WO2008133522A1

WO2008133522A1 - Clamp device for sealing a pipe defect

Info

Publication number: WO2008133522A1
Application number: PCT/NO2008/000120
Authority: WO
Inventors: Jone Mellemstrand; Harald Syse
Original assignee: Tdw Offshore Services As
Priority date: 2007-04-25
Filing date: 2008-04-02
Publication date: 2008-11-06
Also published as: NO20072141L; NO330722B1

Abstract

The present invention regards a clamp device for arrangement in connection with a pipe (1), comprising an outer clamp structure (10) for arrangement around a pipe (1) at least one pressure piston (12) and at least one packer element (13, 17) arranged between the pressure piston (12) and the outer clamp structure (10) or another pressure piston (12), arranged movable relative the outer clamp structure (10). Where the pressure piston (12) comprises a high pressure surface (20) exposed to a fluid at a higher pressure around the clamp device and at least one packer pressure surface (26, 27) in abutments against the packer element (13, 17) where the high pressure surface (20) has a larger area than the packer pressure surfaces (26, 27).

Description

CLAMP DEVICE FOR SEALING A PIPE DEFECT

The present invention relates to a clamp device for arrangement in relation with a pipe, for instance for sealing a hole through the pipe wall from the surrounding fluids around the pipe. There are laid meters of pipes both on land and in water. In water may either be in the sea or in lakes. These pipes may be positioned above the ground or fully or partly buried or a combination. Pipes may stretch a long distance or be relative short. These pipes will sometimes experience leakages through the wall of the pipeline, with the associated need to repair this leakage. Repairing of the leakage may be done in several manners by for instance plugging off the pipeline and thereafter replacing the part of the pipeline with the leakage, with a new pipe section. Another possibility is to find the leakage and thereafter repair the leakage by for instance welding another part onto the pipe or weld the leakage shut. However, such known solutions may not be favorable to use or even possible to use due to the position of the pipe and or the content of the pipe. There is therefore a need for a system to repair a pipe without having to block the flow of fluid through the pipe and without having to perform activities with the pipe as such.

One possible solution to this is to provide an outer clamp which is clamped around the pipeline to stop the leakage through the wall of the pipe. However, there is an additional element of the pipe experiencing a variety of pressures within the pipe over time, and thereby a variety of pressure differences across an outer clamp. There is a need to provide a solution which will provide sufficient sealing of a leakage in a pipe, where the solution gives sufficient sealing for varying pressures differences between the inside and the outside of the pipe. An aim with the present invention is therefore to provide a clamp system, which provides sufficient sealing off a leakage through a pipewall from a surrounding fluid, even with varying pressure differentials across the clamp system.

This aim is achieved with a clamp system as defined in the following claims.

According to the invention there is provided a clamp device for arrangement in connection with a pipe. This clamp device comprises an outer clamp structure for arrangement around a pipe. This outer clamp structure comprises at least two parts connected to each other around the pipe when the clamp device is positioned for sealing off a leakage in the wall of the pipe from the surrounding fluids at the outside of the pipe. The outer clamp structure may comprise one at least partly annular shaped element or more than two elements. In case of several elements they may be hinged to each other and be open between two elements for positioning around the pipe. If the outer clamp structure comprises one annular element, this element may be surrounding the pipe or only partly surrounding the pipe. There are several ways this may be done and a skilled person will have the knowledge to provide a method, the important element is that the connection is secured so that the outer clamp structure is kept in a position relative the pipe.

According to the invention the clamp device comprises at least one pressure piston and at least one packer element arranged between the pressure piston and pressure surface of another element, which other element may be the outer clamp structure or another pressure piston. The pressure piston and packer element is arranged movable relative to the outer clamp structure. At least one of the packer elements is arranged to be in abutment against an outer wall of a pipe when the clamp device is installed in relation to the pipe and is in an active state. A pressure piston may comprise several segments connected to each other so that they together form one pressure piston. In a similar manner the packer element may also comprise several packer segments. This segmentation may give an easier arrangement of the pressure piston and packer element in relation to the pipe for instance around the pipe in the case the invention is used with a configuration where at least one of the packer element is arranged abutting a whole circumference of the pipeline. One may also envisage a clamp device according to the invention where a packer element is not arranged around the pipe but just around a hole in the pipe.

