WO2011083819A1 - Corrosion prevention structure for flexible pipe - Google Patents

Abstract

Disclosed is a corrosion prevention structure such that even in very deep water, corrosive gas in a reinforcing layer can be reliably replaced with fresh air, that corrosion of reinforcing bar assemblies in the reinforcing layer can be prevented, and that it is possible to achieve high strength by using carbon. A flexible pipe (1) is provided with an inner pipe (11) having liquid-tightness; an outer sheath (15); and an inner axial force reinforcing bar assembly (13) and an outer axial force reinforcing bar assembly (14) both of which consist of a plurality of spirally twisted bar members and are disposed in a reinforcing layer (T) between the inner pipe (11) and the outer sheath (15). Said flexible pipe (1) constitutes the corrosion prevention structure such that the corrosive gas in the reinforcing layer (T), which is disposed between the inner pipe (11) and the outer sheath (15), is discharged axially from the tip end side to the base end side. Furthermore, the flexible pipe (1) is configured in such a way that a plurality of small diameter tubes (17) are installed which are disposed in spiral enlarged gaps (14b) that are provided between the bar members of the outer axial force reinforcing bar assembly (14), and which extend continuously along the pipe axial direction.

Description

Corrosion prevention structure for flexible pipes

The present invention relates to a structure for preventing corrosion of a flexible pipe for discharging corrosive gas in a reinforcing layer between an inner tube and an outer sheath from the distal side toward the proximal side in the pipe axial direction.
This application claims priority based on Japanese Patent Application No. 2010-002970 filed in Japan on January 8, 2010, the contents of which are incorporated herein by reference.

フ レ キ シ ブ ル Flexible pipe is used as a riser pipe that is used from the offshore platform to the wellhead of the seabed in the work of extracting oil and natural gas from the seabed oil field. Until now, the development of submarine oil fields in waters with a depth of several hundreds of meters has been promoted, but with the recent deepening of subsea oil field development, flexible pipes that can support oil field development in waters exceeding 2000 m are available. It has come to be required. Such a flexible pipe has a general structure in which an interlock pipe, an inner pipe, an internal pressure reinforcing strip, an axial force reinforcing strip, and an outer sheath are arranged in this order from the inside.

In addition, in recent years, in addition to flexible pipes capable of handling deep water, there has been a demand for improved service life. The oil to be collected contains corrosive gases such as carbon dioxide (CO ₂ ) and hydrogen sulfide (H ₂ S), and the crude oil to be collected from a deep sea area also contains these corrosive gases.
The innermost interlock pipe of the flexible pipe has a caulking structure and has a certain buckling strength, but is not liquid-tight, and leakage of oil in the pipe is prevented by the inner pipe having liquid-tightness.
However, since the inner pipe is made of a resin material, it is generally known that the corrosive gas contained in the oil cannot be completely blocked and the corrosive gas permeates with a certain value of transmittance. The corrosive gas that has permeated the inner tube stays in the space between the outer sheath and the inner tube, that is, in the reinforcing layer. The corrosive gas in the reinforcing layer flows to the pipe end side through a gap provided between the reinforcing strips of the internal pressure reinforcing strip or the axial force reinforcing strip and is discharged to the atmosphere. However, when the water depth becomes deeper and the total length of the flexible pipe becomes longer, the resistance of the corrosive gas to flow through the gap provided between the reinforcing strips increases, and it becomes difficult to discharge the corrosive gas accumulated on the seabed side. Also, if lubricating oil remains in the gap between the reinforcing strips when the flexible pipe is assembled, the resistance of the corrosive gas flow is further increased, and the retention of the corrosive gas in the reinforcing layer is promoted. The corrosive environment in the reinforcing layer on the seabed side becomes even more severe. Furthermore, in the case of a flexible pipe with its lower end installed on the seabed, if the gap provided between the reinforcing strips is clogged somewhere, the corrosive gas that has accumulated on the seabed side of the pipe is discharged from the seabed. Will be discharged from. However, since the discharge mechanism receives a larger pressure than the sea (for example, a pressure of 30 MPa at a depth of 3000 m), the retained corrosive gas does not flow to the sea surface unless a gas pressure exceeding this pressure is applied. For the above reasons, the corrosive gas accumulates on the seabed side and accumulates.
Since steel is used for both the internal pressure reinforcing strip and the axial force reinforcing strip, as described above, if corrosive gas accumulates in the reinforcing layer of the flexible pipe, these reinforcing strips are exposed to the corrosive environment and deteriorated. Progresses, and the malfunction that the lifetime of a flexible pipe falls arises.

