WO2004113862A1

WO2004113862A1 - Methods and apparatus for leak detection in contaminated environments

Info

Publication number: WO2004113862A1
Application number: PCT/US2004/018263
Authority: WO
Inventors: Charles Perkins; Pieter N. Palenstijn
Original assignee: Varian, Inc.
Priority date: 2003-06-11
Filing date: 2004-06-09
Publication date: 2004-12-29

Abstract

Methods and apparatus are provided for leak detection in contaminated environments. The apparatus (10) includes a trace gas permeable member (24), a trace gas sensor (12) having an enclosed connection to the permeable member, and a flange configured to mount the permeable member in gas communication with a conduit (14) that carries a trace gas. The trace gas sensor may be an ion pump or a mass spectrometer. The permeable member may be a quartz material and may be heated to control helium permeability or may be a polymer (e.g. Teflon). The permeable member may be located inside the conduit or outside the conduit.

Description

METHODS AND APPARATUS FOR LEAK DETECTION IN CONTAMINATED

ENVIRONMENTS

FIELD OF THE INVENTION This invention relates to detection of leaks in sealed articles and, more particularly, to methods and apparatus for leak detection in the presence of contaminants, such as water vapor, moisture and particles.

BACKGROUND OF THE INVENTION Helium mass spectrometer leak detection is a well-known leak detection technique.

Helium is used as a tracer gas which passes through the smallest of leaks in a sealed test piece. After passing through a leak, a test sample containing helium is drawn into a leak detection instrument and is measured. An important component of the instrument is a mass spectrometer tube which detects and measures the helium. The input test sample is ionized and mass analyzed by the spectrometer tube in order to separate the helium component. In one approach, a test piece is pressurized with helium. A sniffer probe connected to the test port of the leak detector is moved around the exterior of the test piece. Helium passes through leaks in the test piece, is drawn into the probe and is measured by the leak detector, hi another approach, the interior of the test piece is coupled to the test port of the leak detector and is evacuated. Helium is sprayed onto the exterior of the test piece, is drawn inside through a leak and is measured by the leak detector.

With current leak detector technology, leak testing in wet and dirty environments is very difficult, since the leak detector must be separated from the system to be tested by a trap to remove water vapor and dirt particles before the gas sample enters the leak detector. Any trap used to remove contaminants from the gas sample limits the sensitivity and response of the leak detector. Further, there is a risk that the suction line may be blocked so that an erroneous test result is obtained.

European Patent Application No. 0 352 371 published January 31, 1990 discloses a helium leak detector including an ion pump connected to a probe in the form of a silica glass capillary tube. The silica glass tube is heated to a temperature between 300°C and 900°C and thereby becomes permeable to helium. U.S. Patent No. 5,325,708 issued July 5, 1994 to De Simon discloses a helium detecting unit using a quartz capillary membrane, a filament for heating the membrane and an ion pump. U.S. Patent No. 5,661,229 issued August 26, 1997 to Bohm et al. discloses a leak detector with a polymer or heated quartz window for selectively passing helium to a gas-consuming vacuum gauge.

All of the prior art helium leak detectors have had one or more drawbacks, including limited pressure ranges, susceptibility to contaminants and/or high cost. Accordingly, there is a need for improved methods and apparatus for leak detection.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a method for leak detection is provided. The method comprises providing a trace gas permeable member and a trace gas sensor having an enclosed connection to the permeable member, mounting the permeable member in gas communication with a conduit that carries a trace gas, passing the trace gas carried by the conduit through the permeable member, and sensing the trace gas with the trace gas sensor, while preventing contaminants from reaching the trace gas sensor.

The permeable member may be permeable to helium, and the trace gas permeability of the permeable member may be controllable. In some embodiments, the permeable member comprises a quartz member. The leak detection device may further comprise a heating element in thermal contact with the quartz member. The method may further comprise controlling the heating element to control helium permeability.

According to a second aspect of the invention, apparatus for leak detection is provided. The apparatus comprises a trace gas permeable member, a trace gas sensor having an enclosed connection to the permeable member, and a flange configured to mount the permeable member in gas communication with a conduit that carries a trace gas.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:

Fig. 1 is a schematic block diagram of leak detection apparatus in accordance with a first embodiment of the invention;

Fig. 1A is a simplified, partial cross-sectional diagram of the leak detection apparatus of Fig. 1, showing the permeable member;

Fig. 2 is a schematic block diagram of leak detection apparatus in accordance with a second embodiment of the invention;

Fig. 3 is a schematic block diagram of leak detection apparatus in accordance with a third embodiment of the invention; and Fig. 4 is a schematic block diagram of a prior art leak detector.

DETAILED DESCRIPTION OF THE INVENTION

A schematic block diagram of leak detection apparatus in accordance with a first embodiment of the invention is shown in Fig. 1. Leak detection apparatus 10 is connected to a conduit 14. Conduit 14 may be a vacuum line or may be at ambient pressure or above. Conduit 14 may carry a gas or a liquid, as indicated by arrow A. For example, conduit 14 may be a condenser pipe in a power plant at the exhaust of a steam ejector pump. Conduit 14 may carry contaminants, such as gases, water vapor, liquids and particles, and a trace gas, such as helium, that is to be detected by leak detection apparatus 10. The trace gas may be introduced at an upstream location in conduit 14.