A pressure piston comprises a high pressure surface exposed to a fluid at a higher pressure around the clamp device and at least one packer pressure surface. The packer pressure surface will be a surface of the pressure piston which surface or surfaces is in abutments against the at least one packer element. According to the invention the high pressure surface of the pressure piston, has a larger area than an area of the packer pressure surface which is in abutment against at least one packer element positioned relatively between the pressure piston and the outer clamp structure or another pressure piston. The high pressure surface is normally arranged on an relative opposite side of a pressure piston in relation to a packer pressure surface of the same pressure piston.

The clamp device according to the invention also comprises a pre-stressing system pulling the pressure piston towards the packer element with a given force, to preload the at least one packer element thereby achieving a sealing contact between the packer element and an outer wall of the pipe, the pressure piston and the outer clamp structure, when there are no or only small pressure differences across the clamp device, for instance just when the clamp device is sat. The pre-stressing system prevents the pressure piston to move in one direction but allows the pressure piston to move in the opposite direction, where a movement of the pressure piston in this allowable direction will increase the pressure in the at least one packer element. This also gives that when there is a pressure difference across the clamp device, i.e. pressure differences between the fluid at the outside of the pipe and the fluid inside the pipe, this pressure will assist in pressing the pressure piston towards the packer element and thereby add pressure to the packer element to achieve a good sealing between the clamp device and the wall of the pipeline.

The fluid at a higher pressure should in this application be understood to be the fluid which should be prevented from leaking through the hole in the wall of the pipe. This may be the fluid at the outside of the pipe, which if this fluid has a higher pressure than the fluid within the pipe, will leak into the pipe and mix with the fluid in the pipe. One example of this may be pipelines laid in water at great depths. The other possibility is that this higher pressure fluid is the fluid at the inside of the pipe which fluid will leak out of the pipe if the pressure in the fluid around the pipe has a lower pressure. In this last instance the high pressure surface of the pressure piston is exposed to the fluid within the pipe through the hole in the wall of the pipe.

The pre-stressing system may have several configurations, where the elements in the pre-stressing system together with the pressure piston and the outer clamp structure or another pressure piston, will add pressure to the at least one packer element, which of at least one of these in an installed state of the clamp device, is abutting an outer wall of a pipeline. With the pre-stressing system one may set a minimum desired pressure in the at least one packer element. The pre-stressing system may comprise a bolt connected to the pressure piston, which bolt is guided through the outer clamp structure with a tightening arrangement in connection with the bolt on an outer surface of the outer clamp structure, so that when tightening the pre-stressing system the pressure piston is pulled towards the outer clamp structure and thereby pressing the packer element. The pre-stressing system will also be so arranged that it does not prevent the pressure piston to be pushed further towards the packer element. Another possibility is a pre-stressing system comprising threads arranged on the outer clamp structure and a cooperating locking element in abutment against the pressure piston, where the locking element by movement up the threads will press the pressure piston towards the outer clamp structure and prevent the pressure piston from moving in the opposite direction but allowing further movement in a direction towards the packer element. One may also have a pre-stressing system acting between two pressure pistons keeping them at a given maximum distance from each other, allowing the pressure pistons to move further towards each other. Yet another possibility is to have a pre-stressing system with a snap-in solution possibly arranged in the surfaces of the outer clamp structure and the pressure piston, with a tool moving the pressure piston when the clamp device is installed to a position where the elements interact to a snap-in position. Another possibility is to provide a pre-stressing system which is hydraulically operated or to have a combination of features mentioned above.