As a means for removing the corrosive gas flowing into the reinforcing layer in order to cope with such problems, a carrier gas is supplied from one end of the flexible composite tube to the reinforcing layer between the inner tube and the outer sheath, A gas removing method for releasing the gas in the reinforcing layer from the other end to the outside of the pipe is disclosed in Patent Document 1.

JP-A-63-83486

However, the conventional flexible pipe has the following problems.
That is, in Patent Document 1, for example, when applying at a deep water depth of 3000 m, in order to discharge the corrosive gas from the seabed-side discharge mechanism, the carrier gas is sent to the reinforcing layer near the seabed where corrosive gas tends to accumulate. Since it is necessary to send the carrier gas at a pressure exceeding 30 MPa, it is assumed that the outer sheath swells and bursts at that pressure.

On the other hand, in order to cope with a deep water depth exceeding 2000 m, it is necessary to increase the strength of the metal material used for the internal pressure reinforcing strip and the axial force reinforcing strip. However, when the strength of the metal material used for the internal pressure reinforcing strip and the axial force reinforcing strip is increased, hydrogen brittle fracture tends to occur, and as a result, the life of the flexible pipe is reduced. Therefore, it is necessary to reduce hydrogen sulfide (corrosive gas). However, as described above, there is a problem that there is no suitable method for removing the corrosive gas in the reinforcing layer accumulated near the sea bottom at a large depth.
Therefore, there is a current situation where the corrosive problem and the high strength accompanying the deepening of water cannot be achieved in a well-balanced manner, and there is room for improvement in that respect.

The present invention has been made in view of the above-described problems. It is possible to reliably replace the corrosive gas in the reinforcing layer with fresh air even under a large depth of water. An object of the present invention is to provide a flexible pipe corrosion prevention structure that can prevent corrosion and increase strength.

In order to achieve the above object, a corrosion prevention structure for a flexible pipe according to a first aspect of the present invention comprises a liquid-tight inner tube, an outer sheath, and a plurality of spirally twisted strip members. A reinforcing strip disposed in a reinforcing layer between an inner tube and the outer sheath, and discharges corrosive gas in the reinforcing layer from the distal side to the proximal side of the flexible pipe in the pipe axial direction. In this structure, the reinforcing layer is provided with a small-diameter tube continuously extending along the pipe axial direction.

In the first aspect of the present invention, a space connecting the proximal side to the proximal side of the reinforcing layer can be secured in the range where the small diameter tube is disposed, so suction means such as a vacuum pump is provided at the proximal end of the small diameter tube. By connecting and vacuum-sucking, the corrosive gas accumulated in the reinforcing layer can be forcibly discharged by moving from the distal end to the proximal end side of the small-diameter tube. On the other hand, since negative pressure is generated at the distal end side in the reinforcing layer by vacuum suction, the fresh air is reinforced through the gap provided in the reinforcing strip by opening the proximal end side of the reinforcing layer to the atmosphere. Flows into the bed. Therefore, it is possible to perform ventilation by replacing the corrosive gas with fresh air. Therefore, the corrosive gas concentration in the reinforcing layer is reduced, and the reinforcing strip made of steel is not exposed to the corrosive environment. Therefore, the corrosion of the reinforcing strip can be suppressed and the durability can be improved.

And, since it is a method of sucking out fresh air from the proximal end side with a pressurizing pump in a reinforcing layer, it is a method of sucking out from a small diameter tube, so it is possible to directly suck out air containing corrosive gas of high partial pressure. is there. Moreover, since it is a suction method, the pressure in a reinforcement layer is not raised and the burden of a pressure is not given to an outer sheath, Therefore The malfunction that a flexible pipe is damaged can be prevented. As a result, the design accompanying the increase in pressure becomes unnecessary, and the cost can be reduced.
Furthermore, by providing the small-diameter tube, the position of the end of the small-diameter tube, that is, the corrosive gas sucking position is specified, so that the gas concentration accumulated in the reinforcing layer at the sucking position can be accurately grasped.

