Flexible underwater pipe including a layer including a polyethylene having enhanced heat resistance

Abstract

A flexible underwater pipe for transporting hydrocarbons, including a plurality of layers, at least one of which includes a polyethylene having enhanced heat resistance, to its preparation method and to its use for transporting hydrocarbons.

Claims

1. A method for transporting hydrocarbons wherein the hydrocarbons are transported at a temperature greater than 60? C. and at a pressure greater than 200 bar in a flexible underwater pipe comprising a plurality of layers, at least one layer of which comprises a polymeric matrix comprising a polyethylene with enhanced heat resistance for which the melt index measured at 190? C. under a mass of 5.0 kg is less than 2.0 g/10 min, the density is greater than 0.945 g/cm3, the threshold yield strength is between 20 and 30 MPa, and the elongation at break is greater than 300%, wherein the polyethylene with enhanced heat resistance meets ASTM F2769-10 revised in 2010 or meets ISO 24033 revised in 2009, and wherein the at least one layer, the polymeric matrix of which comprises the polyethylene with enhanced heat resistance, withstands blistering as measured according to the standard API17J.

2. The method according to claim 1, wherein the polymeric matrix is free of dispersed components.

3. The method according to claim 1, wherein the at least one layer which comprises a polymeric matrix comprising the polyethylene with enhanced heat resistance absorbs pressurized gases during transport and allows them to diffuse out of the layer when the pressure in the flexible pipe is reduced.

4. The method according to claim 1, wherein the hydrocarbons are transported at a temperature greater than 90? C.

5. The method according to claim 1, wherein the polyethylene with enhanced heat resistance is non cross-linked.

6. The method according to claim 1, wherein the melt index measured at 190? C. of the polyethylene with enhanced heat resistance is: less than 1.0 g/10 min under a mass of 5.0 kg, and/or less than 0.25 g/10 min under a mass of 2.16 kg, and/or less than 20 g/10 min under a mass of 21.6 kg.

7. The method according to claim 1, wherein the polyethylene with enhanced heat resistance is obtained by polymerization of ethylene and of an ?-olefin selected from 1-butene, 1-hexene and 1-octene.

8. The method according to claim 1, wherein the polymeric matrix of the at least one layer of the flexible underwater pipe comprises a polyethylene with enhanced heat resistance and another polyolefin.

9. The method according to claim 8, wherein, in the polymeric matrix comprising a polyethylene with enhanced heat resistance and another polyolefin, the mass ratio between the polyethylene with enhanced heat resistance and the sum of the polyethylene with enhanced heat resistance and of the polyolefin is greater than 50%.

10. The method according to claim 8, wherein, in the polymeric matrix comprising a polyethylene with enhanced heat resistance and another polyolefin, the mass ratio between the polyethylene with enhanced heat resistance and the sum of the polyethylene with enhanced heat resistance and of the polyolefin is less than 50%.

11. The method according to claim 8, wherein the other polyolefin is a high molecular weight polyethylene.

12. The method according to claim 8, wherein the other polyolefin is a very high molecular weight polyethylene.

13. The method according to claim 1, wherein the flexible underwater pipe comprises, from the outside to the inside: an external polymeric sealing sheath, at least one ply of tensile armors, a pressure vault, an internal polymeric sealing sheath, optionally a metal carcass, and optionally one or several intermediate polymeric sealing sheaths between two adjacent layers, provided that the polymeric matrix of at least one of the polymeric sealing sheaths comprises the polyethylene with enhanced heat resistance.

14. The method according to claim 1, wherein said layer(s), the polymeric matrix of which comprises a polyethylene with enhanced heat resistance is(are): the internal polymeric sealing sheath, and/or one or several intermediate polymeric sealing sheaths located between two adjacent layers, and/or the external polymeric sealing sheath.

15. The method according to claim 1, wherein said layer, the polymeric matrix of which comprises a polyethylene with enhanced heat resistance is the internal polymeric sealing sheath.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other particularities and advantages of the invention will become apparent upon reading the description made hereafter of particular embodiments of the invention, given as an indication but not as a limitation, with reference to the FIGURE.

DESCRIPTION OF PREFERRED EMBODIMENTS

(2) The FIGURE is a partial schematic perspective view of a flexible pipe according to the invention. It illustrates a pipe according to the invention comprising, from the outside to the inside: an external polymeric sealing sheath 10, an external ply of tensile armors 12, an internal ply of tensile armors 14 wound in the direction opposite to the external ply 12, a pressure vault 18 for spread-loading the radial forces generated by the pressure of the transported hydrocarbons, an internal polymeric sealing sheath 20, and an internal carcass 22 for spread-loading the crushing radial forces.
No intermediate polymeric sheath is illustrated in the FIGURE. As explained above, there would be no departure from the field of the present invention if the pipe comprised one or several intermediate polymeric sheaths. When no intermediate polymeric sheath is present in the pipe, like the one illustrated in the FIGURE, it is the external polymeric sealing sheath 10 and/or the internal polymeric sealing sheath 20 which comprise(s) a polyethylene with enhanced heat resistance.

