Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
  • G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
  • G01M3/20—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material
  • G01M3/22—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators
  • G01M3/226—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators for containers, e.g. radiators
  • G01M3/229—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators for containers, e.g. radiators removably mounted in a test cell
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
  • G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
  • G01M3/20—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material

Definitions

• the invention relates to the detection of leaks in hollow industrial parts whose sealing must be controlled.
• the invention relates to the detection of such leaks using a tracer gas.
• the invention finds particular application in the field of manufacturing parts for industry, such as the automotive industry, for the detection of leaks of various parts whose operation requires a perfect seal.
• some consist in pressurizing the inside of the test piece with such a gas and placing it in a chamber to detect the small quantities of gas that would have leaked from the room. to this room.
• Other techniques consist instead of placing the test piece in an environment rich in tracer gas and to search for the presence of this gas inside the test piece.
• US Pat. No. 5,661,229 describes the detection in a measurement space of the passage of helium through a layer of quartz glass designed to let only this gas.
• the patent application WO-1-2017012904 describes a method for controlling the tightness of sealed products, also using helium as a tracer gas, in which the measurement of helium concentration is carried out using a mass spectrometer. .
• a disadvantage of these techniques is that they require creating a high vacuum, which increases their cost of implementation. Such a high vacuum indeed requires the use of an expensive material and significant maintenance. The use of spectrometers also increases costs.
• Other techniques which do not require the implementation of a high vacuum, are to pressurize the test piece of tracer gas and seek the leak using a sniffer type detector. Such methods also make it possible to locate the leak. On the other hand, with such techniques the part is not tested globally, which leaves the possibility of not sniffing sufficiently close to the leak and not to detect it. Sometimes the vanishing point is simply inaccessible.
• test piece In other techniques, which do not require the implementation of a high vacuum, include sealing the test piece, placing it in an enclosure, pressurizing the room and leaving the chamber at atmospheric pressure. then wait for a long enough time to then be able to detect the possible presence of a tracer gas with a detector sensitive to this gas.
• the tracer gas concentration after accumulation may be too low to be detectable by the detectors available on the market.
• the object of the invention is to propose a leak detection method that overcomes at least some of the disadvantages of the prior art mentioned above.
• an object of the present invention is to describe such a method that does not require the implementation of a high vacuum.
• Another object of the present invention is to provide a method requiring a shorter tracer gas detection time.
• Yet another object of the invention is to provide a method for detecting smaller leaks for the same commercial tracer gas detector.
• a leak detection method of a hollow part comprising the steps of sealing said hollow part, creating a pressure difference P1 and P2 between the interior of said hollow part and a compartment or an enclosure, injecting a tracer gas into the injection chamber formed by the interior of one of the hollow part and said compartment or said enclosure, to wait for a time of accumulation T and then to carry out a concentration step of taking at least partly the contents of a control chamber formed by the interior of the other of said hollow part and said compartment or said enclosure where no tracer gas has been injected so as to concentrate in a sampling volume the tracer gas that said contents of the control chamber possibly contains, then to seek the presence of tracer gas in said sampling volume.
• the sampling is carried out by means of an expansion sequence and then re-compression comprising a first substep of relaxation of the contents of the control chamber in order to feed a concentration chamber. with a sampling volume, followed by a second substep of re-compression of the sampling volume to ensure concentration before the step of finding the presence of tracer gas in said sampling volume.
• the method comprises a plurality of trigger sequences and then re-compression of the content of the control chamber, comprising at least two consecutive iterations of said sequence.
• the objective of these sequence reiterations is to ensure a mixing and a homogenization of the control volume to make reliable the tracer gas measurement.
• the method of the invention also covers other methods of mixing the contents of the control chamber so as to prevent any stationary zone in said chamber, using means belonging to the group comprising:
• dynamic stirring means constituted for example by means of the type of an indoor fan and / or a turbine external to said chamber; static stirring means constituted by a conformation of the inner surface of said chamber, which causes a stirring of gas veins during natural or forced gas movements (suction or compression, pumping, fan, turbine, and 7)
• the tracer gas search step is carried out in a detection chamber located downstream of the concentration chamber, the communication circuit of the concentration chamber with the detection chamber comprising a restriction.
• the communication circuit of the concentration chamber with the detection chamber comprises a membrane filtration unit.
• the invention therefore proposes to accumulate during a time T the tracer gas that could have leaked from or into the test piece and then to concentrate it by membrane filtration before searching for it by means of a suitable detector.
