Method for pressurizing 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 testing the inner flow space of an underwater flexible pipe intended for transporting hydrocarbons, comprising: 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 exerting an inner pressure P.sub.i inside the flexible pipe, then c) increasing an inner pressure P.sub.i of the flexible pipe to at least 10 MPa, the inner pressure being exerted by said oil, then d) maintaining the inner pressure P.sub.i 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, the method being carried out in the context of a pressure test.

2. The method according to claim 1, wherein during the steps c) and d), the inner pressure P.sub.i 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 maintaining the step d) is at least one hour.

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

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

7. The method according to claim 1, further comprising: before the filing step b), performing a step b.sub.0 of winding the flexible pipe on a spool or rack.

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

9. The method according to claim 1, further comprising, between the steps of b) filling and c) increasing, performing a step c.sub.0) of pressurizing the inner space of the flexible pipe at an inner pressure P.sub.0 below 10 MPa, and then performing a step d.sub.0) of 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, further comprising: before the step of b) filling, performing a step ) of introducing, in the flexible pipe, a hose having a diameter smaller than the inner diameter of the flexible pipe, and before the step of c) increasing, performing a step ) of filling the hose with a fluid different from the oil that is used for filling the inner space of the flexible pipe at b) the filling step.

11. The method according to claim 1, (the rest of limitations are not presented here).

12. The method according to claim 1, (the rest of limitations are not presented here).

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 flexible pipe comprises, from the outside toward the inside of the pipe: an outer sealing polymer sheath, one or more tensile armor plies, (the rest of limitations are not presented here).

16. A pressure test installation allowing the inner pressurization of an underwater fluid pipe intended to transport hydrocarbons comprising: 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, an oil comprising a kinematic viscosity at 40 C., measured according to the ASTM D445 standard, of more than 10 mm.sup.2/s, said oil being located in the inner space of the pipe, a pump capable of pressurizing the oil to an inner pressure P.sub.i of at least 10 MPa, and at least one valve able to close off the inner space of the flexible pipe for maintaining the inner pressure P.sub.i of the flexible pipe for a time D of at least one minute.

17. The method according to claim 1, further comprising after performing the maintaining step d), performing a step e) of decreasing the inner pressure P.sub.i of the flexible pipe to atmospheric pressure, and then optionally performing a step f) of emptying the oil from the flexible pipe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a partial schematic perspective view of a flexible pipe that may be used in the method according to the invention;

(2) FIG. 2 is a sectional view of the polymer sheath and the reinforcing layer made up of a wound wire with noncontiguous turns;

(3) FIG. 3 illustrates an installation suitable for carrying out the method;

(4) FIG. 4 is a sectional view of the flexible pipe comprising a reinforcing layer and a polymer sheath in an embodiment of the method;

(5) FIG. 5 is a sectional view of the polymer sheath and the reinforcing layer;

(6) FIG. 6 is another sectional view of the polymer sheath and the reinforcing layer;

(7) FIG. 7 is an image obtained by observation with a scanning electron microscope, the inner skin of the inner sealing polymer sheath of the flexible pipe of the example;

(8) FIG. 8 is another image obtained by observation with a scanning electron microscope of the inner skin of the inner sealing polymer sheath of the flexible pipe;

(9) FIG. 9 is another image obtained by observation with a scanning electron microscope of the inner skin of the inner sealing polymer sheath of the flexible pipe; and

(10) FIG. 10 is another image obtained by observation with a scanning electron microscope of the inner skin of the inner sealing polymer sheath of the flexible pipe.

(11) FIG. 1 is a partial schematic perspective view of a flexible pipe that may be used in the method according to the invention and comprising, from the outside toward the inside: an outer sealing polymer sheath 10, an outer tensile armor ply 12, an inner tensile armor ply 14 wound in the opposite direction from the outer tensile armor ply 12, a pressure vault 18 for reacting radial forces generated by the pressure of the transported hydrocarbons, an inner sealing polymer sheath 20, and an inner carcass 22 for reacting radial crushing forces.
No intermediate polymer sheath is shown in FIG. 1. As explained above, it is not outside the scope of the present invention if the pipe comprises one or several intermediate polymer sheath(s).

(12) Due to the presence of the inner carcass 22, this pipe is said to have a rough bore. The method according to the invention can also be implemented with a so-called smooth-bore pipe, not including an inner carcass.

(13) Likewise, it would not be outside the scope of the present invention to eliminate the pressure vault 18, as long as the helix angles of the wires making up the tensile armor plies 12, 14 are close to 55 and in opposite directions.

