GB2457277A

GB2457277A - Methods and apparatuses for detecting strain in structures

Info

Publication number: GB2457277A
Application number: GB0802359A
Authority: GB
Inventors: Damon Roberts; Rogerio Tadeu Ramos
Original assignee: Gemalto Terminals Ltd; Schlumberger Holdings Ltd
Current assignee: Gemalto Terminals Ltd; Schlumberger Holdings Ltd
Priority date: 2008-02-08
Filing date: 2008-02-08
Publication date: 2009-08-12
Anticipated expiration: 2028-02-08
Also published as: GB2457277B; GB0802359D0; WO2009100084A1

Abstract

An apparatus for monitoring physical parameters of a structure, comprises a clamp 11 that in use is placed to embrace the structure to be monitored; and a strain sensor 13 attached to the clamp an arranged so as to detect strain in the direction of the perimeter of the structure. A method of monitoring a structure, comprises placing a clamp 11 to embrace the structure to be monitored, the clamp having a strain sensor 13 attached thereto; and collecting information from the strain sensor 13 attached to the clamp 11 placed in order to detect strain in the direction of the perimeter of the structure.

Description

METHODS AND APPARATUS FOR DETECTING STRAIN IN STRUCTURES

Technical Field

[0001] This invention relates to apparatus and methods for detecting strain in structures. In particular, it relates to strain detection in structures such as oil and gas pipes and supporting structures in oil and gas installations or the like.

Background Art

[0002] The area of concern for this invention is the monitoring of structures by measuring strain. More specifically, the measurement of strain in order to infer the perimeter of a structure as it changes with time, temperature, pressure or any other parameter.

[00031 The monitoring of structures is of great importance in many areas, in particular in the oil and gas industry, even more important in sub sea environment where access to the structures is difficult. For example, a pipeline running at the sea bed between an offshore production location to a transportation hub may need to be monitored to provide information on the perimeter of the pipe in order to estimate internal pressure.

[0004] Flexible pipes are increasingly used in offshore oil and gas installations.

The oil and gas industry currently uses several techniques to identify damage in flexible pipe, such techniques are described in a document prepared by the United Kingdom Offshore Operators Association UKOOA, Rev. 5, of October 2002 "Guidance note on monitoring methods and integrity assurance for unbonded flexible pipe". The methods and techniques commonly used in the industry and described in this document can be time consuming; some require the production of hydrocarbons to be partially or totally stopped. Because of the time inherent to these operations, they are performed infrequently and at great expense to the operators.

[0005] According to the above mentioned document, a large number of failure incidents are annulus flooding, damage to the external sheath and degradation of the internal pressure sheath. The repercussions of such failure incidents include corrosion and/or corrosion-fatigue type failure of the pipe structure.

[0006] It is an object of the invention to provide techniques that can be used to permanently monitor the integrity of a pipe's structures that are less intrusive.

Disclosure of Invention

[0007] A first aspect of the invention provides an apparatus for monitoring physical parameters of a structure, comprising: -a clamp that in use is placed to embrace the structure to be monitored; and -a strain sensor attached to the clamp an arranged so as to detect strain in the direction of the perimeter of the structure, preferably around the periphery of the structure.

[0008] The clamp can be a strap or belt or a compliant material, and may be shaped to the outside shape of the structure. In a preferred embodiment, the clamp is made using composite material. The strain sensor can embedded into the clamp in one preferred embodiment.

[0009] The sensor may comprise an optical sensor such as an optical fibre sensor, for example a fibre Bragg grating based sensor, an interferometric sensor, or the like.

[00101 The structure to which the apparatus is applied is typically a pipe or tube, such an oil and/or gas pipe, or a water pipe. The structure may also be a sub sea structure such as a sub sea riser.

[0011] The structure may be located below the surface and may be totally or partially buried.

[0012] A data collection unit may also be attached to the structure or the clamp.

The data collection unit can include an optical interrogation unit operating, for example, by means of spectrum analysis.

