WO2007020438A2

WO2007020438A2 - Pig for inspecting pipelines internally

Info

Publication number: WO2007020438A2
Application number: PCT/GB2006/003063
Authority: WO
Inventors: Rennie Hill; Peter Ward
Original assignee: Bj Services Company (Uk) Limited
Priority date: 2005-08-18
Filing date: 2006-08-17
Publication date: 2007-02-22
Also published as: WO2007020438A3; GB0516904D0; GB2429254A

Abstract

A pig comprises a pressure vessel (7) having an inner chamber, and at least one sensing element (3) . The sensing element comprises an elongate member (s) extending radially to the centre axis of the pressure vessel and being movable with respect thereto, sensing means (6) for sensing movement of any of the elements, the sensing means comprising an electronic sensor, the said electronic sensor being mounted within the pressure housing, and wherein there is no physical connection between the said at least one sensing element and the inner chamber of the pressure vessel.

Description

Pig for Inspecting Pipelines Internally

Field of the Invention

The present invention relates to a pig for inspecting pipelines internally, and in particular to pigs for assessing pipeline deformation.

Background of the Invention

Pigs are commonly used for cleaning the inside of pipelines, such pigs being relatively simple devices such as foam cylinders or balls that are pushed through the pipeline by fluid pressure. Other more specialised pigs are used for assessing the condition of pipelines.

One type of pig is known as a gauge pig and is commonly used for assessing pipelines for restrictions in the bore during the commissioning of a new pipeline. A gauge pig comprises a deformable metal disc, often fitted onto a cleaning pig. The disc diameter is fractionally smaller than the nominal diameter of the pipeline, typically 5%, so that any deformation greater man 5% will result in a permanent deformation of the disc. Whilst gauge pigs are almost universally used in the process of commissioning a pipeline, there are a number of drawbacks associated with them. For example, it can be assumed that if no deformation has occurred then there is no damage to the pipeline. However, where there is deformation, it is not possible to be certain that there is damage to the pipeline. Poor positioning of the metal disc can result in contact between the plate and the inner wall of the pipeline when the pig traverses a bend causing damage to the plate. The plate may also be damaged if it passes through a partially closed valve. Anodier problem associated with gauge pigs is that if a genuine restriction has been encountered, a gauge pig provides no information regarding the size of the restriction, its location in the pipeline, or its radial position. If the plate of a gauge pig is found to be deformed, it may be necessary to pass a calliper pig through the pipeline. Calliper pigs are used for checking the interior of pipelines for obstacles, bore changes and pipe wall deformation that may impede the movement of product through the pipeline or prevent the passage of subsequently used inspection equipment, or exceed industry guidelines relating to the deformation of the pipe and its effect on the integrity of the pipeline. Calliper pigs are typically driven by discs or cups forming part of the calliper and which engage with the pipe wall. A calliper pig comprises a body mounting a plurality of calliper arms, each being moveable independently of die others and each being provided with sensors to measure movement of the callipers. The distance travelled by the pig is measured by an odometer. A calliper pig would typically further comprise a pressure sealed housing (held at atmospheric pressure of 1 bar absolute internally against an external pressure of up to 400 bar) containing electronics, a battery and a recording system. Electric cables and connectors connect the sensors to the electronics in the sealed housing by at least one pressure sealed connector. By passing the pig through a pipeline and recording data from each calliper at regular intervals a map of surface irregularities is generated. As well as being used to assess new pipelines prior to commissioning, calliper pigs are also used to assess surface irregularities in pipelines that are in service.

The problem associated with calliper pigs is that they are expensive to produce and operate, the calliper arms, wheels and sensors are prone to damage, the pig is capable of travelling in only one direction without damaging the measuring system, the sensors are exposed to fluid in the pipeline which is typically at high pressure and may be corrosive or contain chemically active compounds which may damage or affect the sensors or the sensor cables. Furthermore, the pressure connectors connecting the external sensors to the pressure housing are expensive and are easily damaged.