(14) The tensile armor plies 12, 14 are obtained by long-pitch winding a set of metal or composite wires, with a generally substantially rectangular section. The invention would also apply if these wires had a circular or complex geometry section, for example of the self-stapled T type. In FIG. 1, only two tensile armor plies 12 and 14 are shown, but the pipe could also include one or several additional pairs of reinforcements. The tensile armor ply 12 is said to be outer because here it is the last, starting from the inside of the pipe, before the outer sealing sheath 10.

(15) The flexible pipe may also comprise layers not shown in FIG. 1, such as: a ring made by short-pitch winding of at least one metal wire advantageously with a cross-section around the pressure vault 18 to increase the bursting strength of the pipe, and/or a maintaining layer between the outer polymer sheath 10 and the tensile armor plies 12 and 14, or between two tensile armor plies, and/or one or more anti-wear layers made from a polymer in contact either with the inner face of the aforementioned maintaining layer, or with its outer face, or with both faces, this anti-wear layer making it possible to prevent the maintaining layer from wearing out in contact with the metal reinforcements. The anti-wear layers, which are well known by those skilled in the art, are generally made by helical winding of one or more strips obtained by extruding a polymeric material based on polyamide, polyolefins, or PVDF polyvinylidene fluoride). Reference may also be made to document WO 2006/120320, which describes anti-wear layers made up of ribbons of polysulfone (PSU), polyether sulfone (PES), polyphenol sulfone (PPSU), polyetherimide (PEI), polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK) or polyphenylene sulfide (PPS).

(16) FIG. 2 is a sectional view of the polymer sheath 202 and the reinforcing layer made up of a wound wire with noncontiguous turns 204. The surface 208 of the polymer sheath 202 is on the inner side of the pipe. A butt gap 206 exists between each turn of the reinforcing layer 204.

(17) FIG. 3 illustrates an installation suitable for carrying out the method.

(18) The oil is steered to the inside of the first end 306 of the flexible pipe 301 through a pump 308 (in the direction of arrow A). The flexible pipe 301 is wound on a spool 310 during the method.

(19) When the method is carried out at a temperature higher than the ambient temperature (where the ambient temperature is the outside temperature in the test zone (i.e., temperature on the manufacturing site of the pipe), the installation typically comprises a heating device 304 connected on the one hand to an oil inlet pipe 302 and on the other hand to a supply valve 307. This heating element is not necessary when the method is carried out at ambient temperature.

(20) The oil is pumped inside the inner space of the flexible pipe 301 from an oil reservoir 300 connected to the oil inlet pipe 302. The flexible pipe 301 is also connected to a pressure gauge that makes it possible to check the inner pressure Pi. A supply valve 307 is located between the heating device 304 and the pump 308. The flexible pipe 301 is aerated by an isolating valve 312 that in particular makes it possible to bleed the air from the flexible pipe 301. The oil that leaves the second end 314 of the flexible pipe 301 can be reintroduced through the pump 308 (in the direction of arrow B owing to the pipe 316, only part of which is shown). Next, the second end 314 of the flexible pipe 301 is closed using an isolating valve 312 and the flexible pipe 301 is pressurized owing to the pump 308 to the desired inner pressure Pi, and kept at this pressure for the desired time owing to the closing of the two valves 307, 312. Once this time has elapsed, the isolating valve 312 can be reopened to decrease the pressure inside the flexible pipe 301 to atmospheric pressure (about 1 bar).

(21) FIG. 4 is a sectional view of the flexible pipe comprising a reinforcing layer 401 and a polymer sheath 402 in the embodiment of the method in which a hose 403 has been inserted into the pipe (step )). During step b), the space 405 between the hose and the flexible pipe is filled with oil as defined above. During step ), the space 404 that corresponds to the inside of the hose is filled with fluid.

(22) FIG. 5 is a sectional view of the polymer sheath 502 and the reinforcing layer 504 made up of a wound wire with noncontiguous turns 506 of a flexible pipe subject to a factory acceptance test according to paragraph 10.3 of the API 17J standard (3rd editionJan. 1, 2009), i.e., by inwardly pressurizing it with water (comparative). The inner surface 508 of the polymer sheath 502 is on the inner side of the pipe. The outer surface 510 of the polymer sheath 502 is on the outer side of the pipe. A butt gap 512 exists between each turn 506 of the reinforcing layer 504.

