JP2011141004A - Corrosion preventive structure of flexible pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain high strength by using carbon, by preventing corrosion of a reinforcing strip in a reinforcing layer, by surely substituting corrosive gas in the reinforcing layer with fresh air even under the large depth of water. <P>SOLUTION: This flexible pipe 1 forms a corrosion preventive structure for discharging the corrosive gas in the reinforcing layer T between an inner pipe 11 and an outer sheath 15 toward the base end side from the end side in the pipe axial direction, by arranging an inside axial force reinforcing strip 13 and an outside axial force reinforcing strip 14 constituted by spirally twisting a plurality of strip members between the liquid-tight inner pipe 11 and outer sheath 15, and is constituted so that the reinforcing layer T is provided with a plurality of small diameter tubes 17 arranged in a spiral expansion clearance 14b arranged between the mutual strip members of the outside axial force reinforcing strip 14 and continuously extending along the pipe axial direction. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  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.

  A flexible pipe is used as a riser pipe to be used between the offshore platform and the wellhead of the seabed in the operation 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 recent years, in addition to the flexible pipes capable of handling large depths of water, it has been required to improve the service life. The oil to be collected contains corrosive gases such as carbon dioxide (CO ₂ ) and hydrogen sulfide (H ₂ O), 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 oil in the pipe is prevented from leaking out 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 bars of the internal pressure reinforcing strip or the axial force reinforcing strip and is discharged to the atmosphere. If the extension of the length is long, the resistance flowing through the gap provided between the reinforcing strips becomes large, and it becomes difficult to discharge the corrosive gas accumulated on the seabed side. In addition, if lubricating oil remains in the gap between the reinforcing strips when the flexible pipe is assembled, the resistance to the flow of corrosive gas is further increased, and the corrosive environment in the reinforcing layer on the seabed side is further severed. Furthermore, in a flexible pipe with its lower end installed on the seabed, if the gap between the reinforcing strips is clogged somewhere, the corrosive gas that has accumulated on the seabed side of the pipe is removed from the exhaust mechanism provided on the seabed. Corrosive gas will be discharged, but the discharge mechanism receives a larger pressure than the sea (for example, a pressure of 30 MPa at a depth of 3000 m). If the gas pressure does not exceed this pressure, it will flow toward the sea surface. Since there is no corrosive gas accumulated on the seabed side, it accumulates.
That is, since both internal pressure reinforcing strips and axial force reinforcing strips are made of steel, there is a problem in that these reinforcing strips are exposed to a corrosive environment and deteriorate and the life of the flexible pipe is reduced.

  As a means for removing corrosive gas flowing into the reinforcing layer to cope with such a problem, carrier gas is supplied from one end of the flexible composite tube to the reinforcing layer between the inner tube and the outer sheath, thereby reinforcing A gas removing method for releasing the gas in the layer from the other end to the outside of the tube 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 at a pressure exceeding 30 MPa, a problem that the outer sheath swells and bursts at that pressure is assumed.

On the other hand, it is necessary to increase the strength of the metal material used for the internal pressure reinforcing strip and the axial force reinforcing strip in order to cope with a large depth exceeding 2000 m, but hydrogen brittle fracture occurs when the strength is increased. 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, in the structure for preventing corrosion of a flexible pipe according to the present invention, a reinforcing strip formed by spirally twisting a plurality of strip members between a liquid-tight inner tube and an outer sheath is provided. A flexible pipe corrosion prevention structure for discharging corrosive gas in a reinforcing layer between an inner tube and an outer sheath from the distal side to the proximal side in the pipe axial direction. The reinforcing layer is provided with a small-diameter tube continuously extending along the pipe axial direction.

  In the present invention, it is possible to secure a space connecting the distal end side to the proximal end side of the reinforcing layer in the range where the small diameter tube is disposed. By vacuum suction, the corrosive gas accumulated in the reinforcing layer can be forcibly discharged by moving from the distal end of the small diameter tube toward the proximal end. 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. Will flow 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. In addition, because the suction method does not increase the pressure in the reinforcing layer and does not give a load of pressure to the outer sheath, it is possible to prevent problems such as breakage of the flexible pipe. No design is required, and 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. There is.

In the flexible pipe corrosion prevention structure according to the present invention, it is preferable that the small-diameter tube is disposed in a spiral gap provided between the reinforcing strip members.
In 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 present invention, it is preferable that a plurality of small-diameter tubes are arranged at predetermined intervals in the circumferential direction of the reinforcing strip.
In the present invention, when the reinforcing layer is ventilated, the air in the reinforcing layer containing more corrosive gas can be sucked in a larger amount by simultaneously sucking out using a plurality of small-diameter tubes, thereby shortening the ventilation time. This makes it possible to improve the efficiency of ventilation work.

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

Moreover, in the corrosion prevention structure for a flexible pipe according to the present invention, it is preferable that a suction port that communicates with the gap and is open to the atmosphere is provided on the proximal end side of the reinforcing layer.
In the present invention, fresh air can surely flow into the reinforcing layer from the suction opening 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 hydrogen brittle fracture can be effectively prevented, allowing the use of high-strength reinforcing strips and flexible pipes over long distances. Or, the applicability under deep water can be improved.

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 an embodiment of the first invention will be described with reference to the drawings.

