or flexible pipes, the sheath may be applied by extrusion.

Examples

The invention is further illustrated by the 5 following Examples.

In the Examples a thermoplastic sheath, Smm thick, is extruded around a flexible steel pipe with a diameter of 32 mm, the pipe consisting of turns between which there are hollows and chinks which allow the pipe to articulate.

In order to compare the ability of different sheath materials to coil up, the following procedure was used:

The sheathed pipe is placed on two stationary is supports. Using a bending wheel with a radius of 75 mm, pressure is applied at a point equidistant from those supporting the pipe. The pressure necessary to deform the sheathed pipe and to give it the radius of curvature of the wheel is applied to the wheel. The indentation depth of the wheel shows the ability of the flexible pipe to deform. The maximum depth is 170 mm: it corresponds to the perfect coiling of the sheathed pipe on the wheel. If rupturing takes place before perfect coiling of the sheathed pipe, the depth is noted. The greater it is, the more the flexible pipe is capable of bending.

Moreover, the-test is carried out at different temperatures.

Example 1

Indentation depth of the wheel before rupturing (in mm - 170 ma corresponds to the mmnxiiallin) Sample 1 11 111 IV 200C 120 170 170 170 -300C 80 150 100 160 Sheath 1: VF2 homopolymer - Foraflon 1000 from Elf Atochem.

Sheath ll: W2 homopolymer + 7.5% by weight of N-butylbenzenesulphonamide.

Sheath Ill: Copolymer of VF2 and hexaf luoropropene in the 9515 molar ratio.

Sheath IV: W3 homopolymer.

is Example 2

The 4 sheathed flexible pipes are subjected to thermal aging for 3 months at 1500C. Then the pipes were subjected to the tests described above.

6 indentation depth of the wheel before rupturing (in mm - 170 zm corresponds to the maxlim-n) 200C 100 90 Unusable 170 molten sheath -300C 40 40 Unusable 140 molten sheath Example 3

The 4 flexible pipes are subjected to thermal aging for 3 months at 1800C. The pipes are then subjected to the tests as described above.

Indentation depth of the wheel before rupturing (in mm - 170 mm corresponds to the wmxilrnilin) Sample 1 11 ill 1V 200C Unusable Unusable Unusable 160 sheaths sheaths sheaths -300C molten- molten- moltendeformed deformed deformed

Claims (8)

7 Claims

1. A flexible sheath based on a polymer comprising trifluoroethylene units.

2. A flexible sheath according to Claim 1, 5 in which the polymer also comprises residues of chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropene, vinylidene fluoride or ethylene units.

3. A flexible sheath according to Claim 1 of trifluoroethylene homopolymer.

4. A flexible sheath according to any one of Claims 1 to 3 in which the sheath also contains a filler, pigment or plasticizer.

5. A flexible metal pipe bearing a sheath as defined in any one of Claims 1 to 4.

6. A pipe according to Claim 5 substantially as described in the Examples.

7. A cable bearing a sheath as defined in any one of Claims 1 to 4.

8. Use of a pipe according to Claim 5 for underwater transport of oil or gas.