According to one aspect the outer clamp structure forms a clamp chamber between the outer clamp structure and an outer wall of the pipe. This clamp chamber may run around the circumference of the pipe, and in such an embodiment the pressure piston is formed as an annular pressure piston and the at least one packer element as an annular packer element. These may of course be segmented. There may be arranged one annular pressure piston on the two sides of the clamp chamber seen in an axial direction of the clamp device. One should understand that an axial direction of the clamp device is mainly parallel with a longitudinal axis of a pipe whereto the clamp device should be fastened. In this instance the pressure surface of the pressure piston is exposed to a fluid within the pipeline, and the clamp device provides a good sealing preventing the fluid within the pipe to leak out to the fluid outside the pipe. The clamp chamber may also have a configuration where is does not run around the circumference.

According to another aspect of the invention the pressure piston and packer element are formed as annular elements, and arranged with a pressure surface of the pressure piston facing away from the clamp structure in a direction mainly parallel with a longitudinal axis of the clamp device, i.e. mainly parallel to a longitudinal axis of the pipe whereto the clamp structure should be fastened. There is arranged one set of a pressure piston and at least on packer element on each ends of the clamp device seen in a longitudinal direction. In this instance the clamp device gives a good sealing preventing fluid outside the pipe from entering the pipe through the hole in the wall of the pipe, which hole will be situated between two packer elements each with a pressure piston facing opposite directions.

According to an aspect of the invention the pressure piston is arranged relative to the outer clamp structure together with the packer element and one seal elements in the surfaced between the pressure piston and the outer clamp structure so that the pressure piston together with the outer clamp structure, form one back chamber between them. According to another aspect there is arranged two annular packer element between the pressure piston and the outer clamp structure forming a back chamber between them. These back chambers may be connected with a vent line for venting fluid in the back chamber towards a low pressure side of the clamp device, when the pressure piston is moved relative the clamp structure. The low pressure side of the clamp device would be the side of the clamp device opposite the side with the fluid acting on the pressure surface of the pressure piston.

According to an aspect of the invention the pressure piston is arranged relative the outer clamp structure so that the high pressure surface is forming a side of the clamp chamber formed within the outer clamp structure. According to another aspect the pressure piston is arranged relative to the outer clamp structure so that the high pressure surface is facing a fluid surrounding the clamp device and a pipe. The pressure pistons in both embodiments are arranged to be movable in a direction mainly parallel with a longitudinal axis of a pipe whereto the clamp device should be positioned. One may also have a configuration of the clamp device according to the invention with one pressure piston and this pressure piston is moved in a mainly radial direction.

According to an aspect of the invention the clamp device may be formed so that the surfaces of the outer clamp structure and the pressure piston in abutment against the packer element which is abutting an outer wall of the pipe, have an orientation in a mainly radial direction. Another possibility is to form the element so that these surfaces in a cross section together form a more V-shape with the open end of the V facing the outer wall of the pipe. There is also the possibility of forming the surfaces with changing angles from a radial outer point to a radial inner point of the surface. The surface of the pressure piston and the surface of the outer clamp structure may also be formed in a similar or different manner, thereby giving the desired behavior of the packer element in abutment against the outer wall of a pipe in an active state of the clamp device.

According to an aspect of the invention the clamp device may also be formed with two annular pressure pistons and at least one packer element on each side of a central clamp chamber. In such a configuration a first pressure piston would be positioned with a pressure surface facing into the clamp chamber and exposed to the fluid within the pipe and a second pressure piston would be positioned with a pressure surface facing away from the clamp chamber and be exposed to the fluid at the outside of the pipe. These pressure pistons may be pressing against the same packer element or two different packer elements, in the last instance with a part of the outer clamp structure arranged between them. When the pressure pistons are arranged to abut against the same packer element, the outer clamp structure comprises stopping elements preventing the pressure piston at one position from moving further away from the packer element. This stopping element may also form part of the pre-stressing system.

