Membrane leak test method and associated leak detection device

Abstract

The invention relates to a method for testing the leak of a tank membrane comprising an intermediate isolated space (87) of a detection chamber (61), the leak detection device (54) further comprising a vacuum pump (57) connected to the detection chamber (61) and a measuring instrument connected to the detection chamber (61) and configured to measure a variable representative of the amount of at least one test gas present in the atmospheric gas phase of an external space, the method comprising the step of verifying the reaching of an isolation threshold S i in the intermediate isolated space (87) comprising a so-called neutral gas different from the test gas, the reaching of this isolation threshold S i being a necessary condition to trigger the leak test of the membrane.

Description

Technical Field

[0001] This invention relates to the field of sealed, insulated membrane tanks for storing and / or transporting fluids, such as cryogenic fluids.

[0002] More specifically, the present invention relates to a method for testing the sealing of a membrane for such a container and a leak detection apparatus for carrying out such a method. Background Technology

[0003] Document KR1020100050128 discloses a method for testing the seal of a membrane in a sealed insulated tank for storing liquefied natural gas (GNL). The tank has a multi-layered structure, comprising, from the outside to the inside, a secondary insulating barrier layer, a secondary sealing membrane, a primary insulating barrier layer, and a primary sealing membrane designed to contact the GNL contained within the tank. More specifically, the method aims to detect leaks via a weld bead that seals the metal plate of the primary sealing membrane. The method involves injecting a tracer gas (such as helium) into the primary insulating barrier layer and then moving a detection device equipped with a tracer gas analyzer along the weld bead of the primary sealing membrane within the tank. Therefore, if the detection device detects the presence of the tracer gas, a sealing defect in the primary sealing membrane can be inferred.

[0004] In this method, injecting the tracer gas into the main insulation layer is crucial because reliable results can only be guaranteed when the tracer gas diffuses uniformly and at a high concentration throughout the entire main insulation layer. Furthermore, the injection process is relatively lengthy to achieve satisfactory tracer gas diffusion levels. Additionally, the cost of injecting the tracer gas is high, as a large quantity of gas is required to reach a satisfactory concentration in the main isolation space. Moreover, some tracer gases (such as ammonia) are toxic and harmful. Finally, to ensure test reliability, the tracer gas can only be injected into the main insulation layer when a certain degree of seal is achieved between the main insulation layer and the interior of the tank. Therefore, a seal test cannot be performed without fully assembling the main sealing membrane to seal between the main insulation layer and the interior of the tank.

[0005] Furthermore, the testing device includes a unit for inhaling tracer gas and a tracer gas detector. The inhalation unit moves along the weld bead via a bracket located on the bottom wall of the tank or on a support existing within the tank, and the inhalation unit is secured to the bracket in this manner facing the weld bead of the wall adjacent to the bottom wall. However, due to the device's large size and the need to be attached to the bracket on the bottom wall, it is difficult to use this device to verify the seal of all weld beads in the tank. The device is also slow because it only verifies a small portion of the weld bead at a time, and the device's assembly on the bracket needs to be modified each time the weld bead to be verified is changed. Summary of the Invention

[0006] The applicant aims to overcome the shortcomings of current methods and devices by proposing a membrane seal testing method and a leak detection device for performing this method. The method and device of this application are reliable, simple and quick to use.

[0007] In particular, the present invention aims to provide a reliable method for testing membrane seals in which the detection of leaks does not require tracer gas.

[0008] Therefore, after various experiments and tests, the applicant has developed a method for testing the sealing of tank membranes, which includes the following sequential steps:

[0009] - A leak detection device is arranged in a tank, which includes an atmospheric gas phase and a membrane in an external space, the membrane including an outer surface and an inner surface facing the external space, the membrane including a test area, the seal of which must be tested, the leak detection device including a detection hood, the detection hood including a body and a seal connected to the body, the seal being configured to define a detection chamber between the body and the test area, the seal having a closed profile, the leak detection device including an intermediate isolation space of the detection chamber, the leak detection device also including a vacuum pump connected to the detection chamber and a measuring instrument connected to the detection chamber, the measuring instrument being configured to measure a variable representing the amount of at least one test gas present in the atmospheric gas phase in the external space;

[0010] - Position the test cover on the inner surface of the membrane and face the test area, and press the seal around the test area against the inner surface of the membrane;

[0011] -The pressure in the detection chamber is reduced by a vacuum pump;

[0012] - Determine variables using measuring instruments This variable represents the amount of test gas present in the detection chamber when the pressure is reduced; and

[0013] -Transfer variables Compared with the reference threshold Compare them.

[0014] The method according to the invention is characterized in that it further includes: verifying that an isolation threshold S is reached in an intermediate isolation space containing a so-called neutral gas different from the test gas. i The steps are as follows to obtain the isolation threshold S. i This is a necessary condition for triggering the determination and comparison steps.

[0015] Therefore, the advantage of this invention is that it does not use any test gas, while enabling extremely reliable leak detection tests. The test measurement is only triggered when the detection device determines that a leak in the membrane can be detected, because the intermediate isolation space completely isolates the test area.

[0016] The term "trigger" as used above refers to the start or initiation of the determining or comparing step.

[0017] The terms “internal face” and “external face” for the membrane under test refer to the sides of the membrane that are positioned or oriented toward the contents of the container and toward the outside of the container, respectively.

[0018] In the context of the specification and claims, "atmospheric gas phase" refers to a gas phase having a composition close to that of dry ambient air, that is, the "atmospheric gas phase" includes about 78% nitrogen, 21% oxygen, 0.9% argon and rare gases, as well as volatile organic compounds (which are readily emitted by the adhesives used in the thermal insulation barrier layer or from the solid insulating material), or trace gases (such as carbon dioxide or pentane), for example, as referred to as (chemical or physical) expansion during the formation of the insulating foam.

[0019] In other words, the atmospheric phase includes ambient air. For example, when the thermal barrier is sealed by a sealing film or when outside air is introduced into the tank, the atmospheric phase includes the portion of ambient air in the tank.

[0020] In other words, no tracer gas is injected into the external space before the detection chamber is arranged to press against the membrane and depressurized, even during the depressurization process. Therefore, this sealing test method is simpler and less expensive.

[0021] Furthermore, since no tracer gas is used, this method can be used without a certain degree of sealing between the external space and the interior of the container. The sealing test can then be performed before the membrane assembly is complete. Additionally, the sealing test can be performed, for example, on a test area of ​​the membrane containing a first set of plates, which are welded to each other before and / or simultaneously with the second set of membrane plates.

[0022] Finally, this testing device is easy to manipulate and move, which makes it possible to test all weld lines of the membrane more quickly.

[0023] According to a first embodiment of the present invention, the isolation threshold S is verified. i The steps include: verifying that a preset threshold concentration of neutral gas has been reached in the intermediate isolation space; once the neutral gas concentration is at least equal to the preset neutral gas concentration threshold, the isolation threshold S is... i Verified.

