WO2011051570A1

WO2011051570A1 - Device and method for leak indication

Info

Publication number: WO2011051570A1
Application number: PCT/FI2010/050861
Authority: WO
Inventors: Kari Kurvinen
Original assignee: Anturikeskus Oy
Priority date: 2009-10-28
Filing date: 2010-10-28
Publication date: 2011-05-05
Also published as: FI20096115A0

Abstract

A device (18, 26) for indicating a leak, said leak occurring from an internal volume (7), containing pressurised liquid or gas delimited by a first wall (2), through said first wall, leading out of said internal volume, said device comprising a second wall (2, 10, 17) joined to said first wall on a possible leak point (9, 14) in order to form a leakage volume (8) between said first wall and said second wall around said possible leak point outside said internal volume, and indication equipment (18, 27, 28) for indication of said liquid or gas gathered into said leakage volume due to said leak. According to the invention, said device is arranged to retain in said leakage volume (8) said gas or liquid that gathers into said leakage volume in the occurrence of said leak in order to increase pressure inside said leakage volume to a pre-defined level, and said indication equipment (18, 27, 28) is arranged to use the pressure energy of pressure that has built into said leakage volume (8) after said pressure has reached a pre-defined level.

Description

DEVICE AND METHOD FOR LEAK INDICATION

FIELD OF INVENTION

The invention relates in general to transfer and containment of gases or liquids in pressurised pipes, containers and similar. More specifically, said invention focuses on a device and method for indicating a leak that possibly occurs in said pipe, container or similar.

BACKGROUND OF INVENTION

Different gassy and liquid substances, such as natural gas and oil, are often transferred in solid pipes from primary production site to facilities for further processing or containment or between them. Transfer in said transfer pipe is based on pumping the substance to the pipe as pressurised, wherein the pressure difference creates the flow of the pumped substance through the pipeline.

Due to the often remote location of gas and oil production sites and long distances to refining plants and between refineries and end-users' storages, gas and oil transfer pipes can be hundreds and even thousands of kilometres long. Thus, a transfer pipe is in itself a device of enormous scale, and the condition of the device must naturally be monitored, and the device must be serviced when necessary. Perhaps the most important aspect in monitoring the condition of a pipe is leaks in the pipe. It is clear that since the transfer capacity of a single gas pipeline can be up to several ten billion cubic metres a year, a relatively small leak easily causes extensive economic losses. In addition, an oil leak, for instance, may severely pollute the environment of the pipeline. The monitoring of oil and gas pipelines involves significant challenges, such as the said enormous dimensions of pipes. General-level monitoring of condition has been traditionally carried out through regular visual inspections, which can be performed, for instance, from all-terrain vehicles or low-flying aeroplanes. It is obvious that these methods of monitoring are inaccurate and expensive. Therefore, it would be preferable to use systems and devices that are as automatic as possible. A natural starting point would be to install in contact to the pipeline fixed leak indication devices, which can preferably be read remotely, and that can include various measuring devices and recording and information transfer equipment for recording and/or forwarding information on the detected leak.

A fundamental problem in the said kinds of devices is connecting individual devices to the overall monitoring system in order to supply them with driving force and to transfer information of a detected leak to the administrator of the pipe or storage. Large proportions of transfer pipes are often located in sparsely populated and/or hard-to-access areas, such as wilderness or even at the bottom of a sea, far from electrical grids let alone data transfer connections. Proposals for data transfer connections have included, for example, a network of UHF retransmitting towers, in which a single tower could collect information from indicators on 100 kilometres' length of a pipeline. By contrast, no sufficient solutions have been proposed for the driving force supply of the devices. In principle, a battery or similar could be connected to the indicator device to supply driving force for the device. The service life of these, however, is limited, and their operation in highly varying environments is uncertain. Solar energy may be an option in some ar- eas. However, the operational reliability and, to some extent, the price of solar cells constitute a problem.

In addition, even if monitoring devices and systems were installed only in the most probable leak locations, such as joints or curves of pipeline elements, a very large number of devices would be needed for distances of thousands of kilometres. This means that additional costs of a single device should be as low as possible.