There will also be positioned sealing elements between elements in the clamp device, for instance between the elements of the outer clamp structure, segments of the outer clamp structure and or pressure pistons, and a skilled person will understand this.

In this application one should understand that the reference to a packer element, is an element that is activated by pressure and will due to the configuration of the clamp device give a sealing which is responsive to the pressures around the clamp device. While a seal element is similar to an O-ring or other similar seal that gives a sealing connection relatively independent on the pressures around the clamp device and not influenced by movement of any elements in connection with the seal element.

One possible configuration of the clamp device is to form the pressure piston and the clamp structure such that the pressure piston is allowed to move in one direction, a guided direction towards the packer element, for instance in the axial direction of a pipe, and with the formation of a back chamber between the pressure piston and the clamp structure/other pressure piston, wherein there in relation to this back chamber the packer element is arranged. This gives that in normal cases when the clamp is set there will always be a back chamber between the clamp structure and the pressure piston, giving room for movement of the pressure piston as a response to surrounding pressures, in relation to the outer clamp structure, towards and away from the packer element. The pressure transfer between the pressure piston and the clamp structure in the direction of which the pressure piston is allowed to move, will for most forces in this direction, be through the packer element. Thereby giving that the packer element is responsive to the pressures around the clamp structure, and thereby that the sealing effect is responsive to the pressure around the clamp structure. The pressure piston will not be abutting the clamp structure in this direction; the pressure piston will be allowed to move towards and away from the clamp structure, or other pressure piston, positioned on the opposite side of the packer element in this one direction. This gives a higher pressure internally in the packer element and thereby also toward the surfaces abutting the packer element. Thereby forming a larger sealing pressure in the sealing between the elements than in the fluids around the device. In the case where there in addition is a pre-stressing system there may be formed a limitation on the movement of the pressure piston but this limitation limits the movement of the pressure piston away from the clamp structure or other pressure piston on the opposite side of the packer element, and not in the direction towards the packer element.

The invention will now be explained with more detailed non-limiting embodiments and with reference to the drawings where;

Fig. 1 depicts a cross section of a first embodiment of a clamp device according to the invention arranged around a pipe,

Fig. 2 depict a cross section of a second embodiment, Fig. 3 depict a cross section of a detail of the first embodiment, Fig. 4 depict a cross section of a detail of a third embodiment,

Fig. 5 depicts a cross section of a detail of the second embodiment, Fig. 6 depict a cross section of a detail of a fourth embodiment Fig 7 depict a cross section of a detail of a fifth embodiment and Fig. 8 depicts a cross section of a detail of a sixth embodiment. Similar elements are given the same reference numeral in all the different embodiments. The way of fastening the outer clamp structure around the pipe is not shown or described since a skilled person have ample skills to provide such a solution and those elements are not essential elements of the invention in this application.

In fig. 1 there is shown a first embodiment of the invention. There is around a pipe

I on the outer pipe wall 3 arranged an outer clamp structure 10. This outer clamp structure may comprise two or more elements and is fastened around the pipe 1. There is from an inner pipe wall 2 through the material of the pipe to the outer pipe wall 3 formed a hole 4. This hole 4 could have been made due to corrosion, damage or other incidents. The clamp device should create a barrier between the fluid within the pipeline and the surroundings. The outer clamp structure 10 is formed with an inner clamp chamber 11 , formed between the outer wall 3 of the pipe 1 and the outer clamp structure 10. This clamp chamber 11 is positioned in connection with the hole 4 through the pipe wall, giving communication between the clamp chamber

I 1 and the inner of the pipe 1.

