WO2009070769A1

WO2009070769A1 - Optical fiber leak, rupture and impact detection system and method

Info

Publication number: WO2009070769A1
Application number: PCT/US2008/085042
Authority: WO
Inventors: Rogerio Tadeu Ramos
Original assignee: Schlumberger Technology Corporation; Schlumberger Canada Limited; Services Petroliers Schlumberger; Schlumberger Holdings Limited; Schlumberger Technology B.V.; Prad Research And Development Limited
Priority date: 2007-11-26
Filing date: 2008-11-26
Publication date: 2009-06-04
Also published as: EP2220468B1; US20100315630A1; EP2220468A1; EP2220468A4; US8520195B2; BRPI0819749A2

Abstract

A leak detection system and method, including a structure having a first barrier to a first fluid and a second barrier to a second fluid, the first barrier and the second barrier defining a space therebetween; and at least one sensor, placed in the space, and configured to detect presence of the first fluid or the second fluid in the space due to a leak in the first barrier or the second barrier. The method includes placing the at least one sensor is in the space to detect presence of the first fluid or the second fluid in the space due to a leak in the first barrier or the second barrier; and generating a signal that indicates the presence of the first fluid or the second fluid in the space due to a leak in the first barrier or the second barrier.

Description

Atty. Dock. No. 14459.04 PCT Patent

OPTICAL FIBER LEAK, RUPTURE AND IMPACT DETECTION SYSTEM

AND METHOD

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The invention is related to and claims the benefit of priority from U.S.

Provisional Patent Application Serial No. 60/990,147 of Van Nuffelen et al., entitled "LEAK DETECTION AND LEAK, RUPTURE OR IMPACT DETECTION ON FLEXIBLE RISER," filed on November 26, 2007, the entire contents of which is hereby incorporated by reference herein.

FIELD OF THE INVENTION

[0002] The invention generally relates to methods and systems for detecting leaks, ruptures or impacts on a structure, and more particularly to a system and method employing optical fibers for detecting leaks, ruptures or impacts on a structure.

BACKGROUND

[0003] The complexity of structures, for example, used in oil and gas subsea exploration is increasing to satisfy the many requirements in terms of thermal behavior, geometry, multiple fluid flows, flexibility and mechanical characteristics. For example, some umbilicals or risers can be used to connect wells or facilities at the sea bed to, for example, floating facilities at the sea surface. Further examples of such structures include manifolds, separators and control units. It is desirable to monitor such connections in order to prevent structural failure due to fatigue, corrosion, erosion or blockage, which can be caused by the deposition of parts of the flow components (e.g., such as wax, hydrates, scales, asphaltenes, etc.).

[0004] Damage to such structures also can be due to human activity, such as fishing or laying and removal of anchors. Damage can also be the result of excessive stresses or shocks during transportation or deployment. Manufacturing defects can also compromise the quality of such structures.

[0005] For such reasons, leaks can develop in localized parts of such structures. Often such a leak is detected after it has become large, leading to unplanned repairs that can take a long time, as equipment, material and personnel Atty. Dock. No. 14459.04 PCT Patent

need to be mobilized on short notice. Locating the leak is also an important issue. Sometimes the leak cannot be located with a simple visual inspection, requiring the replacement of long sections of the structure. For example, leaks can be of seawater into the structure, which can promote problems, such as corrosion or contamination of hydraulic lines, or leakage of oil or gas out of the structure.

SUMMARY OF THE INVENTION

[0006] The above and other needs and problems are addressed by the exemplary embodiments of the present invention, which provide a novel leak, rupture or impact detection system and method that employ one or more sensing systems, which can include optical fibers, as part of a structure or in close proximity to the structure to detect and locate a leak, rupture or impact therein. The terms "sensing systems" and "sensors" are used interchangeably herein. The sensors can be based on various principles, such as the detection of water, humidity, oil, gas, and the like. The sensors can be distributed (e.g., using optical time or frequency domain reflectometry) or multipoint sensors and can include optical fiber sensors, and the like. A sensor which detects a change in attenuation or index of refraction of an optical fiber also can be employed. The location of the leak, rupture or impact can be detected using optical time domain reflectometer (OTDR) or frequency domain techniques. The sensor can be based on Brillouin, Raman or Rayleigh scattering, or a fiber Bragg grating, and the like. The optical fiber can be imbedded or placed in close proximity to a material which is affected by the presence of fluid (e.g., water, oil, gas, ) to be detected. Such material can be applied as a coating to the fiber or as a rod twisted with the fiber or as a rod having the fiber wrapped around the rod. Such material can swell, or shrink, or dissolve, or break down or have any other suitable characteristics, which undergo a change in the presence of such a fluid. Such change can affect the optical fiber by increasing or reducing strain on the fiber or chemically reacting with the fiber or an intermediate material thereof and which also can be a material that can swell, or shrink, or dissolve, or break down or have any other suitable characteristics, which undergo a change in the presence of such a fluid. The intermediate material can be the same as or different than the material in which the optical fiber is embedded or can be Atty. Dock. No. 14459.04 PCT Patent