In the corrosion prevention structure for a flexible pipe according to the first aspect of the present invention, the small-diameter tube may be disposed in a spiral gap provided between the reinforcing strip members.
In the said aspect of this invention, the space which connects the base end side from the terminal end side of a reinforcement layer is securable by incorporating a small diameter tube along the clearance gap between the strip members of a reinforcement strip.

In the flexible pipe corrosion prevention structure according to the first aspect of the present invention, a plurality of small-diameter tubes may be arranged at predetermined intervals in the circumferential direction of the reinforcing strip.
In the above aspect of the present invention, when the reinforcing layer is ventilated, a large amount of air in the reinforcing layer containing corrosive gas can be sucked simultaneously by using a plurality of small-diameter tubes. It is possible to shorten the time and improve the efficiency of the ventilation work.

Moreover, in the corrosion prevention structure of the flexible pipe which concerns on the 1st aspect of this invention, you may make it each terminal position of several small diameter tubes differ in a pipe axial direction.
In the above aspect of the present invention, the corrosive gas can be discharged for each end position of each small diameter tube. Therefore, by measuring the amount of corrosive gas discharged from each small diameter tube, the flexible pipe The gas concentration at a plurality of positions can be accurately confirmed in the axial direction.

In the corrosion prevention structure for a flexible pipe according to the first aspect of the present invention, a suction port that communicates with the gap and is open to the atmosphere may be provided on the proximal end side of the reinforcing layer.
In the above aspect of the present invention, fresh air can surely flow into the reinforcing layer from the suction port opened to the atmosphere on the base end side of the reinforcing layer.
Further, one or several small diameter tubes may be used for suction, and the proximal end side may be opened to the atmosphere.
In this case, even when the gap provided between the reinforcing strips is clogged somewhere, fresh air can surely flow into the end side.

According to the corrosion prevention structure of the flexible pipe of the present invention, corrosive gas that permeates the inner pipe and stays in the reinforcing layer is released to the atmosphere or a recovery tank, etc. Since the corrosive gas can be surely replaced with fresh air and the corrosive gas concentration in the reinforcing layer can be reduced, the corrosive environment in the reinforcing layer is improved, and the reinforcing strip in the reinforcing layer is improved. Corrosion of can be prevented.
In addition, the corrosive gas in the reinforcing layer can be surely removed, and the occurrence of hydrogen embrittlement can be effectively prevented, making it possible to use a high-strength reinforcing strip and the long distance of the flexible pipe. It is possible to improve the applicability in use over a wide area or in deep water.

It is a partially broken perspective view which shows the corrosion prevention structure of the flexible pipe by the 1st Embodiment of this invention. It is the partially broken perspective view which looked at the corrosion prevention structure of the flexible pipe from another angle. It is sectional drawing of a flexible pipe. It is a principal part enlarged view of the reinforcement layer of the flexible pipe shown in FIG. It is a schematic diagram which shows the arrangement | positioning state of a small diameter tube. It is a sectional side view which shows the structure of the base end part of a flexible pipe. It is sectional drawing of the flexible pipe by 2nd Embodiment, Comprising: It is a figure corresponding to FIG. It is a principal part enlarged view of the reinforcement layer of the flexible pipe by 3rd Embodiment, Comprising: It is a figure corresponding to FIG. It is sectional drawing of the flexible pipe shown in FIG. 8, Comprising: It is a figure corresponding to FIG. It is a schematic diagram which shows the arrangement | positioning state of the small diameter tube by 4th Embodiment, Comprising: It is a figure corresponding to FIG.

Hereinafter, a corrosion prevention structure for a flexible pipe according to a first embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the corrosion prevention structure for a flexible pipe according to the first embodiment of the present invention is applied to a flexible pipe 1 that is used to extract oil and natural gas by connecting a recovery vessel 2 on the sea and the sea floor. Has been.
Here, the flexible pipe 1 will be described below with the recovery ship 2 side as the base end side and the seabed side as the end in the length direction.