[0013] The sensor can attached to the clamp by mounting means arranged to align the sensor in a predetermined peripheral direction when installed on the structure. The mounting means can be configured to enhance the sensitivity of the sensor in the predetermined direction when installed on 3' the structure, for example the mounting means can have smaller dimensions than the clamp.

[00141 At least one sensor can be arranged to detect strain in the circumferential direction, the axial direction, or both circumferential and axial components when installed on the structure.

[0015] In one embodiment, a pair of clamps is provided which, when installed on the structure, embrace the structure above and below the sensor. At least one sensor can be attached to connecting means that extend between the clamps.

[0016] Preferably, the clamps, when installed on the structure, extend around the circumference of the structure and the sensor is aligned with the clamp axis.

[0017] The clamps can comprises rollers which are arranged to bear against the outer surface of the structure in use. They can also comprise extensions on which the sensor is mounted, the extensions projecting radially away from the structure when the clamp is installed on the structure. In this case, reinforcing arms can be arranged to support the extensions.

[0018] The clamps may also comprise a hinge to allow opening of the clamps for installation on the structure. A roller can be provided at the hinge which is arranged to bear on the outer surface of the structure when the clamp installed on the structure.

[0019] Alternatively, a high friction device can provided at the hinge which is arranged to bear on the outer surface of the structure when the clamp installed on the structure.

[00201 A low friction coating can be positioned on the structure at the point where the clamp is installed.

[0021] A second aspect of the invention provides a method of monitoring a structure, comprising: -placing a clamp to embrace the structure to be monitored, the clamp having a strain sensor attached thereto; and -collecting information from the strain sensor attached to the damp placed in order to detect strain in the direction of the perimeter of the structure. 4, -

[0022] The strain information may be used to calculate the perimeter dimensions of the structure, the temperature of the structure, the outer pressure of the structure, or the inner pressure of the structure.

[0023] Further aspects of the invention will be apparent from the following

description.

Brief Description of Figures in the Drawings

[0024] Figure 1 shows one embodiment of an apparatus according to the invention; Figure 2 shows an embodiment of the invention installed on a structure to be monitored; Figure 3 shows a flow chart of a method according to an embodiment of the invention; Figure 4 shows one embodiment of a mounting means for the sensor; Figures 5-9 show alternative embodiments of the invention with different sensor mountings; and Figures 10-17 show alternative embodiments for the clamp for use in the invention.

Mode(s) for Carrying Out the Invention [0025] Referring now to Figure 1, the embodiment of the invention shown therein comprises a ring-type clamp 11, typically made out of a composite material. In this embodiment, the clamp 11 is formed in two semicircular halves secured together using a securing system 12. In this case, the securing system comprises two nut and bolt arrangements on opposite sides of the damp. Other releasable securing systems can also be used and it is also possible to replace one securing system with a hinge. The shape of the claim 11 in Figure 1 is circular, although other shapes can be used depending on the shape of the structure to be monitored.

[0026] A strain sensor 13 is located on the clamp 11 or imbedded into the clamp material (as is shown in Figure 1). In one possible embodiment, the clamp 11 is made of composite material and the sensor 13 is an optical fibre Bragg grating sensor. By providing the clamp 11 with a sensor that measures strain, securing the clamp 11 to a structure to be monitored, for example a pipe or tube, such an oil and/or gas pipe, or a water pipe, or a sub sea structure such as a sub sea riser, means that strain imposed on the clamp 11 by the structure can in turn be measured by the sensor 13.

The direction of the strain measured will depend on the configuration of the clamp. In the embodiment of Figure 1, the sensor 13 will measure the tangential strain in the clamp 11 which in turn is created by the behaviour of the structure at its periphery or perimeter where the clamp is located.

[0027] Figure 2 shows a clamp 31 attached to a structure 32 such as a pipe. A data collection unit 33 is also be attached to the structure 32 by means of further clamps or other locating devices and connected to the sensor in the clamp 31 by a cable 34. The data collection unit can include a battery or other power source or can be connected to a power source by means of a cable. Likewise, data stored in the unit 33 can be delivered to a processing system directly via a cable, or by periodically downloading the data via a wireless link in response to interrogation by a reader.