As for the indicator device for detecting a leak in a pipeline, container or similar, different approaches are known, of which arranging on the likely leak point a substantially dense leakage volume that gathers the substance coming from the leak point. The actual measurable magnitude can be, for example in the case of a gas leak, the concentration of gas in the leakage volume. The leakage volume increases the gas concentra- tion in a controlled manner to a level at which it is easier and more accurate to measure than if a gas concentration were measured from an open space near the probable leak point. A simple example of this kind of leakage volume is described in the publication US 2007113890 Al, which presents an elastomer sleeve that is placed around the flanged joint of two pipes. There is an opening in the sleeve for measurement of gas concentration. A leakage volume with the corresponding principle can be created around likely leak points of gas and oil pipelines, such as butt welds, using applicable structures and materials. Yet, the detection of and forwarding of the information on a leak remains a problem. Known measuring apparatuses always require electricity, and in the long term, their operation is uncertain in varying, often extreme environmental conditions . It can be summarised that a clear need still exists for a highly independent, reliable and cost-efficient leak indication device and for a method for detecting a leak that occurs in a pressurised pipeline or con- tainer, especially in a gas or oil transfer pipe. The purpose of the invention is to meet this need by presenting solutions that, in addition to being applicable to gas and oil transfer pipelines, are suited for leak indication in general in pipes, containers and similar structures for transfer or storage of pressurised liquid or gas.

SUMMARY OF INVENTION

The device and method of the invention is character- ised by what is presented in patent claims 1 and 9.

Firstly, the invention comprises a device for indicating a leak that occurs from an internal volume containing liquid or gas and bounded by a first wall through said first wall leading out of said internal volume. In this context, pressurised means that liquid or gas exists in the internal volume at a pressure that is higher than the surrounding pressure that exists on the other side of the first wall, i.e. outside the internal volume. Pressure can be created actively and mechanically, as is the case in various gas and liquid flow channels, in which flow in the channel is created by pumping a pressure difference between the ends of the channel. It may also result from hydro- static pressure. Pressurised gas or liquid naturally requires that the said first wall forms a uniform and substantially tight jacket around the internal volume. Rigid materials are advantageous materials for the first wall, for instance a metal or plastic, depending on the object of application. Internal volume can be any transfer channel of gas or liquid, such as a gas or oil transfer pipeline or flow channel in process equipment but also a container volume, designed for storage of gas or liquid that is substantially stationary .

The device of the invention comprises a second wall coupled around a possible leak point in the first wall to form a leakage volume between said first wall and said second wall outside the internal volume around a possible leak point. Possible leak point refers to any point in a pipeline or container in which a leak may occur. In practice, it is favourable to arrange devices according to this invention around the most probable leak points. Such points may include but are not limited to joints of pipeline and container components and curves of pipelines. The purpose of the leakage volume is to collect the liquid or gas discharging from ^'the internal volume due to a leak. The material and connecting method of the second wall to the first wall as well as the shape or size of the leakage volume thus formed may vary depending on the special characteristics of the object of application. Secondly, the device comprises equipment for indicating the liquid or gas that has gathered inside the leakage volume. Indication refers here to generally any measure that is implemented with technical equipment that produces information that signals the occurrence of a leak. Typically, an indication may, for example, comprise formation of a message and/or the forwarding of said message from the leak point to the system that monitors leaks. Formation of the message may be triggered by, for instance, measurement of pressure, temperature, gas concentration, humidity or other variable inside the leakage volume. Some advantageous measures involved in indication are described farther in this document. As per the invention, the device is designed so that it holds the gas or liquid that gathers into the leakage volume in the event of a leak, in order to increase the pressure inside the leakage volume to a pre-defined level. In the event of an intensive leak, it may be sufficient that the leakage volume only increases flow resistance of the leakage flow that discharges from the internal volume yet continuously allowing an open flow channel from the leakage volume leading out of the device. Adequate rise in pressure can be advantageously ensured by using substantially tight structures to form the leakage volume, which prevents flow of gas or liquid entering the leakage volume from flowing out of the leakage volume. To en- sure this, both the first wall and the second wall connected to it as well as the joint of the second wall to the first wall must be tight enough to hold pressure. Thus, the first wall must be substantially uniform at minimum. In several applications, it is preferable that the material is substantially rigid as well. One suitable solution in cases of metallic gas or oil pipelines is manufacturing the second wall of metal as well and welding it onto the first wall forming the pipeline. In some applications, pressure- operated self-tightening joint structures can be used as well. Examples of these are given farther in the detailed description of the invention.