[0024] The concentration of neutral gas in the intermediate isolation space is an important criterion because, given the primary vacuum in the test area, slight gas leakage between the intermediate isolation space and the test area is almost unavoidable. This is why, in one embodiment, it is important to know the concentration of neutral gas in the intermediate space for reliable seal test measurements, and the following step—determining the variable representing the amount of test gas present in the detection chamber—is not initiated unless the concentration of neutral gas in the intermediate isolation space has at least reached a preset / predetermined low threshold value. And variables Compared with the reference threshold The comparison is made; the preset / predetermined concentration threshold value obviously depends on the leakage value to be detected and the seal of the test area (that is, the seal of the latter).

[0025] It should be noted that the leakage of a seal is much greater than the leakage or seal defect being measured; therefore, the concentration of inert gas in the intermediate isolation space should ideally be close to 100%.

[0026] According to one possibility provided by the present invention, a preset concentration threshold for neutral gas is verified by injecting neutral gas into an intermediate isolation space at a pressure of at least about 10 mbar, preferably at a pressure of up to 20 mbar, for a predetermined time. Once the time for injecting neutral gas into the intermediate isolation space has reached at least the predetermined time, the isolation threshold S is verified. i Verification is performed. Here, the characteristics of the various components of the sealing test apparatus—namely, the vacuum pump, measuring instruments, the seal of the test area, the pressure of the neutral gas injected into the intermediate space, etc.—are known, and where applicable, after several tests, the operator can evaluate the results by injecting neutral gas at a predetermined pressure for a specific time. These conditions (essentially the concentration of neutral gas in the intermediate isolation space) combine to enable the determination of the seal. And will and The steps for comparison.

[0027] In this case, verification is performed to reach the isolation threshold S before the determination and comparison steps. i The steps. In fact, generally speaking, whether in the first embodiment, in other cases described above, or in the second embodiment disclosed below, verification is performed to reach the isolation threshold S in the intermediate isolation space. i The verification step does not necessarily need to be performed before the determination and comparison steps; the verification step can be performed after both the determination and comparison steps, or again, only after the determination step. However, verification reaches the isolation threshold S. iThis step is described below prior to the determining and comparing steps, but it should be understood that the invention is not limited to this specific series of steps in any case.

[0028] Advantageously, the intermediate isolation space includes at least one purging port to discharge gas initially present in the space, replacing it with injected neutral gas. The gas initially present in the intermediate isolation space typically includes ambient air.

[0029] Given this latter premise, it is advantageous to use a neutral gas lighter than air (such as helium), and the purging port is located at the bottom or lower height of the intermediate isolation space, while the port for injecting the neutral gas (e.g., helium in this case) is located in the upper or top portion of the space. Therefore, injecting the neutral gas into the intermediate isolation space will displace ambient air heavier than helium, thereby causing the ambient air to occupy a lower space outside the intermediate space relative to the neutral gas, so that it can be discharged via the purging port.

[0030] Of course, if the leak detection device must be used on a vertical surface or at the top of the tank, the feature of this locating purging port loses much of its benefit, considering the weight of the neutral gas relative to the ambient gas (usually atmospheric air). This is why two purging ports can be provided, one located in the upper or top portion of the intermediate isolation space, and the other in the lower or bottom portion. Both ports can be automatically or non-automatically blocked by the operator to accommodate the position of the leak detection device in the tank and to accommodate the relative weight ratio between the neutral gas and the gas initially present in the intermediate isolation space, so that the gas initially present in the intermediate isolation space is replaced by the neutral gas.

[0031] According to a second embodiment of the present invention, the isolation threshold S is verified. i The steps include: verifying that the test gas concentration in the intermediate isolation space reaches a preset concentration threshold; once the test gas concentration is at most equal to the preset concentration threshold, the isolation threshold S is... i Verified.

[0032] Given this premise, the gas concentration to be determined in the intermediate isolation space is preferably the same as the gas concentration to be measured in the test area. This time, the residual amount of the test gas (preferably nitrogen and / or oxygen and / or argon) is measured to trigger the detection step / operation and the comparison step / operation. Of course, this second embodiment of the invention can be combined with the first embodiment: in this case, the neutral gas concentration is verified like the concentration of the test gas—or one of the test gases—and on the one hand, the neutral gas concentration must at least reach—exceed—a preset concentration value for the neutral gas concentration; on the other hand, the test gas concentration must at least reach—decline—a preset concentration value for the test gas concentration to enable the determination to be initiated. And will and The steps for comparison.

[0033] In view of this premise for the second embodiment, according to a possibility provided by the invention, a measuring instrument (preferably including a mass spectrometer) for the test area advantageously measures the concentration of the test gas in the intermediate isolation space. This arrangement allows for the use of, for example, a three-way valve and the connection of the measuring instrument (advantageously a mass spectrometer) to the test area and the intermediate isolation space. A sampling pump can be used to sample a specific volume in the intermediate isolation space and supply said volume to the mass spectrometer at the pressure required for effective use of the mass spectrometer.

[0034] Generally, in order to perform the first and second embodiments of the present invention, a preset concentration threshold for the neutral gas or test gas is verified by means of a thermal conductivity gas analyzer, ultrasonic measurement, infrared radiation, or electrochemical methods. Preferably, this verification is performed by means of a thermal conductivity gas analyzer.

[0035] Regarding ultrasonic measurements, an ultrasonic generator is used, connected to an ultrasonic receiver. These two components are placed in an intermediate isolation space and connected to a data acquisition and processing circuit via a cable. Therefore, the propagation time of the wave from the transmitter to the receiver is measured. Given the distance between the transmitter and receiver, the speed of sound propagation in the intermediate isolation space is derived, thereby enabling the determination of the gas concentration in said space.

[0036] Regarding the use of infrared radiation, an infrared source (typically a diode) and a detector are placed at opposite ends of the intermediate isolation space. Emission and reception are affected at wavelengths corresponding to the absorption peaks of the neutral or test gas whose concentration is to be measured. Therefore, the attenuation of luminescence intensity at the relevant wavelengths allows for the deduction of the amount of gaseous material, thereby enabling an approximate deduction of the gaseous material's concentration. In one possibility, the infrared source is adapted to scan a relatively broad wavelength spectrum, and the detector includes a series of phototransistors for each band to characterize the transmission or reflection spectra. Thus, given the known wavelengths of various gases that readily form gas mixtures within the intermediate isolation space, the precise composition of each gas can be obtained.

[0037] Regarding the use of electrochemical technology, a chemical electrolyte is used, and the change in its potential (directly measured) reflects the concentration of the gas to be measured. For this purpose, an electrochemical cell is arranged in an intermediate, isolated space, and is connected to a data acquisition and processing circuit via wires or other connections.

[0038] Other advantageous features of the invention are briefly described below:

[0039] Advantageously, the neutral gas includes helium or carbon dioxide.

[0040] According to one embodiment of the invention, advantageously, the intermediate isolation space includes a second seal that is connected to the body around the seal. In this embodiment, preferably, the second seal includes a sealing lip designed to be pressed against the inner surface of the membrane around the seal.

[0041] According to a preferred embodiment of the invention, the tank is a sealed insulated tank, and the external space is an insulating barrier layer comprising a solid insulating material.

[0042] According to an advantageous aspect of the invention, the method includes establishing a reference threshold. The phase, which includes:

[0043] - Position the test hood on the inner surface of the membrane in the sealed reference area, such that the test chamber is arranged to face the sealed reference area;

[0044] -The detection chamber is depressurized using a vacuum pump; and

[0045] - Determine the reference threshold using measuring instruments. The reference threshold This indicates the amount of test gas in the test chamber when the pressure is reduced.

