Improved leak detection method and associated device

Abstract

The present invention relates to a method for detecting a leak in an object to be tested, comprising: - a first step of detecting a leak in the object to be tested based on a pressure change measurement method if no leak is detected in the first step, - a second step of leak detection in the object to be tested based on the detection of tracer gas, wherein the detection device used for applying the first step and the second step comprises at least one valve to control the pressure in the predefined volume and a pressure sensor configured to measure the pressure in the predefined volume, wherein the opening and closing of the at least one valve are controlled depending on the pressure measured by the pressure sensor, and wherein the pressure change in the first detection step is determined based on the measurements of the pressure sensor.

Description

Description Title of the invention: Improved leak detection method and associated device

[0001] The present invention relates to a method and device for leak detection to check the airtightness of an object based on the detection of a tracer gas in the environment of an object to be tested, which has been previously filled with the tracer gas. Leak detection methods based on tracer gas detection are known, and the gas generally used is helium or hydrogen due to their small size, which allows the detection of small leaks.

[0002] These detectors can be used to verify the conformity and absence of leaks in industrial equipment intended, for example, for fluid circulation, such as refrigerator cooling circuits. This equipment includes seals that may be misaligned or defective, leading to leaks of varying sizes that must be detected before being placed on the market. Detection methods based on helium detection can detect leaks on the order of 10⁸ mbar·s⁻¹ 1 .

[0003] However, in the case of significant leaks, due for example to an assembly error or a construction problem, a large quantity of tracer gas, for example helium, introduced into the object to be tested escapes through the leak, which leads on the one hand to a large consumption of tracer gas which is costly and on the other hand to the presence of a large quantity of tracer gas in the test chamber which can impair the quality of subsequent detections.

[0004] It is therefore necessary to find a solution that limits the amount of tracer gas used in order to reduce the cost of detection tests while ensuring the same detection performance. It is also necessary to limit the cost of the equipment required for detection.

[0005] To this end, the invention relates to a method for detecting a leak on an object to be tested, comprising: - a first step of leak detection on the object to be tested based on a pressure variation measurement method in which a vacuum or overpressure is imposed in a predefined volume inside or outside the object to be tested and a pressure variation is determined over time in the predefined volume, the presence of a leak being deduced from the determined pressure variation, if no leak is detected in the first step, - a second leak detection step on the object to be tested based on tracer gas detection, wherein the detection device used to implement the first and second steps comprises at least one valve for controlling the pressure in the predefined volume and a pressure sensor configured to measure the pressure in the predefined volume, the opening and closing of at least one valve being controlled according to the pressure measured by said pressure sensor and wherein the pressure variation In the first detection stage, the pressure sensor readings are taken. The detection device comprises a single pumping unit to perform both the first and second leak detection stages. The pumping unit may include several functional blocks, each with multiple stages arranged in series. The pumping unit may also include a Roots-type pump to form a secondary pump combined with a primary pump.

[0006] Using a pressure variation leak detection step allows for the detection of significant leaks without consuming tracer gas. Furthermore, employing a single pumping unit and a single pressure sensor for both pressure variation leak detection and controlling the valve(s) used for tracer gas detection minimizes the equipment costs associated with the leak detection process.

[0007] According to another aspect of the present invention, the tracer gas is helium.

[0008] According to another aspect of the present invention, the detection of tracer gas is carried out by mass spectrometry.

[0009] According to another aspect of the present invention, the detection of tracer gas is carried out by optical spectrometry.

[0010] According to another aspect of the present invention, the second leak detection step comprises: - a fluidic connection between the predefined volume inside the object to be tested and a tracer gas detector, and - spraying tracer gas around the object to be tested.

[0011] According to another aspect of the present invention, the second leak detection step comprises: - a fluidic connection between the predefined volume outside the object to be tested and a tracer gas detector and, - an injection of tracer gas inside the object to be tested.

