METHOD FOR PRESSURISING THE INNER FLOW SPACE OF A FLEXIBLE PIPE INTENDED FOR TRANSPORTING HYDROCARBONS

Abstract

The present application relates to a method for pressurizing the inner flow space of an underwater flexible pipe intended for transporting hydrocarbons, comprising the following steps: a) providing a flexible pipe comprising a reinforcing layer made up of a short-pitch winding of at least one metal wire with noncontiguous turns around a thermoplastic polymer sheath defining an inner space, then b) filling the inner space of the flexible pipe with an oil, then c) increasing the inner pressure Pi of the flexible pipe to at least 10 MPa, the inner pressure being exerted by said oil, then d) maintaining the inner pressure Pi of the flexible pipe at a pressure of at least 10 MPa for a time D of at least one minute,
characterized in that said oil has a kinematic viscosity at 40 C., measured according to the ASTM D445 standard, of more than 10 mm.sup.2/s. This method makes it possible to reduce, or even prevent, the appearance of cavitation and crazing on the polymer sheath.

Claims

1. A method for pressurizing the inner flow space of an underwater flexible pipe intended for transporting hydrocarbons, comprising the following steps: a) providing a flexible pipe comprising a reinforcing layer made up of a short-pitch winding of at least one metal wire with noncontiguous turns around a thermoplastic polymer sheath defining an inner space, then b) filling the inner space of the flexible pipe with an oil, then c) increasing the inner pressure Pi of the flexible pipe to at least 10 MPa, the inner pressure being exerted by said oil, then d) maintaining the inner pressure Pi of the flexible pipe at a pressure of at least 10 MPa for a time D of at least one minute, wherein said oil has a kinematic viscosity at 40 C., measured according to the ASTM D445 standard, of more than 10 mm.sup.2/s.

2. The method according to claim 1, wherein, during steps c) and d), the inner pressure Pi is greater than or equal to 20 MPa.

3. The method according to claim 1, wherein the kinematic viscosity at 40 C. measured according to the ASTM D445 standard is greater than 100 mm.sup.2/s.

4. The method according to claim 1, wherein the time D of step d) is at least one hour.

5. The method according to claim 1, wherein during step d), the temperature of the oil is comprised between 5 and 30 C.

6. The method according to claim 1, wherein during step d), the temperature of the oil is higher than 30 C.

7. The method according to claim 1, comprising: optionally, before step b), a step b0) consisting of winding the flexible pipe on a spool or rack, after step d), a step e) consisting of decreasing the inner pressure Pi of the flexible pipe to atmospheric pressure, then optionally a step f) consisting of emptying the oil from the flexible pipe.

8. The method according to claim 1, wherein steps c) and d) are repeated n times, where n is an integer greater than or equal to 1.

9. The method according to claim 1, comprising, between steps b) and c), a step c0) consisting of pressurizing the inner space of the flexible pipe at an inner pressure P.sub.0 below 10 MPa, then maintaining the inner space of the flexible pipe at the inner pressure P.sub.0 for a time greater than 30 minutes.

10. The method according to claim 1, comprising: before step b), a step ) consisting of introducing, in the flexible pipe, a hose having a diameter smaller than the inner diameter of the flexible pipe, and before step c), a step ) consisting of filling the hose with a fluid of a different nature from the oil.

11. The method according to claim 1, comprising, before step b) or simultaneously with step b), a step ) consisting of inserting a solid material into the flexible pipe.

12. The method according to claim 1, comprising, before step a), a step a.sub.0) for preparing the flexible pipe, typically comprising: an extrusion to form a polymer sheath, the extrusion being done on another layer, then assembling the polymer sheath with the reinforcing layer.

13. The method according to claim 1, wherein the oil is a synthetic oil.

14. The method according to claim 1, wherein the polymer sheath is made from polyolefin, polyamide, polyvinylidene fluoride homopolymer or copolymer of vinylidene fluoride and of at least one other monomer.

15. The method according to claim 1, wherein the reinforcing layer made up of a metal wire winding with noncontiguous turns is a pressure vault and the polymer sheath is an inner polymer sealing sheath.

16. The method according to claim 15, wherein the flexible pipe comprises, from the outside toward the inside of the pipe: an outer sealing polymer sheath, one or more tensile armor ply(plies), the pressure vault, an inner sealing polymer sheath, and optionally a metal carcass.

