WO2009095655A1

WO2009095655A1 - Fatigue and damage monitoring of pipes

Info

Publication number: WO2009095655A1
Application number: PCT/GB2009/000227
Authority: WO
Inventors: Rogerio Ramos; Stephane Vannuffelen
Original assignee: Schlumberger Holdings Limited; Schlumberger Canada Limited; Prad Research And Development Limited; Services Petroliers Schlumberger; Schlumberger Technology B.V.
Priority date: 2008-01-28
Filing date: 2009-01-27
Publication date: 2009-08-06
Also published as: GB0801500D0; GB2456831A; GB2456831B

Abstract

A method of monitoring a pipe to be installed in a predetermined location, comprises installing a distributed strain gauge sensor, such as a FBG optical fibre sensor, along the pipe when it is at a location remote from the predetermined location; connecting the strain gauge sensor to a data acquisition system; and acquiring data from the stain gauge sensor as the pipe is moved from the remote location to the predetermined location.

Description

FATIGUE AND DAMAGE MONITORING OF PIPES Technical field

[0001] This invention relates to techniques for monitoring pipes to detect fatigue and damage. In particular the invention relates to such techniques for use in the offshore oil and gas industry, especially for monitoring of flexible pipes before final installation.

Background art

[0002] Subsea hydrocarbon production requires tubular production components such as flowlines and risers to be installed in mechanically-challenging conditions. These mechanical conditions are due to long length and consequent high initial static loads, but are compounded by dynamic loads arising from waves, currents and ship movements due to weather. Often the system being installed needs to be reeled and unreeled, lifted by cranes, buoyancy devices or other means, and moved on and off decks and barges. These high and complex loads often give rise to tension, torsion, impact or other conditions which can cause incipient failure not immediately visible to external inspection.

[0003] In recent year, the use of flexible pipes such as flexible flow lines and risers has become more commonplace. Such flexible pipes typically do not have a continuous metal layer but have a series of metal plies to reinforce a polymer tube. Failure of the polymer tube can therefore potentially lead to loss of pipe integrity. Because the consequences of failure can be dangerous and expensive, it is becoming commonplace to permanently monitor the pipelines and flow lines in subsea installations.

[0004] Recent developments in distributed optical fibre sensors have made monitoring installations more feasible, especially with the development of temperature and strain gauges based on this technology.

[0005] When monitoring pipes, it is desirable to know when and where failure is likely to occur in order that remedial action can be taken before loss of integrity. By periodically measuring factors that can lead to damage, such as repeated cyclic distortion leading to fatigue, or impacts on the structures, failures can potentially be predicted. [0006] However, it has also been noted that failures can often occur soon after installation, before production operation monitoring can give useful information.

[0007] This invention is based on the recognition that damage and fatigue taking place before the pipe is finally installed in its production configuration has a significant effect on failure after installation. The invention provides a method for continually monitoring a pipe for effects that can affect its ability to perform once installed and so provide an opportunity to take remedial action before problems arise in use.

Disclosure of the invention

[0008] A first aspect of this invention provides a method of monitoring a pipe to be installed in a predetermined location, comprising:

- installing a distributed strain gauge sensor along the pipe when it is at a location remote from the predetermined location;

- connecting the strain gauge sensor to a data acquisition system; and

- acquiring data from the stain gauge sensor as the pipe is moved from the remote location to the predetermined location.

[0009] Preferably the sensor is an optical fibre sensor. One or more sensors can be provided and these can be mounted in channels in the pipe structure or as elements of appropriate size and shape connected to the pipe structure.

[0010] One embodiment of the invention comprises making a series of discrete, point measurements of strain along the pipe. Another comprises making a distributed measurement over part or all of the pipe length.

[0011] The pipe can be flexible, semi-rigid or rigid depending on uses.

[0012] In one embodiment, the sensor is installed during the manufacture of the pipe and data is acquired during the time between completion of manufacture and installation at the remote location.

