Monitoring Cable Integrity During Pipeline Manufacture

Abstract

When manufacturing a pipeline that carries an array of electrical cables, insulation resistance monitoring is performed by a monitoring unit that is connected to the cables of the array and is mounted to a leading end of the pipeline. The monitoring unit tests the cables cyclically in succession. Monitoring is performed on the cables after their application to the pipeline and while the pipeline and the cables advance together through further manufacturing processes, such as insertion of the pipeline into the outer pipe of a pipe-in-pipe structure. If a fault is detected in any of the cables, an alert can be raised quickly enough to stop the process and to rectify the fault before the fault is covered and rendered inaccessible. The pipeline and the cables can advance continuously unless a fault is detected.

Claims

1. A method of manufacturing a pipeline having at least one cable applied thereto, the method comprising: performing insulation resistance monitoring on the at least one cable during application of the at least one cable to the pipeline while the at least one cable is moving relative to the pipeline; and raising an alert if the insulation resistance monitoring detects a fault in the at least one cable applied to the pipeline.

2. The method of claim 1, comprising stopping said relative movement between the at least one cable and the pipeline upon raising the alert.

3. The method of claim 1 or claim 2, comprising: advancing the pipeline or a cable lay apparatus while applying the at least one cable to the pipeline and performing insulation resistance monitoring on the at least one cable; and stopping the advance of the pipeline or of the cable lay apparatus upon raising the alert.

4. The method of claim 3, comprising: performing a process that covers the pipeline and the at least one cable applied to the pipeline; and stopping the advance of the pipeline before the fault in the at least one cable is covered by said process.

5. The method of claim 4, wherein said process is either insertion of the pipeline and the at least one cable into an outer pipe or application of a covering over the pipeline and the at least one cable.

6. The method of claim 4 or claim 5, comprising advancing the pipeline through an inspection zone in which the at least one cable applied to the pipeline is accessible, before the pipeline and the at least one cable applied to the pipeline are covered by said process.

7. The method of claim 6, further comprising rectifying the fault after stopping the advance of the pipeline, while the fault is in the inspection zone.

8. The method of claim 6 or claim 7, wherein the inspection zone has a length D.sub.max, the pipeline is advanced at a velocity V and the alert is raised within a time period T.sub.max being V/D.sub.max.

9. The method of any of claims 3 to 8, comprising advancing the pipeline continuously unless a fault is detected in the at least one cable applied to the pipeline.

10. The method of any preceding claim, comprising repeating insulation resistance monitoring of the at least one cable and raising the alert if a fault is detected on successive monitoring operations.

11. The method of any preceding claim, comprising performing insulation resistance monitoring by a monitoring unit that is connected to a leading end of the at least one cable.

12. The method of claim 11, wherein the monitoring unit is located within or ahead of a leading end of the pipeline.

13. The method of claim 11 or claim 12, comprising transmitting an alert signal in an upstream direction from the monitoring unit to a remote alarm or control unit.

14. The method of claim 13, wherein the alarm unit is positioned to convey the alert signal to a first location at which the at least one cable applied to the pipeline is accessible.

15. The method of claim 14, wherein the monitoring unit is downstream of said first location, at a second location at which the at least one cable applied to the pipeline is substantially inaccessible.

16. The method of claim 15, comprising configuring the monitoring unit remotely when the monitoring unit is at the second location.

17. The method of any preceding claim, comprising: applying a set of cables to the pipeline simultaneously; and performing insulation resistance monitoring on the cables of the set while the set of cables is being applied to the pipeline.

18. The method of claim 17, comprising performing insulation resistance monitoring on the cables of the set cyclically in succession through the set.

19. The method of claim 18, comprising completing at least one cycle of performing insulation resistance monitoring on all cables of the set, between application of the cables to the pipeline and concealment of the cables beneath an outer pipe or other covering.

20. The method of any of claims 17 to 19, comprising performing insulation resistance monitoring on one of the cables of the set against each other cable of the set.

