GB2340245A

GB2340245A - Control and/ or tracking of a pipeline crawler

Info

Publication number: GB2340245A
Application number: GB9916711A
Authority: GB
Inventors: Quinton Francis Lucy; John Macleod; Victor Kurosaev; Alexander Bakoonov; V V Kljuev; V Mujitskiy
Original assignee: JME Ltd
Current assignee: JME Ltd
Priority date: 1998-07-24
Filing date: 1999-07-19
Publication date: 2000-02-16
Also published as: GB9916711D0; GB9816083D0

Description

2340245 Pipeline Crawler Control and/Qr Tracking System This invention

relates to a pipeline crawler control and/or tracking system.

Generally, in the prior art, signals to or from a crawler inside a pipeline have involved the use of signalling devices based on radioactive isotopes, typically CS137 or C060. The use of such signalling devices is becoming increasingly undesirable.

Alternatively, for the inspection of pipeline welds internally, the crawler has been programmed to move forward until a device such as a star wheel is tripped on engagement with the weld internal bead, whereupon an X-ray device on the crawler is triggered.

According to the present invention, in its broadest aspect, there is provided a control and/or tracking system for a pipeline crawler comprising a generally Cshaped or U-shaped permanent magnet for location on the exterior of the pipeline or on the crawler, respectively, magnetic flux sensing means for location on the crawler or on the exterior of the pipeline, respectively, and for sensing the flux field impressed on the line, and means whereby the output of the flux sensing means is utilised at least to determine the direction of travel of the crawler.

In one system, employed for tracking mo vement of the crawler, the Cshaped or U-shaped magnet is mounted on the crawler adjacent the interior surface of the pipeline, with the direction of magnetic flux of the magnet (polar axis) parallel to the axis of the pipeline, and the flux sensing means detects the residual field left impressed on the pipeline by the movement of the crawler.

In this system, the crawler leaves behind it a residual field on the pipeline which, when compared with the flux field impressed on the pipeline at the instantaneous position of the crawler, enables the direction of travel and the exact location of the crawler readily to be determined.

In another system, employed to control the crawler, the C-shaped or Ushaped magnet is positioned on the exterior of the pipeline and an array of magnetic flux sensors is mounted on the crawler.

According to this aspect of the invention, therefore, there is provided a control system for a pipeline crawler comprising a generally C-shaped or U-shaped permanent magnet for location on the exterior of the pipeline, either with the direction of the magnetic flux (polar axis) parallel to or transverse to the axis of the pipeline, an array of magnetic flux sensors adapted to be mounted to a pipeline crawler, and means for processing output signals from the sensors to effect crawler control, the sensors being arranged in the array so that in one ofientation of the magnet a direction drive command is supplied to the crawler and in the other orientation of the magnet a stop command is supplied to the crawler.

In this system, a line array of three flux sensors parallel to the axis of the pipeline, and preferably spaced at half the pole-pitch of the magnet, are able to cause generation of logic stop and X-ray command signals for the crawler when the external magnet is positioned adjacent an externally visible pipeline weld, with the polar axis parallel to the pipeline axis, and the sensors detect the normal component of the magnetic field impressed on the pipeline (the component perpendicular to the pipeline wall). When one end sensor detects a positive field, the other end sensor a negative field, and the intermediate sensor (within positive and negative threshold limits) detects a null condition, it is determined that the crawler is in the correct position to be stopped in readiness for X-ray inspection apparatus to be triggered.

Preferred flux sensors on the crawler are Hall effect sensors laid horizontally assuming, as would usually be the case, that the magnet is positioned externally centrally on top of the pipeline, i.e. vertically above the axial path of movement of the crawler.

By addition to the array of a Hall effect sensor which is laid vertically to detect the tangential component of the magnetic field impressed on the pipeline when the external magnet is orientated with the polar axis normal to the axis of the pipeline, directional drive command signals for the crawler can be generated, forwards and backwards by turning the external magnet through 180 degrees.

Alternatively, instead of a single vertically laid sensor having a horizontal sensing plane, a pair of horizontally laid Hall effect sensors spaced perpendicularly to the pipeline axis, preferably by one pole-pitch of the magnet, can be added to the array, detecting the normal component of the flux field when the magnet is orientated with the polar axis normal to the axis of the pipeline, to generate directional drive commands for the crawler, forwards and backwards by turning the magnet through 180 degrees.

When two additional sensors are employed, they are preferably arranged symmetrically one on each side of the line array of three sensors, for generating stop and X-ray trigger commands, and when one additional sensor is used, it is preferably positioned in line with the aforesaid line array of three sensors.