[00281 The data measured by the strain sensors is stored in a data recording unit, and can be transmitted to surface by several known means. Such means include, for example, an optical or electrical cable operatively connecting the data recording unit to an interface at an FPSO, or a light, acoustic or electromagnetic signal transmitted from the data recording unit to a remote operated vehicle.

[0029] Figure 3 shows a flow diagram of the steps in a method according to one embodiment of the invention to calculate internal pressure of a structure, such as a pipe line, using the clamped system of Figure 2 using a fibre Bragg grating sensor. In a first step 40, data is collected from the sensor referenced to a centre wavelength of the fibre Bragg grating mounted in the clamp. This approach has been used in other fibre Bragg grating devices.

[0030] The data is then translated from the centre-wavelength referenced data into a strain measurement (42). This can be done in one of a number of known ways, dependent on the exact form and orientation of sensor used.

The strain measurement can then in turn be used to calculate the hoop strain on the clamp (44) and from this the perimeter dimensions of the structure beneath the clamp can be determined (46), knowing the 6/ dimensions of the clamp and using the known physical properties of the clamp material and structure. Finally, by knowing the physical structure of the pipe and its material properties, and its environment, the internal pressure of the pipe can be calculated (48). Other properties such as the temperature of the structure, the outer pressure of the structure can also be calculated from this data.

[003 1] Steps 42-48 can be performed in a processing unit remote from the structure and sensor if desired. Also, a series of measurement over time can be made to determine time-varying properties of the pipe or other structure being monitored.

[0032] In its simplest form, the invention provides a measurement of a change in the external diameter of the pipe. This can indicate one of a number of scenarios: a change in the internal pressure of the pipe, a change of the void volume of the annulus and damage of the external or internal sheath of a flexible pipe, etc. By monitoring the changes of the external diameter of the pipe structure one can infer that if there is a change in the diameter then the integrity of the pipe may be compromised. It is also possible to infer internal pressure and pressure changes of the outer sheath of a flexible pipe by measuring changes in outer diameter of flexible pipes.

[0033] A number of conditions can be inferred from measurements of the change of pipe diameter, particularly those due to pressure, or variations in the pressure, inside the annular space of the flexible pipes, for example: -The outer sheath may be damaged and sea water is invading the annular space. Sea water invasion promotes corrosion of the steel internal parts of the flexible pipe making it more likely to rupture.

-The annular space may suffer from over pressure due to clogging or plugging of the venting system, eventually rupturing the outer sheath. This build up of pressure may be due to gas migration through the inner liner.

-A metal strand of the armor of the flexible pipe may rupture and springing out of its intended position. This is not due to a change in pressure, the force applied to the outer sheath by the strand generating the change in diameter of the external sheath. 7'

[0034] The sensor(s) are mounted on the clamp by an appropriate mounting means which allows the sensor to see' the strain imposed on the clamp by the structure below. It is possible to increase the sensitivity of the sensor to that strain system by selecting the shape of the sensor mounting means (the clamp component where the strain is measured) in order to concentrate the strain at the sensor location. Figure 4 shows one example in which the mounting means 50 is narrowed where the sensor is actually mounted 52. In this case the narrowing is responsible for the shift in sensitivity. It is also possible to obtain similar effect by changing the material properties of the mounting means (or both).

[0035] The sensor can be mounted on the structure so as to be aligned with the predetermined direction in which strain is to be measured. Figure 5 shows one example in which the sensor 54 is aligned with the clamp 56 to provide strain measurement in a given direction y on the pipe or structure 58.