[0013] The data acquisition system can be located on a vehicle used to move the pipe, such as a boat or a truck, on a reel or other holder for the pipe, or can be secured to the pipe itself. [0014] A particularly preferred embodiment of the invention involves floating the pipe to the predetermined location and acquiring data from the sensor as the pipe is floated and installed in place.

[0015] The data acquired preferably include data relating to maximum magnitude isolated single events or to repetitive distortions and/or impacts of the pipe.

[0016] Further aspects of the invention will be apparent from the following description.

Brief description of the drawings

[0017] Figure 1 shows a schematic view of a system in which the method according to the invention can be applied;

Figure 2 shows a schematic diagram of transportation of flexible pipes by flotation; and Figure 3 shows a reel for transporting a flexible pipe.

Mode(s) for carrying out the invention

[0018] The present invention allows the use of fibre-optic strain, bending, and other measurements to monitor both offshore and onshore the real-time loads and installation conditions, allowing verification of safe operating conditions, prediction of potentially excessive loads which can be mitigated by taking appropriate actions, and post-installation verification of the complete process as being in conformance to acceptable working loads. In particular, the invention relates to the monitoring of fatigue and damage in pipes such as those used in the subsea oil and gas industry. It has been recognised that such pipes, especially flexible pipes are often subjected to fatigue and/or damage during the process of manufacture and installation. Therefore, this invention provides methods for continually monitoring the pipes up to the point of installation, and beyond as required.

[0019] The preferred embodiment of the invention comprises installing a fibre optic sensor along the pipe structure so that deformations can be monitored. One example of a sensor particularly suited to such use is the fibre Bragg grating (FBR) sensor. Such devices can be installed in the fabric of the pipe itself, for example in channels provided in the pipe wall, or can be strapped to the outside of the pipe (the subCstrip product of lnsensys is an example of a suitable product for this application). The end of the fibre is provided with a connector by which a data acquisition unit including an interrogation unit can be connected.

[0020] Figure 1 shows a schematic view of such a system and comprises a pipe 10 (such as a flexible pipeline or riser), having an optical fibre system 12 secured along its length. In the example of Figure 1, the fibre system 12 is shown in a U-shaped configuration but a simple linear arrangement is also possible. A number of strain gauge sensors 14 are disposed along the fibre 12 so as to measure deformation of the pipe 10 at those locations. Alternatively, the fibre can comprise a continuous sensor that measures deformation at all points along the pipe. A connector 16 is provided at the end of the pipe 10 into which the fibre 12 is directed. The connector 16 provides a connection point for an interrogation unit 18 which can measure the response of the sensors 14 and calculate changes in strain. The output from the unit 18 can b provided continuously or stored for periodic downloading.

[0021] Several strain and stress measurement systems are commercially available (e.g. SubCmat ) that can be used to monitor mechanical conditions in flexible composite or solid metal riser and flowline systems. They can be installed to measure at key points or can measure continuous properties of an optical fibre. These measurements are recorded by an instrument box (interrogation unit or acquisition unit) that is typically intended to record and transmit data during the production process, i.e. after system installation. By starting such a system before installation, it is possible to interrogate the stored data at the end of the installation process to determine effects that could create fatigue and other damage in the structure. In some cases, this may be too late to take effective action. Therefore, the present invention preferably involves use of a system allowing strain and stress data to be available to operations experts within a few seconds of events during the installation process.

[0022] The acquisition unit for a strain and stress monitoring system typically has self-contained battery power that is sufficient for a few days, but which for long-term production use requires an external rig or subsea power cable. As typical installation operations last for hours or days this internal power source is selected so as to be able to power the unit for longer than the maximum expected installation operation time. If there are conditions in which real-time communications are lost for some reason the unit can continue to acquire data which is recorded and which can be re-sent as soon as communication is re-established.