As shown in FIGS. 1 to 3, the flexible pipe 1 includes an interlock pipe 10, an inner pipe 11, an internal pressure reinforcing strip 12 made of a C-shaped strip having a C-shaped cross section, and a pair of flat strips. Axial force reinforcing strips 13 and 14 (inner and outer peripheral sides) and an outer sheath 15 for preventing seawater intrusion are arranged in a multi-layer structure arranged in the order from the inner side to the outer side in the radial direction. . A resin sheet 16 is provided on the inner peripheral side and the outer peripheral side of the inner axial force reinforcing strip 13 and the outer axial force reinforcing strip 14 to reduce wear of the axial force reinforcing strips 13 and 14.

The inner tube 11 and the outer sheath 15 are made of plastic, and the inner pressure reinforcing strip 12 and the axial force reinforcing strips 13 and 14 are made of a metal steel material. The inner pressure reinforcing strip 12 reinforces the pressure inside the pipe, and the inner axial force reinforcing strip 13 and the outer axial force reinforcing strip 14 reinforce the axial force of the pipe.
A space in which the internal pressure reinforcing strip 12, the inner axial force reinforcing strip 13, and the outer axial force reinforcing strip 14 are disposed between the inner tube 11 and the outer sheath 15 is referred to as a reinforcing layer T.

As shown in FIGS. 1 to 4, the inner axial force reinforcing strip 13 is composed of a plurality of strip members 13 </ b> A arranged in a spiral shape along the longitudinal direction (axial direction). A gap 13a is provided between the strip members 13A and 13A adjacent in the circumferential direction.

As shown in FIGS. 1 to 4, the outer axial force reinforcing strip 14 is twisted and arranged in a spiral direction opposite to the spiral direction of the inner axial force reinforcing strip 13 along the longitudinal direction (axial direction). It consists of a plurality of strip members 14A. A gap 14a is provided between the strip members 14A and 14A adjacent to each other in the circumferential direction, and an enlarged gap 14b in which the gap between the strip members 14A and 14A is larger than the gap 14a at three predetermined positions (the present invention). Corresponding to the gaps). The enlarged gaps 14b are provided at three locations at a constant interval (that is, a pitch of 120 degrees) in the circumferential direction.

As shown in FIGS. 3 and 4, each enlarged gap 14b continuous in the axial direction of the flexible pipe 1 is provided with a small-diameter tube 17 made of metal such as stainless steel over almost the entire length of the flexible pipe 1. As shown in FIG. 5, the three small- diameter tubes 17A, 17B, and 17C have a base end portion 17a that is an open end and is connected to a recovery tank 4 that will be described later, and a terminal end 17b that is a predetermined position P1 near the pipe terminal end 1b. Is located.

As shown in FIG. 6, the upper end portion of the small-diameter tube 17 is connected to a recovery tank 4 that is provided on the recovery vessel 2 (FIG. 1) at sea and connected to suction means (not shown) such as a vacuum pump.
As a specific configuration, the base end portion 17a of the small-diameter tube 17 can be inserted into the upper end portion 1a of the flexible pipe 1, and each of the inner pressure reinforcing strip 12, the inner axial force reinforcing strip 13, and the outer axial force reinforcing strip 14 is provided. The end structure 3 having a plurality of air pipes 5 connected to the gap formed in the space 3a through the space 3a is fixed. The air pipe 5 has an opening 5a (suction port) that is open to the atmosphere at one end, and the other end 5b is connected to a space 3a that communicates with the gaps between the reinforcing strips 12, 13, and 14.

Next, the ventilation method using the flexible pipe 1 having the above-described configuration and the operation of the flexible pipe 1 will be described with reference to the drawings.
As shown in FIGS. 1 to 6, in the flexible pipe 1, the small-diameter tube 17 is assembled by incorporating the small-diameter tube along the gap (enlarged gap 14 b) between the strip members 14 </ b> A and 14 </ b> A of the outer axial force reinforcing strip 14. A space connecting the base end side to the base end side of the reinforcing layer T can be ensured in the range where is disposed. Therefore, the corrosive gas G accumulated in the reinforcing layer T is moved from the distal end of the small diameter tube 17 toward the proximal end side by connecting the collection tank 4 to the proximal end portion 17a of the small diameter tube 17 and performing vacuum suction. Can be forcibly discharged.