[0046] Advantageously, the measuring instrument is a mass spectrometer.

[0047] Advantageously, the pressure in the detection chamber is reduced until the threshold Ps is reached.

[0048] According to the advantageous possibilities provided by the present invention, the seal includes an outer sealing lip that presses against the inner surface of the membrane when the detection chamber is depressurized.

[0049] Advantageously, the measuring instrument is configured to detect the presence of multiple test gases in the atmospheric gas phase present within the thermal insulation barrier layer, and for each test gas, advantageously, the variable is determined by the measuring instrument. The variable This indicates the amount of the test gas in the detection chamber when the pressure is reduced, and this variable... With the corresponding reference threshold Compare them.

[0050] Advantageously, the gas phase contained in the detection chamber is delivered to the measuring instrument to determine the variable.

[0051] According to one embodiment, when the detection chamber is depressurized, the external space is in the atmospheric phase.

[0052] According to one embodiment, the test gas is selected from nitrogen, oxygen, and argon.

[0053] According to another embodiment, the test gas is selected from water vapor, carbon dioxide, neon, krypton, or other components of air.

[0054] According to another embodiment, the test gas is selected from volatile organic compounds emitted by an adhesive used to bond two solid insulating materials together, or volatile organic compounds emitted when the insulating foam degasses, the insulating foam forming one of the solid insulating materials.

[0055] Similarly, it is conceivable to detect combinations of the aforementioned gases, more specifically, to detect multiple increases in the amount of these gases, or even to detect all of these gases present in the environment below or behind the area where the seal is being tested.

[0056] Reference threshold Leakage is not necessarily determined by positioning the detection hood over a reference area of ​​the membrane, but can be established directly on the test area at the moment a (partial) vacuum is achieved by a vacuum pump. In other words, in this case, leakage at the test area is detected by increasing the amount of one or more gases measured by the measuring instrument.

[0057] Therefore, refer to the threshold This indicates the amount of test gas present in the detection chamber when there is no leak. It should be understood that this reference threshold... It is a function of the vacuum level formed or generated in the detection chamber, or in other words, the reference threshold. It is a variable associated with the required / obtained (partial) vacuum.

[0058] According to one embodiment, the mass spectrometer is of the residual gas analyzer type.

[0059] According to one embodiment, a vacuum pump, a detection chamber, and a measuring instrument are interconnected via a vacuum circuit. This vacuum circuit includes a first channel connected to the detection chamber, a second channel connected to the vacuum pump, and a third channel connected to the measuring instrument. The first, second, and third channels are interconnected. The detection chamber is depressurized via the first and second channels. The third channel is equipped with a metering pump, which is activated after the depressurization step of the detection chamber to determine a variable. The variable This indicates the amount of test gas present in the testing chamber.

[0060] Therefore, thanks to the metering pump, even though the pressure level in the detection chamber exceeds the operating range of the measuring instrument, a vacuum compatible with the operating range of the measuring instrument can be obtained at the inlet of the measuring instrument.

[0061] According to one embodiment, the detection chamber is depressurized to a threshold value Ps.

[0062] According to one embodiment, the threshold value Ps is between 10 Pa and 1000 Pa and includes 10 Pa and 1000 Pa, for example, on the order of the absolute range of 25 Pa to 70 Pa.

[0063] According to one embodiment, the leak detection device includes a mechanical pressure device comprising at least one pressure element configured to apply pressure oriented toward the membrane onto a portion of the sealing lip when the body is arranged to face the test area, and to apply pressure to the sealing lip by the mechanical pressure device before depressurization, thereby pressing the sealing lip against the sealing membrane. Thus, the mechanical pressure device enables the sealing lip to be pressed against one or more portions (particularly at locations where there is a risk of seal removal from the sealing membrane) to reliably detect leaks through the detection chamber.

[0064] According to one embodiment, the mechanical pressure device is supported by the main body.

[0065] According to one embodiment, a gas phase contained in a detection chamber is delivered toward a measuring instrument to determine a variable.

[0066] According to one embodiment, the test area includes a first set of plates to which the membrane is welded to each other, and a sealing test method is performed before or simultaneously with a second set of plates to which the membrane is welded to each other to seal the membrane.

[0067] The present invention also relates to a leak detection device for testing the seal of a can by performing the method briefly defined above, the can comprising: a heat-insulating barrier layer comprising a solid insulating material in an atmospheric gas phase; a membrane comprising an outer surface and an inner surface facing the heat-insulating barrier layer, the membrane comprising a test area whose seal must be tested; the leak detection device comprising a detection hood arranged to face the test area, the detection hood comprising a body and a seal connected to the body and configured to define a detection chamber between the body and the test area, the seal having a closed profile intended to be pressed against the inner surface of the membrane around the test area; the leak detection device comprising an intermediate isolation space of the detection chamber; and the leak detection device further comprising a vacuum pump and a measuring instrument connected to the detection chamber, the measuring instrument being connected to the detection chamber and configured to measure a variable representing the amount of at least one test gas present in the atmospheric gas phase of the heat-insulating barrier layer.

[0068] The leak detection device is characterized in that an intermediate isolation space is connected to a reservoir that stores a neutral gas different from the test gas, thereby enabling the injection of the neutral gas into the intermediate isolation space, and the intermediate isolation space and its contents define the isolation threshold S of the detection chamber. i Once the isolation threshold is reached, the measurement of the variable, which represents the amount of the test gas, is initiated to characterize the detection of leakage at the membrane.

[0069] Advantageously, the intermediate isolation space includes a second seal that is connected to the body around the seal.

[0070] Preferably, the second seal includes a sealing lip that is designed to be pressed against the inner surface of the membrane around the seal.

[0071] Advantageously, the measuring instrument is configured to measure a variable representing the amount of at least one test gas present in the atmospheric gas phase within the thermal insulation barrier layer, the at least one test gas being selected from nitrogen, oxygen, argon, and volatile organic compounds that are readily released when the solid insulating material of the thermal insulation barrier layer is degassed.

[0072] According to an advantageous aspect of the invention, the vacuum pump, the detection chamber, and the measuring instrument are interconnected via a vacuum circuit comprising a first channel connected to the detection chamber, a second channel connected to the vacuum pump, and a third channel connected to the measuring instrument. The first, second, and third channels are interconnected, and the third channel is equipped with a metering valve located upstream of the measuring instrument.

[0073] According to one embodiment, the seal includes an outer peripheral sealing lip that is designed to be pressed against the inner surface of the membrane.

[0074] According to one embodiment, the apparatus further includes a mechanical pressure device comprising at least one pressure element configured to apply pressure oriented toward the membrane onto a portion of the sealing lip when the body is arranged to face the test area.

[0075] According to one embodiment, the pressure element is an elastically deformable element that applies pressure to a portion of the sealing lip through elastic deformation. Therefore, the elasticity of the pressure element during its elastic deformation allows a rebound force to be applied to the sealing lip in the direction toward the sealing membrane.

[0076] According to one embodiment, the pressure element is oriented perpendicular to the profile of the outer peripheral sealing lip.