According to the invention, the indication equipment is organised to be activated by the pressure energy of the pressure that has gathered inside the leakage volume when the pressure has risen to a pre-defined level. On one hand, this means that at least a proportion, and profitably and substantially all of the en- ergy required by the operation of the indication equipment is obtained from the accumulated pressure energy inside the leakage volume without an external source of energy. By using appropriate equipment, pressure energy can be converted into a form of energy that can be utilised by the indication equipment, such as kinetic energy of mechanical components or electric energy needed by electrical apparatuses. Some examples of equipment used in conversion are presented farther in this document. On the other hand, pressure energy can be in some cases used directly, for example, so that the force created by the pressure breaks a separating film or similar that delimits a volume containing pigment or chemical needed in the formation of an indication message of a leak. If indication equipment is set to operate when pressure increases to a predefined level, indication measures are activated only then. Therefore, indication equipment is used only when it is really needed, i.e. when a leak has^" occurred, which increases their service life. Said predefined pressure level may, depending on the form of implementation and object of application, be any pressure that is higher than the normal state within the leakage volume prior to a leak.

The invention solves very efficiently - and in a way that can be implemented as a reliable device - a known technical problem of energy supply for devices used in the indication of leaks in pipes etc. It is a big step forward for the sector and opens entirely new possibilities in monitoring of leaks. In addition to removing the need for a separate external source of energy, energy is produced in a solution according to the invention only when a leak that needs to be indicated has actually occurred.

By allowing pressure to rise to a pre-defined level that has been selected correctly, it can be ensured that there actually is sufficient pressure energy for the operation of the indication equipment. Given the basic physical equation of pressure P P = — , in which

A

F is the force applied by the molecules of a pressurised liquid or gas on a surface A, it can be derived

F Fd W E , . ,

P = — = = — = — , m which d is an imaginary dis-

A Ad V V

tance of a wall moved by the force F and W is the work done by the force. Finally, E = PV is the pressure energy engaged in volume V. Thus, the pressure energy engaged in pressurised liquid or gas increases in direct proportion to pressure.

A device that allows pressure to build in the

volume also functions in itself as a means for

minor leaks, and therefore neither repairing no eating the leak is needed urgently.

In a particular advantageous form of implementation, the device comprises a valve for opening a flow channel from the leakage volume leading out of the leakage volume when pressure in the leakage volume has reached a pre-defined level. The flow channel may serve multiple purposes. Firstly, it enables the conversion of pressure energy to kinetic energy exerted via the flow channel, which can be utilised as the driving force of the indication equipment as such or upon conversion to another form of energy. Secondly, exerting the pressure in the leakage volume in a controlled way through the flow channel opened by the valve naturally prevents the device from breaking due to excessive pressure. After controlled decreasing of pressure the valve can be closed using, for example, a spring, after which pressure begins to rebuild in the leakage volume if the leak still continues. Eventually, this causes simultaneous re-opening of the valve and activation of the indication equipment. Hence, the fre- quency of activations of the indication equipment di- rectly indicates the intensity of a leak, and thus, no actual measurement of intensity of leakage flow or another magnitude proportionate to the intensity of a leak is necessarily needed. Pressure-triggered activa- tion of the indication equipment can comprise a particular standard procedure, for example forming and/or sending a certain standard message reporting a detected leak. This also contributes to the implementation of the indication equipment as simple and there- fore cost-efficient and reliable apparatuses.

In its inexpensive form of implementation, the device comprises electricity generation equipment for generating electric energy for the operation of the indica- tion equipment using the pressure energy of the pressure built inside the leakage volume. Electricity is a highly usable and flexible form of energy and enables various alternative implementations of indication equipment .

One inexpensive form of implementation for utilisation of the leakage flow and generation of electric energy is a device that includes a generator and a runner supported on the generator shaft, the runner which is rotated by the flow through the flow channel, which is opened by the valve, to produce electricity using the generator to operate the indication equipment. The specific assembly of the generator and, for example, intermediate storage and supply of electric energy to the indication equipment can be implemented using known electrical and electronic equipment, and details pertaining to them are not essential for the core ideas of the invention. An alternative implementation utilises an electrochemical cell comprising two electrodes and an electrolyte between them to generate electric energy using the pressure energy of the accumulated pressure in the leakage volume. In this approach, it is possible to force the electrolyte between the electrodes using the pressure in the leakage volume or, by contrast, move the electrodes to the space in which the electrolyte already is. Alternatively, the device may include an otherwise operational electro-chemical cell formed by electrodes and an electrolyte in which the electrolytes are separated from each other with a protective film, which the pressure energy breaks. In the case of a transfer pipeline of flammable gas, an electrochemical cell is a safe solution for generating electric energy for the indication equipment since flammable sparkling does not usually occur in the operation of an electro-chemical cell.