21. A cable monitoring arrangement for monitoring at least one cable being installed along a pipeline, the arrangement comprising: an inspection zone through which the pipeline may be advanced continuously, the inspection zone extending between an upstream location at which the at least one cable is applied to the pipeline and a downstream location at which the at least one cable is concealed beneath an outer pipe or other covering; and an insulation resistance monitoring unit connected to the at least one cable and to earth, the monitoring unit being configured to monitor the at least one cable and to raise an alert on detecting a fault in the at least one cable, before the fault exits the inspection zone as the pipeline and the at least one cable advance through the downstream location.

22. The arrangement of claim 21, further comprising an alarm unit that is remote from the monitoring unit and that is positioned to convey the alert signal to the inspection zone.

23. The arrangement of claim 21 or claim 22, wherein the monitoring unit comprises a wired or wireless communications interface in communication with the alarm unit.

24. The arrangement of any of claims 21 to 23, wherein the monitoring unit is remotely configurable.

25. The arrangement of any of claims 21 to 24, wherein the monitoring unit is supported by the pipeline.

26. The arrangement of claim 25, wherein the monitoring unit is disposed within a leading end portion of the pipeline.

27. The arrangement of any of claims 21 to 26, wherein a set of cables is applied to the pipeline and connected to the monitoring unit and the monitoring unit is configured to perform insulation resistance monitoring on all the cables of the set.

28. The arrangement of claim 27, wherein the monitoring unit comprises a switching unit for performing insulation resistance monitoring cyclically in succession through the cables of the set.

Description

[0061] To put the invention into context, reference has already been made to FIGS. 1 and 2 of the accompanying drawings, in which:

[0062] FIG. 1 is a schematic side view of a pipeline production facility as known in the prior art; and

[0063] FIG. 2 corresponds to FIG. 1 but shows the facility assembling a PiP structure as also known in the prior art.

[0064] In order that the invention may be more readily understood, reference will now be made, by way of example, to the remainder of the accompanying drawings, in which:

[0065] FIG. 3 is a schematic side view of a pipeline production facility in accordance with the invention, while assembling a PiP structure like that shown in FIG. 2 in which the pipeline serves as the inner pipe of the PiP structure;

[0066] FIG. 4 corresponds to FIG. 3 but shows the pipeline now inserted telescopically into the outer pipe of the PiP structure; and

[0067] FIG. 5 is a block diagram of an insulation resistance monitoring module of the invention, as depicted schematically in FIGS. 3 and 4.

[0068] To the extent that FIGS. 3 and 4 correspond to FIG. 2, like numerals are used for like features. FIGS. 3 and 4 show the invention in the context of assembling a PiP structure like that shown in FIG. 2. However, the principles of the invention can also be applied to a situation like that shown in FIG. 1, in which the cables 14 on the pipeline 12 are instead covered by some other process such as application of a coating 24, insulation blanket or spacer. In that case, it will be appreciated that a work station 22 as shown in FIG. 1 may be substituted for the outer pipe 26 of the PiP structure shown in FIGS. 3 and 4.

[0069] FIG. 3 shows a leading end of the pipeline 12 approaching the trailing end of the outer pipe 26 whereas FIG. 4 shows the leading end of the pipeline 12 received telescopically within the outer pipe 26. Both FIGS. 3 and 4 show an insulation resistance monitoring unit or module 32 connected to all of the cables 14 on the pipeline 12 and to earth. In this example, the module 32 is positioned inside the leading end of the pipeline 12, which conveniently both supports and protects the module 32. The cables 14 therefore extend around the leading end and into the central lumen of the pipeline 12 to connect to the module 32.

[0070] FIGS. 3 and 4 also show an alarm unit 34 that is responsive to the module 32 by activating a visual display and/or an audible alarm, such as a buzzer, to indicate the presence of a fault 28 in one of the cables 14 when detected by the module 32. With reference to FIG. 4, the alarm unit 34 is positioned so that workers attending to the inspection zone 30 of the pipeline 12 immediately upstream of the outer pipe 26 can 35 react to a display or alarm and respond promptly to an alert generated by the module 32 that indicates the presence of a fault 28.