placed in close proximity thereto. The material affected by the presence of fluid can be any suitable polymer, metal, ceramic, gel, or combination thereof, and the like.

[0007] In one embodiment, the sensor or sensors can be imbedded into the structure, e.g., a flexible pipe, for example, during a manufacturing process thereof, including processes, such as extrusion, pulltrusion or laying of the sensor on the surface of the polymer as it cures, and the like. Such flexible pipes can include any suitable pipes e.g., flexible riser or umbilical, used, for example, for subsea, marine applications, and the like, such as subsea oil and gas exploration and production, and the like.

[0008] Accordingly, in an exemplary aspect of the present invention there is provided a leak detection system for a structure, including a structure having a first barrier to a first fluid and a second barrier to a second fluid, the first barrier and the second barrier defining a space therebetween; and at least one sensor, placed in the space, and configured to detect presence of the first fluid or the second fluid in the space due to a leak in the first barrier or the second barrier.

[0009] In a further exemplary aspect of the present invention there is provided a leak detection method for a structure having a first barrier to a first fluid and a second barrier to a second fluid, the first barrier and the second barrier defining a space therebetween, the method including placing at least one sensor in the space to detect presence of the first fluid or the second fluid in the space due to a leak in the first barrier or the second barrier; and generating a signal that indicates the presence of the first fluid or the second fluid in the space due to a leak in the first barrier or the second barrier.

[0010] Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary embodiments and implementations. The invention is also capable of other and different embodiments, and its several details can be modified in various respects, all without departing from the spirit and scope of the invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Atty. Dock. No. 14459.04 PCT Patent

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

[0012] FIG. 1 is an exemplary structure in the form of a flexible pipe such as a pipe that can be used for subsea oil and gas exploration;

[0013] FIGs. 2A-2B illustrate exemplary placements for an exemplary leak detection sensor for the structure of FIG. 1 ;

[0014] FIG. 3 illustrates an exemplary leak detection sensor, which can be the sensor of FIGs. 2A-2B, including an exemplary sensing fiber wrapped onto a material affected by the presence of a fluid (e.g., water, oil or gas);

[0015] FIG. 4 illustrates the exemplary leak detection sensor of FIG. 3 after the material has increased in volume (e.g., swelled) due to the presence of the fluid, adding stress to the sensing fiber;

[0016] FIG. 5A illustrates a further exemplary embodiment of an exemplary leak detection sensor which can be the sensor used in FIGs. 2A-2B, including an exemplary material coating a fiber, wherein the material swells or contracts in the presence of the fluid, thereby changing the stress on the fiber;

[0017] FIG. 5B illustrates a further exemplary embodiment of an exemplary leak detection sensor which can be the sensor of FIGs. 2A-2B, including a coating or surface provided on a fiber which changes the characteristics of the fiber in the presence of the fluid;

[0018] FIG. 6 illustrates an exemplary sensing fiber wrapped onto a pipe, such as a flexible pipe, to make temperature, vibration and strain measurements thereon; and

[0019] FIG. 7 illustrates an exemplary sensing fiber embedded into a pipe, such as a flexible pipe, to make temperature, vibration and strain measurements thereon. Atty. Dock. No. 14459.04 PCT Patent

DETAILED DESCRIPTION

[0020] Various embodiments and aspects of the invention will now be described in detail with reference to the accompanying figures. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited. Further, whenever a composition, a group of elements or any other expression is preceded by the transitional phrase "comprising", "including" or "containing", it is understood that it is also contemplated the same composition, the group of elements or any other expression with transitional phrases "consisting essentially of, "consisting", or "selected from the group of consisting of, preceding the recitation of the composition, the elements or any other expression.