For directional drive control of the crawler, it is not necessary precisely to position the external magnet over the sensor array, as the magnet casing is preferably equipped with wheels to enable its movement across the location of the sensor array once said magnet has been placed on the pipe. The magnet casing is preferably also equipped with a lever to facilitate its removal from the pipe.

It is also possible to use only three horizontally laid Hall effect sensors in line parallel to the pipeline axis. For directional control of the crawler, it is then possible to move the magnet over these sensors and form signals controlling the motion of the crawler as a combination of the output signals of the sensors.

Moreover, it is possible to measure changes in the output signals of the sensors which exclude the influence of temperature drift of the sensors.

The external permanent magnet requires to be relatively powerful and is therefore preferably made of high intensity, rare earth materials.

"Me pipeline crawler control and/or tracking system in accordance with the invention will now be further described with reference to the accompanying drawings, in which:- Figure I diagrammatically illustrates one pipeline crawler control system in accordance with the invention; Figures 2 and 3 illustrate two possible arrangements of sensor array for use in the system of Figure 1; Figure 4 shows the relative positioning of the magnet and sensor array required for generation of a crawler stop command in the system of Figure 1; Figure 5 is an explanatory diagram; Figure 6 shows a preferred construction of magnet; and Figures 7 and 8 relate to a pipeline crawler tracking system, and show profiles of the magnetic flux field impressed on the pipeline during and after movements -5of a pipeline crawler carrying the magnet.

The pipeline crawler control system shown in Figure 1, to be used for the interior inspection of welds in a pipeline 10, includes a C-shaped permanent magnet 12 positioned centrally on top of the pipeline at the site of an externally visible weld.

The C-shaped form of the permanent magnet 12 is best shown in Figure 6.

Typically it may be 150 mm long, 75 mm high and 50 mm wide, but its dimensions may vary to some extent dependent on the size of the pipeline. The magnet 12 is made of high intensity rare earth materials, and is carried by a casing (not shown) equipped with small wheels facilitating movement of the magnet on the pipeline once it has been placed in contact therewith. The magnet casing is also equipped with a lever facilitating detachment of the magnet from the pipeline.

The control system also includes an array 14 of magnet flux sensors constituted by Hall effect devices. This sensor array 14 is, as shown, adapted to be mounted on the pipeline crawler 16 so that it is positioned close to the pipeline interior wall just beneath the top centre thereof.

As will later be made clear, the sensor array 14 is required to be sensitive to the flux field of the magnet in two orientations of the latter, specifically when the magnet 12 is placed on the pipeline with its polar axis (principal direction of the flux field) parallel to the pipeline axis, as shown on the left-hand side of Figure 1, and when the magnet 12 is placed on the pipeline with its polar axis normal to the pipeline axis, as shown on the right-hand side of Figure 1.

However, in a system employing three in-line Hall effect sensors, the magnet is positioned with its polar axis parallel to the axis of the pipeline.

Two possible embodiments of sensor array 14 are shown in Figures 2 and 3, in relation to the magnet 12 when in the orientation shown on the lefthand side of Figure 1.

In both cases, a line array H1, H2, H3 of three Hall effect sensors are usefully operative when the axis of magnet 12 is parallel to the pipeline axis. The sensors Hl, H2, H3, spaced by one half the pole pitch of the magnet, detect the vertical component of the magnetic flux field (normal to the pipeline wall) impressed on the pipeline by the permanent magnet. For this purpose, the Hall effect sensors Hl, H2, H3 are laid horizontally.

The field impressed on the pipeline is shown in Figure 5. A null condition appears in line with the centre point between the magnet poles. Tlius, when sensor H1 detects a positive field, H3 a negative field, and sensor H2, within small threshold limits Vth+ and Vth-, detects a null condition, then it is determined that the sensor army is correctly aligned with the magnet, as depicted in Figure 4, and thus that X-ray equipment 18 on the crawler is correctly aligned for inspection of the interior of the pipeline weld. Hence, when this condition is detected, it is appropriate to generate a stop signal for the crawler. This is achieved by passing the output signals from the sensors HI, H2, H3 to an amplifier and thence to state interpretation circuitry, which generates logic level command signals compatible with the existing protocol of the crawler control system.

With the crawler stopped, it is appropriate to generate an X-ray command signal, and this is achieved by removing the magnet, thereby to leave a residual field of reversed polarity on the pipeline. Thus, after a stop command has been issued and the magnet removed, sensors H1 and H3 provide signals to the state interpretation circuit giving rise to the generation of the X-ray command signal, which triggers an X-ray machine 18 carried by the crawler. However, it is alternatively possible to generate the X-ray command signal as a change in one or more of the output signals of the sensors HI to H3.