• the method of the invention can also be applied by carrying out the tracer gas search step in the concentration chamber itself, by means of a gas detector brought into contact with the detection volume.
• Such a concentration step makes it possible to detect very small leaks.
• the detection of the tracer gas is, according to the invention, performed not on a raw content but on a concentrated content.
• the amount of leaking tracer gas is negligible and, in the absence of such concentration, possibly undetectable unless complex detectors are used. expensive such as spectrometers.
• Such a result is moreover obtained without the need to implement a high vacuum involving the use of complex and expensive equipment for obtaining and maintaining it.
• the invention thus proposes a very interesting alternative to leak detection methods of the prior art.
• This method may be implemented according to at least two preferred variants. These two variants are described below in connection with the second embodiment principle (use of a filtration membrane), but they are equally usable mutatis mutandis according to the first embodiment principle (without membrane).
• the hollow part to be tested will have a compartment A and a compartment B adjacent to the compartment A.
• the method according to the invention will then comprise the steps of putting under pressure P1 of a tracer gas inside the one of said compartment A and said adjacent compartment B after sealing, to put under pressure P2 ⁇ P1 of a gas other than the tracer gas inside the other of said compartment A and said adjacent compartment B , to wait for a accumulation time T, to filter on at least one membrane the contents of one of the compartment A or the compartment B where no tracer gas has been put so as to concentrate in a volume downstream of said membrane tracer gas optionally contained in the compartment A or the compartment B in which no tracer gas has been put.
• the method will comprise the steps of placing said hollow part, previously sealed, in a chamber forming an enclosure, to put under pressure P1 of a tracer gas inside one of said hollow part and said enclosure, to put under pressure P2 ⁇ PI of another gas than the tracer gas inside the other of said hollow part and said enclosure, to wait a time T, to filter on at least one membrane the contents of said hollow part or of said enclosure in which no tracer gas has been placed so as to concentrate in a volume downstream of said membrane the tracer gas contained, if any, in said hollow part or said enclosure in which no tracer gas has been put.
• This second variant may itself be implemented according to two sub-variants.
• the method comprises the successive steps of placing said hollow part in a chamber forming an enclosure, to put under pressure P1 of said tracer gas inside said hollow part, to put under pressure P2 ⁇ P1 of said other gas inside said enclosure, to wait a time T, to filter on membrane the contents of said enclosure and to seek the presence of tracer gas downstream of said membrane.
• the successive steps consist in placing said hollow part in a chamber forming an enclosure, in pressurizing P1 of said tracer gas inside said enclosure, in pressurizing P2 ⁇ P1 of said other gas inside. of said hollow part, to wait a time T, to filter on a membrane the contents of said hollow part and to seek the presence of tracer gas downstream of said membrane.
• the tracer gas will preferably be selected from the group consisting of helium and a mixture of helium or hydrogen in air or nitrogen.
• the other gas is preferably air.
• the pressure P 1 is between 1 bar and 40 bar.
• the pressure P2 may be equal to the atmospheric pressure but may advantageously also be lower.
• the time T corresponding to the time when the tracer gas can accumulate in the compartment where it has not been put before being concentrated through the membrane, may in particular vary depending on the size of the test piece. , in particular that of its interior volume, and the desired level of leakage. In general, it will preferably be between 30 seconds and 30 minutes. This time can therefore be relatively brief, may allow to observe relatively high coin control rates.
• the enrichment step of the process according to the invention is carried out on at least two membranes mounted in cascade, thus making it possible to filter on a second membrane the filtrate originating from a first membrane.
• Such an option makes it possible to concentrate the tracer gas molecules even more with a view to their detection.
• membranes available on the market may be implemented in the context of the process according to the invention.
• said membranes are chosen from polymeric membranes and membranes based on microporous silica.
• different types of non-selective restriction available on the market can be implemented as soon as they make it possible to obtain the desired effect, namely the creation and maintenance of a sufficient pressure difference for a time sufficient to allow detection and / or measurement of tracer gas by a suitable detector.
• the restriction is constituted by a duct with orifice calibrated to form a pressure drop in the circuit.
• the invention also relates to an installation for implementing the method according thereto.
• Such an installation includes:
• control chamber formed by the interior of the other of said hollow part and said compartment or said enclosure where no tracer gas has been injected
• sampling means from said control chamber of a sampling volume to said concentration chamber, of all or part of the contents of said control chamber,
• the installation according to the invention may also comprise means for mixing the contents of the control chamber belonging to the group comprising:
• dynamic stirring means constituted by means of the type of an indoor fan and / or a turbine external to said chamber;
• static stirring means constituted by a conformation of the inner surface of said chamber.