[0023] Under typical production conditions the measured data can be transmitted by a standard protocol such as MODBUS or other standard by a serial wire link. During installation this system will typically not yet be available, so a special purpose wire or wireless data transmission unit can be provided. This may be either a modification of the system intended for permanent production use, or an installation-only unit which can be deactivated after the installation is complete.

[0024] Under typical production conditions the measured data can be recorded by a production unit SCADA system. During installation this system may not be available. In this case, a special-purpose surface acquisition unit can be provided, typically installed on the ship, barge, or installation unit from which the subsea system is being deployed. Strain and other data measured by the sensors are available in real-time on this unit, and can be displayed to an operator at this location. However, the operator may be at a remote location. In this case, real-time data acquisition packets can be sent to a real-time remote data monitoring system (e.g. the Schlumberger InterAct system) by satellite, radio, or fibre-optic data link.

[0025] The real-time remote data monitoring system can allow two-way interaction between the special-purpose surface acquisition unit and authorised remote users who have access to the system, for example via a server. Remote onshore users can thus monitor in real time the actual strains and stresses on the subsea system being installed and view either the basic engineering measurements or suitable diagnostic graphics allowing comparison of measured data with the values expected from previous simulations of the process. Two way real-time communications then allow authorised persons to control the installation process and avoid damage which could contribute to potentially hazardous situations of potential future failure caused by excessive loads.

[0026] The invention is based on the monitoring of the strain gauge output up to the time at which the pipe is installed in its in production use location. Data acquisition can begin as soon as the sensor system is installed and operational, for example in the factory where the cable is being manufactured. Data acquisition can continue during manufacturing, handling, transportation and installation steps, and optionally after installation. By reviewing the strain gauge data, the loads imposed on the pipe, and any deformations and impacts can be detected. Where these exceed previously known tolerances for the particular pipe in question, the location at which they were detected can be subjected to closer investigation and testing to ensure that the pipe integrity and performance are not compromised, or to allow remedial work or repair to be conducted before the pipe is installed.

[0027] One particular application of the invention is to monitor flexible pipes to be installed in subsea installations. One common way to transport flexible pipes to offshore locations is by towing them behind a boat. Figure 2 shows a schematic diagram of how this is done. The flexible pipe 20, with optical fibre system installed, is floated in the sea 22 at the surface 24 or just below using its natural buoyancy and/or attached flotation devices (not shown). The pipe 20 is connected to a towing vessel 26 and the optical fibre sensor output is provided to a data acquisition unit 28 mounted on the vessel 26.

[0028] Because the pipe 20 is close to the surface, it will be affected by wave motion which will cause deformation. While this may be below the levels that cause immediate permanent damage, the repetitive nature of the wave motion can cause fatigue in certain locations on the pipe leading to potential weakening and failure. Also, impacts can be detected and the pipe inspected for damage.

[0029] The data acquisition unit 28 can be mounted on the pipe itself and periodically interrogated to download data. [0030] Another method of transporting the pipe is on a reel. Figure 3 shows a reel 30 onto which a flexible pipe 32 is wound for transportation. The reel 30 is supported by a frame 34 for rotation so that the cable can be unwound for installation. In this case, the data acquisition unit 36 is mounted inside the reel 30. Thus the cable can be wound onto the reel when it is manufactured and the reel positioned on the transportation vehicle (truck, boat, etc.) and moved to the location of use where the pipe can then be unreeled and installed as required. The pipe can be completely removed from the reel, or can remain connected and rewound at the end of use. In this case, the strain monitoring will be useful to detect fatigue resulting from the deformation caused by winding and unwinding of the pipe. (Coiled tubing is another typical example of such a use).

[0031] A particular application of the method is to monitor the reeling and unreeling process of complex flexible risers, as it appears that major cause of flexible riser failures is over-stressing during this process. A continuous record of stress during these processes allows the operator to be confident that the system will perform for the designed operational lifetime, and allows demonstration that the system has been correctly installed.