In the arrangement of Figure 2, sensors H4 and H5, arranged symetrically on opposite sides of the line of sensors Hl, H2, H3, are provided for control of the direction of movement of the crawler. Sensors H4 and H5 are again laid horizontally, but spaced by one pole pitch, and detect the normal component of the flux field impressed on the pipeline by the magnet, which is now orientated in the direction shown on the right-hand side of Figure 1. The signal outputs of the sensors H4 and H5 are amplified and passed to state interpretation circuitry, whereby to generate logic drive signals for the crawler. The direction of drive is dependent on the direction of the flux field of the magnet. Thus, if for example the sensor H4 detects a positive flux field and sensor H5 detects a negative flux field, a forward drive command results for use by the crawler's existing control system protocol. If the magnet was to be rotated through 180 degrees, then sensor H5 would detect a positive flux field and sensor H4 a negative flux field, and a reverse (backward) drive signal for the crawler would be produced.

The single sensor H6 of Figure 3 functions in a similar manner. However, this sensor is laid vertically instead of horizontally, so that its sensing plane is horizontal and at 90 degrees to the axis of the pipeline, thereby to detect the tangential flux field impressed on the pipeline by the magnet. Again, rotating the magnet through 180 degrees reverses the direction of drive.

However, the sensor H6 is not essential to the system. In a three in-line Hall effect sensors system, it is possible to form command signals for control of the motion of the crawler as a change in one or more of the output signals of the sensors. For example, it can be seen from Figure 4 that if the magnet is moved in a forwards or backwards direction from the stop position, the change in output signal of sensor H2 has a different polarity. This feature can be used to determine the direction of motion of the crawler. Another possible means of determining the direction of the motion of the crawler is, for example, to move the magnet over the HO effect sensors twice for signalling forward motion or once for signalling reverse motion. An advantage of the three sensor system is that it requires a shorter length of accessible pipeline and smaller movements of the magnet.

Thus far, it has been shown how the present invention can be used to deliver control commands to an X-ray crawler. This, however, is not its sole crawler associated application, as it can also be employed as an aid to locating a crawler, in situations where it has become lost or its precise position is uncertain.

In this tracking application, a C-shaped magnet similar to that shown in Figure 6 is mounted on the chassis of the crawler, such that its poles are close to, but not touching, the wall of the pipe, and its polar axis is parallel to the axis of the pipe.

The sensor means for this application is a hand-held, battery powered instrument, containing a pair of Hall effect sensors, amplification and decoding circuitry, and an array of LED indicators. 'Me Hall effect sensors are mounted at the front of the instrument casing (i.e. furthest from the operator) and aligned to detect a magnetic field normal to the pipeline wall. As with the previously described detector system, the centres of these two sensors have a spacing equal to the pitch of the poles of the magnets. In order to correspond with the alignment of the magnet on the crawler, the unit must be presented to the pipe with the line between its sensors parallel to the axis of the pipe.

If the magnet is mounted such that the pole nearest to the front of the crawler produces a positive sensing signal, then the variations in the detected field can be interpreted in the following manner.

When the crawler is in forward motion, or is stationary, having previously moved forward, then the detectable magnetic flux profile is as shown in Figure 7. As can be seen, the residual field left in the pipe wall is of opposite polarity to the last pole of the magnet to pass over that section. In front of the magnet, however, there is no significant field, even though magnetisation of pipes by the earth's field is not unusual.

If, having passed through a section of pipe in the forward direction, the crawler is set into reverse drive, then the resulting flux profile is as shown in Figure 8. Here, as before, the residual field to the rear of the crawler has a positive value, but now there is a residual field forward of the crawler, and this has a negative value.

From this information, it can be seen that if both sensors in the tracking instrument have a zero output (or a level below a detection threshold), then the crawler has yet to reach that point. If both sensors produce a positive signal, then the crawler is forward of that position, whilst if both sensor signals are negative, then the crawler is rearward of it. When signals of different polarity are produced, it is necessary to clearly identify each sensor, so, for the purposes of this decription, they may conveniently be labelled Sensor A (nearest to the front of the crawler) and Sensor B (nearest to the rear of the crawler). If the signals are: A, negative and B, positive then, as can be seen in Figure 8, there are two possible detector positions where this condition could exist. T'his, of course, only indicates the close proximity of the tracking magnet on the crawler, and varies from the exact position by approximately the length of the magnet.

As can also be seen in Figure 8, the precise position of the tracking magnet, and thus of the crawler, is found when Sensor A signal is positive and Sensor B signal is negative. These five possible conditions are decoded by the tracking electronics incorporated in the sensing instrument and are indicated to the operator by the LEDs.