• the sampling and concentration means are constituted by a pneumatic pump unit.
• said means for transferring said sampling volume are constituted by a routing circuit comprising non-selective restriction means, said detection means of said tracer gas being located downstream of said non-selective restriction.
• said transfer means are constituted by a routing circuit comprising selective restriction means, constituted for example by a membrane filtration unit comprising at least one filtration membrane, said means for detecting said tracer gas. being located downstream of said membrane filtration unit.
• the detection means include a tracer gas detector which may notably include a chemical sensor, a heat-sensitive sensor, an ion pump sensor, a spectrometer, etc.
• the restriction and / or the membrane filtration unit are in particular designed to provide the tracer gas detection means with a gas flow rate at a sufficient pressure, for a sufficient time, to allow the detection operation, typically by generating a pressure difference across the detection means.
• the unit will also have the function of increasing the concentration of tracer gas, to facilitate further detection.
• the installation comprises a chamber for receiving the hollow part.
• said membrane filtration unit includes at least two cascaded membranes.
• Figures 1 and 2 show schematically two examples of leak detection facilities according to the invention, in the context of the implementation of the second embodiment of the invention with membrane filtration unit;
• Figures 3 and 4 illustrate the successive steps of a preferred process for implementing the invention in a test installation
• Figures 5 and 6 illustrate two embodiments in which the plant comprises a turbine for circulating air in the test volume, or a fan within the test volume, respectively. Description of a first embodiment of an installation according to the invention
• the installation for the leak detection of a part 1 comprises a compartment 2 forming an enclosure, inside which a part 1 to be tested can be arranged after having been sealed, that is to say that is to say after hermetically sealing all its openings.
• the compartment 2 has a volume external to the coin 1 of 300 cc.
• This installation also comprises means 3 for injecting a tracer gas, for example helium, into the interior volume of the part 1, to place this volume under pressure P1 of said tracer gas.
• a tracer gas for example helium
• These injection means include a tank 4 of tracer gas under higher pressure and a regulator 5.
• a membrane filtration unit 12 including a membrane 6, is connected to the inside of the compartment 2 forming enclosure.
• This filtration unit includes a jack pump 8.
• the pump 8 makes it possible to bring the gas contained in the compartment 2 in order to filter it on the membrane 6.
• the filtrate of the membrane 6 is then fed to a tracer gas detector 10.
• the membrane is a Hyflon ® AD60X membrane showing a selectivity of 50 with respect to the air and the detector is a detector measuring the thermal conductivity.
• the sealed part 1 is placed in the chamber forming enclosure 2 and the internal volume of this part is placed under a pressure PI tracer gas higher at atmospheric pressure, in practice up to 40 bar.
• the enclosure chamber 2 which contains air, is meanwhile left at atmospheric pressure or at a lower pressure.
• the pump 8 is actuated to force this content through the membrane 6.
• the detector 10 measures the amount of tracer gas filtrate obtained downstream of the membrane 6 .
• the relevance of the present invention was confirmed by considering a leakage of 0.01 sccm (sccm: cubic centimeter per minute at atmospheric pressure and standard temperature) and an accumulation time T of 1 minute.
• the detector has, at the end of this time, measured a helium content of 1650 ppm in the filtrate coming from the membrane 6.
• the accumulation time of one minute would have been 50 times lower (Hyflon ® AD60X membranes showing a selectivity of 50 with respect to air) of only 33 ppm and below the detection threshold of the detector used.
• the invention makes it possible, by concentrating the contents of the chamber after a relatively short accumulation time, to detect amounts of tracer gas present therein which would be undetectable in the absence of the membrane filtration step. .
• this second embodiment differs from the first described above only in that the membrane filtration unit 12a includes two membranes 6, 7 cascaded and two pumps 8a, 9.
• the pump 8a makes it possible to bring the gas contained in the compartment 2 in order to filter it on the membrane 6 and the pump 9 makes it possible to bring the filtrate thus obtained to the membrane 7.
• the retentate from the membrane 7 is recycled upstream of the membrane 6 by a recycle line 11.
• the filtrate of the membrane 7 is then fed to a detector 10 tracer gas.
• the pumps could be provided upstream of the membranes, and not downstream, in order to force the fluid to be filtered therethrough).
• FIGS. 3 and 4 illustrate in greater detail five main stages of implementation of the method according to the invention.
