WO2010139914A1

WO2010139914A1 - Multi-membrane reservoir sealing test

Info

Publication number: WO2010139914A1
Application number: PCT/FR2010/051113
Authority: WO
Inventors: Julien Glory; Jean Marc Quenez
Original assignee: Gaztransport Et Technigaz
Priority date: 2009-06-05
Filing date: 2010-06-04
Publication date: 2010-12-09
Also published as: CN102460103A; MY161967A; JP5658241B2; ES2389088B2; KR101378455B1; TWI436046B; CN102460103B; SG176195A1; FR2946428A1; JP2012529026A; TW201104235A; FR2946428B1; KR20120027464A; ES2389088A1

Abstract

Testing method for the sealing of a reservoir, said reservoir comprising a carrier structure (6), a primary membrane (8), intended to be in contact with a product contained in the reservoir, and a secondary membrane (7), placed between the primary membrane and the carrier structure, in which the space between the primary membrane and the secondary membrane is called the primary space (10) and the space between the secondary membrane and the carrier structure is called the secondary space (9), characterized in that it comprises the steps consisting in: injecting an incondensable first gas or one having a condensation temperature below the average temperature of the primary membrane in the primary space; injecting a second gas, having a condensation temperature above the average temperature of the primary membrane in the secondary space; generating an overpressure in the secondary space relative to the primary space; and detecting one or more possible hotspots (22) in the primary membrane.

Description

TEST FOR SEALING A MULTIMEMBRANE TANK

Technical field of the invention

The present invention relates to the leak test of a multi-membrane reservoir. In particular, the present invention relates to a method for testing the tightness of the secondary membrane of a multi-membrane reservoir, without having to dismantle the primary membrane. STATE OF THE ART Multi-diaphragm tanks are used industrially in various fields to contain gaseous, liquid or solid materials of different types. This type of reservoir comprises a support structure which provides the mechanical rigidity, a primary membrane intended to be in contact with the product contained in the reservoir, and a secondary membrane arranged between the primary membrane and the carrier structure. The secondary membrane is intended to retain the product in case of leakage into the primary membrane.

There are different methods to diagnose the tightness of the secondary membrane. In case of non-conformity of the secondary membrane to the tests, it is necessary to repair this membrane. Now the location of the non-compliance without disassembly of the primary membrane is not easy and imprecise.

For example, in documents FR 2 517 802 and WO 2007/144458, a nonconformity is detected by analysis of the composition of a gas. To locate a nonconformity, it is necessary to provide a multitude of pipes taking the gas to be analyzed in different places. This implies a complex and expensive structure, and whose accuracy is limited.

FR 2,531,516 describes a method for detecting leaks in the secondary membrane of a liquefied gas tank, in which carbon dioxide ice cubes solidified on the outer face of the primary membrane at-160 ^° C. are detected as points. cold during heating of the primary membrane due to their thermal inertia. However, it is difficult to operate an optical camera or a thermograph at the very low temperatures employed in this process. Summary of the invention

A problem that the present invention proposes to solve is to provide a test method that does not exhibit at least some of the aforementioned drawbacks of the prior art. In particular, an object of the invention is to locate a nonconformity of the secondary membrane, without requiring disassembly of the primary membrane or the carrier structure. Another object of the invention is to make it possible to locate a nonconformity of the secondary membrane with a simple structure, in particular without requiring numerous channels.