On the other hand, since negative pressure is generated at the distal end side in the reinforcing layer T by vacuum suction, the internal pressure reinforcing strip 12 and the axial force reinforcing strip 13 are opened by opening the proximal end side of the reinforcing layer T to the atmosphere. The fresh air E flows into the reinforcing layer T through the gaps provided in. Therefore, it is possible to perform ventilation by replacing the corrosive gas G with fresh air E. Therefore, the corrosive gas concentration in the reinforcing layer T is reduced, and the internal pressure reinforcing strips 12 and the axial force reinforcing strips 13 and 14 made of steel are not exposed to a corrosive environment. Corrosion can be suppressed, and the durability of the flexible pipe can be improved.

And since it is the method of sucking out from the small diameter tube 17 not the method of enclosing fresh air in a reinforcement layer from a base end side with a pressurization pump, the air containing the corrosive gas G of high partial pressure can be directly sucked out. Is possible. In addition, since air containing a large amount of corrosive gas on the end side is sucked up to the base end through the small-diameter tube, it can be discharged separately from the middle and upper reinforcing strips during the discharge process. Damage to the reinforcing strip due to gas stagnation can be avoided. Further, since the suction method is used, the pressure in the reinforcing layer T is not increased, and the external sheath 15 is not subjected to a pressure load, so that a problem such as breakage of the flexible pipe 1 can be prevented. This eliminates the need for a design associated with the shift to cost and can reduce costs.
Further, by providing the small-diameter tube 17, the position of the end of the small-diameter tube 17, that is, the sucking position of the corrosive gas G is specified. Therefore, the gas concentration accumulated in the reinforcing layer T at the sucking position P1 (FIG. 5). Can be grasped accurately.

Further, since a plurality (three) of small-diameter tubes 17 (17A, 17B, 17C) are arranged at predetermined intervals in the circumferential direction of the outer axial force reinforcing strip 14, when the reinforcing layer T is ventilated, the plurality of small-diameter tubes 17 (17A, 17B, 17C) are arranged. By simultaneously sucking out using the tubes 17A, 17B, and 17C, a larger amount of air in the reinforcing layer T containing corrosive gas can be sucked, and the ventilation time can be shortened. Can be achieved.

As described above, in the flexible pipe corrosion prevention structure according to the first embodiment, the corrosive gas G that permeates the inner pipe 11 and stays in the reinforcing layer T is discharged to the recovery tank 4, so In addition, the corrosive gas G in the reinforcing layer T can be surely replaced with fresh air E, and the corrosive gas concentration in the reinforcing layer T can be reduced. As a result, the corrosive environment in the reinforcing layer T is improved, and corrosion of the internal pressure reinforcing strips 12 and the axial force reinforcing strips 13 and 14 in the reinforcing layer T can be prevented.
In addition, the corrosive gas G in the reinforcing layer T can be surely removed, and hydrogen brittle fracture can be effectively prevented, so that a high strength reinforcing strip can be used. The applicability in use over a long distance, or applicability under deep water can be improved.

Next, examples carried out to support the effects of the corrosion prevention structure for flexible pipes according to the above-described embodiment will be described below.

In this example, when the flexible pipe was applied at a water depth of 3000 m, the time required to ventilate the gap in the reinforcing layer was calculated, and the feasibility of discharging corrosive gas and the ventilation effect were confirmed.
Specifically, the time required to ventilate the air volume in the reinforcing layer is calculated based on the following conditions using the Darcy-Weissbach formula, which is a known pressure loss calculation formula shown in Formula (1). did.
The flexible pipe was calculated for the case where three small-diameter tubes were arranged in the circumferential direction at regular intervals in the outer axial force reinforcing strip as in the first embodiment described above, and in the case of one and two flexible pipes.
h = f (L / d) (v ² / 2g) Formula (1)

