Helium Leak Detection Techniques - METROVAC

1 VACUUM TECHNOLOGYH elium Leak Detection Techniques391 Adixenby Alcatel Vacuum TechnologyVACUUM TECHNOLOGYWe have assembled in the following pages a number of useful elements thatwill help you: to get information about the various Helium leak Detection methodswhich are commonly used in the field to determine the best product for your have not presented an exhaustive examination in this chapter. Pleasecontact the technical departments of Alcatel Vacuum Technology for advise andassistance on unusual leak Detection OF THE LEAK :- maintenance applications- quality control- the system or piece to be tested canbe placed under vacuum- you need to detect very small leaksSPRAYING TEST(vacuum methods)- the system or piece to be testedcannot be placed under vacuum - the sensitivity is not a major issueSNIFFING TEST(sniffing methods)see page 394see page 400A. IntroductionHelium Leak Detection TechniquesLeak Detection is used to detect micro-openings, porosities, etc.

2 In test parts. Thedetection of these cracks involves the use of a light tracer gas which is capableof infiltrating the smallest leak quickly: detector samples and measures the Helium flow rate entering the test partvia the methods can be used to test the part. The right one will be selectedaccording to the test part and the measurement accuracy TEST :- industrial applications- quality control- you need to detect small the piece can be HARD VACUUM TEST(vacuum methods)see page 397- you need to detect small the piece to be tested is a smallsealed TEST(vacuum methods)see page 399- you only need to detect large leaks. - the piece to be tested can TEST WITH ACCUMULATION(sniffing methods)see page 402 Helium Leak Detection TechniquesVACUUM TECHNOLOGYThe vacuum method is the mostsensitive leak Detection requires that one side of the part beplaced under hard vacuum and theother side to be pressurized side which is placed undervacuum is connected to the leakdetector.

3 If there is a leak, the heliumthat penetrates this side will bedetected by the leak will detail three variants of thismethod in the following pages : spraying test global hard vacuum test bombing spraying method (inboard testing) involves removing air from the test part,connecting it to the analyzer cell and then spraying Helium over the leaking areas are sprayed with detector measures the flow of Helium penetrating the part, and the leak canbe Spraying test394B. Vacuum methodsHelium Leak Detection TechniquesApplicationsLeak test of vacuum systems (vacuum chambers, gas panel, ..) and vacuumcomponents (pumps, valves, gauges, mass-flow).Quality control performed by the manufacturers (OEMs, vacuum manufacturers)and maintenance tests performed by the applications: Semiconductor: thin-film systems, etching, sputtering Instrumentation: electronic microscopes, analytical systems R & D laboratories: particle accelerators, vacuum systemsMain advantages high sensitivity easy to perform local (or global) test relatively inexpensiveNotesThe system or piece to be tested mustbe placed under connection between the piece tobe tested and the detector must beperfectly tight (which means it isimportant to design adapted tools toconnect the piece).

4 Check carefully that the materialOperating conditionsHelium rises in air, so the first rule for spraying Helium is to start spraying at thetop of the vacuum system and work the way second rule is to fully engulf the leak area with Helium to properly size theleak (in other words, the placement of the Helium spray is more important thanthe amount of Helium sprayed).One other reason for limiting the amount of Helium is that excess Helium canpermeate the O-rings on your vacuum system and contribute a background levelthat may be high enough to mask the leaks you are Spraying test (continued)395 Response timeWhen spraying starts, the leak signal is not displayed instantaneously on theanalyzer : the response time depends on the volume V being tested and thehelium pumping speed S of the system at the opening of the part, according tothe following relation:Q = Qf(1 - e )tTT =VSThe response time T is defined as the time to obtain 63 % of :AssumeV = 50 lS= 4 l/sThe time to obtain 63 % of the finalleak rate will be sBEST PRODUCTS Basic needs : ASM 142 Specific needs (large volume, very small leaks): ASM 182 T series Applications requiring dry HLD.