[0021] The structures which can be the subject of this invention can include any suitable structures, wherein detection of leaks is needed, such as any subsea pipe, subsea structure, e.g., a flexible pipe, such as a flexible riser or an umbilical. Such structures are known in the art, see, e.g., U.S. Patent Nos. 7,296,480 and 5,918,641, incorporated herein by reference.

[0022] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1 thereof, there is illustrated an exemplary structure 100, for example, in the form of a flexible pipe or riser used in subsea applications. In FIG. 1, element 1 is an internal reinforcement layer (e.g., made of metal, etc.), while elements 3 and 4 are external reinforcement layers (e.g., made of metal, etc.). Element 2 is a layer used to provide fluid isolation from fluids traveling inside of the structure 100 and element 5 is an outer protection shell for fluid isolation from fluids outside of the structure 100. The layers 2 and 5 can be made of any suitable material, such as polymers, and the like. Accordingly, the various layers or barriers can include any suitable a polymer layers, metal layers, insulation layers, pipes, buoyancy layers, and the like, of the structure 100. Atty. Dock. No. 14459.04 PCT Patent

[0023] FIGs. 2A-2B show possible placement for exemplary sensors 6A and

6B (either one of each or both can include, e.g., an optical fiber) in the flexible pipe 100 of FIG. 1. For example, if the outer shell 5 experiences a leak, seawater can invade the outer reinforcement layers 3 and 4 and can induce corrosion. Advantageously, the sensor 6B can detect and locate the point of water ingression and can be used to warn an operator to take preventative measure or schedule repairs. Similarly, if the internal reinforcement layer 1 experiences a leak of the fluids carried by the flexible pipe 100, the sensor 6A can detect and locate the leak and can be used to warn an operator to take preventative measure or schedule repairs. Accordingly, one or more of the exemplary sensors 6A and/or 6B can be employed depending on the application.

[0024] FIG. 3 further illustrates an exemplary sensor 6A or 6B, including a sensing fiber 7 (e.g., an optical fiber.) that is wrapped onto a material 8 that is affected by a fluid (e.g., water, oil, or gas, depending on the application.). FIG. 4 illustrates the exemplary sensor 6A or 6B of FIG. 3, after the material 8 has increased in volume (e.g., swelled) due to the presence of the fluid, thereby adding stress to and changing the optical characteristics of the sensing fiber 7. FIG. 5A illustrates a further exemplary embodiment of the sensor 6 A or 6B, wherein the material 8 is coated onto the fiber 7 and such material can change the stress on the fiber 7 when the material 8 is in the presence of a fluid (e.g., water, oil, gas, depending on the application). Although the exemplary sensor 6A or 6B are described in terms of measuring a change in stress in the sensing fiber 7 caused by the material 8, in further exemplary embodiments, the exemplary sensor 6 A or 6B can be configured to employ the sensing fiber 7 that is made sensitive to other changes in the material 8. For example, the material 8 can be configured such that it reacts with the fluid to be detected, creating a species that can affect the sensing fiber 7 reading, wherein such change in sensing fiber 7 reading can be caused by a change in temperature, chemical attack, attenuation or stress, and the like.

[0025] In further exemplary embodiments, the sensor 6 A or 6B configured as the optical fiber 7 can be modified to make the fiber 7 sensitive to fluids (e.g., water, Atty. Dock. No. 14459.04 PCT Patent

oil, gas, depending on the application). For example, as shown in FIG. 5B, this can be achieved by providing a coating (or a surface) 11 on the optical fiber 7, thereby making the fiber sensitive to various fluids, such as water, gas, oil, and the like. For example, an employed polymer material, such as acrylate or polypropylene can swell in the presence of water or oil, providing a strain to the fiber 7. This strain can then be detected using any suitable methods, such as the use of fibre Bragg gratings, interferometers, Brillouin scattering, attenuation due to micro or macro bending, and the like. Accordingly, imparting sensitivity to the optical fiber 7 can modify its optical characteristics. This modification (or change) can be measured in any known manner, as summarized herein. Advantageously, such modification enables the optical fiber 7 to detect a leak of water, gas or oil into or out of the structure, without the use of intermediate materials, such as the material 8 of FIGs. 3-5A.