The configuration of the clamp device in figure 1 is adapted for a higher pressure in the fluid within the pipe 1 than the fluid outside the pipe 1 , as indicated with the arrows marked HP for high pressure within the pipe 1 and within the clamp chamber 11. On each side of the clamp chamber 11 seen in the longitudinal direction of the pipe I₅ there is arranged an annular pressure piston 12, arranged moveable relative the outer clamp structure. The pressure within the clamp chamber 11 will act on these pressure pistons 12, and press them away from each other. When looking at one of these pressure pistons 12, there is between the pressure piston 12 and the outer clamp structure 10 arranged an annular packer element 13, which packer element 13 is arranged to press against the outer wall 3 of the pipeline and thereby create a barrier between the clamp chamber 11 and the outside of the outer clamp structure 10. The surface of the pressure piston exposed to the fluid within the clamp chamber 11 is larger than the surface of the pressure piston 12 pressing on the packer element 13, giving a relative larger pressure force in the packer element 13. Since the areas are not similar and in one system there is pressure balance the pressure against a unit of the high pressure surface is lower than the pressure against a unit of the packer pressure surface, since there is a ratio between these surfaces and one has a pressure balance. This gives that with an increase in pressure on the high pressure surface of the pressure piston one gets a larger increase in the pressure in the packer element. There is between the pressure piston 12 and the outer clamp structure 10 also arranged a seal element 14. Between the seal element 14 and the packer element 13 there is formed a back chamber 18. This chamber is vented to the outside of the outer clamp structure 10 through a vent line 16, to prevent any fluid from being trapped in the back chamber and forming a fluid lock stopping or limiting movement of the pressure piston 12 relative the outer clamp structure 10. In addition there is arranged a pre-stressing system 19, for pressing the packer element 13 against the outer wall 3 of the pipe 1 , when there are no or minimal pressure within the clamp chamber 11 pressing the pressure pistons 12 away from each other and towards the packer element, pressing the packer element 13 between the pressure piston 12 and the outer clamp structure 10 and thereby into contact with the outer wall of the pipe 1. The pre-stressing system 19 may for instance as shown in fig. 1 be bolts and nuts, where the bolt is connected to the pressure piston and where when the nut is tightened the system will pull the pressure piston towards the outer clamp structure and thereby press the packer element into contact with an outer wall of the pipe. The pre-stressing system is favorably so arranged that the pressure piston is allowed to move further towards the packer element and press this further against the outer wall of the pipe, when fluid is acting on the pressure piston. The pre-stressing system will however prevent the pressure piston to move in the opposite direction, away from the packer element.

In fig. 2 there is shown a cross section of a second embodiment of the clamp device, where this clamp device is configured for a higher pressure on the outside of the outer clamp structure 10 than within the pipe 1, as indicated with the arrow named LP, low pressure, indicating the areas inside of the pipe and the clamp chamber of the outer clamp structure 10. One will find the same elements in this configurations, the change is that the pressure pistons 12 are arranged at the outer side of the outer clamp structure 10, where these pressure pistons 12 when a pressure in the external fluid surrounding the pipe will act on the pressure pistons 12, will press the pressure pistons 12 towards each other, and by this action press packer elements 13, arranged between the pressure pistons 12 and the outer clamp structure 10 into sealing abutment with an outer wall 3 of the pipe. The venting line 16 leads in this configuration from the back camber 18 to the clamp chamber 11 , which in this configuration will comprise a fluid at a lower pressure than the fluid surrounding the pipe 1 and the outer clamp structure 10. In fig. 3 there is shown a cross section of a detail of the embodiment shown in fig. 1. As one may see more clearly from this figure, the pressure piston 12, has a high pressure surface 20 exposed to the fluid with the higher pressure, facing into the clamp chamber 11. On the opposite side of the pressure piston 12, seen in a longitudinal direction of the pipe 1 the pressure piston comprises a first low pressure side 21 and a second low pressure side 22, these surfaces are mainly parallel with the high pressure surface 20, where these surfaces are joined by a transition surface 24. The pressure piston also comprises an inner surface 25 which is facing the outer wall 3 of the pipe and an outer surface 23, forming a surface faced against an radial outer wall of the clamp chamber 11. The pressure piston 12 also comprises a pressure surface 27, in abutment against the packer element 13, this pressure surface is arranged between the inner surface 25 and the second low pressure surface 22. The outer clamp structure 10 comprises an first clamp surface 30 forming a radial outer wall of the clamp chamber 11, a first radial surface 31, i.e. a surface stretching in a direction manly transverse to a longitudinal axis of the pipe, a second inner surface 32, mainly parallel with the first clamp surface 30, a second radial surface 33 and a pressure surface 34, arranged on the opposite side of the packer element 13 relative the pressure surface 27 of the pressure piston 12. These surfaces of the outer clamp structure gives a stepped formed on the total inner surface of the outer clamp structure 10 from the clamp chamber 11 towards the outside of the outer clamp structure 10. A seal element 14 is arranged in the outer surface 23 of the pressure piston 12 and is in abutment against the first clamp surface 30. This configuration may of course be opposite with a seal arranged in the clamp surface 30 in abutment against the outer surface 23 of the pressure piston 12. By this arrangement there is formed a back chamber 18 between the pressure piston 12 and the outer clamp structure 10.

