WO2008041844A1

WO2008041844A1 - Method and apparatus for inspecting a pipeline

Info

Publication number: WO2008041844A1
Application number: PCT/NL2007/050476
Authority: WO
Inventors: Willem Frederik Masson; Robert Van Agthoven
Original assignee: Röntgen Technische Dienst B.V.
Priority date: 2006-10-02
Filing date: 2007-10-02
Publication date: 2008-04-10
Also published as: NL1032608C2; WO2008041844A8

Abstract

A method for inspecting a pipeline (1), comprising: a. introducing a transport unit (16) with a sealing element (28) into the pipeline, such that the sealing element forms a fluid sealing with an inner wall (22) of the pipeline; b. introducing a measuring unit (18) into the pipeline for inspecting the pipeline; c. mechanically interconnecting the measuring unit and the transport unit; d. creating a fluid pressure difference in the pipeline between the two sides of the sealing element, so that as a result of the pressure difference the transport unit with the measuring unit is transported in a first direction (60) through the pipeline; and e. inspecting the wall of the pipeline with the measuring unit.

Description

Title: Method and apparatus for inspecting a pipeline.

This invention relates to a method for inspecting a pipeline, comprising a. introducing a transport unit with a sealing element into the pipeline, such that the sealing element forms a fluid sealing with an inner wall of the pipeline; b. introducing a measuring unit into the pipeline for inspecting the pipeline; c. mechanically interconnecting the measuring unit and the transport unit; d. creating a fluid pressure difference in the pipeline between the two sides of the sealing element, so that as a result of the pressure difference the transport unit with the measuring unit is transported in a first direction through the pipeline; and e. inspecting the wall of the pipeline with the measuring unit. Further, the invention relates to an apparatus for inspecting a wall of a pipeline, at least provided with a measuring unit and a transport unit which are mechanically interconnected and a cable which is connected with the transport unit and/or the measuring unit, wherein the measuring unit is arranged for carrying out measurements on the wall of the pipeline and wherein the transport unit is provided with a sealing element for, in use, forming a fluid sealing with an inner wall of the pipeline, so that, in use, the measuring unit and the transport unit can be transported through the pipeline by creating a fluid pressure difference between the two sides of the sealing element.

Such a method and apparatus are known per se. The method and apparatus known per se are used in particular for inspecting pipelines having a diameter that is less than 16 inches. In the case of pipelines having a greater diameter, the transport unit is typically provided with a motor drive and wheels or caterpillar treads to transport the transport unit and the measuring unit coupled thereto through the pipe for the purpose of carrying out the inspection. In the case of pipelines of smaller diameter, it is more difficult to make a sufficiently small motor-driven transport unit. That is why in that case it is elected to provide the transport unit with the sealing element, and then a fluid pressure difference is created on opposite sides of the sealing element, so that as a result of the pressure difference the transport unit with the measuring unit can be transported through the pipeline. The pressure difference can for instance be created by supplying a pressurized fluid to the pipeline on a first side of the sealing element. This fluid can for instance consist of water. On the second side of the sealing element, situated opposite the first side, the pipeline may already be filled with, for instance, water, or oil. By opening a control valve on the second side, the liquid between the transport unit and measuring unit and the second side can be discharged in a controlled manner. As a result of the removal of this volume and the higher pressure behind the transport unit, the transport unit moves in the direction of the second side. When the transport unit has reached the end of the pipeline, the control valve is closed and on this side a fluid pump is connected. Then, with the fluid pump, water is supplied under pressure to the pipeline on a side that lies on the second side of the sealing element, so that again a pressure difference is created across the sealing element, albeit that presently the pressure on the second side of the sealing element is greater than the pressure on the first side of the sealing element. To this end, using a control valve, liquid is discharged on the first side in a controlled manner. As a result, the transport unit with the measuring unit will move back in the pipeline to a position where it has originally been placed in the pipeline. Thus, using the measuring unit, the pipeline can be inspected over a particular path. Inspection can be carried out during the forward and/or backward movement. Also, the transport unit may each time be moved forward and/or backward over a particular path, allowing inspection to be done also when the transport unit stands still. After having been moved back entirely, the apparatus can be taken out of the pipeline in a known manner, after which the inspection is completed.