The C-shaped magnet employed in the tracking system may be mounted on the side of the crawler with its polar axis horizontal, thus making possible use of the tracking system in conjunction with the crawler control system of Figures 1 to 6.

Claims

1. A control and/or tracking system for a pipeline crawler comprising a generally C-shaped or U-shaped permanent magnet for location on the exterior of the pipeline or on the crawler, respectively, magnetic flux sensing means for location on the crawler or on the exterior of the pipeline, respectively, and for sensing the flux field impressed on the line, and means whereby the output of the flux sensing means is utilised at least to determine the direction of travel of the crawler.

2. A system according to claim 1, employed for tracking movement of the crawler, wherein the C-shaped or U-shaped magnet is mounted on the crawler adjacent the interior surface of the pipeline, with the direction of magnetic flux of the magnet (polar axis) parallel to the axis of the pipeline, and the flux sensing means detects the residual field left impressed on the pipeline by the movement of the crawler.

3. A system according to claim 2, wherein the crawler leaves behind it a residual field on the pipeline which is compared with the flux field impressed on the pipeline at the instantaneous position of the crawler to enable the direction of travel and the exact location of the crawler readily to be determined.

4. A system according to claim 1, employed to control the crawler, wherein the C-shaped or U-shaped magnet is positioned on the exterior of the pipeline and an array of magnetic flux sensors is mounted on the crawler.

5. A control system for a pipeline crawler comprising a generally Cshaped or U-shaped permanent magnet for location on the exterior of the pipeline, either with the direction of the magnetic flux (polar axis) parallel to or transverse to the axis of the pipeline, an array of magnetic flux sensors adapted to be mounted to a pipeline crawler, and means for processing output signals from the sensors to effect crawler control, the sensors being arranged in the array so that in one orientation of the magnet a direction drive command is supplied to the crawler and in the other orientation of the magnet a stop command is supplied to the crawler.

6. A system according to claim 5, wherein a line array of three flux sensors parallel to the axis of the pipeline is employed to cause generation of logic stop and X-ray command signals for the crawler when the external magnet is positioned adjacent an externally visile pipeline weld, with the polar axis parallel to the pipeline axis, the sensors detecting the normal component of the magnetic field impressed on the pipeline (the component perpendicular to the pipeline wall).

7. A system according to claim 6, wherein, when one end sensor detects a positive field, the other end sensor a negative field, and the intermediate sensor (within positive and negative threshold limits) detects a null condition, it is determined that the crawler is in the correct position to be stopped in readiness for X-ray inspection apparatus to be triggered.

8. A system according to claim 6 or claim 7, wherein the three flux sensors are spaced at half the pole pitch of the magnet.

9. A system according to any of claims 5 to 8, wherein the flux sensors on the crawler are Hall effect sensors.

10. A system according to claim 9, wherein the sensors are laid horizontally with the magnet positioned externally centrally on top of the pipeline, i.e. vertically above the axial path of movement of the crawler.

11. A system according to any of claims 6 to 10, wherein, by addition to the array of a Hall effect sensor which is laid vertically to detect the tangential component of the magnetic field impressed on the pipeline when the external magnet is orientated with the polar axis normal to the axis of the pipeline, directional drive command signals for the crawler can be generated, forwards and backwards by turning the external magnet through 180 degrees.

12. A system according to claim 11, wherein the additional sensor is positioned in line with the aforesaid line array of three sensors.

13. A system according to any of claims 6 to 10, wherein a pair of horizontally laid Hall effect sensors spaced perpendicularly to the pipeline axis are added to the array, detecting the normal component of the flux field when the magnet is orientated with the polar axis normal to the axis of the pipeline, to generate directional drive commands for the crawler, forwards and backwards by turning the magnet through 180 degrees.

14. A system according to claim 13, wherein the additional pair of sensors is spaced by one full pitch of the magnet.

15. A system according to claim 13 or claim 14, wherein the two additional sensors are arranged symmetrically one on each side of the line array of three sensors, for generating stop and X-ray trigger commands.

16. A system according to any of claims 6 to 10, wherein, for directional control of the crawler, the magnet is moved over the three sensors and signals for co ntrolling the motion of the crawler are developed as a combination of the output signals of the sensors.

17. A system according to any of claims 5 to 16, wherein the magnet casing is equipped with wheels to enable its movement across the location of the sensor array once said magnet has been placed on the pipe.

18. A system according to claim 17, wherein the magnet casing is preferably also equipped with a lever to facilitate its removal from the pipe.

19. A system according to any of claims 5 to 18, wherein the magnet is made of high intensity, rare earth material.

20. A control and/or tracking system for a pipeline crawler substantially as hereinbefore described with reference to the accompanying drawings.