The solution proposed by one embodiment of the invention is a leaktightness test method of a reservoir, said reservoir comprising a carrier structure, a primary membrane intended to be in contact with a product contained in the reservoir, and a secondary membrane arranged between the primary membrane and the supporting structure, in which the space between the primary membrane and the secondary membrane is called primary space and the space between the secondary membrane and the supporting structure is called secondary space, the space primary containing a first incondensable gas or having a condensing temperature lower than the average temperature of the primary membrane. This method comprises the steps of:

injecting a second gas having a condensation temperature higher than the average temperature of the primary membrane into the secondary space; generating an overpressure in the secondary space with respect to the primary space,

detecting one or more hot spots of the primary membrane corresponding to a deposition of the second condensed gas in contact with the primary membrane. Thanks to these characteristics, in case of non-compliance of the secondary membrane, the second gas escapes into the primary space and comes into contact with the primary membrane, close to the leak. Since it has a condensation temperature higher than the average temperature of the primary membrane, the second gas condenses and. in doing so, it transfers energy in the form of heat, corresponding to its latent heat of change of state, to the membrane primary. A hot spot is generated on the primary membrane. The detection of this hot point from the inside of the tank allows the location of the nonconformity of the secondary membrane.

Advantageously, the detection is carried out during a detection period which is substantially simultaneous with the generation of overpressure in the secondary space or immediately after this generation, but before the temperatures are fully equilibrated between the different zones of the membrane.

The second gas may be selected to condense in a solid or liquid form. The formation of a liquid phase, however, has the advantage of allowing a flow of the condensed gas deposit as the formation of the deposit to the right of the leak. Thus, the condensation reaction can be more easily maintained by maintaining the pressure in the secondary space for a significant time, for example one or more minutes. The ability to maintain absi over time the hot spot resulting from the condensation reaction greatly facilitates the detection of this hot spot, especially if it has a limited contrast.

According to one embodiment, the overpressure is maintained in the secondary space for a duration greater than 10 minutes.

Preferably, the method comprises cooling the primary membrane to an average temperature below room temperature. This allows good control of the condensation conditions. In an advantageous embodiment, the process is carried out at an average membrane temperature above -5 ° C. preferably greater than 0 ^° C. Thus the process can be carried out under practical, low-constraining conditions and with a limited energy expenditure. Advantageously, the second gas is a mixture, the process comprising generating the mixture according to a composition which depends on the average temperature of the primary membrane. This makes it possible to adapt the condensation temperature as a function, for example, of the ambient temperature or the average temperature of the primary membrane. Preferably, the condensation temperature of second gas thus obtained is between the average temperature and the ambient temperature.

According to one embodiment, the second gas is a mixture of pentane and / or perfluoropentane and nitrogen. These gases are particularly suitable for a test in which, initially, the secondary space is at ambient temperature and where it is desired to obtain a liquid phase in contact with the primary membrane.

Preferably, the possible hot spots or spots of the primary membrane are detected using at least one temperature sensor and / or at least one infrared detector, arranged inside the tank.

According to one embodiment, the surface of the primary membrane inside the tank is temporarily covered with a coating capable of substantially eliminating the specular reflectivity of the surface, and the hot spots are detected using a thermal camera. .

For example, the coating may include water droplets.

Advantageously, the method comprises the steps of evacuating the first gas from the primary space and the second gas from the secondary space, and heating the primary membrane to room temperature. This allows, after the test, to repair the tank or put it into operation, if no nonconformity has been detected.

The invention also proposes a reservoir comprising a supporting structure, a primary membrane intended to be in contact with a product contained in the reservoir, and a secondary membrane arranged between the primary membrane and the supporting structure, in which the space between the membrane primary and the secondary membrane is called primary space and the space between the secondary membrane and the supporting structure is called secondary space, characterized in that it comprises:

a first injector capable of injecting a first incondensable gas or having a condensation temperature lower than the average temperature of the primary membrane in the primary space,

a second injector capable of injecting a second gas having a condensation temperature higher than the average temperature of the primary membrane in the secondary space, a pressurization device capable of generating an overpressure in the secondary space with respect to the primary space, and

a delimiter able to detect one or more hot spots of the primary membrane. This reservoir is suitable for putting a work of the test method according to one embodiment of the invention.

According to one embodiment, said second gas is a mixture, said second injector being capable of producing said mixture according to a composition determined as a function of the average temperature of the primary membrane.