In fig. 4 there is shown another possible configuration of a detail of a clamp device according to the invention. Only differences will be explained. Instead of the first and second seal there is arranged a second packer element 17 in abutment between a second packer pressure surface 28 of the pressure piston and a pressure surface 34B of the outer clamp structure. The pressure surface 34 B is arranged between the first clamp surface 30 and the first radial surface 31. The second packer pressure surface 28 is arranged between the outer surface 23 and the low pressure surface 21. The total area of the pressure surfaces 27, 28 of the pressure piston 12 is smaller than the area of the high pressure surface 20 exposed to the fluid around the clamp device with the higher pressure. There is in this configuration formed one back chamber 18, which is vented through the venting line 16.

In fig. 5 there is shown a detail of the embodiment in fig. 2. This detail is for a configuration with the fluid with the higher pressure on the outside of the clamp device, but the configuration has the same features as the detail of fig. 3, and it is referred to the explanation of that figure.

In fig. 6 there is given a cross section through another detail, where the packer element 13 has a more triangular cross section, and the pressure piston 12 is formed with an angled first packer pressure surface 27 and an angled pressure surface 34 of the outer clamp structure 10 forming a mainly V-shape of a cross section of the two pressure surfaces pressing against the packer element 13, for pressing the packer element 13 against the outer wall of the pipe 1. A skilled person will understand that the pressure surfaces pressing against the packer element may be formed mainly parallel, with a V-shape, a lopsided V-shape or even with a varying angle of one or both of the pressure surfaces from an inner to an outer point of the pressure surfaces. In fig. 7 there is a cross section of a detail of a given possible double sided clamp device, where the clamp device will comprise four pressure pistons, whereof two are shown in the figure, the other two will be arranged in reversed order on the other side of the clamp chamber. The clamp device is constructed with a system as the one explained with reference to fig. 1 and 3 and in addition to this a system as the one explained with reference to fig. 2 and 5. In this configuration the venting line 16 from one back chamber 18, will lead to the back chamber 18 of the second system. With such a clamp device one will have pressure activated packer elements 13, reacting to pressures both within and outside the clamp device. The pre- stressing system may be a system as explained before or a system with a locking element with outer threads interacting with threads in a surface of the outer clamp structure 10, and thereby locking the movement of the pressure piston relative the clamp structure in one direction but allowing movement of the pressure piston in the opposite direction to further press against the packer element, due to an increase in the pressure in the fluid acting on the high pressure surface of the pressure piston.