Indication equipment may include various devices for creating, for example, an electric message signalling a leak. Such a message can be, for instance, recorded on a recording device connected to the device for reading on regular intervals on site or using applicable remote reading technology. In one inexpensive form of implementation of the invention, the device comprises sending equipment for sending from the device a message indicating a leak. A message that is sent from the device and received at a distance from it enables a centralised information gathering system, which gathers messages coming from several devices. This is beneficial especially if the object of monitoring is for example an extensive gas or oil pipeline with a hard-to-access location.

In a form of implementation usable for various applications, sending equipment comprises a radio transmitter for sending a radio-frequency electromagnetic signal from the device. As stated above, this kind of signal can include a simple message with a standard content. For example, if a centralised information gathering system is used, it is sufficient to simply send the information specifying the location of the device. Reception of the message in itself indicates that a leak has occurred, and the identification information indicates the location of the leak. As described above, the device may also be configured to indicate the intensity of a leak by the transmission frequency of the leak messages.

In some forms of implementation of the invention, however, sending equipment may comprise functions for sending a leak message by sending from the device an object indicating a leak. This kind of message may at its simplest be received on the basis of visual perception of the object.

A specific form of implementation based on sending an object applies to situations in which the pressurised gas or liquid is in its normal state less dense than the environment outside the internal volume. In such a case, the object indicating a leak comprises advantageously a substantially tight jacket, which includes a filling volume, and the sending equipment comprises filling equipment for filling the filling volume with the flow discharging from the flow channel opened by the valve in order to send the object from the device using buoyant force. The object can be, for instance, a gas-filled ball or similar. This method of implementation of the invention is possible, for example, in the case of a submarine gas pipeline, in which case the supply of driving force to the device and, for example, sending of an electric message to the surface is particularly challenging. Pressure energy is used in this application for creating a flow that is needed in filling a gas ball or similar. It is clear that buoyancy can also be used to send other objects in ad- dition to objects filled with pressurised liquid or gas. Utilisation of pressure energy can be implemented as movement of the mechanical functional components of the sending equipment using pressure energy.

In addition to sending an electromagnetic signal or an object, the leak indication message can be sent as, for example, a light, acoustic or ultrasonic signal.

The object of the invention comprises also the method for indicating a leak, which occurs from the internal volume containing liquid or gas and bounded by the first wall through the first wall leading out of the internal volume. In the method, a leakage volume is formed outside the internal volume around the possible leak point, and the liquid or gas gathered into the leakage volume as a consequence of a leak is indicated.

According to the invention, the method involves retaining in the leakage volume gas or liquid that gathers into the leakage volume in order to increase the pressure inside the leakage volume to a pre-defined level and indication using the pressure energy of the pressure that has built into the leakage volume after the pressure has reached a pre-defined level.

In an inexpensive form of implementation of the method, a flow channel from the leakage volume leading out of it is opened when pressure in the leakage volume has risen to the aforementioned pre-defined level. Pressure energy causes a flow through the opened flow channel, and the flow can be utilised in generating driving force for the indication equipment either directly using the kinetic energy of the flow or by converting the kinetic energy into another form of energy. In an advantageous form of implementation of the invention, electric energy for performing an indication is generated using the pressure energy of the pressure that has built inside the leakage volume. In an inexpensive form of implementation, the said opening of the flow channel and generation of electric energy are combined so that in the method electricity for the driving force required in performing an indication is generated by running a generator using the effect of the flow discharging via the opened flow channel.

In order to forward the information on the occurrence of a leak, a leak message is sent inexpensively in the method. In an inexpensive form of implementation, a radio-frequency electromagnetic signal is transmitted. Alternatively, an object that indicates a leak can be sent. In a particular form of implementation, pressurised gas or liquid is in its normal state less dense than the environment outside the internal volume, and the object indicating a leak comprises a substantially tight jacket, which encloses a filling volume. In this form of implementation, the filling volume is filled with the flow discharging from the said opened flow channel in order to send the object using buoyant force .

DETAILED DESCRIPTION OF INVENTION

In this section, the invention is described more specifically with the aid of the attached figures of inexpensive examples of implementation of the invention. Figures la-Id illustrate one method of implementation of the leakage volume according to the invention. Figures 2a-2c present alternatives for creating the self- tightening leakage volume according to the invention. Figure 3 presents the principle of one device accord- ing, to the invention. Figure 4 presents one form of implementation of the invention for monitoring leaks of an underwater pipeline.