US 2004/0134289 describes a pig that may be used as a gauge pig or a calliper pig. In its configuration as a calliper pig, spring levers each mount a magnet and a sensing switch is mounted on the pig in close proximity to each magnet. As the pig traverses a pipeline any deformations cause the spring levers and the magnets attached thereto to move with respect to the sensing switches. Electronic signals from the sensing switches are transmitted via leads to electronic recording equipment in a pressurised vessel.

It would therefore be desirable to provide an improved pig for internally inspecting pipelines.

Summary of the Invention

According to a first aspect of the invention there is provided a pig for internally inspecting pipelines as specified in Claim 1.

According to a second aspect of the invention there is provided a gauge pig as specified in Claim 20.

According to a third aspect of the invention there is provided a calliper pig as specified in Claim 21.

According to a fourth aspect of the invention there is provided a method of testing the gauge of a pipe line as specified in Claim 22.

According to a fifth aspect of the invention there is provided a method of obtaining information representative of the profile of the inner surface as specified in Claim 23.

The principal advantage provided by the invention is that all electronic components are housed ^■within the pressurised housing. There is no requirement for connecting leads extending between the high pressure environment of the fluid being transported through the pipe line and the environment within the pressurised vessel. Dispensing with the requirement for electrical cables, connectors and sensors in the high pressure environment is a significant advance in the art, as they are expensive and liable to failure. The gauge pig of the invention is significantly more useful than a conventional gauge pig, insofar as the approximate location of any obstruction in the pipe line can be established, false indications of obstructions can be identified and discounted, and the size of an obstruction can be established. In the case where the segments of the disc are made of a resilient material the pig may detect multiple obstructions. Further, where the pig is configured as a gauge pig with flexible disc segments, the pig can be passed through known constrictions which a gauge pig of the prior art would not generally pass, for example a section of smaller bore pipe. Whilst passing through the smaller bore pipe, the segments will indicate a constriction. However, this data can be removed or disregarded during analysis.

A calliper pig configured with disc segments of a resilient material dispenses with the requirement for mechanical moving parts and linkages which may be damaged, corroded or otherwise affected by the environment inside the pipeline. Also, such a pig may be moved in both directions in the pipeline, which is a significant advantage over calliper pigs of the prior art.

Brief Description of the Drawings

In the drawings, which illustrate preferred embodiments of the invention, and are by way of example:

Figure 1 is a schematic representation of a calliper pig of the prior art;

Figure 2a is a schematic representation of a first embodiment of a calliper pig according to the invention;

Figure 2b is a close-up view of the sensor of the embodiment illustrated in Figure 2a;

Figure 3 is a schematic representation of a second embodiment of a calliper pig according to the invention; Figure 4 is a schematic representation of a third embodiment of a calliper pig according to the invention;

Figure 5 is a schematic representation of a first embodiment of a gauge pig according to the invention;

Figure 6 is a schematic representation of a second embodiment of a gauge pig according to the invention; and

Figure 7 is a schematic representation of a fourth embodiment of a calliper pig.

Detailed Description of the Preferred Embodiments

Referring now to Figures 2a and 2b, there is shown the relevant components of a calliper assembly including a calliper arm 3, and a mount 4 located on a pressure housing 7. The calliper arm 3 is pivotally mounted at a pivot point 4a in the mount 4 and a magnet 5 is attached to the arm 3 at the pivot point. The arm 3 is biased outwardly in order that the end 3a of the arm 3 engages with the inner surface of a pipe 30 through which the pig is being passed. A sensor 6 of the type that detects magnetic field is located inside of the pressure housing and in proximity to the location of the magnet 5. Sensor 6 has a sensitive axis perpendicular to the face of the sensor such that the sensor gives a maximum output when the magnetic lines of flux from the magnet 5 are aligned in the direction of the sensitive axis.