(3) Because of the presence of the internal carcass 22, this pipe is said to be a rough-bore pipe. The invention may also be applied to a smooth-bore pipe not including any internal carcass.

(4) Also, there would be no departure from the field of the present invention by suppressing the pressure vault 18, provided that the helical angles of the wires making up the armor plies 12, 14 are close to 55? and in the opposite direction.

(5) The armor plies 12, 14 are obtained by winding with a long pitch a set of wires in a metal or composite material, with a generally substantially rectangular section. The invention would also apply if these wires had a circular or complex geometrical section, for example of the self-stapled T type. In the FIGURE, only two armor plies 12 and 14 are illustrated, but the pipe may also include one or several additional pairs of armors. The armor ply 12 is said to be external since it is the last here, starting from the inside of the conduit, before the external seal sheath 10.

(6) The flexible pipe may also comprise layers not illustrated in the FIGURE, such as: a holding layer between the external polymeric sheath 10 and the tensile armor plies 12 and 14, or between two tensile armor plies, one or several anti-wear layers in a polymeric material in contact either with the internal face of the aforementioned holding layer or with its external face, or with both faces.

EXAMPLE

Blistering Resistance Test

(7) Blistering resistance tests according to the API17J standard were conducted on PE-RT samples as mentioned earlier (Dow 2377, RT70) 20 times subject to a temperature of 90? C. under a pressure of 250 bars while having been saturated in diesel (reference liquid for the tests) without exhibiting any blistering (observation with the naked eye and then with an optical microscope (a binocular microscope LEICA MZ 125)).

(8) As a comparison, the limits of the polyethylene materials (Finathene? 3802 (Petrofina)) and cross-linked polyethylene (Crossflex? (Technip)) materials used in applications of flexible pipes because of the blistering phenomenon are respectively: a temperature of 60? C. and a pressure of 105 bars in the presence of liquid hydrocarbons, or 210 bars in the presence of only dry gas, or a temperature of 90? C. and a pressure of 175 bars in the presence of liquid hydrocarbons.

(9) Thus, the use of a polyethylene with enhanced resistance as a sealing sheath gives the possibility: for a temperature of 60? C., of increasing the pressure use range as compared with polyethylene presently used, for temperatures above 60? C., i.e. in temperature ranges reserved up to now for cross-linked polyethylene, of increasing the pressure use range as compared with cross-linked polyethylene.

(10) Other blistering resistance tests according to the API17J standard were conducted on PE-RT samples with a thickness of 7 mm as mentioned earlier (Total Petrochemical XSene XRT70) 20 times subject to a temperature of 90? C. under a pressure of 300 bars without exhibiting any blistering (observation with the naked eye and then with an optical microscope (binocular microscope LEICA MZ 125)).

(11) A cross-linked polyethylene material (Crossflex? (Technip)) was subject to the same conditions. Many blisters appeared.

(12) Other blistering resistance tests according to the API17J standard were conducted on PE-RT samples with a thickness of 7 mm of different natures, 20 times subject to a given temperature and pressure. The characteristics of the PE-RTs and the results of the blistering phenomenon resistance are provided in the following table.

(13) TABLE-US-00001 TABLE Characteristics of the PE-RTs used and results of the blistering resistance tests. Grade Dowlex 2344 Dowlex 2388 XRT 70 Provider Dow Chemical Dow Chemical Total Petrochem Co-monomer Octene C8 Octene C8 Hexene C6 Type according I II II to ISO 15494-1 Density (g/cm.sup.3) 0.933 0.941 0.947 Melt index 0.7 g/10 min 0.54 g/10 min 0.7 g/10 min (190? C.) (2.16 kg) (2.16 kg) (5 kg) 2.2 g/10 min 1.9 g/10 min (5 kg) (5 kg) Tensile yield 16.5 20 23 strength (MPa) Tensile break- 34 37 ing strength (MPa) Elongation >800 780 ?350 at break (%) Flexure mod- 550 660 750 ulus (MPa) (580 rigid) 850 (rigid) Blistering Occurrence of Occurrence of No blisters phenomenon blisters at a blisters at a observed at a pressure of 250 pressure of 300 temperature of bars and at a bars and at a 400 bars and at temperature of temperature of a temperature 90? C. 90? C. of 90? C.

(14) These results show that a PE-RT for which the density is greater than 0.945 g/cm.sup.3 and for which the melt index measured at 190? C. under a mass of 5.0 kg is less than 2.0 g/10 min (PE-RT XRT 70) better withstands the blistering phenomenon than a PE-RT not having these characteristics (PE-RT Dowlex with densities of less than 0.945 g/cm.sup.3).