[0077] According to one embodiment, the mechanical pressure device includes a plurality of pressure elements configured to apply pressure to multiple portions of a sealing lip located at two longitudinal ends of the sealing lip. Therefore, when the detection device is placed on the corrugated membrane portion, the mechanical pressure device applies pressure to different areas where there is a risk of seal lift-off, namely, laterally on the seal, at the ends of the seal lip, and in the corrugated bottom region.

[0078] According to one embodiment, the sealing lip includes at least one notch having a shape corresponding to the shape of the membrane corrugations, the notch being designed to straddle the corrugations.

[0079] According to one embodiment, the membrane comprises at least two metal plates connected to each other by weld beads.

[0080] According to one embodiment, the test area of ​​the membrane includes a portion of the weld bead.

[0081] According to one embodiment, the outer peripheral sealing lip bends outward toward the detection shroud, and the outer peripheral sealing lip is configured to bend and press against the membrane when the detection chamber is depressurized.

[0082] According to one embodiment, a portion of the weld bead is crossed by at least one corrugation of the membrane.

[0083] According to one embodiment, the sealing lip is adapted to the geometry of the at least one corrugation.

[0084] According to one embodiment, a portion of the weld bead is traversed by at least two parallel corrugations (e.g., three parallel corrugations) of the membrane, and the sealing lip is adapted to the geometry of the corrugations.

[0085] According to one embodiment, a portion of the weld bead is traversed by at least two parallel corrugations (e.g., three parallel corrugations) of the membrane, and the sealing lip is adapted to the geometry of the corrugations.

[0086] According to one embodiment, the sealing lip includes at least two notches having a shape corresponding to the shape of the corrugations of the membrane protruding toward the interior of the can, the notches being designed to straddle the corrugations.

[0087] According to one embodiment, the portion of the sealing lip pressed by the mechanical pressure device is located at the base of the recess. Therefore, the mechanical pressure device applies pressure to areas where there is a risk of seal lift-off due to changes in the notch's slope. According to another embodiment, the mechanical pressure device includes a plurality of pressure elements configured to apply pressure to multiple portions of the sealing lip located at the base of one or more recesses. Therefore, the mechanical pressure device applies pressure to different areas where there is a risk of seal lift-off, namely the base of one or more recesses.

[0088] According to one embodiment, the pressure element includes a curved blade that includes a pad that contacts a sealing lip at one of its ends. According to another embodiment, the pad is cylindrical in shape and has a cylindrical axis extending in a direction generally parallel to the base facing the notch. Therefore, the pad allows pressure to be uniformly applied to a portion of the sealing lip by a mechanical pressure device.

[0089] According to one embodiment, the detection cover has an elongated shape.

[0090] According to one embodiment, the seal is made of an elastomeric material having a Shore A hardness between 20 and 50, including 20 and 50.

[0091] According to one embodiment, the elastomeric material of the seal is selected from elastomeric polyurethane, EPDM rubber, silicone, nitrile, and...

[0092] According to one embodiment, a vacuum pump, a detection chamber, and a measuring instrument are interconnected via a vacuum circuit, which includes a first channel connected to the detection chamber, a second channel connected to the vacuum pump, and a third channel connected to the measuring instrument. The first, second, and third channels are interconnected, and the third channel is equipped with a metering pump located upstream of the measuring instrument.

[0093] Another idea behind this invention is a leak detection device that enables the use of measuring instruments that operate at very low pressures.

[0094] According to one embodiment, the present invention provides a leak detection device for testing the seal of a canister including a membrane having a test area whose seal must be tested. The leak detection device includes a detection shroud arranged to face the test area and comprising a body and a seal connected to the body and configured to define a detection chamber between the body and the test area. The seal has a closed profile intended to be pressed against the inner surface of the membrane around the test area. The leak detection device also includes a vacuum pump and a measuring instrument connected to the detection chamber and configured to measure a variable representing the amount of at least one test gas. The vacuum pump, the detection chamber, and the measuring instrument are interconnected via a vacuum circuit including a first channel connected to the detection chamber, a second channel connected to the vacuum pump, and a third channel connected to the measuring instrument. The first, second, and third channels are interconnected, and the third channel is equipped with a metering valve arranged upstream of the measuring instrument.

[0095] The advantage of this leak detection device is that, although the pressure level in the detection chamber is higher than the operating range, the pressure obtained at the inlet of the measuring instrument is compatible with the operating range of the measuring instrument. If this detection device is advantageous when not using a tracer gas, then it can also be used if the method uses a tracer gas. Attached Figure Description

[0096] The invention will be better understood in the following description of specific embodiments of the invention, which are given by way of non-limiting illustration with reference only to the accompanying drawings, and other objects, details, features and advantages of the invention will become more apparent.

[0097] [ Figure 1 [ ] is a schematic diagram of the multi-layered structure of the membrane tank wall.

[0098] [ Figure 2 [Illustration of an apparatus for detecting membrane leakage according to one embodiment]

[0099] [ Figure 3 [This is based on] Figure 2 A schematic diagram of a variant of the embodiment of a device for detecting membrane leakage.

[0100] [ Figure 4 ]yes Figure 1 A cross-sectional view taken along line II-II of the detection hood of the leak detection device.

[0101] [ Figure 5 [This is based on] Figure 2 and Figure 3 A perspective view of the seal in an embodiment.

[0102] [ Figure 6 [Illustration] is a schematic diagram of a variant of a leak detection device, in which the detection shroud is equipped with a mechanical pressure device.

[0103] [ Figure 7 [This refers to the process of depressurizing the testing chamber beforehand.] Figure 6 A schematic diagram of the cross-section of the detection cover.

[0104] [ Figure 8 [This refers to the process of depressurizing the testing chamber.] Figure 6 A schematic diagram of the cross-section of the detection cover.

[0105] [ Figure 9 The image schematically illustrates the positioning of a detection hood facing a portion of a weld bead that provides a seal between two adjacent corrugated metal plates of the membrane.

[0106] [ Figure 10 [Illustration] is a schematic diagram of a first embodiment of a device for detecting membrane leakage according to the present invention.

[0107] [ Figure 11 [Illustration] is a schematic diagram of an apparatus for detecting membrane leakage according to another embodiment of the present invention.

[0108] [ Figure 12 [This shows the reference thresholds provided by the measuring instrument for when a sealing defect is not detected (curve a) and when a sealing defect is detected (curve b).] and variables The graph, the variable This indicates the amount of test gas present in the detection chamber. Detailed Implementation

[0109] The present invention is described below using a thermally conductive gas analyzer as an instrument for verifying a preset concentration threshold for a gas (in this case, a neutral gas). However, it should be understood that all the instruments and methods described above, while not exhaustive, are possible solutions for performing the following steps: verifying that an isolation threshold S is reached in an intermediate isolation space. i .

[0110] By convention, the terms "external" and "internal" are used to define the position of one element relative to another element, referring to the exterior and interior of a can.

[0111] The sealing test method for membranes used to seal heat-insulating membrane tanks will be described below. For example, particularly regarding Mark Such a membrane can is described in patent application FR2691520.