The magnet 5 is mounted on the arm 3 in such a manner that its north south axis is perpendicular to the longitudinal axis of the pressure housing 7. The sensor 6 is located inside the pressure housing where it is mounted on the inside wall thereof and aligned with the magnet 5. The sensor 6 is of the type that detects changes in magnetic field in the X axis (see Figure 2b). Rotation of the magnet 5 produces a measurable and predictable change in output voltage of the magnetic flux sensor 6, which when calibrated generates an output representative of movement of the tip 3a of the arm 3 and hence variation in internal diameter of the pipe.

As the pig travels through a pipe line the end 3a of the arm 3 follows the inner surface of the pipe 30. Any variations in diameter of the pipe line result in the arm 3 pivoting about the pivot point 4a, which in turn causes changes in the orientation of the magnet relative to the sensitive axis of sensor 6 and hence changes in the output of sensor 6. The electronic signal from the sensor 6 is recorded either continuously or at discrete intervals, thereby permitting the internal diameter of the pipe line and any perturbations in that diameter to be mapped.

The pressure vessel 7 is manufactured from a non-magnetic material such as stainless steel so that there is no distortion or attenuation of the magnetic flux lines passing through the pressure vessel wall.

Referring now to Figure 3, the pig illustrated is similar to that shown in Figures 2a and 2b, and like numerals are therefore used to indicate like parts. In the pig of Figure 3, the magnet 5 is mounted on the end of an extension piece 3b. The main arm 3 and its extension piece 3b intersect at the pivot point 4a. The sensor 6 is mounted on the inside wall of the housing 7 and its sensitive axis is aligned with the north south axis of the magnet 5. The caliper arm 3 is connected to the extension piece 3b through the pivot point 4a such that movement of the caliper arm in one direction causes movement of the extension arm and the magnet mounted on the arm, in the opposite direction, the amount of movement being reduced in proportion to the respective lengths of the two arms. Movement of the caliper arm 3 due to variations of the inner surface of the pipeline 30 will result in movements of the magnet 5 towards and away from the sensor 6, changing the strength of the magnetic field detected and the magnitude of the electrical output from the sensor. Referring now to Figure 4, the mount 4 is attached to the outside of the pig body Ia rather than the outside of the pressure housing 7. The pig body Ia includes an opening Ib through which a rod 8 passes. One end of the rod 8 is attached to an arm 3d extending from the pivot point 4a, the other end of the rod being attached to one end of a magnet 9 which sits against an end wall 7a of the pressure housing 7. Aligned with the magnet 9 and on the inside of the pressure housing 7 is a sensor 10. Any perturbations in the inside wall of the pipe cause the arm 3 to pivot about pivot point 4a, thereby moving the magnet 9 in one or other of the directions indicated by the arrow Y. The relative lengths of lever 3 and arm 3d cause a large lever movement to be transformed into a small movement of the magnet 9. Movement of the magnet 9 outside of the pressure vessel is detected by the sensor 10 inside of the pressure vessel producing a change in electrical output of the sensor. Various orientations of magnet 9 and sensor 10 can be used to detect the movement but one arrangement which is preferred is for the north south axis of the magnet to be in the direction of travel of the magnet, the Y direction, and the sensitive axis of the sensor 10 to be perpendicular to the direction of travel of the magnet 9. The advantage of this arrangement is that the change in the magnetic flux cutting the sensor 10 in the direction of its sensitive axis is proportional to the movement of the magnet 9 in the Y direction. The electrical output of the sensor therefore follows a linear relationship to the movement of the magnet 9 and the caliper arm 3.

In Figure 4 the magnet 9 may be rotatably mounted in die pig, and the rod 8 attached to said magnet such that movement of the lever 3 generates rotation of the magnet, causing a detectable change in magnetic flux sensed by the flux sensor 10.

The different configurations illustrated in Figures 2 to 4 provide for different pig diameters. For small diameter pigs, the pressure vessel acts as the pig body and the calliper arms are mounted directly on the pressure vessel, whereas for larger diameter pigs the pressure vessel is located inside a pig body and the calliper arms are mounted on the pig body. Figures 2 to 4 show only single caliper arms for ease of illustration but multiple caliper arms will normally be used, each caliper independently mounted "with a magnet and associated sensor inside of the pressure vessel.