Leak detection apparatus 10 may include a vacuum flange 12, a trace gas permeable member 24 and a trace gas sensor 18. In the embodiment of Fig. 1, trace gas sensor 18 includes an ion pump 20 and an ion pump controller 22. Ion pump 20 and permeable member 24 are mounted in a sealed housing 30, with permeable member 24 interposed between conduit 14 and ion pump 20. Controller 22 is connected to ion pump 20 via a vacuum feedthrough 32. Controller 22 supplies power to ion pump 20 and senses ion pump current.

Ion pump 20 is typically energized by a high voltage, between 2000 and 9000 volts, supplied by controller 22. The ion pump current is proportional to the vacuum pressure inside the ion pump. Helium that permeates through permeable member 24 affects the vacuum pressure at a rate that is proportional to the leak rate. The ion pump current is therefore proportional to the leak rate.

Trace gas permeable member 24 is located between conduit 14 and ion pump 20. Permeable member 24 is a material that is permeable to the trace gas used in the leak detection apparatus, typically helium, under specified conditions. Permeable member 24 substantially passes, or permeates, the trace gas while substantially blocking other gases, liquids and particles. The permeable member 24 thus acts as a trace gas window in the sense of allowing the trace gas to pass, as indicated by arrow B, while blocking other gases, liquids and particles. Permeable member 24 may have the shape of a disk, for example. Quartz, or silica glass, is an example of a material that is permeable to helium. In particular, the helium permeability of quartz varies with temperature. At elevated temperatures in the range of 300° C to 900° C, quartz has a relatively high helium permeability. At room temperature, quartz has a relatively low helium permeability. As shown in Fig. 1 A, the leak detection apparatus may be provided with a heating element 40 in thermal contact with quartz permeable member 24. The heating element heats the quartz material to increase helium permeability while the quartz selectively blocks most other gases, water vapor and particles. The quartz has a constant permeability for a given temperature. The temperature can be adjusted to control the permeability and therefore the sensitivity. Heating element 40 may be energized by a controller 42. By controlling the temperature of permeable member 24, a helium window is provided. At a relatively high temperature (e.g., 300° C to 900° C), helium permeability is high and the helium window is open. At a relatively low temperature (e.g., room temperature), helium permeability is low and the helium window is closed. Permeable member 24 may be heated by resistive heating, radiant heating, or any other suitable heating technique. Permeable member 24 can be made of any suitable material that is permeable to the trace gas, typically helium, and may have any shape or dimension. Examples of suitable materials include quartz and permeable polymers such as tetrafluoroethylene, known under the trade name Teflon. The heating element is not required in the case of a permeable polymer. The permeable member can operate at vacuum, at atmospheric pressure or at a pressure slightly higher than atmospheric pressure. The permeable member can operate in an atmosphere that contains gases, particles and in wet environments.

A schematic block diagram of leak detection apparatus in accordance with a second embodiment of the invention is shown in Fig. 2. Like elements in Figs. 1 and 2 have the same reference numerals. Leak detection apparatus 60 is connected to conduit 14. Leak detection apparatus 60 may include vacuum flange 12, trace gas permeable member 24 and trace gas sensor 18. In the embodiment of Fig. 2, trace gas sensor 18 includes a leak detector 62, such as a helium mass spectrometer leak detector. Vacuum flange 12 may be connected by a conduit 64 to the test port of leak detector 62. Permeable member 24 is located in conduit 64 between conduit 14 and the test port of leak detector 62. In the embodiment of Fig. 2, permeable member 24 is located in conduit 64 external to conduit 14.

Leak detector 62 may be any leak detector which is capable of sensing helium or other trace gas utilized for leak detection. An example of a suitable leak detector is shown in Fig. 4 and is described below. However leak detector 62 is not limited to the example shown in Fig. 4. A schematic block diagram of leak detection apparatus in accordance with a third embodiment of the invention is shown in Fig. 3. Like elements in Figs. 1-3 have the same reference numerals. Leak detection apparatus 100 is connected to conduit 14. Leak detection apparatus 100 may include vacuum flange 12, trace gas permeable member 24 and trace gas sensor 18. Trace gas sensor 18 may include an ion pump and an ion pump controller as shown in Fig. 1 and described above, a leak detector as shown in Figs. 2 and 4 and described herein, or any other trace gas sensor that is configured for sensing helium or other trace gas utilized in the leak detection apparatus.

Vacuum flange 12 is connected to an inlet of trace gas sensor 18 by conduit 64. Permeable member 24 is mounted in a conduit 110 which extends from vacuum flange 12 into conduit 14. Thus, permeable member 24 is positioned within conduit 14. Conduit 110 may be an extension of conduit 64 or may be a separate conduit. Conduits 64 and 110 provide an enclosed connection between permeable member 24 and trace gas sensor 18. As a result, helium in conduit 14 may pass through permeable member 24 to trace gas sensor 18, while other gases, water vapor, liquids and particles are blocked by permeable member 24 from reaching the trace gas sensor 18.