According to one embodiment, said primary space and said secondary space contain a thermally insulating material, said reservoir being able to contain liquefied natural gas. The tank may be for example a land tank or a tank integrated with a ship, Brief description of the figures

The invention will be better understood, and other objects, details, features and advantages thereof will appear more clearly in the following description of a particular embodiment of the invention, given solely for illustrative purposes and not limiting, with reference to the accompanying drawings. On these drawings:

FIG. 1 is a diagram illustrating the principle of forced condensation,

FIG. 2 is a graph illustrating the condensation temperature of a gas as a function of its concentration in a gaseous mixture,

FIG. 3 is a sectional view of a tank wall whose tightness is tested,

FIG. 4 is a diagram of a tank suitable for implementing the test method according to one embodiment of the invention, and

- Figure 5 schematically shows one of the components of Figure 4.

^* Detailed description of an embodiment of the invention

FIG. 1 represents a wall 1 whose average temperature is Tm. A gas at the pressure P is brought into contact with the wall 1, as shown by arrow 2. If the condensation temperature Tc of FIG. The gas will be condensed in the form of a liquid or solid deposit 3. In doing so, the gas transfers energy in the form of heat, corresponding to its latent heat of condensation, to the wall. 1. This heat transfer is represented by the arrows 4. Thus, locally, the wall I has a temperature T greater than Tm. It is called forced condensation when the temperature Tm, the pressure P and the nature of the gas are controlled. The gas can be:

- A pure gas whose intrinsic physical characteristics correspond to the desired condensation temperature.

- A mixture of an incondensable gas and a condensable gas whose concentration is controlled to adjust the condensation temperature. Indeed, as shown in the graph of Figure 2, a pure gas which has a condensing temperature Tp will, once diluted to the X% concentration in an incondensable gas, a condensing temperature Tc less than Tp.

- A mixture of several condensed gases which, once associated, have a desired condensation temperature Tc.

With reference to FIGS. 3 to 5, it is now explained how the principle of forced condensation makes it possible to detect a leak in the secondary membrane of a multi-membrane reservoir.

The reservoir 5 comprises a carrier structure 6 which provides the mechanical rigidity, a primary membrane 8 intended to be in contact with the product contained in the reservoir 5, and a secondary membrane 7 arranged between the primary membrane 8 and the supporting structure 6. The The space between the primary membrane 8 and the secondary membrane 7 is called the primary space 10. The space between the secondary membrane 7 and the carrier structure 6 is called the secondary space 9.

The construction of the tank 5 will not be described in detail because several possibilities are known to those skilled in the art. This may be, for example, a tank for LNG made according to a known technique. In this case, thermally insulating material is present in the primary space 10 and in the secondary space 9. The reservoir 5 also comprises an injector 11 connected to the primary space 10 by a pipe 12, an injector 13 connected to the secondary space 14 via a pipe 14, a cooling device 15 connected to the inside of the tank 5 by a pipe 16, and pipes 17 respectively connecting the interior of the tank, the primary space 10 and the secondary space 9 to an exhaust and pressure management device. The aforementioned components can detect and locate a leak 18 in the secondary membrane 7, as described below. The sealing test method according to one embodiment of the invention successively involves the conditioning of the tank for the test, the actual test, then the deconditioning of the tank,

The tank conditioning for the test includes: - Set the temperature of the primary membrane to reach a desired temperature. This can be achieved by cooling devices or by injecting a coolant into the reservoir 5. For example, the cooling device 15 injects the liquid nitrogen in the tank 5. Ideally _"after this step, the membrane temperature primary is uniform. However, due to various thermal stresses, the primary membrane may have a slightly non-uniform temperature. Thus, below, we speak of the average temperature Tm of the primary membrane.

Injecting a neutral gas into the primary space 10. By neutral gas is meant a gas that does not condense at the temperature Tm, either because it is an incondensable gas or because its condensation temperature is less than Tm. This can be achieved by the injector 11 or, in the case of ambient air, by placing the primary space in communication with the atmosphere. - Inject a reactive gas into the secondary space 9. Reactive gas means a gas that condenses at a temperature above Tm. As explained above, it may be a pure gas or a mixed. This can be achieved by means of the injector 13.