[0026] As will be appreciated by those ordinarily skilled in the relevant arts, the exemplary sensors 6A or 6B can be employed with any suitable material, e.g., material 8, that is affected by the presence of fluids, gases, and/or liquids, such as water, seawater, gas, oil, and the like. In a further exemplary embodiment, the role of the material 8 can be performed by the layer 2 or any other suitable layer of the structure 100 and used to change the stress on the sensor 6 A (or 6B in the case of the other layers) configured as the fiber 7 embedded in the layer 2, when the layer 2, for example, increases or decreases in volume (e.g., swells or contracts) due to the presence of a fluid (e.g., water, oil, gas, depending on the application).

[0027] Advantageously, a change in stresses on the sensing fiber 7 due to the expanded material 8 or layer 2 (or any other suitable layers of the structure 100) or the coating 11 (or surface 11) and/or modification of optical characteristics of the optical fiber, can be used for locating and detecting a leak in the structure 100. For example, this can be done by using any suitable known techniques which can measure the change in stress and the corresponding changes in the optical characteristics of the sensing fiber 7, including distributed (e.g., using optical frequency domain reflectometry) or multipoint sensor techniques, detection of change in attenuation or index of refraction of the optical fiber 7, optical time domain reflectometer (OTDR) Atty. Dock. No. 14459.04 PCT Patent

or frequency domain techniques for detecting changes in the optical fiber 7, optical interferometer techniques, Brillouin, Raman or Rayleigh scattering, or a fiber Bragg grating techniques, and the like. Such techniques enable the detection of and the determination of the location of the leak. In one embodiment, the Bragg grating can be suitably designed so that it can detect and measure the change in the strain of the fiber 7 or of the change in the strain of the material around which the fiber 7 is wrapped or embedded.

[0028] In an exemplary embodiment, the material 8 can include any suitable material that deforms in shape (e.g., swells or contracts) due to the presence of (e.g., contact with) a fluid (e.g., water, oil, gas, depending on the application), such any suitable metals, ceramic, gel, plastics, polymers (e.g., acrylate or polypropylene for water), polypropylene or acrylate (e.g., for oil), and the like. For example, the sensor 6A or 6B can include the optical fiber 7 that is wound around a polymer layer 8 (FIG. 3) or embedded in a polymer layer 8 (FIG. 5A), which deforms in the presence of a fluid, such as water or oil. In one embodiment, the sensor is wound around a material, such as a polymer, with a pitch of less than 70 layer diameters.

[0029] In further exemplary embodiments, the novel leak detection system of

FIGs 1-5, including the at least one sensor can be used in known pipe-in-pipe structures. Such structures usually include thermal insulation, such as foam, placed in an annular area between two pipes, with each of the two pipes forming an impermeable barrier to a fluid. Advantageously, a sensor, based on the exemplary embodiments of FIGs. 1-5, placed in the annular area can detect the presence and location of a leak or leaks in such pipe-in- pipe structures.

[0030] In a further embodiment, at least one sensor, based on the exemplary embodiments of FIGs. 1-5, can be embedded in a composite material, which can be placed in a space defined by two impermeable barriers (e.g., in a flexible pipe, a riser, an umbilical or in a pipe-in-pipe structure) to detect a leak.

[0031] In further exemplary embodiments, distributed temperature, vibration, and strain measurements, based on the exemplary embodiments of FIGs. 1-5, can be performed along the structure, for example, a flexible pipe, such as a flexible riser, or Atty. Dock. No. 14459.04 PCT Patent

an umbilical, using optical fibers to detect leaks, ruptures or impacts that can affect the integrity of the flexible riser. For example, the optical fibers can be used for distributed temperature (T) measurements, distributed strain measurements (e.g., using Brillouin scattering), distributed vibration measurement (e.g., using Raleigh scattering), and the like. In an exemplary embodiment, as shown in FIGs. 6-7, such an exemplary sensing system 200 can include one or more optical fibers 9 deployed along a flexible riser 10 either in an internal structure of the flexible riser 10, as shown in FIG. 7, or strapped on or wrapped around the outside of the flexible riser 10, as shown in FIG. 6. Such fibers 9 can be connected to a surface unit (e.g., OTDR, etc., not shown) for distributed temperature, vibration, and strain measurements, and the like, performed in any known manner.