17. A device allowing the inner pressurization of an underwater fluid pipe intended to transport hydrocarbons comprising: i) a flexible pipe comprising a reinforcing layer made up of a short-pitch winding of at least one metal wire with noncontiguous turns around a thermoplastic polymer sheath defining an inner space, ii) a piece of equipment for giving the flexible pipe an inner pressure Pi of at least 10 MPa, and iii) a piece of equipment for maintaining the inner pressure Pi of the flexible pipe for a time D of at least one minute, wherein said piece of equipment for giving the flexible pipe an inner pressure Pi is an oil comprising a kinematic viscosity at 40 C., measured according to the ASTM D445 standard, of more than 10 mm.sup.2/s.

Description

EXAMPLES

[0159] Pressurization tests with two pressure maintenance sequences (n=1) were done with three different fluids, the natures, densities and viscosities of which are provided in table 1.

TABLE-US-00001 TABLE 1 density and kinematic viscosity of the three tested fluids measuring Marcol 52 Durasyn 174I method water oil oil kinematic viscosity ASTM D 445 0.66 7.50 412 at 40 C. (mm.sup.2/s) kinematic viscosity ASTM D 445 0.29 2.20 50 at 100 C. (mm.sup.2/s) density at 20 C. ASTM D 4052 1 825 to 834 846

[0160] The three identical ST 63.60103 (Technip) flexible pipes used:

[0161] comprised, from the outside toward the inside of the pipe: [0162] an outer sealing polymer sheath (10), [0163] one or more tensile armor ply(plies) (12, 14), [0164] a pressure vault (18), [0165] an inner sealing polymer sheath (20) made from weakly plasticized PVDF (Gammaflex TP22) (inner diameter of 77.50 mm), and [0166] a metal carcass (22), [0167] had an initial length of the flexible pipe (with tips) of 5.67 m, an inner diameter of 2.5, an outer diameter of 142 mm, a high design pressure (702 bar) and a factory acceptance test (FAT) pressure of 1054 bar.

[0168] The tests were done at a temperature of 20 C.

[0169] Each flexible pipe was wound on a spool, the radius R of which was 672 mm (radius chosen so as to have a deformation level on the stretched generatrix of the PVDF polymer sheath greater than 5%). The initial deformation level on the inner skin of the pressure sheath was 5.22%.

[0170] At the end of this phase, the inner space of the flexible pipe was connected to valves and to a pump, then filled with test fluid at atmospheric pressure for at least 24 hours. The following steps were then carried out: [0171] Pressure increase at 5 bar/min to 850 bar, then 1 bar/min to Pi=1054 bar. [0172] Maintenance of the pressure at Pi=1054 bar for 1 hour. [0173] Depressurization from 1054 bar to 1 bar with a depressurization speed of 100 bar/hour. [0174] Pressure increase at 5 bar/min to 850 bar, then 1 bar/min to Pi=1054 bar. [0175] Maintenance of the pressure at Pi=1054 bar for 24 hours. [0176] Depressurization from 1054 bar to 1 bar with a depressurization speed of 100 bar/hour. [0177] Emptying of the inner space of the flexible pipe.

[0178] The flexible pipe was then unwound and straightened.

[0179] The flexible pipe was then dissected starting from the last layer (outer sheath) to the inner polymer sealing sheath.

[0180] The inner polymer sealing sheath was next removed in a zone corresponding to a winding greater than 5.0% and over the stretched generatrix.

[0181] The inner polymer sealing sheath was then characterized at the inner skin. An observation by scanning electron microscope (SEM) (JEOL JSM 6390-LV apparatus) with a magnification of 5000 made it possible to compare the condition of the material in this zone on the micron scale, in order to observe the evolution of the cavitation rate.

[0182] The results of the SEM observations obtained on an untested sheath (reference) and on the sheaths removed on the 3 tested flexible pipes with the 3 fluids are shown in FIGS. 7 to 10.

From these snapshots, it is possible to conclude that: [0183] a pressurized test on a flexible pipe done with water or the Marcol 52 oil causes a significant increase in the cavitation rate of the PVDF sheath. [0184] a pressurized test on a flexible pipe done with the Durasyn 174I oil does not cause a significant increase in the cavitation rate of the PVDF sheath.