The above-mentioned method known per se is for instance used in the case of pipelines which run from an oil rig to the bottom of the sea and, via a collecting pipeline, are for instance connected to another rig.

Communication between the two rigs enables control of the liquid flow.

A pipeline running from the rig to the collecting pipeline is provided with a non-return valve at the point where it is connected to the collecting pipeline. This non-return valve has as a property that a fluid such as water, air or oil can flow through the valve in one direction only. In this example, this is in the direction from the rig to the collecting pipeline. What is thus achieved is that the fluid, such as oil, flowing through the collecting pipeline cannot flow back into the pipeline that is connected with the rig. The fluid in question flowing from the rig to the collecting pipeline is oil in this example.

A drawback of the above-mentioned method and apparatus is that they cannot be applied in the case of a pipeline that is provided with such a non-return valve, since due to the presence of the non-return valve in the pipeline, the fluid can flow through the pipeline in one direction only, viz. in the direction from the rig to the collecting pipeline. Due to the non-return valve, it is not possible to have a fluid flow in an opposite direction. This makes it impossible to create such a pressure difference across the sealing element that the transport unit with the measuring unit is going to move back to the position where it was originally placed in the pipeline (in this example the position at or on the rig).

The invention contemplates providing a solution to the problem mentioned. To that end, the method according to the invention is characterized in that the method furthermore comprises the following steps: f. removing the fluid sealing between the transport unit and the inner wall of the pipeline; and g. after step f., retracting the transport unit and the measuring unit in a second direction of the pipeline by pulling a cable which is connected with the transport unit and/or the measuring unit, with the second direction being opposite to the first direction. Removing the fluid sealing allows the transport unit and the measuring unit to be retracted on the cable. The fluid that is present on either side of the sealing element can, so to say, pass the sealing element during the retraction of the transport unit and the measuring unit with the cable.

Preferably, a command for removing the sealing is supplied to the transport unit remotely, more preferably from an outside of the pipeline.

Preferably, it holds here that in step d. the sealing is obtained with a swelling element with a variable volume, while in step a. the volume is such that the swelling element forms the sealing with the inner wall of the pipeline and that in step f. the volume of the swelling element decreases so that the sealing is removed. The swelling element can be designed in various ways. Thus, it is for instance possible that the swelling element is provided with an inflatable body and that in step f. the inflatable body deflates at least for a part, so that the sealing is removed.

Preferably, it holds here that after carrying out step f., the sealing element is situated in the pipeline with clearance relative to the inner wall.

This facilitates retraction further, since retraction of the transport unit and the measuring unit with the cable will then entail, at least substantially, no friction between the sealing element and the inner wall of the pipeline.

In particular, it holds that the measuring unit and the transport unit are introduced into the pipeline via a first opening of the pipeline.

In particular, it holds here furthermore that in step d. the cable is transported along with the transport unit and the measuring unit while the cable reaches and continues to reach to near a first end of the pipeline or continues to reach through a second opening of the pipeline to outside the pipeline. According to a practical further elaboration, it holds that the cable is a signal cable for transporting measuring results of the measuring unit and is reinforced to enable retraction of the transport unit and the measuring unit. Furthermore, it holds that via the cable the measuring unit is provided with electrical energy.

Preferably, it holds furthermore that via the cable an instruction is given, in response to which the sealing is removed.

The invention will presently be further elucidated with reference to the drawing. In the drawing:

Fig. 1 shows a rig and a collecting pipeline which are connected with each other through a pipeline to be inspected;

Fig. 2 shows a part of Fig. 1 during the practice of the method;

Fig. 3 shows a part of Fig. 1 during the practice of the method; Fig. 4 shows a part of Fig. 1 during the practice of the method;

Fig. 5 shows a part of Fig. 1 during the practice of the method;

Fig. 6 shows a part of Fig. 1 during the practice of the method;

Fig. 7a shows an elevational view of the transport unit in the direction of the arrow P of Fig. 2; and Fig. 7b shows an elevational view of the transport unit in the direction of the arrow P of Fig. 6.

In Fig. 1, reference numeral 1 designates a pipeline to be inspected. The pipeline 1 extends from an oil rig 2 to a collecting pipeline 4, which in this example rests on the bottom of the sea. A first end 3 of the pipeline is situated at the rig.