The leak detection apparatus described herein is connected directly to the conduit to be tested and therefore has better sensitivity, accuracy and response time than prior art techniques. In addition, water vapor, moisture and particles cannot block the leak detection apparatus or interfere with leak detection. The permeable member can be mounted on a vacuum chamber, on a vacuum flange on a conduit to be tested or on an extension located within the conduit and directly within the flow path, as shown in Fig. 3.

In the disclosed embodiments, permeable member 24 is in gas communication with the interior of conduit 14 through housing 30 and vacuum flange 12 (Fig. 1), through conduit 64 and vacuum flange 12 (Fig. 2), or by location within conduit (Fig. 3). In addition, trace gas sensor 18 has an enclosed connection to permeable member 24 through housing 30 (Fig. 1), through conduit 64 (Fig. 2), or through conduits 64 and 110 (Fig. 3). Thus, helium or other trace gas passes from conduit 14 through permeable member 24 to trace gas sensor 18.

An example of a prior art leak detector suitable for use in the leak detection apparatus of Figs. 2 and 3 is shown in Fig. 4. A test port 230 is coupled through a roughing valve 232 to a roughing pump 234. The test port 230 is also coupled through a test valve 236 to the foreline of a high vacuum pump 240. Vacuum pump 240 may be a turbomolecular pump, a diffusion pump or a hybrid turbomolecular pump which includes axial pumping stages and molecular drag stages. The foreline 238 is also coupled to a forepump 242 which maintains the required operating pressure at the foreline 238. The inlet of vacuum pump 240 is coupled to the inlet of a spectrometer tube 244.

In operation, the roughing pump 234 initially evacuates the test port to a pressure in the range of 100 to 300 millitorr. The test valve 236 is then opened and the helium tracer gas drawn in through the test port 230 passes in reverse direction through vacuum pump 240 to the spectrometer tube 244. Since the vacuum pump 240 has a much lower reverse flow rate for the heavier gases in the sample, it blocks these gases from spectrometer tube 244, thereby efficiently separating the tracer gas.

Having thus described various illustrative non-limiting embodiments, and aspects thereof, modifications and alterations will be apparent to those who have skill in the art. Such modifications and alterations are intended to be included in this disclosure, which is for the purpose of illustration and explanation, and not intended to define the limits of the invention. The scope of the invention should be determined from proper construction of the appended claims and equivalents thereof.

Claims

WHAT IS CLAIMED IS:

1. A method for leak detection, comprising: providing a trace gas permeable member and a trace gas sensor having an enclosed connection to the permeable member; mounting the permeable member in gas communication with a conduit that carries a trace gas; passing the trace gas carried by the conduit through the permeable member; and sensing the trace gas with the trace gas sensor, while preventing contaminants from reaching the trace gas sensor.

2. A method as defined in claim 1, wherein the permeable member comprises a quartz member.

3. A method as defined in claim 1, wherein the permeable member comprises a quartz member, the method further comprising heating the quartz member.

4. A method as defined in claim 1, wherein the permeable member comprises a polymer member.

5. A method as defined in claim 1, wherein the permeable member is permeable to helium.

6. A method as defined in claim 1 , wherein passing the trace gas through the permeable member comprises controlling helium permeability of the permeable member.

7. A method as defined in claim 6, wherein controlling helium permeability of the permeable member comprises controlling temperature of the permeable member.

8. A method as defined in claim 1, wherein sensing the trace gas with the trace gas sensor comprises sensing helium with an ion pump.

9. A method as defined in claim 1, wherein sensing the trace gas with the trace gas sensor comprises sensing helium with a mass spectrometer.

10. A method as defined in claim 1, wherein mounting the permeable member comprises mounting the permeable member inside the conduit.

11. A method as defined in claim 1, wherein mounting the permeable member comprises mounting the permeable member outside the conduit.

12. Apparatus for leak detection comprising: a trace gas permeable member; a trace gas sensor having an enclosed connection to the permeable member; and a flange configured to mount the permeable member in gas communication with a conduit that carries a trace gas.

13. Apparatus as defined in claim 12, wherein the permeable member comprises a quartz member.

14. Apparatus as defined in claim 12, wherein the permeable member comprises a quartz member, the apparatus further comprising a heating element in thermal contact with the quartz member and a heater controller configured to control the heating element.

15. Apparatus as defined in claim 12, wherein the permeable member comprises a polymer member.

16. Apparatus as defined in claim 12, wherein a trace gas permeability of the permeable member is controllable.

17. Apparatus as defined in claim 12, wherein the permeable member is permeable to helium.

18. Apparatus as defined in claim 12, wherein the trace gas sensor comprises an ion pump.

19. Apparatus as defined in claim 12, wherein the trace gas sensor comprises a mass spectrometer.

20. Apparatus as defined in claim 12, wherein the flange is configured to mount the permeable member inside the conduit.

21. Apparatus as defined in claim 12, wherein the flange is configured to mount the permeable member outside the conduit.