[0112] The membrane tank contains multiple walls with a multi-layered structure, such as in Figure 1As shown in the diagram. Each wall 1, from the outside to the inside of the tank, includes: a secondary heat-insulating barrier layer 2, which includes a secondary insulation plate 3 fixed to a support structure 4; a secondary membrane 5 resting on the secondary heat-insulating barrier layer 2; a primary heat-insulating barrier layer 6, which includes a primary insulation plate 7 resting on the secondary membrane 2 and fixed to the support structure 4 or fixed to the secondary insulation plate 3; and a primary membrane 8 resting on the primary heat-insulating barrier layer 6 and intended to contact the liquefied gas contained in the tank.

[0113] Before this membrane tank is put into use, and before the tracer gas is injected into the secondary heat-insulating barrier layer 2 and the primary heat-insulating barrier layer 6, the gas phase present in the secondary heat-insulating barrier layer 2 and the primary heat-insulating barrier layer 6 is the atmospheric gas phase, that is, its composition is close to that of ambient air.

[0114] According to one embodiment, the gas phase also includes volatile organic compounds emitted by one or more adhesives used in the heat-insulating barrier layer, such as bonding the insulating materials used to manufacture the barrier to each other, or the volatile organic compounds originating from any other element of the heat-insulating barrier layer, such as from the degassing of the insulating foam of the barrier.

[0115] The primary membrane 8 and / or the secondary membrane 5 comprise multiple metal plates welded to each other. More specifically, the sealing test method described below is designed to test the seal of a weld that connects the metal plates for one and / or the other of the primary membrane 8 and the secondary membrane 5 to each other. According to one embodiment, the membranes 5, 8 to be tested have corrugations that allow the membranes to deform under thermal and mechanical loads generated by a fluid stored in the tank. For this purpose, each metal plate comprises two series of mutually perpendicular corrugations.

[0116] Reference Figure 2 Leak detection device 54, used to test the seal of membranes 5 and 8, can be seen.

[0117] The leak detection device 54 includes a detection cover 55, which is designed to be arranged on the inner surface of the membranes 5, 8 and facing the weld portion to be tested.

[0118] The test cover 55 has an elongated shape and a length between 0.5m and 5m, including 0.5m and 5m (e.g., on the order of 1m). Advantageously, the length of the test cover 55 is as long as possible to verify the seal of a larger area in the same test process.

[0119] As in Figure 4As shown, the test cover 55 includes a rigid body 100 and a flexible seal 60, which are fixed to each other and are arranged to define a sealed test chamber 61 together with the membranes 5, 8 to be tested, which is arranged to face the portion of the weld 62 to be tested.

[0120] Refer again Figure 2 As can be seen, the leak detection device 54 also includes a measuring instrument 56 connected to the detection chamber 61 and a vacuum pump 57 associated with the measuring instrument 56. The vacuum pump 57 is connected to the detection chamber 61 of the detection shroud 55 on the one hand to allow the detection chamber 61 to be depressurized, and on the other hand to the measuring instrument 56 to deliver the gas contained in the detection chamber 61 to the measuring instrument 56.

[0121] Vacuum pump 57 is connected to detection hood 55 via pipe 58 (preferably flexible). Pipe 58 is connected to a channel formed in body 100 and leads to detection chamber 61.

[0122] exist Figure 3 In another embodiment shown, the leak detection device includes a second vacuum pump 84 connected to pipe 58 via valve 85. Advantageously, this second vacuum pump is more efficient than the vacuum pump 57 associated with measuring instrument 56. In this case, the second vacuum pump 84 is used to depressurize the detection chamber 61, while the vacuum pump 57 is used to deliver the gas contained in the detection chamber 61 to the measuring instrument 56 after the detection chamber 61 has been pre-depressurized.

[0123] As in Figure 4 and Figure 5 As shown, the body 100 includes a rigid core 59. The seal 60 includes an encapsulation 63 adapted to the shape of the rigid core 59 and an outer peripheral sealing lip 64 extending downwards from the encapsulation 63. The encapsulation 63 has a bottom 83 covering the upper surface of the rigid core 59 and an outer peripheral wall 74 adapted to the outer periphery of the rigid core 59. The bottom 83 includes at least one hole (not shown), to which a tube 58 connected to the vacuum pump 57 is sealed. The rigid core 59 includes an opening 79 on its lower surface 80, which extends the entire length of the rigid core 59. When the detection chamber 61 is depressurized, the opening 79 ensures that the test area 62 is always in fluid contact with the detection chamber 61, even though the rigid core 59 descends toward the membranes 5, 8 due to deformation of the sealing lip 64. Furthermore, the rigid core 59 may also include a channel in… Figure 2 Not shown in the diagram, because the channel exists only in the plane passing through the tube 58, the channel facing outwards from the hole formed in the bottom 83 of the encapsulation 63, and therefore, as in Figure 2 and Figure 3As shown, this enables the establishment of a connection between the detection chamber 61 and the tube 58, which leads to the vacuum pump 57 and / or the vacuum pump 84 and the measuring instrument 56.

[0124] The sealing lip 64 bends outward toward the detection chamber 55, and thus the sealing lip is configured to bend and press against the membranes 5 and 8 when the detection chamber 61 is depressurized. In other words, the sealing lip 64 has a cross-section that is generally L-shaped.

[0125] The portion of the sealing lip 64 that bends outward has a width on the order of 15 mm to 40 mm. The sealing lip 64 conforms to the geometry of membranes 5 and 8 along the weld bead to be tested. Furthermore, in Figure 5 In the middle, the sealing lip 64 includes a notch 65 having a shape corresponding to the corrugated shape of the membranes 5 and 8, and the test cover 55 is designed to straddle when it is in a position against the portion of the weld to be tested.

[0126] Advantageously, the seal 60 is made of an elastomeric material having a Shore A hardness between 20 and 50 (inclusive). For example, the seal 60 is made of elastomeric polyurethane, EPDM rubber, silicone, nitrile, or... Made.

[0127] Figure 6 , Figure 7 and Figure 8 A detection cover 55 according to another embodiment is shown. Figures 6 to 8 The detection shield 55 in the middle is similar to Figure 4 and Figure 5 The test chamber 55 is designed in a manner similar to the test chamber 61, but with a significant difference in that it includes a mechanical pressure device 66 adapted to press the outer peripheral sealing lip 64 against the membrane to be tested in a manner that ensures the test chamber 61 is sealed. The test chamber 55 includes: a body 100 extending longitudinally; a flexible seal 60 fixed to the body 100; and the mechanical pressure device 66, carried by the body 100 and configured to apply pressure to the seal 60 in a direction toward the membranes 5 and 8. The rigid core 59 includes a channel 82 for connecting the lower surface 80 of the rigid core 59 to the upper surface 81. The channel 82 enables communication between the test chamber 61 and a gas outlet connector 78, which is intended to connect to a tube 58, as shown in... Figure 2 and Figure 3 As shown, the tube leads to one or more vacuum pumps 57, 84 and measuring instrument 56.

[0128] The seal 60 includes an encapsulation 63 that is secured to the rigid core 59 by a fixing device 110, which includes, for example, an open ring that surrounds the entire periphery of the rigid core 59 and the seal 60, and the fixing device secures the rigid core 59 and the seal 60 to each other in a sealing manner by fixing members (such as bolts).