In fig. 8 there is shown a different configuration of the system shown in fig, 7. However in this embodiment the two pressure pistons 12 reacting to outside fluid pressure and pressure within the pipe 1, are both acting on the same packer element 13. In this configuration the opposite pressure piston is forming the opposite pressure surface acting on the packer element. The pre-stressing system 19 will in this system both work as a pre-stressing system but also as a stopper element. It is shown a configuration where the two pressure pistons have similar outer diameters and the outer clamp structure 10 is form with a mainly even internal diameter for easy mantling and dismantle of the clamp device. With such a double configuration the outer diameter of the two pressure pistons on one side of the clamp chamber, may be different diameters, and the outer clamp structure may be formed with a stepped inner surface faced towards the pipeline, to provide for good and correct positioning of the different pressure pistons with different diameters and an easy and correct mantling an dismantling of the clamp device. In one configuration the pre-stressing system 19 may be connected to the two pressure pistons and not at all to the outer clamp structure, such a pre-stressing system 19 will pulling the pressure pistons together and thereby stressing the packer element towards the outer wall of the pipe.

The invention has now been explained with different embodiments. A skilled person will understand that there may be made several alterations and modifications to the embodiments that are within the scope of the invention as defined in the following claims. One may envisage that there is arranged one packer element in a circle around the hole in the wall of the pipeline and there is arranged pressure piston segments in a circle on the outside of the packer element all moveable in a radial direction towards the hole. There may also be an arrangement with a pressure piston arranged radially outside the hole in the wall pressing radially inwards toward a packer element arranged around the hole, thereby the pressure piston forming somewhat of a lid in the configuration.

Claims

1. Clamp device for arrangement in connection with a pipe (1), comprising an outer clamp structure (10) for arrangement at least partly around a pipe (1), comprising at least one pressure piston (12) arranged movable relative the outer clamp structure (10) and where the pressure piston (12) comprises a high pressure surface (20) exposed to a fluid at a higher pressure around the clamp device and at least one packer pressure surface (26,27) where the high pressure surface (20) has a larger area than the packer pressure surfaces (26,27), characterize d in that there is at least one packer element (13,17) arranged between the pressure piston (12) and the outer clamp structure (10) or another pressure piston (12) and the at least one packer pressure surface (26,27) is in abutments against the packer element (13, 17).

2. Clamp device according to claim 1, characterized in that the clamp structure (10) and pressure piston (12) have a shape which in use forms a back chamber (18) between them, wherein the at least one packer element (13,17) is arranged, allowing for movement of the pressure piston (12).

3. Clamp device according to claim 1, char acteri z e d in that it comprises a pre-stressing system (19) pulling a pressure piston towards the at least one packer element (13,17) to pre-stressing the at least one packer element (13,17).

4. Clamp device according to claim 1, char act e ri z e d i n that the outer clamp structure (10) forms a clamp chamber (11) between the outer clamp structure (10) and an outer wall (3) of the pipe (1) and where the clamp structure further comprises an annular pressure piston (12) and at least one annular packer element (13), arranged on the two sides of the clamp chamber (11) seen in a axial direction of the clamp device.

5. Clamp device according to claim 4, char act eriz e d i n that the pressure piston (12) arranged within the outer clamp structure (10) together with the outer clamp structure (10) forms a back chamber (18) between them, sealed towards the surroundings by at least one packer element (13) and at least one seal element (14).

6. Clamp device according to claim 4, char acteri z e d i n that there is arranged two annular packer element (13,17) between the pressure piston and the outer clamp structure (10) forming a back chamber (18) between them.

7. Clamp device according to claim 5 or 6, char act eri z e d i n that the back chamber (18) is connected with a vent line (16) for venting fluid in the back chamber (18) towards a low pressure side of the clamp structure (10), when the pressure piston (12) is moved relative the clamp structure (10).

8. Clamp device according to one of the preceding claims, charact eri z e d in that the pressure piston (12) is arranged within the outer clamp structure (10) so that the high pressure surface (20) is forming a side of the clamp chamber (11).

9. Clamp device according to one of the claims 1-7, char act eri z e d in that the pressure piston (12) is arranged within the outer clamp structure (10) so that the high pressure surface (20) is facing a fluid surrounding the clamp device and a pipe.

10. Clamp device according to one of the preceding claims, characte ri z e d in that the outer clamp structure (10) and pressure pistons (12) comprises at least two segments around a circumference of a pipe.