[0012] The present invention also relates to a leak detector comprising: - a pressure sensor configured to measure pressure within a predefined volume inside or outside the object to be tested, - a device for injecting or spraying tracer gas outside the predefined volume, - a tracer gas analyzer configured to detect the presence of tracer gas in a predefined volume, - a pumping unit configured to apply a vacuum within a predefined volume inside or outside the object to be tested and to convey the pumped gases to the gas analyzer, - at least one valve configured to establish fluidic communication between the tracer gas analyzer and the predefined volume, - a treatment unit configured to control, via the pumping unit, the application of a vacuum in the predefined volume, to determine, from the measurements of the cap- pressure sensor, a pressure variation in the predefined volume, to compare the determined pressure variation with a predefined threshold associated with the presence of a leak and, in the event of no leak detection by the pressure variation measurement method, to inject a tracer gas outside the predefined volume and to detect, via the tracer gas analyzer, a presence of tracer gas in the predefined volume, said pressure sensor also being used to control the opening and closing of at least one valve.

[0013] The present invention also relates to a leak detector comprising: - a compression device configured to apply overpressure within a predefined volume inside or outside the object to be tested, - a pressure sensor configured to measure pressure within a predefined volume, - a device for injecting or spraying tracer gas outside the predefined volume, - a tracer gas analyzer configured to detect the presence of tracer gas in a predefined volume, - a pumping unit configured to apply a vacuum within a predefined volume inside or outside the object to be tested and to transmit the pumped gases to the gas analyzer, - at least one valve configured to establish fluidic communication between the tracer gas analyzer and the predefined volume, - a processing unit configured to control, via the compression device, the application of overpressure in the predefined volume, to determine, from the measurements of the pressure sensor, a pressure variation in the predefined volume, to compare the determined pressure variation with a predefined threshold associated with the presence of a leak and, in the event of no leak detection by the pressure variation measurement method, to inject a tracer gas outside the predefined volume and to detect, via the tracer gas analyzer, a presence of tracer gas in the predefined volume, said pressure sensor also being used to control the opening and closing of at least one valve.

[0014] According to another aspect of the present invention, the pressure sensor is a Pi-rani gauge in which a filament is heated and the pressure value is deduced from the amount of heat given off by the filament by thermal conduction into the environment.

[0015] According to another aspect of the present invention, the pressure sensor is a combined Piezo-Pirani gauge which combines a piezoresistive gauge and a Pirani gauge and the processing unit is configured to compare the values ​​measured by the two gauges and to determine, in the case of a pressure increase, whether the pressure variation determined by the pressure sensor is due to a leak or to degassing.

[0016] According to another aspect of the present invention, the tracer gas analyzer is a mass spectrometer.

[0017] According to another aspect of the present invention, the tracer gas analyzer is an optical spectrometer.

[0018] According to another aspect of the present invention, the tracer gas analyzer comprises a turbomolecular pump. The pumping unit includes a primary pump.

[0019] According to another aspect of the present invention, the leak detector also includes a test chamber configured to receive the object to be tested, the test chamber being fluidly connected to the pumping unit and the gas analyzer.

[0020] Other features and advantages of the invention will become clearer upon reading the following description, given by way of illustrative and non-limiting example, and the accompanying drawings, among which:

[0021] [Fig 1] represents a diagram of a leak detector according to a first embodiment of the present invention;

[0022] [Fig 2] represents a diagram of a leak detector according to a second embodiment of the present invention;

[0023] [Fig.3] represents a diagram of a leak detector according to a third embodiment of the present invention;

[0024] [Fig.4] represents a diagram of a leak detector according to a fourth embodiment of the present invention;

[0025] [Fig.5] represents a diagram of a leak detector according to a fifth embodiment of the present invention;

[0026] [Fig.6] represents a diagram of a leak detector according to a sixth embodiment of the present invention;

[0027] [Fig.7] represents a flowchart of the steps of a leak detection process according to the present invention.

[0028] In these figures, identical elements carry the same references.

[0029] The following are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features from different embodiments can also be combined or interchanged to provide other embodiments.

[0030] The present invention relates to a leak detector enabling the detection of large leaks, for example greater than 10' 3 mbar.s' 1 and small leaks, for example less than 10' 3 mbar.s' 1 while limiting the amount of tracer gas needed for these detections.