• This test facility was designed to create a 0.062sccm leak under 220kPa of H2N2 (H2 5%) leaking in a 2 liter volume.
• the concentration principle of the invention allows a detection and measurement much better than 'a direct measure.
• the installation comprises a test piece 31 situated in a control enclosure 32, which in the context of FIG. of the test was 2 liters.
• the part to be tested 31, and more specifically its internal chamber acting as an injection chamber, is fed and pressurized by a tracer gas accumulator 33, the tracer gas being composed of 95% of N 2 and 5% of H2.
• the pressure injection circuit 35 of the tracer gas comprises a pressure reducer 34 located upstream of a valve 40, followed by a control manometer Pa.
• the installation also comprises a circuit 36 for partial evacuation, for example at 8 kPa.
• the evacuation circuit 36 is connected to the tracer gas injection circuit by a valve 46, and to the control enclosure 32 by a pressure reducer 37 and a valve 47.
• a sampling and concentration device Downstream of the enclosure 32, a sampling and concentration device comprises a set of two pneumatic drawers 41, 42 which control a jack 38 for actuating a piston 39 (acting as a pump) connected to the enclosure 32 via two valves 43 and 44.
• the pump 39 is used to take a sampling volume in the chamber 32, and to re-compress it to concentrate before sending to the means 50 tracer gas detection.
• the concentration operation takes place in a concentration chamber constituted in the circuit downstream of the enclosure 32 and the valve 44, in the direction of a valve 45 leading to a flow restrictor 49, constituted by a non-selective restriction or a membrane filtration unit.
• This restriction selective or non-selective, supplies the means 50 for tracer gas detection.
• the element 49 was a restriction consisting of a 0.1mm diameter orifice.
• the implementation method of the invention is carried out in five steps as follows:
• STEP 1 EMPTYING the injection chamber and the injection circuit, as well as the chamber for controlling the chamber 32 and the circuit downstream of the chamber 32 intended to act as a chamber of concentration.
• Vacuuming involves lowering the pressure to about 8kPa. To do this, the valves 43, 44, 46 and 47 are open, and the slide 41 supplies and pressurizes the compression chamber of the control cylinder 38 which empties the working compartment of the pump 39. The cylinder 38 and the piston of the pump 39 are therefore in the position of Figure 4. The valves 45 and 48 are closed. During the tests, the evacuation step was maintained for 30 seconds.
• - STEP 2 ACCUMULATION: for this step, which lasted 30 seconds during the tests, the valves 46 and 47 are closed, and the valve 40 is opened to allow the pressurization and the injection of tracer gas in the chamber of injection of the test piece 31.
• the test piece had a test leak of 0.062 sccm at 220 kPa.
• valve 44 is closed, the slide 41 is actuated to drive the cylinder 38 to the right and actuate the pump 39 under pressure (return to Figure 4), and the circuit located between the two valves 44 and 45 form re-compression chamber and concentration up to a value of 140kPa absolute (40kPa relative to the atmospheric pressure). This step lasted 5 seconds during the tests.
• STEP 5 DETECTION: The valves 45 and 48 are open, and the re-compressed sampling volume has taken about 15 seconds to flow through the restriction 49 before the pressure drops below the pressure necessary to ensure a sufficient flow rate to the hydrogen sensor 50. It is during these 15 seconds that the detection measurement is carried out.
• Several tests were carried out with this test bench, which confirmed the effectiveness of the concentration by sampling and re-compression to measure small amounts of tracer gas, and thus detect small leaks with a standard detector.
• the re-compression pressure be higher (for example 6 bar or more) and the downstream sensor 50 operate at a lower flow rate (in the test with restriction without diaphragm, the operating flow rate of the sensor is 50cc / min, with a diaphragm it is better to operate under approximately 1cc / min).
• the method and the installation ensure mixing of the contents of the control chamber, in order to limit or eliminate the stationary zones in the gaseous mixture, and to ensure homogenization of the control volume. , and thus reliability of the detection and measurement of the tracer gas.
• One of the means for ensuring such mixing is to perform a sudden relaxation and / or compression of the contents of the control chamber, the volume that is taken and / or the volume of concentration.
• the sudden expansion is ensured for example by the use of a plunger in syringe, which is pulled to increase the detection volume, which has the effect of reducing the pressure: more specifically, the larger the volume thus added ( therefore the greater the pressure drop) and the more sudden the relaxation, the better the stirring.
• the invention covers each of the two cases (sudden relaxation or sudden recompression), as well as their combination in the form of a relaxation sequence + re-compression.