Adjacent a second end 6 of the pipeline 1, it is provided with a non-return valve 8 as well as a stop valve 10.

In use, oil 12 is fed from the oil rig 2 into the pipeline 1. The oil 12 flows through the non-return valve and via the stop valve, which is open, into the collecting pipeline 4. Connected to the collecting pipeline 4 in this example is further a second pipeline 1', which is likewise provided with a non-return valve 8' and a stop valve 10'. Via this pipeline I¹, in this example, oil 12' is fed into the collecting pipeline 4. By virtue of the use of the non-return valve 8, this oil 12' cannot flow into the pipeline 1, for instance when the pipeline 1 is not in use.

Presently, it will be explained in more detail in what way the pipeline 1 can be inspected. Inspection is for instance carried out to see if there aren't any thin spots present in a wall of the pipeline 1, for instance as a result of corrosion. The pipeline is inspected with an apparatus 14, which is shown in Fig. 2. The apparatus 14 is provided with a transport unit 16 and a measuring unit 18. The transport unit 16 in this example is provided with small centering wheels 20, allowing easy riding in the pipeline. In Fig. 7a, 7b and in Fig. 2 it can be seen that the wheels 20, in use, abut against an inner wall 22 of the wall 24 of the pipeline. The measuring unit 18 is likewise provided with such wheels 20. The transport unit 16 is provided with a rigid frame 26 from which the wheels 20 are suspended. Arranged around the rigid frame 26 is a sealing element 28. This sealing element 28 is provided with a swelling element 30. The swelling element has a controllable variable volume. To this end, the swelling element is provided with an inflatable body 32 for obtaining the controllable variable volume. In this example, the sealing element, the swelling element 30 and the inflatable body 32 are one and the same element. However, this is not requisite, as will be briefly explained hereinafter.

The inflatable body 32 is further provided with an operable valve 34. As can be seen in Fig. 2, the transport unit 16 and the measuring unit

18 are mechanically interconnected through a coupling, in this example designated with reference number 36, such as a flexible tube, for instance made of rubber, or a mechanical coupling. The apparatus is further provided with a cable 38 which, in this example, is connected with the measuring unit 18. The method for inspecting the pipeline can for instance be carried out as follows. It is noted here that in Figs. 2-6 the oil rig has been omitted for simplicity.

First of all, the measuring unit and the transport unit are introduced into the pipeline 1 via a first opening 42. The measuring unit and the transport unit in this example have been interconnected beforehand using the coupling 36. However, this connection may also be effected in the pipeline. The inflatable body has not yet been pumped up and thus has a relatively small volume. This situation is shown in Fig. 7a. Fig. 7a shows how the transport unit 16 is situated in the pipeline 1. It is clear to see that the inflatable body 32 is still clear of the inner wall 22 of the wall 24. Thereupon, in this example, the cable 38 is temporarily detached from the measuring unit 18. To this end, the cable 38 may be connected with the measuring unit 18 through an electrical connector 44. Thereupon the cable 38 is inserted through a second opening 46 of a sealing 48, and the cable is connected with the measuring unit 18 again. This lead-through may also be done prior to the introduction of the transport unit and the measuring unit. Also, via the valve 34, for instance a fluid such as air is pumped into the inflatable body 32. As a result, the volume of the inflatable body will increase until the inflatable body comes to lie against the inner wall 22. This is shown in Fig. 7b and in Fig. 3. Thereupon, a first opening 42 is closed with the sealing 48. This is a controllable sealing which prevents leakage of water under pressure to the atmosphere. The cable thus reaches via the first opening 42 and via the second opening 46 to outside the pipeline 1. The cable in this example is a reinforced signal cable for transporting measuring results of the measuring unit. Also, via the cable the measuring unit is provided with electrical energy. In this example, the cable is coupled with a computer 50 for recording the measuring data obtained with the aid of the measuring unit. To that end, the measuring unit may for instance be provided with ultrasonic probes known per se, or other testing means and the like for scanning the pipeline. In this example, the computer 50 further provides the electrical energy for the measuring unit.