[0129] The mechanical pressure device 66 includes a support element 73 that extends along the entire length of the body 100 above it and is fixed to the body 100. A handle 76 is fixed to both longitudinal ends of the support element 73 to allow an operator to manipulate the detection cover 55 and, where applicable, to actuate the mechanical pressure device 66.

[0130] The mechanical pressure device 66 consists of multiple pressure elements, which here take the form of curved blades 72. The curved blades 72 are distributed on the sealing lip 64 and are fixed to the support element 73 by a fixing device 77. The curved blades 72 are elastically deformable, such that when deformation occurs, the curved blades apply elastic force to the sealing lip 64 to press the sealing lip against the membranes 5 and 8. To ensure a reliable seal in the detection chamber 61, it is necessary to press the sealing lip 64 in areas with higher risk of removal. This is why the ends of the curved blades 72 press against the sealing lip 64, particularly at the base of the notch 65 of the sealing lip 64 and at the longitudinal end of the detection cover 55.

[0131] One end of some of the curved blades 72 is fixed to the support element 73, while the other end rests on the sealing lip 64. These blades 72 are positioned at the ends of the detection cover 55. Other curved blades 72 are fixed to the support element 73 at their middle portions, while the two ends of other curved blades rest on the sealing lip 64, in this way to apply pressure to two different areas, specifically these curved blades 72 are positioned between the two recesses 65.

[0132] Each curved blade 72 has a pad 75 at its end that contacts the sealing lip 64. This pad is designed to limit impact phenomena that could easily reduce the integrity of the sealing lip 64. For this purpose, the pad 75 has a support surface larger than the cross-section of the curved blade 72. Furthermore, advantageously, the support surface of the pad 75 is cylindrical, with the axis of the cylinder extending in a direction generally parallel to the base of the recess 64. Additionally, the length of the pad 75 is approximately equal to the dimension of a portion of the sealing lip 64 that protrudes from the body 100 along the direction in which the pad 75 extends. Therefore, the pad 75 allows the mechanical pressure device 66 to apply uniform pressure to the sealing lip 64.

[0133] As in Figure 8As shown, when vacuum pump 57 or vacuum pump 84 is activated, a reduced pressure is generated in the test chamber 61, which allows the test cover 54 to be secured to the membranes 5, 8 to be tested. This pressure reduction then activates the mechanical pressure device 66, in which the mechanical pressure device presses the sealing lip 64 against the membranes 5, 8 in certain clearly defined areas. Specifically, the curved blades 72 are tensioned such that they transmit the force on the sealing lip 64 via the pad 75 to the areas where the sealing lip 64 is most likely to be lifted, namely the longitudinal end of the body 100 and the base of the notch 65.

[0134] According to a particularly significant aspect of the invention, the sealing test method for membranes 5 and 8, described below, does not involve the injection of tracer gas into the heat-insulating barrier layers 2 and 6 covering the membranes 5 and 8 to be tested. Furthermore, during the sealing test on membranes 5 and 8, the objective is to detect the migration of atmospheric gas phase present in the heat-insulating barrier layers 2 and 6 along the direction of the detection chamber 61 via defective weld lines, in order to identify sealing defects.

[0135] The sealing test can then be performed either before or after the membrane (the membrane's seal must be tested) is fully assembled. Therefore, according to the possibility provided by the invention, the test is performed on the test area of ​​the membrane involving the first set of welded plates, and after or in parallel with the sealing test in said area, the second set of plates of the sealing membrane is assembled and welded to each other.

[0136] exist Figure 1 The measuring instrument 56 shown is configured to measure a variable representing the amount of one or more test gases present in the atmospheric gas phase of the thermal barrier layers 2 and 6 covering the membranes 5 and 8 to be tested, within the testing chamber 61. Advantageously, the test gases are selected from gases present in dry air at a concentration greater than 0.5%, namely nitrogen, oxygen, and argon. This allows for limiting the uncertainty relative to the measurement value provided by the measuring instrument 56. According to alternative or supplementary embodiments, the test gases are selected from volatile organic compounds emitted from the adhesive of the thermal barrier layers or any other component.

[0137] According to one embodiment, the measuring instrument 56 is a mass spectrometer, and more specifically, a residual gas analyzer. The residual gas analyzer is a type of mass spectrometer used to measure the chemical composition of gases present in a low-pressure environment. The residual gas analyzer includes an ionization source that ionizes molecules of one or more gases that will subsequently be analyzed by one or more mass analyzers, which separate the generated ions according to their mass-charge ratios. The residual gas analyzer also includes an ion detection system that measures the corresponding current generated for each mass-charge ratio, making it possible to infer the number of molecules of each analyzed gas.

[0138] The process for detecting sealing defects in welds is as follows.

[0139] First, the method includes establishing one or more reference thresholds. The procedure involves placing the inspection cover 55 in the sealed reference area (e.g., an area without weld lines) of the membranes 5 and 8 by one or more operators.

[0140] Vacuum pump (reference) Figure 2 Vacuum pump 57 or Figure 3 The vacuum pump 84 is activated to depressurize the detection chamber 61, thereby ensuring that the detection shroud 55 is secured to the membranes 5, 8 to be tested. Once the pressure within the detection chamber 61 reaches the pressure threshold Ps, the vacuum pump 57 or vacuum pump 58 stops. Advantageously, the pressure threshold Ps is within the absolute range of 10 Pa to 1000 Pa, including, for example, on the order of 25 Pa to 70 Pa. Once the pressure is reached or shortly thereafter, the vacuum pump 57 associated with the measuring instrument 56 is activated to deliver the gas phase contained in the detection chamber 61 to the measuring instrument 56 within a time Tm of less than or equal to 5 seconds, and advantageously less than 1 second. The vacuum pump 57 associated with the measuring instrument 56 is controlled according to a pressure setpoint or a volume setpoint within the detection chamber.

[0141] Then, measuring instrument 56 provides a reference threshold. This reference threshold represents the amount of test gas present in the detection chamber 61 when the detection shroud 55 is positioned facing the area of ​​membrane 5 and membrane 8 without sealing defects. According to one embodiment, when the measuring instrument 56 is configured to detect multiple test gases present in the atmospheric gas phase within the thermal barrier layers 2 and 6, a reference threshold is measured for each test gas.

[0142] Subsequently, when one or more reference thresholds Once determined, the inspection cover 55 is then arranged to face the portion of the weld 62 to be tested, as shown in... Figure 9 As shown, the inspection cover 55 is appropriately centered on the weld bead 62, such that the two lateral components of the curved portion of the sealing lip 64 are arranged on the corresponding opposite sides of the weld bead 62.

[0143] The intermediate isolation space 87 includes a thermally conductive gas separator 200 placed within the space 87, for example, the thermally conductive gas separator is fixed to the inner surface of wall 190, which, together with seal 86, defines the intermediate isolation space 87. It should be noted that the intermediate isolation space 87 can also be entirely defined by seal 86, as in... Figure 11In the illustrated embodiment, the smaller volume of the intermediate isolation space 87 is more likely to be this case. However, preferably, at least a portion of this defined space consists of a wall 190, which may be made of a material that is more rigid than the material constituting the seal 86 (such as a plastic material or a mixture of plastic materials, a metal (preferably aluminum), or a composite material combining layers of plastic material and metal, or even ceramic).