As shown in FIG. 1, the structure for preventing corrosion of a flexible pipe according to the first embodiment is applied to a flexible pipe 1 used for collecting oil and natural gas by connecting a recovery vessel 2 on the sea and the sea bottom. Yes.
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, and a pair of flat strips (an inner peripheral side and an outer peripheral side). ) And the outer sheath 15 for preventing the intrusion of seawater are arranged in a radial direction in the order from the inner side to the outer side. And the resin sheet 16 for reducing the abrasion of each axial force reinforcement strips 13 and 14 is provided in the inner peripheral side and outer peripheral side of the inner side axial force reinforcement strip 13 and the outer side axial force reinforcement strip.

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.

  In the inner axial force reinforcing strip 13, a plurality of strip members 13A, 13A,... Are spirally arranged along the longitudinal direction (axial direction), and between the strip members 13A, 13A adjacent in the circumferential direction. Is provided with a gap 13a.

  The outer axial force reinforcing strip 14 is arranged by twisting a plurality of strip members 14A, 14A,... In a spiral direction opposite to the spiral direction of the inner axial force reinforcing strip 13 along the longitudinal direction (axial direction). A gap 14a is provided between the strip members 14A, 14A adjacent in the circumferential direction, and an enlarged gap 14b in which the gap between the strip members 14A, 14A is larger than the gap 14a at predetermined three locations. (Corresponding to the gap of the present invention) is provided. 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, a small-diameter tube 17 made of metal such as stainless steel is provided in each enlarged gap 14 b continuous in the axial direction of the flexible pipe 1 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) with one end opened to the atmosphere, and the other end 5b is connected to a space 3a communicating with the gap 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. Since a space connecting the distal end side to the proximal end side of the reinforcing layer T can be ensured in the range where is disposed, the collection tank 4 is connected to the proximal end portion 17a of the small diameter tube 17 and vacuum suction is performed. The corrosive gas G accumulated in the reinforcing layer T can be forcedly discharged by moving from the distal end of the small diameter tube 17 toward the proximal end side.

  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 durability 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. Furthermore, since the suction method does not increase the pressure in the reinforcing layer T and does not impose a pressure load on the outer sheath 15, it is possible to prevent problems such as breakage of the flexible pipe 1. This eliminates the need for a design and reduces 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). There is an advantage that can be accurately grasped.

  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 By simultaneously sucking out using the tubes 17A, 17B, and 17C, a larger amount of air in the reinforcing layer T containing a more corrosive gas can be sucked, and the ventilation time can be shortened. Can be achieved.

As described above, in the structure for preventing corrosion of flexible pipes according to the first embodiment, the corrosive gas G that permeates the inner tube 11 and stays in the reinforcing layer T is discharged to the recovery tank 4, thereby reducing the depth of water. 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. And the 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 the occurrence of hydrogen embrittlement can be effectively prevented, so that a high-strength reinforcing strip can be used. Applicability at long distances or deep water depths 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 equation, which is a known pressure loss calculation equation shown in equation (1). did.
The flexible pipe was calculated for the case where three small-diameter tubes were arranged at regular intervals in the circumferential direction on the outer axial force reinforcement strip as in the first embodiment described above, and for the case of one and two flexible pipes. .
h = f (L / d) (v ² / 2g) (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 continuously for 3 to 4 days and replace 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. A description of the configuration different from that of the embodiment will be given by omitting the description using FIG.

As shown in FIG. 7, the corrosion prevention structure of the flexible pipe 1A according to the second embodiment has a small diameter in the inner axial force reinforcing strip 13 in addition to the outer axial force reinforcing strip 14 of the first embodiment described above. A tube 17 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 prevention 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. Are arranged adjacent to each other in 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 in the pipe axial direction (X direction). It has a different 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 this flexible pipe 1C, corrosive gas is discharged using the recovery tank 4 (see FIG. 6) of the first embodiment for each of the positions P1, P2, and P3 of the end 17b of each small diameter tube 17A, 17B, and 17C. Therefore, by measuring the amount of corrosive gas discharged from each of the small-diameter tubes 17A, 17B, and 17C, the gas concentrations at a plurality of positions in the axial direction X of the flexible pipe 1 can be accurately confirmed. be able to.

The embodiment of the corrosion prevention structure for a flexible pipe according to the present invention has been described above. However, the present invention is not limited to the above embodiment, and can be appropriately changed without departing from the spirit of the present invention.
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.

  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. However, the present invention is not limited to this, and the proximal end portion 17a of the small diameter tube 17 is exposed to the atmosphere. The gas may be released directly to the atmosphere without using the collection 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.

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 (5)

A reinforcing layer formed by spirally twisting a plurality of strip members between a liquid-tight inner tube and an outer sheath is arranged, and a reinforcing layer between the inner tube and the outer sheath The corrosion prevention structure of the flexible pipe for discharging the corrosive gas in the pipe axial direction from the end side toward the base end side,
A structure for preventing corrosion of a flexible pipe, characterized in that a small-diameter tube extending continuously along the pipe axial direction is disposed in the reinforcing layer.   The said small diameter tube is arrange | positioned in the helical clearance gap provided between the strip members of the said reinforcing strip, The corrosion prevention structure of the flexible pipe of Claim 1 characterized by the above-mentioned.   The corrosion prevention structure for a flexible pipe according to claim 1 or 2, wherein a plurality of the small-diameter tubes are arranged at a predetermined interval in the circumferential direction of the reinforcing strip.   The structure for preventing corrosion of a flexible pipe according to claim 3, wherein the terminal 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, wherein a suction port that communicates with the gap and is open to the atmosphere is provided on a proximal end side of the reinforcing layer.

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