[0036] Another way of mounting the sensor is shown in Figure 6, in which a pair of damps 60, 62 are mounted spaced apart on the pipe 64, with a sensor carrier 66 extending between the clamps. The sensor 68 is mounted on the carrier 66 and aligned to measure strain in the direction of the pipe axis(direction z). In this case, the points on the clamps where the carrier connects are axially aligned. Figure 7 shows another embodiment in which the connection points are offset so that the carrier 66 lies obliquely to the pipe axis and the sensor 68 measures strain having components in both directions y and z. [0037] Figures 8 and 9 show other embodiments for mounting the sensor. In these cases, a pair of clamps 70, 72 is provided which are installed on the pipe 74 on either side of the location at which the sensor 78 is to be located. The clamps 70, 72 are disposed at an angle rather than simply encircling the pipe 74 so that they are close to each other at the point where the sensor 78 is located. In Figure 8, the sensor 78 is aligned so as to be sensitive to strain in the y direction, whereas in Figure 9 the sensor 78 is aligned in the z direction. 8i

[0038] Figures 10-17 show various embodiments of the clamp construction. In Figure 10, a number of rollers 80 are disposed around the clamp 82 so that when the clamp is installed on the pipe 84 (in this case there are four equally spaced rollers), the rollers 80 bear on the surface of the pipe 84 and transmit strain due to expansion or contraction of the pipe 84 to the sensor mounting means 86. In figure 10, the mounting means 86 is in line with the rest of the clamp 82.

[0039] Figure 11 shows another embodiment in which the clamp is arranged to amplify the effect of strain on the clamp. In this case, rollers 80 are provided as before. However, instead of providing the sensor mounting means 86 in line with the clamp 82, a pair of radial extensions 88, 90 are provided with the sensor mounting means located at the end of the extensions. By moving the mounting point of the sensor away from the surface of the pipe 84, changes at the surface are amplified mechanically.

Figure 12 shows a variation of the embodiment of Figure 11 in which a hinge 92 is provided in the clamp 82 opposite to the extensions. This allows the clamp 82 to be opened for installation around the pipe 84, after which it can be closed by bringing the extensions 88, 90 back together. In Figure 13, the simple hinge 92 of Figure 12 is replaced by a sliding or flexing hinge 94. As is shown in Figure 14, a roller 96 can be associated with the hinge with the same effect as described above. In this case, three equally spaced rollers are present. In the embodiment of Figure 15 the two rollers 80 are positioned close to the inner ends of the extensions 88,90.

[0040] In Figure 16, stiffening arms 98, 100 are provided to connect the ends of the extensions 88, 90 to the main parts of the clamp 82. This avoid the sensor mounting being subjected to strain by deformation of the extensions and providing readings that are unrelated to the strain at the periphery of the pipe 84.

[0041] Figure 17 provides a construction that does no use rollers. In this case, the hinge 92 is provided with a high friction device 102 which helps to hold the clamp 82 in place on the pipe 84. The clamp 82 contacts the pipe 84 near the end of the extensions 88, 90 and when the pipe expands or contracts, the surface slides under the clamp 82 at this point. To improve this sliding motion, a low friction surface 104 can be applied to the pipe in this region.

[0042] Other changes can be made while remaining within the scope of the invention. For example, multiple sensors can be provided in a single clamp. Also, multiple damps can be provided spaced along the structure of interest.