[0031] Figure 1 shows a schematic of a leak detector 1 according to a first embodiment of the present invention. The leak detector 1 comprises a test chamber 3 configured to receive the object to be tested 5. Alternatively, the test chamber 3 may be external to the leak detector 1. The test chamber 3 is fluidly connected to an inlet 7a of a detection device 7, for example via a conduit 9.

[0032] The detection equipment 7 includes a tracer gas analyzer 11, a pumping unit 13 configured to apply a vacuum in the test chamber 3 and to transmit pumped gases from the test chamber 3 to the tracer gas analyzer 11, a set of valves 15 configured to allow or prevent the passage of gases between the inlet 7a of the detection equipment 7 and the tracer gas analyzer 11 and / or the pumping unit 13. The tracer gas analyzer 11 is, for example, a mass spectrometer or an optical spectrometer.

[0033] In this case, the detection equipment 7 comprises three valves, a first valve 15a to allow or not the passage of gas between the inlet 7a of the detection equipment 7 and an inlet of the tracer gas analyzer 11, a second valve 15b between an outlet of the tracer gas analyzer 11 and the pumping unit 13 and a third valve 15c between the inlet 7a of the detection equipment 7 and the pumping unit 13.

[0034] The detection equipment 7 also includes a pressure sensor 17 configured to measure the pressure at the inlet 7a of the detection equipment 7. The pressure sensor 17 can be internal or external to the detection equipment 7.

[0035] The pumping unit 13 includes for example a primary pump such as a diaphragm pump or a dry pump and may also include a turbomolecular pump.

[0036] The pressure sensor 17 is, for example, a Pirani gauge in which a filament is heated and the pressure value is deduced from the amount of heat transferred by the filament through thermal conduction into the environment. Preferably, the pressure sensor 17 is a combined Piezo-Pirani gauge that combines a piezoresistive gauge and a Pirani gauge. With this combined gauge, the values ​​measured by the two gauges can be compared to determine whether a pressure variation measured by the combined gauge is due to a leak or to degassing. Indeed, in the case of degassing, the humidity increases, which disturbs the pressure value measured by the Pirani gauge (which is sensitive to the nature of the gas), unlike the piezoresistive gauge. Therefore, if the measured values ​​differ significantly, degassing is detected.

[0037] The detection equipment 7 also includes a processing unit 19 configured to control, in particular, all the elements of the detection equipment 7. The processing unit 19 is thus configured to receive the measurements from the pressure sensor 17 and to control the opening and closing of the valves 15.

[0038] The leak detector 1 also includes a tracer gas injection or spraying device 21. The tracer gas is, for example, helium or hydrogen. The tracer gas is injected outside a predefined volume fluidically connected to the detection equipment 7

[0039] In the case of Figure 1, the predefined volume corresponds to the interior of the object to be tested 5, so the tracer gas injection device 21 is configured to inject the tracer gas into the internal volume of the test chamber 3 (outside the object to be tested 5). According to another embodiment, the tracer gas injection device 21 is a spray nozzle, such as a spray gun.

[0040] Alternatively, the tracer gas injection device 21 can be configured to inject the tracer gas inside the object to be tested 5 as shown in Figure 2. In this case, the predefined volume corresponds to the internal volume of the test chamber 3 outside the object to be tested 5. This predefined volume is then fluidically connected to the inlet 7a of the detection equipment 7.

[0041] The processing unit 19 can also be configured to drive the tracer gas injection or spraying device 21 into the predefined volume inside (Fig. 2) or outside (Fig. 1) the object to be tested 5. The processing unit 19 can be located inside or outside the detection equipment 7, or the leak detector 1 can include several interconnected processing units to control the different elements of leak detector 1.

[0042] During a leak detection test on an object to be tested 5, the processing unit 19 is configured, firstly, to perform leak detection by measuring pressure variation and then, secondly, if no leak is detected by measuring pressure variation, to perform leak detection by detecting tracer gas.

[0043] For leak detection by pressure variation measurement, the processing unit 19 controls the closing of valve 15a and the opening of the third valve 15c to apply a vacuum via the pumping unit 13, down to a predefined pressure level, for example, a few millibars or a few tens of millibars, in the predefined volume. When the pressure level is reached (the pressure level is provided to the processing unit 19 by the pressure sensor 17), the processing unit 19 controls the closing of the third valve 15c.The processing unit 19 is then configured to monitor the evolution of the pressure measured by the pressure sensor 17 over time during a predetermined time interval (the predetermined time interval depends on the size of the predetermined volume, for example a few seconds for a small volume to a few tens of minutes for a large volume), to determine a pressure variation over the predetermined time interval and to compare the determined pressure variation with a predetermined threshold associated with the presence of a leak.