[0071] Additionally, a process controller 36 that is responsive to the module 32 either directly or via the alarm unit 34, as shown, may stop movement of the pipeline 12 and unspooling of the cables 14 from the reels 16 automatically. The process may then remain stopped until the fault 28 has been traced and rectified, whereupon the process can be restarted on command from a supervising operator.

[0072] In the example shown in FIGS. 3 and 4, the module 32 and the alarm unit 34 have respective antennae 38 for wireless communication between them. Such wireless communication could be effected directly by radio signals but optionally, as shown in FIG. 4, an intermediate communication system 40 could relay signals from the module 32 to the alarm unit 34, for example by Wi-Fi. FIG. 4 also shows the further option of a wired connection 42 between the module 32 and the alarm unit 34, extending along the annulus 44 between the pipeline 12 and the outer pipe 26. The wired connection 42 could be an optical fibre data link or other wired data connection.

[0073] FIG. 5 exemplifies the functional structure of the insulation resistance monitoring module 32. The module 32 is electrically powered from an external supply via an external power link 46, such as a power cable that may extend along the annulus 44 of a PiP structure. The power link 46 is connected to a wide-range power supply 48 that charges an internal battery 50 as a back-up in case of failure of the power link 46. The internal battery has sufficient capacity to power the module 32 during a specified autonomy period, for example of at least two weeks, at the required testing rate. The module 32 could instead be powered solely by the power link 46 or by the internal battery 50.

[0074] Insulation resistance testing is performed continuously and automatically at 52 under the control of a CPU 54, testing each cable 14 against all other cables 14, or against a limited selection of cables 14, and earth. For example, an acceptance resistance criterion of between 1 GΩ and 10 GΩ may be configured and set.

[0075] The CPU 54 receives monitoring inputs from a switching unit 56 to which the cables 14 and an earth connection 58 are connected via respective terminals. The switching unit 56 cycles rapidly through the cables 14 to perform insulation resistance tests on each cable 14 in turn. Optionally, as shown, the CPU 54 may be supported by a memory 60 that can store the results of monitoring until the end of a measurement period.

[0076] The CPU 54 controls and responds to a communications interface 62 that establishes one or more permanent and continuous external communication links, including an output 64 to the alarm unit 34. More generally, the communications interface 62 may convey events or commands from or to the module 32 in operation, such as: alarm raised, in case of measurement of a faulty cable 14; stop alarm; measurement standby; restart measurement cycles; or transmit data recorded in the memory 60.

[0077] Using a laptop connected to the module 32 or a dedicated interface embedded in the module 32, an operator may use the communications interface 62 to configure the module 32 remotely, adjusting parameters such as: sampling period; acceptance criteria; number of cable inputs connected; whether or not to repeat measurement of a possibly faulty cable 14 before raising an alarm; whether or not to store each measurement in the memory 60; and accessing and reading or downloading any data recorded in the memory 60 after the end of a measurement period for subsequent download.

[0078] In this example, the communication links are effected by a wired or optical interface although wireless transmission is also possible as explained above. Wireless transmission may be effected by a radio link as noted above or by a sonic (such as ultrasonic) link or other electromagnetic (such as infrared) link. Potentially, communications signals could be transmitted to and from the module 32 along one or more of the cables 14.

[0079] Many other variations are possible within the inventive concept. For example, the insulation resistance monitoring module 32 could be positioned outside the pipeline 12, for instance ahead of the pipeline 12 on the central longitudinal axis 20.

[0080] Whilst, in the above examples, the pipeline 12 moves past stationary cable-laying equipment comprising the reels 16 and guides 18, it would be possible instead for that cable-laying equipment to move past a stationary pipeline 12. Similarly, it would be possible for the outer pipe 26 of a PiP arrangement to be advanced over a stationary pipeline 12, or to be assembled around the pipeline 12.