Presently, following the situation as shown in Fig. 3, a pump 52 is connected to the pipeline (Fig. 4). Using the pump 52, in this example, a liquid 53 such as water is pumped into the pipeline. Any air between the sealing 54 and 48 is bled via an air relief valve A until only water is present between the sealing 54 and 48. It is noted here that the second opening 46 forms a fluid sealing with the cable 38. It is further noted that the inflated body 32 abuts against the inner wall 22 of the wall 24 and there forms a fluid sealing 54. When the water under pressure is supplied to the pipeline, this has as a consequence that pressure is built up on a first side 56 of the sealing 54 in the pipeline. As a result, a pressure difference is created across the sealing 54. In the second side 58 of the pipeline, situated opposite the first side 56, there is also water or oil. As a result of the pressure difference across the sealing 54, the transport unit is going to transport in a first direction, indicated by the arrow 60. Doing so, the transport unit 16 drags the measuring unit 18 behind it. During transport in the direction of the arrow 60, the liquid possibly present in the second side 58 of the pipeline will flow via the valve 8 and the opened valve 10 into the collecting pipeline 4. With the aid of the measuring unit 18, the inspection of the inner wall can be carried out. During inspection, the measuring unit can be halted by interrupting the water supply. To that end, there is a control valve B between pump 52 and the pipeline 1. The measuring results are supplied via the cable to the computer 50. Thus, the entire pipeline 1 can be inspected. Having arrived at the non-return valve 8, the transport unit 16 stops. To this end, the traveled path of the transport unit and the measuring unit is measured through an odometer C (Fig. 5). Then the supply of water under pressure via the pump 52 is stopped. In this example, the valve 34 is electrically connected with the cable 38. Accordingly, in this example, the electrical connection of the cable extends through the flexible coupling 36. The electrical connection, at least a part 64 thereof, is shown in Figs. 7a and 7b.

An operator can presently operate the computer 50 to send a command signal through the cable, in response to which the valve 34 is opened. The command for removing the sealing 54 is thus supplied to the transport unit 16 remotely, here from an outside of the pipeline. The result is that the inflatable body 32 will deflate, at least for a part. The air escapes from this body because the pressure in the swelling element is higher than in the pipeline 1. As a result, the air can easily escape via the valve 34.

When the inflatable body 32 has deflated at least for a part, this has as an effect that the fluid sealing 54 is removed (Fig. 6). As a result, the liquid pressure in front of and behind the transport unit and the measuring unit will equalize. Through valve A the liquid pressure can be lowered or even removed. The non-return valve 8 and possibly the stop valve 10 ensure that no liquid can flow back into the pipeline 1. Thereupon the transport unit and the measuring unit are retracted in a second direction 65, which is opposite to the first direction 60, by pulling the cable which is connected with the transport unit and/or with the measuring unit and in this example is connected directly to the measuring unit. For the purpose of pulling the cable, the sealing 48 can be removed or relaxed. When the sealing 48 has been removed, the whole apparatus can be pulled out of the pipeline. Upon retraction, the water present in the first part 56 can flow freely around the inflatable body 32 to the second part 58. In this example, it holds furthermore that the sealing element, when it has partially deflated, is situated in the pipeline with clearance. Thus, during retraction, no relevant friction between the inflatable body 32 and the inner wall of the pipeline is generated. It is also possible to perform measurements during the retraction of the measuring unit. Also, during actual inspection, the measuring unit can be halted at a particular zone. So, inspection can be carried out both during the forward and/or the backward movement. Also, inspection may thus be carried out without the measuring unit being stopped. The invention is not limited in any way to the embodiments outlined above.

Thus, the inflatable body may also be inflated using a liquid instead of a gas such as air. It is also conceivable that the swelling element 30 is provided not with an inflatable body, but with a body that swells under the influence of for instance heating. In that case, the swelling element 30 could for instance be provided with a heating element that obtains energy via the cable 38. Thus, by heating the swelling element, it swells so that the fluid sealing 54 is created, and by allowing the sealing element to cool again, which will happen when electrical energy is no longer supplied to the heating element, the volume of the swelling element will decrease, so that the fluid sealing is removed.