Typically, the calliper pig illustrated in Figures 2 to 4 would be equipped -with distance measuring wheels. Such measuring wheels do not form part of the invention and are well known to dαose skilled in the art, and as such are not described in detail in this application.

Referring now to Figure 5, there is shown a gauge pig. A gauge pig typically comprises a disc having a diameter five percent less than the internal diameter of the pipe. If the pipe encounters an obstruction greater than five percent of the internal pipe diameter the disc will hit the obstruction and be deformed permanently. The gauge pig illustrated in Figure 5 includes a pressure housing 7 upon one end of which is mounted a ferrous disc 20 by means of a disc support stud 22 and a disc clamp collar 23. The disc 20 is comprised of a centre element 21 and a plurality of disc segments 20a extending radially therefrom. Adjacent segments 20a are separated by a gap (not shown) so mat each segment 20a may be deflected independently of other segments 20a.

Inside the housing 7 at the end thereof mounting the disc 20, for each disc segment 20a there is provided a magnet 24 and a magnetic flux sensor 25. When the pig encounters an obstruction 27 greater than a threshold size, the distal end of one of the disc segments 20a engages with the said obstruction 27 causing the disc segment 20a to swing in the direction Z, the disc segment 20a bending at its intersection with the centre element 21. The magnet 24 generates a magnetic field and the disc segment lies within that field generating a magnetic flux. It is this magnetic flux that the sensor 25 detects. As the disc segment 20a moves away from the magnet 24 (as illustrated in Figure 5) a change in magnetic flux is caused and it is this change in magnetic flux that die sensor 25 detects. The change in magnetic flux sensed by the sensor 25 is representative of the radial distance moved by the tip of the disc segment 20a from the inside of the pipe wall. The disc 20 may be formed from a non-ferrous material, -with a ferrous element being attached to or located -within the disc segments 20a. The disc 20 may also be a continuous disc, as opposed to one formed from a number of segments 20a, or segments could be defined by lines of weakness formed in the disc.

As the pig travels along a pipe multiple measurements are recorded from each sensor, the measurements being separated by a short time interval. The said measurements include the position of each of the segments 20a. If one or more segments are deflected due to contact -with the pipe wall or another interfering object, the size of each deflection and the time at which the deflection occurred are recorded. Time markers are recorded for the beginning and end of each run, thereby allowing an approximate position of any obstruction to be estimated.

The gauge pig illustrated in Figure 6 differs from that shown in Figure 5 insofar as the disc segments 20a are made of a resilient material and the magnets 24 are each located in a disc segment 20a rather than in the pressure housing 7. The magnet 24 generates a magnetic field and the sensor 25 detects magnetic flux generated by the field. When an obstruction 27 is encountered the disc segment 20a flexes at its intersection with the centre element 21 and moves in the direction Z causing the magnet 24 to move away from the sensor 25 causing a change in magnetic flux which is sensed by the said sensor 25. Once the pig has moved beyond the obstruction 27 it returns to a substantially vertical orientation.

Figure 7 illustrates a calliper pig in which the arm consists of a plurality of disc segments 20a pivotally attached to and extending from a centre 21. The calliper pig illustrated in Figure 7 differs from the gauge pig illustrated in Figure 6 in that the disc segments 20a are slightly longer so that they engage continuously with the inner wall of the pipeline, any obstruction 27 causing a disc segment 20a to be deflected. The calliper pig of Figure 7 can be operated in both directions, allowing the pig to be reversed out of the pipe in the event of the pig encountering a severe obstacle. Standard calliper pigs can only be operated in one direction due to the configuration of calliper arms.

In the case of both the calliper pigs and gauge pigs as the pig travels along a pipe multiple measurements are recorded from each sensor, the measurements being separated by a short time interval. The longitudinal extent of any restriction can therefore be estimated.