[0044] If a leak is not detected by the pressure variation measurement method, the processing unit 19 is then configured to perform leak detection using tracer gas. To do this, the processing unit 19 controls the injection of tracer gas outside the predefined volume, i.e., into the test chamber 3 in the configuration of Figure 1 or into the object to be tested 5 in the configuration of Figure 2. The processing unit 19 is then configured to open the third valve 15c until a third predetermined pressure level, reached via the pumping unit 13, is reached, for example, below 25 mbar, up to 10 minutes. 5 mbar, then to open the first valve 15a and the second valve 15b and close the third valve 15c so as to convey the gases from the predefined volume to the tracer gas analyzer 11.

[0045] The pressure sensor 17 is used to determine the pressure level in the predefined volume and therefore to control the opening and closing of valves 15a, 15b, 15c.

[0046] The tracer gas analyzer 11 is, for example, a mass spectrometer or an optical spectrometer. Tracer gas injection can be carried out after the predetermined volume has been depressurized to the third predetermined pressure level. The tracer gas analyzer 11 is configured to detect the presence of tracer gas among the pumped gases from the predetermined volume, and even to determine the tracer gas concentration among the pumped gases. The use of tracer gas detection makes it possible to detect very small leaks, for example, down to 10⁻¹⁰ µm. 8 mbar.s' 1 .

[0047] According to an alternative embodiment shown in Figure 3, the leak detector 1 includes a compression device 23 configured to apply overpressure in the predefined volume (here outside the object to be tested 5, but the overpressure could also be...) The compression device 23 can be applied inside the object to be tested (5) as in the configuration shown in Figure 4. The compression device 23 can be implemented using a compressor or a cylinder containing a compressed gas such as compressed air. In this case, a fourth valve 15d is positioned between the cylinder and the predefined volume. The opening and closing of the fourth valve 15d are controlled, for example, by the processing unit 19, based in particular on the values ​​measured by the pressure sensor 17.

[0048] In this embodiment, pressure variation detection is achieved by applying overpressure to the predefined volume; for example, a pressure of 3 bar is applied (a higher pressure can be applied if the device, and in particular the seals (extrusion issue), are designed accordingly). The evolution of the pressure measured by the pressure sensor 17 is then monitored by the processing unit 19, and the pressure variation determined over a predetermined period is compared to a predetermined threshold associated with the presence of a leak. If no leak is detected by pressure variation measurement, detection using tracer gas is performed, as in the other embodiments described previously.

[0049] As with the embodiment examples described previously, the pressure sensor 17 can be external to the sensing equipment 7, for example fluidly connected to the test chamber 3 as shown in Figure 5 or fluidly connected to the conduit 9 as shown in Figure 6.

[0050] As with the other embodiments, the processing unit 19 is configured to perform leak detection by measuring pressure variation using the pressure sensor 17 and, in the event of no leak detected by measuring pressure variation, to perform leak detection by detecting tracer gas.

[0051] The different steps of the leak detection process on an object to be tested 3 by a detection equipment 7 according to one of the embodiments described in figures 1 to 6 will now be described from the flowchart in figure 7.

[0052] The first step 101 concerns leak detection by measuring pressure variation. This first step 101 includes a first substep 1011 in which a vacuum is applied to a predefined volume, for example, the internal volume of the object to be tested 5 in the embodiment shown in Figure 1. For this purpose, the processing unit 19 controls the opening of the third valve 15c. According to an alternative first substep 1011', a pressure surge is applied to a predefined volume, for example, the internal volume of the object to be tested 5 in the embodiment shown in Figure 4. For this purpose, the processing unit 19 controls the actuation of the compression unit 23 or the opening of the fourth valve 15d.

[0053] When the pressure measured by the pressure sensor 17 reaches the desired pressure, the processing unit 19 is configured to close the third valve 15c (or the fourth valve 15d in the case of substep 1011').