The small-diameter tube has an inner diameter d of 3 mm and a length L arranged along the spiral of the axial force reinforcing strip, so that the length of the flexible pipe of 3000 m (loss head h) is 6000 m, and the roughness f is 0.015. The capacity of the vacuum pump was 95% in terms of ultimate vacuum. The physical properties of air are 1.165 kgf / m ³ at a density of 30 ° C. and 1 atm, and a viscosity coefficient of 0.0182 × 10 ⁻³ Pa · s at 25 ° C. Further, the thickness of the reinforcing layer is 16 mm, the porosity in the reinforcing layer is 3%, the outer diameter of the inner tube is 166.4 mm, the amount of voids in the reinforcing layer is 1.644 m ³ (total length = 6000 m), The amount of air in the reinforcing layer at 30 ° C. and 1 atm was 1.644 m ³ . The average flow velocity v in the small diameter tube is 0.245 m / s, and the gravitational acceleration g is 9.8 m / s ² . It should be noted that the pressure in the reinforcing layer at the end of the seabed is equal to the atmospheric pressure.

According to the calculation results shown in Table 1, the ventilation time is 264 hours when one small-diameter tube is used, 132 hours when two tubes are used, and 88 hours when three tubes are used. It became. In other words, by arranging three small diameter tubes, it is possible to perform ventilation work for 3 to 4 days continuously and replace the corrosive gas accumulated in the reinforcing layer with clean air. I can confirm. Further, if the number of small-diameter tubes is increased within a range that does not reduce the reinforcing performance of the reinforcing strip, the ventilation work time can be further shortened.

Next, another embodiment of the flexible pipe corrosion prevention structure of the present invention will be described with reference to the accompanying drawings. The same reference numerals are used for members and parts that are the same as or similar to those of the first embodiment. Description is omitted, and a configuration different from the embodiment will be described.

As shown in FIG. 7, the corrosion prevention structure for the flexible pipe 1 </ b> A according to the second embodiment has a small-diameter tube 17 in the inner axial force reinforcement strip 13 in addition to the outer axial force reinforcement strip 14 of the first embodiment described above. Is provided. That is, the inner axial force reinforcing strip 13 is provided with enlarged gaps 13b (corresponding to the gaps of the present invention) in which the space between the strip members 13A and 13A is larger than the gap 13a at predetermined three locations. The enlarged gaps 13b are provided at three locations at a constant interval (that is, a pitch of 120 degrees) in the circumferential direction, and the small-diameter tubes 17 are provided over the entire length of the flexible pipe 1 in each enlarged gap 13b. The small-diameter tube 17 of the inner axial force reinforcing strip 13 is arranged at a position shifted in the circumferential direction with respect to the small-diameter tube 17 of the outer axial force reinforcing strip 14.
Moreover, in order to give the resin sheet 16 air permeability, it is also possible to efficiently ventilate the reinforcing strips by using a porous sheet or by winding with a gap.

Next, as shown in FIGS. 8 and 9, the corrosion preventing structure for the flexible pipe 1 </ b> B according to the third embodiment includes three small-diameter tubes 17 (17 </ b> A, 17 </ b> B, 17 </ b> C) in the outer axial force reinforcing strip 14. It is the structure arrange | positioned adjacent to the circumferential direction. In this case, the gap (enlarged gap 14c) between the strip members 14A, 14A of the outer axial force reinforcing strip 14 is wide enough to arrange the three small- diameter tubes 17A, 17B, 17C.

Next, in the corrosion prevention structure for the flexible pipe 1C according to the fourth embodiment shown in FIG. 10, the positions of the ends 17b of the three small diameter tubes 17 (17A, 17B, 17C) are different in the pipe axial direction (X direction). It has a configuration. The distal end 17b of the first small-diameter tube 17A is provided at a position near the pipe distal end 1b (first position P1), and the distal end 17b of the second small-diameter tube 17B is a predetermined position on the base end side by a predetermined distance from the first position P1. Provided at (second position P2), the distal end 17b of the third small diameter tube 17C is provided at a predetermined position (third position P3) on the base end side by a predetermined distance further than the second position P2.
In the flexible pipe 1C, the corrosive gas is discharged using the collection tank 4 (see FIG. 6) of the first embodiment for each of the positions P1, P2, and P3 of the ends 17b of the small diameter tubes 17A, 17B, and 17C. Therefore, it is possible to accurately confirm the gas concentration at a plurality of positions in the axial direction X of the flexible pipe 1 by measuring the amount of corrosive gas discharged from each of the small diameter tubes 17A, 17B, and 17C. Can do.