[0144] The leak detection device 54 also includes a reservoir 88 for storing a neutral gas, which is connected in a sealed manner to an intermediate space 87. The neutral gas must be a gas different from one or more test gases. The reservoir 88 for storing the neutral gas is connected to the intermediate space 87 via a valve and / or a pump.

[0145] The thermal conductivity gas separator 200 is connected to the control circuit via a wired or wireless connection and sends a visual or audible signal to the operator indicating that the isolation threshold S of the intermediate space 87 has been reached. i Alert. The isolation threshold S has been reached. i The alarm may constitute a simple message for the operator, or the alarm or the sound and / or visual signal may enable unlocking, i.e., when the isolation threshold S has been reached. i Previously, the operator could not continue measuring one or more test gases in test area 62. Of course, this was related to the isolation threshold S already reached in intermediate space 87. i The alarm can also automatically trigger the measurement of one or more test gases in test area 62 without the need for operator or similar personnel.

[0146] Before or after a partial vacuum is generated in the test area 62 by the vacuum pump 84, and preferably once the pressure threshold Ps is reached, and a reference threshold is determined by the measuring instrument 56. or variable Within a certain time frame, neutral gas is injected into the intermediate space 87. Advantageously, the neutral gas is also injected during and optionally before the depressurization of the test chamber 61. Thus, the intermediate space 87 forms a neutral gas barrier layer that prevents or restricts the introduction of ambient air into the test chamber 61. This allows for maintaining excellent reliability of the seal test even if the seal 60 does not produce a sufficient seal.

[0147] Once the pressure inside the detection chamber 61 reaches the pressure threshold Ps or shortly thereafter, and if the isolation threshold S is reached... i Then, the vacuum pump 57 associated with the measuring instrument 56 is activated to deliver the gas phase contained in the detection chamber 61 to the measuring instrument 56 within time Tm. The measuring instrument 52 then measures the variable. The variable This indicates the amount of test gas present in detection chamber 61. For one or more gases, a reference threshold has been established.

[0148] If the tested portion of weld 62 has no sealing defects, the variable provided by measuring instrument 52 The value is approximately equal to the reference threshold. The value of . This situation corresponds to Figure 12 Curve a is shown in the figure.

[0149] Conversely, if the portion of weld 62 under test includes one or more sealing defects, test gas molecules migrate from the gas phase in the heat insulation layers (equal to or close to atmospheric pressure) into the test chamber 61 via the sealing defects due to the pressure difference between the atmospheric gas phase in the heat insulation layers 2 and 6 (equal to or close to atmospheric pressure) and the pressure in the test chamber 61. Furthermore, in this case, once the pressure threshold Ps is reached, the amount of one or more test gases present in the test chamber 61 increases. Moreover, the amount of test gas measured by the measuring instrument 62 is greater than the amount of test gas measured when the test chamber 61 is arranged in the sealed reference area of ​​the membranes 5 and 8. This situation corresponds to... Figure 12 Curve b is shown in the figure.

[0150] Then, in order to determine whether a sealing defect exists in a portion of the tested weld 62, the variable... Compared with the reference threshold Compare them.

[0151] If variables Less than or equal to (where Δ is a constant or variable representing the absolute or relative measurement uncertainty), then the conclusion is that the tested portion of weld 62 has no sealing defects. In this case, the inspection cover 55 is then arranged to face adjacent portions of weld 62, with overlap between the two portions being tested consecutively, to ensure that the entire length of weld 62 has been sealed.

[0152] Otherwise, if the variable Greater than The conclusion was that a portion of weld 62 tested contained sealing defects. Corrective welding measures were then taken to rectify the defects.

[0153] When using multiple test gases, the variables for each test gas will be... The reference threshold corresponding to the test gas This comparison ensures redundancy in the sealing test and further guarantees the reliability of the sealing test employed.

[0154] Based on the possibilities provided by the present invention, and Figure 11As can be seen, advantageously, the vacuum circuit includes three interconnected channels 89, 90, and 91: a first channel 91 connected to the detection chamber 61, a second channel 90 connected to the vacuum pump 84, and a third channel 91 connected to the measuring instrument 56, which itself is equipped with a pumping device 57. Advantageously, the pumping device 57 equipped with the measuring instrument includes two pumps: a main pump and a turbomolecular pump capable of maintaining a high vacuum.

[0155] In this embodiment, the third channel 91 is equipped with a metering valve 92, which is arranged upstream of the measuring instrument 56. The metering valve 92 enables the sampling of a very low flow rate of gas from the detection chamber 61 and sends the sampled gas to the measuring instrument 56. Thus, the metering valve 92 enables a gas flow at a pressure lower than that in the detection chamber 61 to be obtained at the inlet of the measuring instrument 56.

[0156] Therefore, although the pressure level in the detection chamber 61 is higher than the operating range of the measuring instrument 56, a high vacuum compatible with the operating range of the measuring instrument can be obtained at the inlet of the measuring instrument by using this metering valve.

[0157] According to an advantageous embodiment, when the measuring instrument 56 is a residual gas analyzer type mass spectrometer, the operating pressure of such measuring instrument 56 is typically less than or equal to 1 × 10⁻⁶. -4 Therefore, the adjustment of metering valve 92 is determined based on the pressure in the first channel 89 and the second channel 90, such that the pressure in the third channel downstream of the metering valve is less than or equal to 1 × 10 mbar. - 4 mbar.

[0158] Advantageously, the control valve has an operating range between 5 × 10⁶ mbar and 1000 mbar·l / s.

[0159] Furthermore, the metering valve 92 is equipped with an on / off tap located upstream of the flow regulating device. Therefore, when performing a sealing test, the tap of the metering valve 92 remains closed as long as the pressure in the test chamber does not reach a threshold, and then opens for a period of time Tm when the threshold is reached.

[0160] Although the invention has been described in conjunction with several specific embodiments, it is apparent that the invention is by no means limited to these embodiments, and that the invention includes all technical equivalents and combinations of the described methods if they fall within the scope of the invention.

[0161] The use of the verbs “comprising” or “including” and their cognate forms does not exclude the presence of elements or steps other than those described in the claims.

[0162] In the claims, any reference numerals between parentheses shall not be construed as limiting the claims.