[0032] With the basic strain measurements, relevant ancillary data such as hook load and wave motion etc., applications can be developed that allow diagnosis of other conditions such as damage to connections, pipe insulation, or other components of the complete subsea system. Further variations of this method can be made within the scope of the invention. For example, strain gauges other than optical fibre devices can be used. Also, multiple data acquisition units can be used instead of a single unit as described above.

[0033] In another embodiment, the fibres and sensors can be configured so as to be particularly sensitive to pipe bending and so provide an output that is indicative of the bending deformation undergone by the pipe. It is particularly preferable to monitor the pipe for over-bending (i.e. bending beyond the limit at which permanent damage occurs). By monitoring the pipe for such damage, the weakened region can be localised.

[0034] The data acquired by the method of the invention can be used to estimate the remaining lifetime of the structure of which the pipe (or pipes) is a part. This may involve modelling of the pipe and the structure to estimate lifetime loads and the like.

[0035] The data acquisition system can incorporate alarms so that by comparing the acquired data with the predetermined alarm levels, an alarm can be generated when the data passes that level. The data can be either of an instantaneous single event amplitude, or of an integrated time series of events which together in summation exceed an event threshold.

[0036] The data can be transmitted from the acquisition unit to another location for analysis and/or storage. In particular, this data can be used to optimise the installation process and minimise its impact on structure lifetime.

[0037] Other such changes will be apparent.

Claims

1. A method of monitoring a pipe to be installed in a predetermined location, comprising:

- connecting the strain gauge sensor to a data acquisition system; and

2. A method as claimed in claim 1 , wherein the sensor is an optical fibre sensor.

3. A method as claimed in claim 1 or 2, wherein one or more sensors is provided.

4. A method as claimed in claim 1 , 2 or 3, wherein the sensors are mounted in channels in the pipe structure or are connected to the outside of the pipe structure.

5. A method as claimed in any preceding claim, wherein the strain gauge sensors are configured so as to be sensitive to bending of the pipe

6. A method as claimed in any preceding claim wherein the pipe is flexible, semirigid or rigid.

7. A method as claimed in any preceding claim, comprising installing the sensor is installed during the manufacture of the pipe and acquiring data during the time between completion of manufacture and installation at the remote location.

8. A method as claimed in any preceding claim, comprising locating the data acquisition system on a vehicle used to move the pipe, on a reel or other holder for the pipe, or can be secured to the pipe itself.

9. A method as claimed in any preceding claim, comprising floating the pipe to the predetermined location and acquiring data from the sensor as the pipe is floated and installed in place.

10. A method as claimed in any preceding claim, comprising acquiring data relating to maximum magnitude isolated single events or to repetitive distortions and/or impacts of the pipe.

11. A method as claimed in any preceding claim, comprising monitoring the pipe for over-bending leading to permanent damage and localisation of the location of any over-bending measured.

12. A method as claimed in any preceding claim, comprising using the acquired data to estimate the remaining lifetime of a structure of which the pipe is a part.

13. A method as claimed in any preceding claim, comprising comparing the acquired data with predetermined alarm levels, and generating an alarm when the data passes that level.

14. A method as claimed in any preceding claim, wherein data is transmitted from the acquisition unit to another location for analysis and/or storage.

15. A method as claimed in any preceding claim, comprising using the acquired data to optimise installation processes and minimise the impact of the installation process on the lifetime of structures incorporating the pipe.

16. A method as claimed in any preceding claim, comprising making a series of discrete point measurements at locations along the pipe.

17. A method as claimed in any preceding claim, comprising making a distributed measurement along a length of part or all of the pipe.

18. A method as claimed in any preceding claim, comprising providing a stand alone power source for the data acquisition system that allows it to operate in the absence of connection to other power sources.

19. A method as claimed in any preceding claim, comprising transmitting the data from the acquisition unit to a remote location for analysis.

20. A method as claimed in any preceding claim, comprising providing the data to a control system for controlling the installation process and operating the control system in accordance with the data.