[0032] Advantageously, such measurements by the exemplary sensing system

200 can be used for leak detection. For example, if fluid starts leaking from the riser 10, which may be submerged in water, the riser will undergo an instant pressure change from the flow line internal pressure to the pressure of the water surrounding the riser. Such depressurization process generates acoustic waves due to the decompression of the fluid, as well as temperature changes (e.g., based on the Joule- Thompson effect in the case of a gas leaking from the riser). Accordingly, the distributed temperature and vibration measurements using the fiber 9 coupled to the surface unit can be used to detect where the leak is coming from on the riser 10 in any known manner.

[0033] In the case of impact detection, if an object (e.g., fishing net, etc.) impacts the riser 10, distributed strain and vibration measurements using the fiber 9 coupled to the surface unit can be used for detection of the impact and its location in any known manner. Distributed strain measurements using the fiber 9 coupled to the surface unit can be used for the detection of damage through the detection of permanent deformation after the impact in any known manner.

[0034] In the case of breakage of internal armor of the riser, excessive loading, corrosion or fatigue issues on the flexible riser 10 can cause internal structure thereof to be damaged and eventually break. For example, potential damages can be Atty. Dock. No. 14459.04 PCT Patent

on the pressure vault and on the tensile armor of the flexible riser 10, wherein a break in the pressure vault or tensile armor generates noise that propagates along the flexible riser 10. Distributed vibration measurements using the fiber 9 coupled to the surface unit can be used for the detection of the area where the damage has taken place in the coating or surface on the sensors any known manner.

[0035] Although the exemplary embodiments are described in terms of the structure 100 and 200 and the flexible riser 10, the exemplary embodiments can be applied to any suitable structures, such pipes, pipes in pipes, integrated production bundles, offloading pipes, jumpers, risers, umbilicals, Christmas trees, flexible pipes, manifolds, control units, well heads, pieces of subsea equipment, and the like, as will be appreciated by those of ordinary skill in the relevant art(s).

[0036] Although the exemplary embodiments are described in terms of the exemplary sensors being sensitive to changes in stress, e.g., caused by a material or materials whose properly or properties change when contacted with gas or liquid, the sensors (or sensors' reading) may be made sensitive to other changes in the material used, such as at least one property that changes in the presence of a liquid or gas. For example, the material, such as a polymer, or a composite material, could be such that it reacts with the fluid to be detected creating a species that could affect the fibre sensor reading. This change in sensor reading could be caused by a change in temperature, chemical attack, attenuation or stress among others. Similarly, the sensors (or sensors' reading) could be made sensitive to changes other than stress, in the material of the sensors, such as the coating or surface on the sensors. Thus, the material of the sensors, e.g., the coating or surface, may react with the fluid to be detected, e.g., liquid or gas, creating a species that can affect the sensor or the material, e.g., the coating or surface on the sensors. The change in sensor reading could be caused by a change in one or more property, such as a change in temperature, chemical attack, attenuation or stress.

[0037] Further, the at least one property that changes in the presence of liquid or gas includes one or more of deformation, swelling, shrinking, dissolution, cracking, rupture, heating, cooling, softening, hardening, and chemical reaction. Atty. Dock. No. 14459.04 PCT Patent

[0038] While the inventions have been described in connection with a number of exemplary embodiments, and implementations, the inventions are not so limited, but rather cover various modifications, and equivalent arrangements, which fall within the purview of the present claims.

Claims

Atty. Dock. No. 14459.04 PCT PatentWHAT IS CLAIMED IS:

1. A leak detection system for a structure, the system comprising: a structure having a first barrier to a first fluid and a second barrier to a second fluid, the first barrier and the second barrier defining a space therebetween; and at least one sensor, placed in the space, and configured to detect presence of the first fluid or the second fluid in the space due to a leak in the first barrier or the second barrier.

2. The system of claim 1, wherein the at least one sensor comprises an optical fiber sensor.

3. The system of claim 1, wherein the at least one sensor comprises at least one Fiber Bragg Grating.

4. The system of claim 1, wherein the at least one sensor is based on Brillouin, Raman or Rayleigh scattering.

5. The system of claim 1, wherein the at least one sensor employs at least one optical interferometer.

6. The system of claim 1, wherein the structure is at least partially an underwater structure or an underground structure.

7. The system of claim 1, wherein the at least one sensor is imbedded into a polymer that has at least one property that changes in the presence of a liquid or gas.