The above three steps can be performed simultaneously or consecutively, in any order. The actual test comprises placing the reactive gas in overpressure in the secondary space 9 and detecting any hot spots on the primary membrane 8, advantageously from the inside of the tank. Indeed, as shown in more detail in Figure 3, if the secondary membrane 7 has a leakage 18, reactive gas escapes into the primary space 10, due to the pressure difference between the secondary space 9 and the primary space 10. This is symbolized by the cloud 19 and the arrow 20. Thus, at the level of the leak 18, the reactive gas comes into contact with the primary membrane 8 and forms condensation 21. As explained above, the reactive gas transfers heat to the primary membrane 8, which is therefore locally warmer than the temperature Tm. By detecting this hot spot 22, it is possible to locate the leak 18. The hot spot detection 22 can be performed for example by temperature sensor or by detecting the infrared radiation emitted, arranged inside the tank.

The deconditioning of the reservoir for the test includes:

- Evacuation of the primary space of the gases 10. This can be achieved using in particular one of the pipes 17, or by evacuation of this space, then filling if necessary, or by scanning with the gas provided during operation

- Evacuation of the reactive gas from the secondary space 9. This can also be achieved using in particular one of the pipes 17, either by evacuation of this space, then filling if necessary, or by scanning with the gas provided during operation.

- Raising temperature of the primary membrane. This can be achieved either by air conditioning devices or by convection of air at room temperature.

The above three steps can be performed simultaneously or consecutively, in any order.

In an exemplary implementation, the neutral gas is nitrogen and the reactive gas is a mixture of 50% by volume of nitrogen and 50% by volume of pentane. Pentane is liquid at atmospheric pressure and ambient temperature. Its vaporization temperature is 36 ° C. In the aforementioned mixture, its condensation temperature in the liquid phase drops to about 18 ⁰ C.

The tank 5 to be tested is for example a tank of LNG tanker whose primary membrane 8 is at ambient temperature of 25 ° C. The inside of the tank is cooled so that. the primary membrane has a mean temperature of a Tm of 10 ^° C. Because of the thermal insulation, the temperature in the secondary space 9 is greater than 20 ^° C. Thus, the nitrogen / pentane mixture can be injected into space secondary 9 without risk of condensation. Then, an overpressure of a few millibars is generated. The nitrogen / pentane mixture passes into the primary space 10 at the level of the leak 18 and condenses in contact with the primary membrane 8, generating a hot spot.

Moreover, the dilution rate of pentane in nitrogen can be modified to adapt the condensing temperature of pentane. Thus, if the ambient temperature is, for example, 35 ^° C. or 10 ^° C., it is possible to carry out the test by adapting the temperature Tm and the pentane dilution ratio.

For this, advantageously, the injector 13 allows a mixture to be produced according to a desired rate. For example, as shown in FIG. 5, the injector 13 comprises a reservoir 23 intended to contain the carrier gas (nitrogen in the abovementioned example) and a reservoir 24 intended to contain, in liquid form, the condensable gas ( pentane in the above example). These two tanks are connected, respectively via a pipe 25 and a pipe 26, to an evaporator 30 in which the mixing is carried out. The evaporator 30 is connected to the secondary space 9 via the pipe 14. A control device 29 makes it possible to control the dilution ratio of the pentane by acting on the evaporator 30 and on two flow meters 27 and 28 respectively arranged on the pipes 25 and 26. Many other gases can be selected depending on the desired condensation temperatures. For example perfluoropentane may at least partially replace pentane in the above example and proves safer because of its poor flammability.