Figure la displays part of a round pressurised gas transfer pipeline 1 formed by the metal wall 2. The pipeline is assembled in the longitudinal direction of separate pipe components, which are joined together with butt welds 3. Butt welds of a pipeline are points in which leaks typically may occur as the pipeline ages.

Figure lb presents gaskets 4 around a pipeline on the external surface of the wall on both sides of a butt weld 3. Figure lc presents a sleeve 5, which is in- stalled around the pipeline slightly off the surface of the pipeline and extends over the butt weld and the gaskets. The sleeve is fastened with tightening bands 6. Both the sleeve and the tightening bands can be made of metal or plastic, as the suitability of mate- rials and specific structures depend on the special characteristics of the target application, such as the pressure in the internal volume 7 of the pipeline and the environmental conditions of the pipeline. Figure Id presents a cross profile of the arrangement in fig- ure lc. The wall 2 of the pipeline and the sleeve 5 delimit a leakage volume 8 between them. Gas leaking through a crack 9 in the wall of the pipeline occur- ring in the area of the leakage volume remains in the leakage volume and builds pressure inside the leakage volume until the pressure is released, for example through a valve (not displayed in figures la-Id) , or until the pressure inside the leakage volume has reached the same level as in the pipeline.

In the self-tightening structures forming a leakage volume in figures 2a-2c, a leakage volume 8 is formed to the wall 2 of a pipeline or container for transfer or storage of gas or liquid, around a presumed leak point, using a jacket 10 with an arched cross-section. In each alternative presented in figures 2a-2c, the jacket is connected to the wall with flanges 11 that are parallel to the wall and cavities 12 parallel to the wall that are machined to the wall or arranged by adding supplementary parts to it and where the flanges are set. Seals 13 are located on the external surface of the wall, between the flanges and cavities. When a leak point 14 occurs through the wall of the pipeline, the flow of liquid or gas discharging via the leak point into the leakage chamber increases the pressure within the leakage volume, due to which the jacket tries to separate off the wall thereby tightening the joints formed by the cavities of the wall and the flanges placed in them. In figure 2a, the cavity 12 is machined to the wall itself for example by milling. In figure 2b, the cavity is formed with a protruding fold 15 that is cast on the wall of the pipeline. Also in the solution in figure 2c, a fold is arranged on the external surface of the wall using a rail 16 that is fastened to the wall. The last-mentioned form of implementation applies well for retrofitting.

Figure 3 presents a cross-section of a leakage volume 8 formed outside the wall 2 of a pipeline or container using a second wall 17. A leak indication unit 18 is installed to extend through the second wall. It comprises a flow channel 19 and valve 20 installed to it, the valve that is arranged to open a flow connection from the leakage volume to the flow channel when pres- sure in the leakage volume has reached a pre-defined level. As seen from the leakage volume, behind the valve in the flow channel there is a runner 21, rotated by the effect of the flow. Behind the runner, the flow connection opens out of the leak indication unit to the surroundings of the pipeline. The rotating shaft of the runner is connected to a generator 22 belonging to the leak indication unit in order to rotate its rotor. The generator is connected electrically to an electronics unit 23, comprising a battery for stor- age of electricity generated by the generator and a radio transmitter and its antenna 24 for transmitting a radio-frequency electromagnetic signal due to a leak. The signal can be, for example, a specific standard message that identifies the particular leak indi- cation unit and its location. In order to receive the signal, the monitoring system of a pipeline or container includes a radio signal reception station (not presented in the figure) for receiving messages sent by one or several leak indication units.

In the device in figure 3, the valve 20 is -arranged to inexpensively close after opening when pressure in the leakage volume has declined to a specified lower level. If the leak continues, pressure begins to re- build into the leakage volume after the valve has closed, which eventually triggers sending of a new message. Thus, the frequency of sending messages indicates the intensity of a leak. Figure 4 presents an underwater gas pipeline 25 in principle. A leak indication device 26 is installed to the gas pipeline, comprising a launch unit 27 that is operated with pressure of the gas that accumulates inside the leakage volume in the leak indication device for filling a gas ball indicating a leak, comprising a flexible and tight jacket 28 and a volume 29 that it encloses, with gas that has gathered into the leakage volume and releasing the gas ball from the device. The gas-filled ball rises due to buoyancy to water surface, thus forming a visually perceivable message on a leak. In addition to the visual signal, the launch unit can send with the ball to the water surface a radio transmitter, which sends a radio-frequency signal that indicates a leak. The radio signal can be received considerably far from the gas ball itself on water surface.