Claims

1. A method for testing the seal of a canister membrane (5, 8), the method comprising the following sequential steps: - The step of arranging a leak detection device (54) in a tank containing an atmospheric gas phase and a membrane (5, 8) in an external space, the membrane including an outer surface and an inner surface facing the external space, the membrane (5, 8) including a test area (62), the seal of the test area must be tested, the leak detection device (54) including a detection cover (55), and the detection cover including a body (100) and a seal (60) connected to the body (100), and the seal being configured to be in the body (100) and the A test chamber (61) is defined between test areas (62), the seal (60) has a closed profile, the leak detection device (54) includes an intermediate isolation space (87) surrounding the test chamber (61), the leak detection device (54) also includes a vacuum pump (57, 84) connected to the test chamber (61) and a measuring instrument (56) connected to the test chamber (61), and the measuring instrument is configured to measure a variable representing the amount of at least one test gas present in the atmospheric phase in the external space; - The step of positioning the detection cover (55) on the inner surface of the membrane (5, 8) and facing the test area (62) and pressing the seal (60) against the inner surface of the membrane (5, 8) around the test area (62); - The step of depressurizing the detection chamber (61) by means of the vacuum pumps (57, 84); - Determine the variable φ using the measuring instrument (56) t The steps, the variable φ t The amount of test gas present in the detection chamber (61) when the pressure is reduced; as well as - The variable φ t Compared with the reference threshold φ r The steps for comparison; The method is characterized in that the intermediate isolation space (87) includes a second seal (86) connected to the body (100) around the seal (60), and the method further includes: verifying that an isolation threshold S is reached in the intermediate isolation space (87) containing a so-called neutral gas different from the test gas. i The steps are as follows to obtain the isolation threshold S. i It is the trigger for the deterministic variable φ t The steps and the variable φ t Compared with the reference threshold φ r The necessary condition for the comparison step.

2. The method according to claim 1, wherein, Verify the isolation threshold S i The steps include: verifying that a preset threshold concentration of neutral gas is reached in the intermediate isolation space (87), and once the neutral gas concentration is at least equal to the preset neutral gas concentration threshold, the isolation threshold S is... i Verified.

3. The method according to claim 1, wherein, Verify the isolation threshold S i The steps include: verifying that a preset concentration threshold for the test gas in the intermediate isolation space (87) is reached; once the test gas concentration is at most equal to the preset concentration threshold for the test gas, the isolation threshold S... i Verified.

4. The method according to claim 2 or 3, wherein, The verification of preset concentration thresholds for neutral or test gases is carried out using thermal conductivity gas analyzers, ultrasonic measurements, infrared radiation, or electrochemical methods.

5. The method according to claim 2, wherein, The preset concentration threshold of neutral gas is verified by injecting neutral gas at a pressure of at least 10 mbar into the intermediate isolation space (87) within a predetermined time. Once the time for injecting neutral gas into the intermediate isolation space (87) reaches at least the predetermined time, the isolation threshold S is verified. i Verified.

6. The method according to claim 5, wherein, In determining the variable φ t The steps and the variable φ t Compared with the reference threshold φ r Before the comparison step, verification is performed to reach the isolation threshold S. i The steps.

7. The method according to claim 5 or 6, wherein, The intermediate isolation space (87) includes at least one purging hole to discharge gas initially present in the intermediate isolation space (87), thereby replacing the gas initially present in the intermediate isolation space with injected neutral gas.

8. The method according to claim 1, wherein, The neutral gas is helium.

9. The method according to claim 1, wherein, The second seal (86) includes a sealing lip that is designed to be pressed against the inner surface of the membrane (5, 8) around the seal (60).

10. The method according to claim 1, wherein, The tank is a sealed, insulated tank, and the external space is an insulating barrier layer (2, 6), which comprises a solid insulating material.

11. The method according to claim 1, wherein the method includes establishing the reference threshold φ r The phase, the phase includes: - Position the detection cover (55) on the inner surface of the membrane (5, 8) in the sealed reference area of ​​the membrane, such that the detection chamber (61) is arranged to face the sealed reference area; - The detection chamber (61) is depressurized by the vacuum pumps (57, 84); as well as - The reference threshold φ is determined by the measuring instrument (56). r The reference threshold φ r This indicates the amount of test gas in the test chamber (61) when the pressure is reduced.

12. The method according to claim 3, wherein, The measuring instrument (56) used in the test area (62) also measures the concentration of the test gas in the intermediate isolation space (87).

13. The method according to claim 1, wherein, The pressure in the detection chamber (61) is reduced to the threshold value Ps.

14. The method according to claim 1, wherein, The seal (60) includes an outer peripheral sealing lip (64) that presses against the inner surface of the membrane (5, 8) when the detection chamber is depressurized.

15. The method according to claim 5, wherein, The preset concentration threshold of neutral gas is verified by injecting neutral gas at a pressure of up to 20 mbar into the intermediate isolation space (87) within a predetermined time. Once the time for which neutral gas is injected into the intermediate isolation space (87) reaches at least the predetermined time, the isolation threshold S is verified. i Verified.

16. The method according to claim 12, wherein, The measuring instruments include a mass spectrometer.

17. A leak detection device (54) for performing the method according to claim 1, the leak detection device comprising: A heat insulation barrier layer (2, 6), the heat insulation barrier layer comprising a solid insulating material (3, 7), the solid insulating material being in the atmospheric gas phase; A membrane (5, 8) comprising an outer surface and an inner surface facing the heat-insulating barrier layer (2, 6), the membrane (5, 8) comprising a test area (62) whose seal must be tested, the tank seal test leak detection device (54) comprising a detection hood (55) arranged to face the test area (62), and the detection hood comprising a body (100) and a seal (60) connected to the body (100), and the seal being configured to define a detection chamber (61) between the body (100) and the test area (62), the seal (60) being... Having a closed profile, designed to be pressed against the inner surface of the membrane (5, 8) around the test area (62), the can seal test leak detection device (54) includes an intermediate isolation space (87) surrounding the test chamber (61), and the can seal test leak detection device also includes a vacuum pump (57, 84) and a measuring instrument (56), the vacuum pump being connected to the test chamber (61), the measuring instrument being connected to the test chamber (61), and the measuring instrument being configured to measure a variable representing the amount of at least one test gas present in the atmospheric gas phase within the thermal barrier layer (2, 6). The intermediate isolation space (87) is characterized in that it includes a second seal (86) connected to the body (100) around the seal (60), the intermediate isolation space (87) is connected to a reservoir (88) for storing a neutral gas different from the test gas so that the neutral gas can be injected into the intermediate isolation space (87), and the intermediate isolation space (87) and its contents define an isolation threshold S of the detection chamber (61). i Once the isolation threshold is reached, the measurement of a variable representing the amount of the test gas is initiated, thereby characterizing the detection of leakage at the membranes (5, 8).

18. The tank seal test leakage detection device according to claim 17, wherein, The second seal (86) includes a sealing lip that is designed to be pressed against the inner surface of the membrane (5, 8) around the seal (60).

19. The tank seal test leakage detection device (54) according to claim 17 or 18, wherein, The measuring instrument (56) is configured to measure a variable representing the amount of at least one test gas present in the atmospheric phase of the heat insulation barrier layer (2, 6), the at least one test gas being selected from nitrogen, oxygen, argon and volatile organic compounds that are easily released during the degassing process of the solid insulating material (3, 7) of the heat insulation barrier layer (2, 6).

20. The tank seal test leakage detection device (54) according to claim 17 or 18, wherein, The vacuum pump (84), the detection chamber (61), and the measuring instrument (56) are connected to each other via a vacuum circuit, which includes a first channel (89) connected to the detection chamber (61), a second channel (90) connected to the vacuum pump (84), and a third channel (91) connected to the measuring instrument (56). The first channel, the second channel, and the third channel are connected to each other. The third channel (91) is equipped with a metering valve (92) which is located upstream of the measuring instrument (56).

21. The tank seal test leakage detection device (54) according to claim 17 or 18, wherein, The measuring instrument (56) is a mass spectrometer.

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