In an embodiment where the primary membrane is at a positive temperature and an infrared camera is used to detect hot spots, it is advantageous in the conditioning the reservoir, coating the interior of the membrane with water droplets, for example by sweeping its surface with a stream of vapor, to form a diffusing layer that significantly reduces the specular reflectivity of the surface. Such a diffusing or opacifying coating can improve the measurement of the local emissivity of the membrane surface by means of an infrared camera.

Although the invention has been described in connection with a particular embodiment, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims

1. A method of testing the tightness of a tank (5). said reservoir comprising a carrier structure (6), a primary membrane (8) intended to be in contact with a product contained in the reservoir, and a secondary membrane (7) arranged between the primary membrane and the carrier structure, in which the space between the primary membrane and the secondary membrane is called primary space (10) and the space between the secondary membrane and the supporting structure is called secondary space (9), the primary space containing a first incondensable gas or having a temperature of condensation below the average temperature of the primary membrane, said method comprising the steps of:

injecting a second gas having a condensation temperature higher than the average temperature of the primary membrane into the secondary space,

generating an overpressure in the secondary space with respect to the primary space, and

detecting one or more hot spots (22) of the primary membrane corresponding to a deposition of the second condensed gas in contact with the primary membrane.

2. A method of leak test according to claim 1, characterized in that the second gas is condensed in a liquid form in contact with the primary membrane.

3. A method of leak test according to claim 1 or 2, characterized in that the detection is carried out during a detection period which is substantially simultaneous with the generation of overpressure in the secondary space.

4. The sealing test method according to claim 3, wherein the overpressure is maintained in the secondary space for a period greater than 10 minutes.

The test method according to claim 1, comprising cooling the primary membrane to a mean temperature below room temperature,

The sealing test method according to claim 5, wherein the average temperature of the primary membrane is greater than

-5 ⁰ C, preferably greater than 0 ⁰ C.

7. Test method according to one of claims 5 and 6, wherein the second gas is a mixture, the method comprising generating the mixture according to a composition which depends on the average temperature of the primary membrane, so that the condensation temperature of the second gas is between the mean temperature and the ambient temperature.

8. Test method according to one of the preceding claims, wherein the second gas is a mixture of pentane and / or perfluoropentane and nitrogen.

9. Test method according to one of the preceding claims, wherein the possible hot spots or the primary membrane are detected using at least one temperature sensor and / or at least one detector of infrared, arranged inside the tank.

10. The sealing test method according to one of claims 1 to 9, wherein is covered temporarily the surface of the primary membrane inside the tank of a coating capable of substantially eliminating the specular reflectivity of the surface and the hot spots are detected by means of a thermal camera.

11. A method of leak test according to claim 10, wherein the coating comprises droplets of water.

12. Test method according to one of the preceding claims, comprising the steps of:

- evacuate the first gas from the primary space and the second gas from the secondary space, - warm the primary membrane to room temperature.

13. Reservoir (5) comprising a carrier structure (6), a primary membrane (8) intended to be in contact with a product contained in the reservoir, and a secondary membrane (7) arranged between the primary membrane and the carrier structure, in which the space between the primary membrane and the secondary membrane is called primary space (10) and the space between the secondary membrane and the supporting structure is called secondary space (9), characterized in that it comprises:

a first injector (11) able to inject a first condensable gas or having a condensation temperature lower than the average temperature of the primary membrane in the primary space. a second injector (13) able to inject a second gas having a condensation temperature higher than the average temperature of the primary membrane in the secondary space;

a pressurization device capable of generating an overpressure in the secondary space with respect to the primary space, and

a detector capable of detecting one or more hot spots (22) of the primary membrane corresponding to a deposition of the second condensed gas in contact with the primary membrane.

14. Tank according to the preceding claim, wherein said second gas is a mixture, said second injector being adapted to perform said mixture according to a composition determined according to the average temperature of the primary membrane, so that the condensation temperature of the second gas is between the average temperature and the ambient temperature.

15. Tank according to one of claims 13 and 14, wherein said primary space and said secondary space contain a thermally insulating material, said tank being adapted to contain liquefied natural gas.