• the re-compression can be done either against a membrane or through a restriction in the gas detector, or simply in the detection volume (which then regains its initial pressure), the gas detector then being put in contact with the detection volume, in "sniffing" (suction flow caused for example by means of a lower pressure on the other side of a restriction or a membrane, or obtained using a fan).
• suction flow caused for example by means of a lower pressure on the other side of a restriction or a membrane, or obtained using a fan.
• this round-trip piston several times during the accumulation time, to stir better in the case where the test volume is large compared to the volume of the piston.
• the assembly allowing the use of the syringe piston is identical or similar to that shown in Figures 3 and 4, where the two cylinders 38, 39 are mechanically linked, the left one (38) being activated pneumatically via the drawers 41, 42 , and pulling and pushing the right cylinder 39 which extracts and represses the gas.
• Example 1 Test of a vehicle transmission circuit.
• the part volume to be tested is 2 liters. This is the internal volume of the test piece into which the gas is injected.
• the gas used is H2N2 (5% hydrogen in 95% nitrogen)
• test pressure was 220 kPa.
• the test assembly is that of FIGS. 3 and 4.
• the sampling piston volume is 2 liters.
• the chamber was initially vacuumed under 8kPa absolute.
• the volume of the piston was isolated from that of the chamber by closing the valve.
• the piston was then closed, compressing its contents in a very small volume: the pressure went from 4.8 kPa to 140 kPa absolute (higher than the atmosphere). This recompression was also performed in 5 seconds.
• the stirring also results from the turbulence that occurs in the pipe between the test chamber and the piston, at the time of expansion, then again in the volume of the piston at the time of re-compression.
• the increase of the concentration is obtained thanks to the degree of initial vacuum of the chamber and the necessary re-compression (because the sensor does not work under vacuum).
• the stirring is obtained thanks to the sudden relaxation phase.
• test piece had a volume of about 40 liters.
• the test chamber also had a volume of about 40 liters.
• Gas used Helium
• control chamber was at atmospheric pressure, the part can not withstand a high pressure difference, which prevented the chamber from being pulled to a high vacuum.
• the plunger was activated to pull and push into the chamber multiple times (typically at least 5 or 6 times minimum) throughout the accumulation time of 1 minute, so as to obtain a good quality brewing despite the fact that the pressure of the chamber fluctuated only 5% each time because the piston volume was 20 times smaller than that of the chamber.
• test volume (the chamber) was then opened towards the helium detector (spectrometer type) by suctioning via a restriction.
• the homogeneity of the test volume and the repeatability of the measurement were obtained thanks to the piston stirring.
• the stirring effect can also be achieved by using for example a turbine to circulate the air in the test volume, or a fan within the test volume.
• FIG. 5 shows schematically the insertion into the installation of a turbine 53 outside the test volume, in one embodiment of the invention in which the test piece 51 is placed inside. of a test chamber 52.
• the turbine 53 ensures suction of the test volume gas mixture outside the chamber 52 to re-inject it again, so as to perform a stirring.
• FIG. 6 schematically shows the insertion of a fan 63 inside the test chamber 62 in which the test piece 61 is placed.
• stirring means are however not as effective as the realization of a sudden depression / compression (s), especially if the test piece has a geometry with recesses such that at these locations the air in the test volume will remain stationary.
• the formation of a sudden change in volume and / or pressure, especially by expansion and / or re-compression, further ensures that no air pockets will remain stationary anywhere.
• the objective of the installation and the method according to the invention is to implement a concentration phenomenon by using one or the other, or the two following concentration functions:
• the pressure in the control chamber of the chamber has dropped to 8kPa, there is 12 times less air and therefore the hydrogen concentration will be 12 times greater, and thus 12 times more "easy” to detect ; the operation of relaxation and recompression then facilitates the detection;
• a second enrichment concentration function obtained by the use of a selective restriction, for example in the form of a membrane filtration unit, which ensures a selective concentration downstream of the membrane.
• the invention provides that each of these two functions may be used separately, or in combination with each other.
• the objective is to perform a detection and / or a calibration which consists of detecting a leakage level greater than a given threshold and / or measuring a known calibrated leak and teaching the system that the measured value corresponds to the value of the known standard leak.

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• Examining Or Testing Airtightness (AREA)

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• 2018
  • 2018-07-06 WO PCT/EP2018/068433 patent/WO2019008169A1/fr active Application Filing
  • 2018-07-06 CN CN201810738910.8A patent/CN109211485B/zh active Active

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