The data recorded by a pig of the invention can be enhanced by the inclusion of a device that detects the rotational position of the disc relative to gravity, commonly referred to as a clock position sensor. By recording the output of such a sensor as a pig travels along a pipe die radial position of the restriction in the bore can be determined.

As mentioned above, approximate position information can be calculated by recording start and end times and time as the pig passes through the pipe. This position information can be enhanced by recording flow rate of the product in the line during the run and making corrections for short term changes in speed of the pig.

The pig of the invention provides for false hits to be identified so that they can be removed or discounted from a dataset False data can arise when the pig traverses a tight bend (when dynamics tend to push the pig off-centre). The recorded data can be associated with knowledge of the pipeline architecture and data identified as false can be deleted during subsequent analysis.

Claims

1. A pig comprising a pressure vessel having an inner chamber, and at least one sensing element located outside the pressure vessel and being movable with respect thereto, sensing means for sensing movement of any of the at least one sensing element, the sensing means comprising an electronic sensor, the said electronic sensor being mounted ^■within the pressure housing, and wherein there is no physical connection between the said at least one sensing element and the inner chamber of the pressure vessel.

2. A pig according to Claim 1, wherein the at least one sensing element is an elongate element.

3. A pig according to Claim 1 or 2, wherein the at least one sensing element extends radially of the centre axis of the pressure vessel.

4. A pig according to any preceding claim, wherein the sensing means includes a magnet.

5. A pig according to Claim 4, where the sensor is a magnetic flux detector and each of the sensing elements includes a material capable of causing a detectable change in magnetic flux upon movement of a sensing element with respect to the sensor.

6. A pig according to Claim 4, wherein the north south axis of the magnet is substantially aligned with the direction of movement of the magnet, and the sensitive axis of the sensor is substantially perpendicular to the said direction of movement of the magnet.

7. A pig according to Claim 4 or 5, wherein the at least one sensing element is ferrous.

8. A pig according to Claim 4 or 5, wherein the at least one sensing element is non-ferrous and a ferrous element is located in or attached to the said sensing element.

9. A pig according to Claim 4 to 8, wherein at least one magnet is located within the pressure vessel.

10. A pig according to Claim 9, wherein the or each magnet is proximal to the said magnetic flux sensor.

11. A pig according to any preceding claim, wherein the magnet is mounted in or on a sensing element.

12. A pig according to any preceding claim, wherein the at least one sensing element is pivotally mounted with respect to the pressure vessel

13. A pig according to Claim 12, wherein the at least one sensing element is pivotally mounted on die pressure vessel

14. A pig according to Claim 12, wherein die at least one sensing element is pivotally mounted on an outer body of die pig.

15. A pig according to Claim 12, wherein die at least one sensing element is pivotally mounted on a member adjacent one end of die pressure vessel.

16. A pig according to Claim 12, wherein the magnet is fixed to the sensing element.

17. A pig according to Claim 16, wherein the magnet is fixed to the sensing element at the point of pivotal attachment of the said element to the pressure vessel.

18. A pig according to any of Claims 12 to 16, wherein a lever projects from die sensing element and me magnet is attached to the free end of die lever.

19. A pig according to Claim 18, wherein die magnet is attached direcdy to the free end of die lever.

20. A pig according to Claim 18, wherein the magnet is attached to the free end of the lever by an intermediate connector.

21. A pig according to any preceding claim, wherein die said pig is a gauge pig.

22. A pig according to any preceding claim, wherein die said pig is a calliper pig.

23. A method of testing die gauge of a pipe comprising die steps of: i) introducing a gauge pig according to Claim 21 into die pipe; ϋ) driving die gauge pig tiirough die pipe; ϋi) recording substantially continuously any movement of die at least one sensing element as die pig passes tiirough the pipe.

24. A method of obtaining information representative of the profile of the inner surface comprising the steps of: i) introducing a calliper pig according to Claim 22 into the pipe; ii) driving the calliper pig through the pipe; and ϋi) recording substantially continuously any movement of the at least on sensing element as the pig passes through the pipe.

25. A pig substantially as shown in, and as described with reference to, the drawings.