The swelling element may further be provided with at least one stretchable rubber ring which in use forms the actual sealing. This at least one stretchable rubber ring can for instance be arranged around the swelling element. The swelling element and the at least one stretchable ring in combination then form the sealing element 28. In this example, the cable 38 is used for transporting measuring results, for transporting energy, for transporting an instruction in response to which the sealing is removed, and for the actual retraction of the assembly of measuring unit and transport unit. Naturally, the actual retraction can also be carried out with a separate cable, such as a steel cable. In this example, the instruction for operating the valve is passed via an electric command through the cable. However, the instruction could also be given mechanically, for instance in that the valve is connected with a cable which can be given a pull for opening the valve. Naturally, this cable then also extends from the valve through the opening 46 of the sealing, all analogously to the cable 38, as discussed. Using the cable with which the valve is opened, also the measuring unit and the transport unit may then be retracted from the pipeline. This may also be the cable 38 again. The cable 38 may also comprise a glass fiber for the transport, i.e. optically, of information from and to the measuring unit and/or the valve.

In this example, the volume of the swelling element was raised after the transport unit was placed in the pipeline. However, this may also be done before the transport unit is placed in the pipeline. The swelling element will then have to be pushed into the pipeline with some force. Such variants are each understood to fall within the framework of the invention.

Claims

1. A method for inspecting a pipeline, comprising: a. introducing a transport unit with a sealing element into the pipeline, such that the sealing element forms a fluid sealing with an inner wall of the pipeline; b. introducing a measuring unit into the pipeline for inspecting the pipeline; c. mechanically interconnecting the measuring unit and the transport unit; d. creating a fluid pressure difference in the pipeline between the two sides of the sealing element, so that as a result of the pressure difference the transport unit with the measuring unit is transported in a first direction through the pipeline; and e. inspecting the wall of the pipeline with the measuring unit; characterized in that the method furthermore comprises the following steps: f. removing the fluid sealing between the sealing element and the inner wall of the pipeline; and g. after step £, retracting the transport unit and the measuring unit in a second direction of the pipeline by pulling a cable which is connected with the transport unit and/or the measuring unit, with the second direction being opposite to the first direction.

2. A method according to claim 1, wherein a command for removing the sealing is supplied to the transport unit remotely.

3. A method according to claim 1 or 2, wherein a command for removing the sealing is supplied to the transport unit from an outside of the pipeline.

4. A method according to any one of claims 1-3, characterized in that in step d. the sealing is obtained with a swelling element with a variable volume, while in step a. the volume is such that the swelling element forms the sealing with the inner wall of the pipeline and that in step f. the volume of the swelling element decreases so that the sealing is removed.

5. A method according to claim 4, characterized in that the swelling element is provided with an inflatable body and that in step f. the inflatable body deflates at least for a part, so that the sealing is removed.

6. A method according to claim 5, characterized in that in step a. the inflatable element is pumped up for obtaining the sealing.

7. A method according to any one of the preceding claims 4-6, characterized in that after carrying out step f. the sealing element is situated in the pipeline with clearance relative to the inner wall.

8. A method according to any one of the preceding claims, characterized in that the measuring unit and the transport unit are introduced into the pipeline via a first opening of the pipeline.

9. A method according to any one of the preceding claims, characterized in that in step d. the cable is transported along with the transport unit and the measuring unit, while the cable reaches and continues to reach to near a first end of the pipeline or through a second opening of the pipeline continues to reach to outside the pipeline.

10. A method according to claims 8 and 9, characterized in that the first opening is equal to the second opening.

11. A method according to claims 9 and 10, characterized in that the first and/or second opening is/are situated at the first end of the pipeline.

12. A method according to any one of the preceding claims, characterized in that the cable is a signal cable for transporting measuring results of the measuring unit.

13. A method according to any one of the preceding claims, characterized in that via the cable an instruction is given in response to which the sealing is removed.

14. A method according to claim 13, wherein the instruction is given by giving the cable at least one pull.

15. A method according to claim 13, wherein the instruction is given by transporting an electrical or optical command through the cable to the transport unit.

16. A method according to any one of the preceding claims, characterized in that via the cable the measuring unit is provided with electrical energy.

17. A method according to any one of the preceding claims, characterized in that step c. is carried out prior to steps a. and b.