Claims

Claims 1. An apparatus for monitoring physical parameters of a structure, comprising: -a clamp that in use is placed to embrace the structure to be monitored; and -a strain sensor attached to the clamp an arranged so as to detect strain in the direction of the perimeter of the structure.
2. Apparatus as claimed in claim 1, wherein the clamp is shaped to the outside shape of the structure.
3. Apparatus as claimed in claim I or 2, wherein the clamp is made using composite material.
4. Apparatus as claimed in any preceding claim, wherein strain sensor is embedded into the clamp.
5. Apparatus as claimed in any preceding claim, wherein the sensor comprises an optical sensor.
6. Apparatus as claimed in claim 5, wherein the sensor is an optical fibre sensor.
7. Apparatus as claimed in claim 6, wherein the optical fibre sensor comprises a fibre Bragg grating based sensor, or any other interferometnc sensor.
8. Apparatus as claimed in any preceding claim, wherein the structure to which the apparatus is applied is a pipe or tube.
9. Apparatus as claimed in claim 8, wherein the structure is an oil, gas pipe and/or water pipe.
10. Apparatus as claimed in any of claims 1-7, wherein structure is a sub sea structure.
11. Apparatus as claimed in claim 10, wherein the structure is a sub sea riser.
12. Apparatus as claimed in any preceding claim, wherein the structure is located below the surface.
13. Apparatus as claimed in any preceding claim, wherein the structure is totally or partially buried.
14. Apparatus as claimed in any preceding claim, wherein a data collection unit is attached to the structure or the clamp.
15. Apparatus as claimed in claim 14, wherein the data collection unit includes an optical interrogation unit.
16. Apparatus as claimed in claim 15, wherein the optical interrogation unit operates by means of spectrum analysis. I 1
17. Apparatus as claimed in any preceding claim, wherein clamp is a strap or belt or a compliant material.
18. Apparatus as claimed in any preceding claim, wherein the sensor is attached to the clamp by means of a mounting means arranged to align the sensor in a predetermined peripheral direction when installed on the structure.
19. Apparatus as claimed in claim 18, wherein the mounting means is configured to enhance the sensitivity of the sensor in the predetermined direction when installed on the structure.
20. Apparatus as claimed in claim 19, wherein the mounting means has smaller dimensions than the clamp.
21. Apparatus as claimed in any preceding claim, comprising at least one sensor arranged to detect strain in the circumferential direction of the structure when installed on the structure.
22. Apparatus as claimed in any preceding claim, comprising at least one sensor arranged to detect strain in the axial direction of the structure when installed on the structure.
23. Apparatus as claimed in any preceding claim, comprising at least one sensor arranged to measure strain in a direction that includes both circumferential and axial components when installed on the structure.
24. Apparatus as claimed in claim 21 or 22, comprising a pair of clamps which, when installed on the structure, embrace the structure above and below the sensor.
25. Apparatus as claimed in claim 24. wherein at least one sensor is attached to connecting means that extend between the clamps.
26. Apparatus as claimed in claim 21, wherein the clamp, when installed on the structure, extends around the circumference of the structure and the sensor is aligned with the clamp axis.
27. Apparatus as claimed in any preceding claim, wherein the clamp comprises rollers which are arranged to bear against the outer surface of the structure in use.
28. Apparatus as claimed in any preceding claim, wherein the clamp comprises extensions on which the sensor is mounted, the extensions projecting radially away from the structure when the clamp is installed on the structure.
29. Apparatus as claimed in claim 28, further comprising reinforcing arms arranged to support the extensions.
30. Apparatus as claimed in any preceding claim, wherein the clamp comprises a hinge to allow opening of the clamp for installation on the structure.
31. Appartus as claimed in claim 30, wherein a roller is provided at the hinge which is arranged to bear on the outer surface of the structure when the clamp installed on the structure.
32. Appartus as claimed in claim 30, wherein a high friction device is provided at the hinge which is arranged to bear on the outer surface of the structure when the clamp installed on the structure.
33. Appartus as claimed in any preceding claim, further comprising a low friction coating positioned on the structure at the point where the clamp is installed.
34. Apparatus as claimed in any preceding claim, further comprising means for transmitting data from the sensor by an optical, acoustic or electromagnetic signal.
35. Apparatus as claimed in any preceding claim, further comprising an optical or electrical cable for transmitting data from the sensor to a remote location.
36. A method of monitoring a structure, comprising: -placing a clamp to embrace the structure to be monitored, the clamp having a strain sensor attached thereto; and -collecting information from the strain sensor attached to the clamp placed in order to detect strain in the direction of the perimeter of the structure.
37. A method as claimed in claim 36, comprising using the strain information to calculate the perimeter dimensions of the structure, the temperature of the structure, the outer pressure of the structure, or the inner pressure of the structure.
38. A method as claimed in claim 36 or 37 wherein the clamp comprises an apparatus as claimed in any of claims 1-35.
39. A method as claimed in claim 37, wherein the structure comprises a flexible pipe in a subsea installation,
40. A method as daimed in claim 39, further comprising using the information to identify, damage to a sheath of the flexible pipe, plugging of a venting system, gas migration through an inner liner, and/or rupture of a reinforcing strand mt eh structure of the pipe.