8. The system of claim 1, wherein the at least one sensor is imbedded in a composite material that has at least one property that changes in the presence of a liquid or gas. Atty. Dock. No. 14459.04 PCT Patent

9. The system of claim 1, wherein the at least one sensor is imbedded into a material that has at least one property that changes in the presence of a liquid or gas or is placed on or under a polymer layer that has at least one property that changes in the presence of a liquid or gas.

10. The system of claim 1, wherein the at least one sensor is an optical fiber sensor that is wound around a polymer layer that has at least one property that changes in the presence of a liquid or gas and with a pitch of less than 70 layer diameters.

11. The system of claim 1, wherein the at least one sensor is imbedded into a polymer layer.

12. The system of claim 1, wherein the at least one sensor detects the presence of at least one of water, oil, and gas.

13. The system of claim 1, wherein the at least one sensor is placed under an outer shell of the structure to detect leaks of sea water into the structure.

14. The system of claim 1, wherein the at least one sensor is placed between the two barriers to sense a leak of oil or gas out of the structure or to sense a leak of a fluid into the structure through an external wall of the structure.

15. The system of claim 1, wherein the structure is a pipe, a pipe in pipe, a riser, an umbilical, a flexible pipe, an integrated production bundle, and offloading pipe, a jumper, a manifold, a control unit, a well head or subsea equipment.

16. The system of claim 1, wherein at least one of the first barrier or the second barrier is one of a polymer layer, a metal layer, an insulation layer, a pipe, a buoyancy layer. Atty. Dock. No. 14459.04 PCT Patent

17. The system of any one of claims 7, 8, 9 or 10, wherein the property change includes at least one of deformation, swelling, shrinking, dissolution, cracking, rupture, heating, cooling, softening, hardening, and chemical reaction.

18. A leak detection method for a structure having a first barrier to a first fluid and a second barrier to a second fluid, the first barrier and the second barrier defining a space therebetween, the method comprising: placing at least one sensor in the space to detect presence of the first fluid or the second fluid in the space due to a leak in the first barrier or the second barrier; and generating a signal that indicates the presence of the first fluid or the second fluid in the space due to a leak in the first barrier or the second barrier.

19. The method of claim 18, wherein the at least one sensor comprises an optical fiber sensor.

20. The method of claim 18, wherein the at least one sensor comprises at least one Fiber Bragg Grating.

21. The method of claim 18, wherein the at least one sensor is based on Brillouin, Raman or Rayleigh scattering.

22. The method of claim 18, wherein the at least one sensor employs at least one optical interferometer.

23. The method of claim 18, wherein the structure is at least partially an underwater structure or an underground structure.

24. The method of claim 18, wherein the at least one sensor is imbedded into a polymer that has at least one property that changes in the presence of a liquid or gas. Atty. Dock. No. 14459.04 PCT Patent

25. The method of claim 18, wherein the at least one sensor is imbedded in a composite material that has at least one property that changes in the presence of a liquid or gas.

26. The method of claim 18, wherein the at least one sensor is imbedded into a material that has at least one property that changes in the presence of a liquid or gas or is placed on or under a polymer layer that has at least one property that changes in the presence of a liquid or gas.

27. The method of claim 18, wherein the at least one sensor is an optical fiber sensor that is wound around a polymer layer that has at least one property that changes in the presence of a liquid or gas and with a pitch of less than 70 layer diameters.

28. The method of claim 18, wherein the at least one sensor is imbedded into a polymer layer.

29. The method of claim 18, wherein the at least one sensor detects the presence of at least one of water, oil, and gas.

30. The method of claim 18, wherein the at least one sensor is placed under an outer shell of the structure to detect leaks of sea water into the structure.

31. The method of claim 18, wherein the at least one sensor is placed between the two barriers to sense a leak of oil or gas out of the structure or to sense a leak of a fluid into the structure through an external wall of the structure.

32. The method of claim 18, wherein the structure is a pipe, a pipe in pipe, a riser, an umbilical, a flexible pipe, an integrated production bundle, and offloading pipe, a jumper, a manifold, a control unit, a well head or subsea equipment. Atty. Dock. No. 14459.04 PCT Patent

33. The method of claim 18, wherein at least one of the first barrier or the second barrier is one of a polymer layer, a metal layer, an insulation layer, a pipe, a buoyancy layer.

34. The method of any one of claims 24, 25, 26 or 27, wherein the property change includes at least one of deformation, swelling, shrinking, dissolution, cracking, rupture, heating, cooling, softening, hardening, and chemical reaction.