18. A method according to any one of the preceding claims, wherein the pipeline to be inspected is provided with a non-return valve which is so positioned in the pipeline that during transport of the transport unit in step d. the transport unit with the measuring unit is transported in the direction of the non-return valve and the fluid partly causing the pressure difference flows through the non-return valve, and that in step g. the transport unit with the measuring unit is retracted in a direction directed away from the non-return valve .

19. A method according to claim 9, characterized in that in step f. the transport unit and the measuring unit, by pulling the cable, are transported in the direction of the first end of the pipeline and/or in the direction of the first and/or second opening.

20. A method according to any one of the preceding claims, characterized in that step f. is carried out after step e.

21. A method according to any one of the preceding claims, characterized in that the pressure difference is created by pumping a fluid into the pipeline on a side of the sealing.

22. A method according to any one of the preceding claims, characterized in that the fluid pressure difference is created with a liquid such as water.

23. A method according to claim 9, characterized in that the first end of the pipeline is situated at an oil rig and a second end of the pipeline is situated under water.

24. A method according to claims 18 and 23, characterized in that the non-return valve is situated near the second end.

25. An apparatus for inspecting a wall of a pipeline, at least provided with a measuring unit and a transport unit which are mechanically interconnected and a cable which is connected with the transport unit and/or the measuring unit, wherein the measuring unit is arranged for carrying out measurements on the wall of the pipeline and wherein the transport unit is provided with a sealing element for, in use, forming a fluid sealing with an inner wall of the pipeline, so that, in use, the measuring unit and the transport unit can be transported through the pipeline by creating a fluid pressure difference between the two sides of the sealing element, characterized in that the transport unit is arranged such that the sealing obtained with the sealing element can be removed when the transport unit is in the pipeline.

26. An apparatus according to claim 25, characterized in that the apparatus is arranged such that a command for removing the sealing can be supplied to the transport unit remotely.

27. An apparatus according to claim 25 or 26, characterized in that the apparatus is arranged such that a command for removing the sealing can be supplied to the transport unit from an outside of the pipeline.

28. An apparatus according to any one of claims 25-27, characterized in that the sealing element is provided with a swelling element with a controllable variable volume, while the swelling element is arranged, in use, in a swollen condition with a relatively large volume, to form the sealing with the inner side of the pipeline and, with a relatively small volume, to remove the sealing.

29. An apparatus according to claim 28, characterized in that the swelling element is provided with an inflatable body for obtaining the controllable variable volume.

30. An apparatus according to claim 29, characterized in that the inflatable body is provided with an operable valve for allowing the inflatable body, when pumped up, to deflate, so that as a result of deflation the relatively large volume decreases to the relatively small volume.

31. An apparatus according to any one of claims 25-30, characterized in that, in use, at the relatively small volume, the sealing element is situated in the pipeline with clearance relative to the inner wall.

32. An apparatus according to any one of the preceding claims 25-31, characterized in that the cable is a signal cable for transporting measuring results of the measuring unit.

33. An apparatus according to any one of the preceding claims 25-32, characterized in that the apparatus is arranged such that via the cable an instruction can be given in response to which the sealing is removed.

34. An apparatus according to claim 33, characterized in that the apparatus is arranged such that the instruction can be given by giving the cable at least one pull.

35. An apparatus according to claim 33, characterized in that the apparatus is arranged such that the instruction can be given by transporting an electrical or optical command through the cable to the transport unit.

36. An apparatus according to any one of claims 25-35, characterized in that the apparatus is arranged to provide the measuring unit with electrical energy via the cable.

37. An apparatus according to any one of the preceding claims 25-36, characterized in that the transport unit and the measuring unit each comprise a carriage.

38. An apparatus according to any one of the preceding claims 25-36, characterized in that the measuring unit is arranged on the transport unit, with the transport unit comprising a carriage.

39. An assembly of a pipeline and an apparatus according to any one of claims 25-38.

40. An assembly according to claim 39, characterized in that the pipeline is provided with a non- return valve.

41. An assembly according to claim 39 or 40, provided with the apparatus according to claim 29, characterized in that, at the relatively small volume, the swelling element is situated in the pipeline with clearance relative to the inner wall thereof.