[0054] The second substep 1012 following the first substep 1011 or 1011' concerns monitoring the evolution of the pressure measured by the pressure sensor 17 and comparing the variation of this pressure over a predetermined time interval with a predetermined threshold associated with a leak (if the determined pressure variation exceeds the (A predetermined threshold is reached when a leak is detected). If a leak is detected, the process stops and the object under test 5 is considered defective. The extent of the leak can be determined from the magnitude of the pressure variation, and a signal indicating this magnitude can be emitted. If no leak is detected, the process proceeds to the second step 102.

[0055] The second step 102 concerns leak detection by tracer gas detection. This step includes a first substep 1021 in which a vacuum is applied via the pumping unit 13 into the predefined volume, for example, inside the object to be tested 5 in the embodiment shown in Figure 1 (alternatively, outside the object to be tested 5 in the embodiment of Figure 2). For this purpose, the third valve 15c is opened. When the desired vacuum is reached in the predefined volume, corresponding to the pressure measured by the pressure sensor 17, the third valve 15c is closed and the first and second valves 15a and 15b are opened to establish fluid communication between the predefined volume and the tracer gas analyzer 11.

[0056] The second substep 1022 concerns the injection or spraying of tracer gas outside the predefined volume, for example into the test chamber outside the object to be tested 5 in the case of Figure 1 (alternatively inside the object to be tested 5 in the embodiment of Figure 2). The order of substeps 1021 and 1022 can be reversed.

[0057] The third substep 1023, following the first and second steps 1021 and 1022, involves the analysis, by the gas analyzer 11, of the aspirated gases from the predefined volume to detect the presence of tracer gas in these gases. Tracer gas detection is carried out, for example, by mass spectrometry or optical spectrometry. If a leak is detected, the extent of the leak can be determined based on the tracer gas concentration measured by the tracer gas analyzer 11, and a signal can be emitted to indicate the extent of the leak. If no leak is detected, the test object 5 is compliant, and a certificate of conformity associated with the test object 5 can be issued by the leak detector 1. The procedure can then be repeated with another test object 5.

[0058] It should be noted that the process described above can, in certain embodiments, be implemented without requiring a test chamber (if the depression or overpressure is applied inside the object to be tested during the pressure variation measurement step and the tracer gas spraying is carried out outside the object to be tested during the tracer gas detection step in particular).

[0059] Thus, implementing a process comprising a first step 101 of leak detection using a pressure variation measurement method, followed by a second step 102 of leak detection by tracer gas detection if no leak is detected during the first step 101, makes it possible to limit the consumption of tracer gas while allowing the detection of small leaks (up to 10' 8 mbar.s' 1). In addition, the use of a single pumping unit 13 and a single pressure sensor 17 to perform detection by measuring pressure variation and to control the opening and closing of valves 15a, 15b, 15c, 15d when the desired pressure is reached helps to limit the material costs associated with leak detection.

Claims

Demands

1. A method for detecting a leak on an object to be tested (5) comprising: - a first step (101) of leak detection on the object to be tested (5) based on a pressure variation measurement method in which a vacuum or overpressure is imposed in a predefined volume inside or outside the object to be tested (5) and a pressure variation over time is determined in the predefined volume, the presence of a leak being deduced from the determined pressure variation, if no leak is detected in the first step (101), - a second leak detection step (102) on the object to be tested (5) based on tracer gas detection, in which the detection device used to implement the first step (101) and the second step (102) comprises at least one valve (15a, 15b, 15c) to control the pressure in the predefined volume and a pressure sensor (17) configured to measure the pressure in the predefined volume, the opening and closing of the, at least one, valve (15a, 15b, 15c) being controlled according to the pressure measured by said pressure sensor (17) and in which the pressure variation in the first detection step (101) is determined from the measurements of said pressure sensor (17), the detection device comprising a single pumping unit (13) to carry out the first (101) and the second (102) leak detection step.

2. A method according to claim 1 wherein the tracer gas is helium.

3. A method according to any one of the preceding claims wherein the detection of tracer gas is carried out by mass spectrometry.