As mentioned above, although embodiment of the corrosion prevention structure of the flexible pipe by this invention was described, this invention is not limited to said embodiment, In the range which does not deviate from the meaning, it can change suitably.
For example, the arrangement | positioning location of the small diameter tube 17 provided in the reinforcement layer T is not limited to embodiment mentioned above. For example, the small-diameter tube 17 may be disposed only on the inner axial force reinforcing strip 13, or the small-diameter tube 17 may be disposed along the gap of the internal pressure reinforcing strip 12 formed of a C-shaped strip.

Further, in the present embodiment, the recovery tank 4 is provided on the sea, and the corrosive gas sucked out by the small diameter tube 17 is released to the recovery tank 4, but not limited to this, the base end portion 17a of the small diameter tube 17 is opened to the atmosphere. However, the gas may be directly released to the atmosphere without using the recovery tank 4.

Further, the configuration of the small diameter tube 17 such as the inner diameter, the material, the number, the arrangement interval, and the position of the end portion 17b can be arbitrarily set according to conditions such as the type of reinforcing strip, the configuration and length of the flexible pipe, and the like. It is.
In addition, it is possible to appropriately replace the constituent elements in the above-described embodiments with well-known constituent elements without departing from the spirit of the present invention, and the above-described embodiments may be appropriately combined.

The corrosive gas accumulated in the reinforcing layer can be forcibly discharged by moving from the end of the small diameter tube toward the base end. Further, the concentration of the corrosive gas in the reinforcing layer can be lowered by ventilating the corrosive gas with fresh air. As a result, corrosion of the reinforcing strip made of steel can be suppressed, and the durability of the flexible pipe can be improved.

DESCRIPTION OF SYMBOLS 1 Flexible pipe 2 Recovery ship 3 End part structure 4 Recovery tank 5 Air pipe 5a Opening part (suction part)
DESCRIPTION OF SYMBOLS 11 Inner tube 12 Internal pressure reinforcement strip 13 Inner axial force reinforcement strip 13a Clearance 13b Expansion gap 14 Outer axial force reinforcement strip 14a Clearance 14b, 14c Expansion clearance 15 Outer sheath 17, 17A, 17B, 17C Small diameter tube 17a Base end portion 17b End portion T reinforcement layer

Claims (7)

1. A corrosion prevention structure for flexible pipes,
   An inner tube having liquid tightness;
   An outer sheath,
   Comprising a plurality of spirally twisted strip members and disposed on a reinforcing layer between the inner tube and the outer sheath,
   A structure for preventing corrosion of a flexible pipe for discharging corrosive gas in the reinforcing layer from the distal side to the proximal side of the flexible pipe in the axial direction of the pipe,
   A corrosion prevention structure for a flexible pipe, wherein the reinforcing layer is provided with a small-diameter tube continuously extending along the pipe axial direction.
2. The structure for preventing corrosion of a flexible pipe according to claim 1,
   The said small diameter tube is a corrosion prevention structure of the flexible pipe arrange | positioned in the helical clearance gap provided between the strip members of the said reinforcing strip.
3. The flexible pipe corrosion prevention structure according to claim 1 or 2,
   The said small diameter tube is a corrosion prevention structure of the flexible pipe arrange | positioned with predetermined spacing in the circumferential direction of the said reinforcing strip.
4. The structure for preventing corrosion of a flexible pipe according to claim 3,
   A corrosion prevention structure for a flexible pipe, wherein the end positions of the plurality of small-diameter tubes are different in the pipe axial direction.
5. The flexible pipe corrosion prevention structure according to claim 1 or 2,
   A structure for preventing corrosion of a flexible pipe, wherein a suction port that is communicated with the gap and opened to the atmosphere is provided on a proximal end side of the reinforcing layer.
6. The structure for preventing corrosion of a flexible pipe according to claim 3,
   A structure for preventing corrosion of a flexible pipe, wherein a suction port that is communicated with the gap and opened to the atmosphere is provided on a proximal end side of the reinforcing layer.
7. The flexible pipe corrosion prevention structure according to claim 4,
   A structure for preventing corrosion of a flexible pipe, wherein a suction port that is communicated with the gap and opened to the atmosphere is provided on a proximal end side of the reinforcing layer.

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