(23) The outer surface 510 has local deformations at the butt gaps 512, and in particular radial deformations. Thus, the surface 510 has, aligned with the butt gaps 512, a massive excursion 514 of the polymer material inside the butt gaps 512 and on each side of the massive excursions 514, substantially aligned with the inner edges 516, 518 of the turns 506, a recess 520 of the polymer material. Indeed, under the action of the pressure, the polymer sheath 502 presses forcibly against the turns 506 of the reinforcing layer 504 and the polymer material creeps through the butt gaps 512. However, when one ceases to apply pressure, the material retracts at the inner edges 516, 518. This creep through the butt gaps 512 may lead to an unsticking of the polymer material within the massive excursions 514 and a withdrawal and damage of the material at the outer surface 510 of the polymer sheath 502. These phenomena manifest either during the factory acceptance test, or later when it is operating on the hydrocarbon production site. Furthermore, opposite the side of the inner surface 508 of the polymer sheath 502, flaws 522 are observed due to the cavitation phenomenon. These phenomena are related to the pressurization of the inside of the flexible pipe.

(24) Against all expectations, the pressurization of the inner space of the flexible pipe by an oil as defined above makes it possible not only to reduce the damage phenomena of the outer surface 510 at the butt gaps 512, but also the consequences of the cavitation phenomena. Indeed, as explained below in reference to FIG. 6, by replacing the water with oil as defined above, the withdrawal at the inner edges 516, 518 of the butt gaps 512 as well as the spreading of the flaws 522 present in the excursions 514 and at the inner face 508 of the polymer sheath 502 are minimized.

(25) FIG. 6 is a sectional view of the polymer sheath 502 and the reinforcing layer 504 made up of a wound wire with noncontiguous turns 506 of a flexible pipe subject to the method according to the invention, i.e., inwardly pressurizing it with an oil as defined above. It is observed that on each side of the butt gaps 512, the outer surface 510 of the polymer sheath 502 is tangent to the inner edges 516, 518 of the turns 506, and that the withdrawn zones, as illustrated in FIG. 5, have disappeared. Furthermore, within the excursions 514 and on the side of the inner surface 508 of the polymer sheath 502, no traces of cavitation phenomena appear anymore, or unsticking zones previously observed.

(26) Replacing the water with an oil as defined above makes it possible to fill the inside of the butt gaps 512 while minimizing the inner stresses in the polymer material. This minimization of the stresses makes it possible not to generate cavitation.

(27) FIG. 7 is an image obtained by observation with a scanning electron microscope (SEM) with a magnification of 5000 of the inner skin of the inner sealing polymer sheath of the flexible pipe of the example and which has not been pressurized (reference).

(28) FIG. 8 is an image obtained by observation with a scanning electron microscope (SEM) with a magnification of 5000 of the inner skin of the inner sealing polymer sheath of the flexible pipe of the example and which has been pressurized, the pressure having been exerted by water (comparative).

(29) FIG. 9 is an image obtained by observation with a scanning electron microscope (SEM) with a magnification of 5000 of the inner skin of the inner sealing polymer sheath of the flexible pipe of the example and which has been pressurized, the pressure having been exerted by Marcol 52 oil (comparative).

(30) FIG. 10 is an image obtained by observation with a scanning electron microscope (SEM) with a magnification of 5000 of the inner skin of the inner sealing polymer sheath of the flexible pipe of the example and which has been pressurized, the pressure having been exerted by Durasyn 174I oil (according to the invention).

EXAMPLES

(31) 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.

(32) 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

(33) The three identical ST 63.60103 (Technip) flexible pipes used:

(34) comprised, from the outside toward the inside of the pipe: an outer sealing polymer sheath (10), one or more tensile armor ply(plies) (12, 14), a pressure vault (18), an inner sealing polymer sheath (20) made from weakly plasticized PVDF (Gammaflex TP22) (inner diameter of 77.50 mm), and a metal carcass (22), 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.

(35) The tests were done at a temperature of 20 C.

(36) 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%.

(37) 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: Pressure increase at 5 bar/min to 850 bar, then 1 bar/min to Pi=1054 bar. Maintenance of the pressure at Pi=1054 bar for 1 hour. Depressurization from 1054 bar to 1 bar with a depressurization speed of 100 bar/hour. Pressure increase at 5 bar/min to 850 bar, then 1 bar/min to Pi=1054 bar. Maintenance of the pressure at Pi=1054 bar for 24 hours. Depressurization from 1054 bar to 1 bar with a depressurization speed of 100 bar/hour. Emptying of the inner space of the flexible pipe.

(38) The flexible pipe was then unwound and straightened.

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

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

(41) 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.

(42) 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.

(43) From these snapshots, it is possible to conclude that:

(44) 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. 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.