4. A method according to any one of claims 1 or 2 wherein the detection of tracer gas is carried out by optical spectrometry.

5. A method according to any one of the preceding claims, wherein the second leak detection step (102) comprises: - a fluidic connection between the predefined volume inside the object to be tested (5) and a tracer gas detector (11) (1021) and, - a spray of tracer gas around the object to be tested (5) (1022).

6. A method according to any one of claims 1 to 4, wherein the second leak detection step comprises: - a fluidic connection between the predefined volume outside the object to be tested (5) and a tracer gas detector (11) (1021) and, - an injection of tracer gas inside the object to be tested (5) (1022).

7. Leak detector (1) comprising: - a pressure sensor (17) configured to measure pressure in a predefined volume inside or outside the object to be tested (5), - a device (21) for injecting or spraying tracer gas outside the predefined volume - a tracer gas analyzer (11) configured to detect the presence of tracer gas in the predefined volume, - a pumping unit (13) configured to apply a vacuum in a predefined volume inside or outside the object to be tested (5) and to convey the pumped gases to the gas analyzer (11), - at least one valve (15a, 15b, 15c) configured to establish fluidic communication between the tracer gas analyzer (11) and the predefined volume, - a processing unit (19) configured to control, via the pumping unit (13), the application of a vacuum in the predefined volume, to determine, from the measurements of the pressure sensor (17), a pressure variation in the predefined volume, to compare the determined pressure variation with a predefined threshold associated with the presence of a leak and, in the event of no leak detection by the pressure variation measurement method, to inject a tracer gas outside the predefined volume and to detect, via the tracer gas analyzer (11), a presence of tracer gas in the predefined volume, said pressure sensor (17) also being used to control the opening and closing of at least one valve (15a, 15b, 15c).

8. Leak detector (1) comprising: - a compression device (23) configured to apply overpressure in a predefined volume inside or outside the object to be tested (5), - a pressure sensor (17) configured to measure pressure in a predefined volume, - a device for injecting or spraying tracer gas (21) outside the predefined volume, - a tracer gas analyzer (11) configured to detect the presence of tracer gas in the predefined volume, - a pumping unit (13) configured to apply a vacuum in a predefined volume inside or outside the object to be tested (5) and to transmit the pumped gases to the tracer gas analyzer (11), - at least one valve (15a, 15b, 15c) configured to connect the tracer gas analyzer (11) and the predefined volume in fluidic communication, in which a processing unit (19) is configured to control, via the compression device (23), the application of overpressure in the predefined volume, to determine, from the measurements of the pressure sensor (17), a pressure variation in the predefined volume, to compare the determined pressure variation with a predefined threshold associated with the presence of a leak and, in the event of no leak detection by the pressure variation measurement method, to inject a tracer gas outside the predefined volume and to detect, via the tracer gas analyzer (11), the presence of tracer gas in the predefined volume, said pressure sensor (17) also being used to control the opening and closing of the, at least one, valve (15a, 15b, 15c).

9. Leak detector (1) according to claim 7 or 8 wherein the pressure sensor (17) is a Pirani gauge in which a filament is configured to be heated and the pressure value is deduced from the amount of heat given off by the filament by thermal conduction into the environment.

10. Leak detector (1) according to any one of claims 7 or 8 wherein the pressure sensor (17) is a combined Piezo-Pirani gauge which combines a piezoresistive gauge and a Pirani gauge and wherein the processing unit (19) is configured to compare the values ​​measured by the two gauges and to determine, in the event of a pressure increase, whether the pressure variation determined by the pressure sensor (17) is due to a leak or to outgassing.

11. Leak detector (1) according to any one of claims 7 to 10 wherein the tracer gas analyzer (11) is a mass spectrometer.

12. Leak detector (1) according to any one of claims 7 to 10 wherein the tracer gas analyzer (11) is an optical spectrometer.

13. Leak detector (1) according to any one of claims 7 to 12 wherein the tracer gas analyzer (11) comprises a turbomolecular pump.

14. Leak detector (1) according to any one of claims 7 to 13 also comprising a test chamber (3) configured to receive the object to be tested (5), the test chamber (3) being fluidly connected to the pumping unit (13) and to the gas analyzer (11).

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