The structural or other specifications of the devices described above are not relevant for the basic idea of the invention. Therefore, they are not described further. The devices can in practice be designed and implemented through ordinary engineering and by utilising known mechanical and electronic solutions.

It should be noted that the invention is not limited to the said examples; the forms of implementation can vary freely within the patent claims.

Claims

PATENT CLAIMS

1. A device (18, 26) for indicating a leak, said leak that occurs from an internal volume. (7), containing pressurised liquid or gas delimited by a first wall (2), through said first wall leading out of said internal volume, said device comprising a second wall (2, 10, 17), joined to said first wall on a possible leak point (9, 14) in order to form a leakage volume (8) outside said internal volume between said first wall and said second wall around said possible leak point, and indication equipment (18, 27, 28) for indication of said liquid or gas gathered into said leakage volume due to said leak, characterised by that

said device is arranged to hold gas_. or liquid that gathers into said leakage volume (8) in the possible event of a leak in order to increase pressure in said leakage volume to a pre-defined level; , and by that said indication equipment (18, 27, 28) is arranged to be activated by the pressure energy of pressure that has gathered inside said leakage volume (8) when said pressure has risen to said pre-defined level .

2. Device (18, 26) according to claim 1, characterised by that said device comprises a valve (20) for opening a flow channel from said leakage volume (8) leading out of it, when said pressure in said leakage volume has reached a pre-defined level.

3. Device (18, 26) according to claim 1 or 2, char- acterised by that said device comprises equipment for generating electric energy (21, 22), for using said indication equipment (18) with the pressure energy of said pressure accrued into said leakage volume .

4. Device (18, 26) according to claim 2 or 3, char- acterised by that said equipment for generating electric energy comprises a generator (22) and a runner (21) , supported on a generator shaft, arranged to be rotated by the effect of the flow discharging from a flow channel opened by said valve (20), in order to generate electricity with said generator.

5. Device (18, 26) according to any of claims 1-4, characterised by that said device comprises sending equipment (23, 24, 27), for sending a leak message from said device.

6. Device (18) according to claim 5, characterised by that said sending equipment comprises a radio transmitter (23, 24) for sending a radio- frequency electromagnetic signal.

7. Device (26) according to claim 5 or 6, characterised by that said sending equipment comprises functional components (27) for sending from said de- vice an object that indicates said leak.

8. Device (26) according to claim 2 and 7, characterised by that said pressurised gas or liquid is in its normal state less dense than the external envi- ronment outside said internal volume, that said object that indicates said leak comprises a substantially tight jacket (28), enclosing a filling volume (29), and that said sending equipment comprises filling equipment for filling said filling volume with the flow discharging through said flow channel opened by said valve, for sending said object from said device with buoyant force.

9. Method for indication of a leak, said leak occurring from an internal volume (7) containing pressurised liquid or gas delimited by a first wall (2), through said first wall leading out of said internal volume, wherein said method comprises forming a leakage volume (8) outside said internal volume around a possible leak point, and indicating said liquid or gas gathered into said leakage volume due to said leak, wherein the method is characterised by that said gas or liquid that gathers into said leakage volume (8) in the possible event of a leak is retained, in order to increase pressure in said leakage volume to a pre-defined level; and by that said indication is performed by the pressure energy of said pressure that has gathered inside said leakage volume, when said pressure has risen to a pre-defined level.

10. Method according to claim 9, characterised b y that in said method a flow channel is opened from said leakage volume (8) leading out of it, when the pressure in said leakage volume has reached said predefined level.

11. Method according to claim 9 or 10, characterised by that in said method electric energy is generated using the pressure energy of pressure built inside said leakage volume, in order to perform said indication.

12. Method according to claim 10 or 11, charac- terised by that in said method electricity is generated by rotating a generator (22) by the effect of the flow discharging from said flow channel.

13. Method according to any of claims 9-12, characterised by that in said method a leak message signalling said leak is sent.

14. Method according claim 13, characterised b y that in said method a radio-frequency electromagnetic signal is sent.

15. Method according to claim 13 or 14, characterised by that in said method an object (28) signalling said leak is sent.

16. Method according to claim 10 and 15, c h a r a c - terised by that said pressurised gas or liquid is in its normal state less dense than the external environment outside said internal volume, that said object that indicates said leak comprises a substantially tight jacket (28), enclosing a filling volume (29), and that said filling volume is filled with the flow discharging through said flow channel, for sending said object with buoyant force.