5 ASM 122 D/ASM 182 TD+/ASM 192 T2D+ Helium Leak Detection TechniquesVACUUM Spraying test (continued)396 Advanced configurationsHelium Leak Detector connected at the exhaust of the advantage: the ability to reduce the response time(because the Helium pumping speed is higher) whilekeeping the highest sensitivity. Main issue: difficulty for reaching the fine leak test mode,due to limitation of base pressure of the primary Leak Detector in parallel operation (the detector isused in parallel with the pumping group to test the system).Main advantage: the ability to increase the response time(because the Helium pumping speed is higher).Main issue: sensitivity affected by parallel operation,because of the timeDisappearance time is the time required for the leak detector to recover to itsdesired sensitivity after being exposed to a specific leak x x log VSQQmExample: Assume V = 10 lS= l/sQ= (10 ) x xlog ( ) = 21 sWhere:Td= disappearance time in = volume in litersS= Helium pumping speed inliters/secondQ = leak rate in (measured)Qm= smallest detectable leak(expected background) Helium Leak Detection Techniques397 The hard vacuum test involves fillingthe test part with Helium , placing it ina test chamber connected to the theanalyzer cell and removing air fromthe detector measures the flow ofhelium escaping from the partthrough all the leaks at the end of thetest leak cannot be located (globaltest).

6 Global hard vacuum testApplicationsMainly used to perform an industrialquality test in a production facilityThe test is performed thanks to adedicated leak test system integratedinto the production applications : Automotive: evaporators,condensors, airbags, radiators,fuel tanks, .. Refrigeration: compressors Mechanical: drums, fireextinguishers Electrical: SF6 circuit breakers,lightbulbs Pharmaceutical: blistersHelium Leak Detection TechniquesPumping unit integrated in an industrialLeak Detection SystemsVACUUM TECHNOLOGYMain advantages high sensitivity high throughput easy integration in a productionline (loading/unloading + interfacewith PLC/PC)NotesThe connection between the piece tobe tested and the detector must beperfectly tight (which means it isimportant to design adapted tools toconnect the piece).Some leaks can be missed if the partto test is not pressurized underoperating Global hard vacuum test (continued)398 Helium Leak Detection SystemPump down calculationT= x log x VSP1P2 Example: ConditionsV = 40 lS = l/sP1= 1000 mbarP2= 2 mbarT= (( ) x 40 ) x log (1000/2) = 71 sWhere:T= time in = volume in inlet pumping speed in l/sP1= start pressure in mbarP2= test pressure in mbarNote: The above formula is valid forclean, dry, and empty parts with aconstant pumping configurationsPiece to be tested with a complete system (integrating a pumping package):-> large pieces-> high throughput (ex: condensers/evaporators, airbags)Piece to be tested with a standaloneunit:-> small pieces-> small vacuum chamber(ex: Airbags with ASM 182 T or ASI 20 MD)BEST PRODUCTS Basic needs.

7 ASM 142 orASM 182 T (depending on thevolume of the test chamber) Integration in a turnkey system(very high throughput):ASI 20 MDHelium Leak Detection Techniques399 The bombing method is used forsealed objects that cannot beconnected directly to the detector(semiconductors, waterproof watches,..).The part is placed in a chambercontaining pressurized Helium (bombing chamber). The heliumpenetrates the part if it has a part is then removed from thechamber and placed in a vacuumchamber which is connected to thedetector. The Helium escapes from thepart through the leak and produces asignal (Refer to Global hard vacuumtest page 397, for more information).A measurement of the signal can bemade, but it is necessary to take intoaccount several parameters : the pressurization time the Helium bombing pressure the internal volume the size of the Bombing testApplicationsProduction quality test performedthanks to a dedicated leak test system(DGC type).

8 Some applications: Electronic (back-end): sealedsemi conductor devices (quartz, Instrumentation: thermalsensors, infrared detectors Medical: pacemakers, auditive implantsMain advantages The only solution to test sealedcomponents with high sensitivity High throughputNotes Reserved for small components Possible to miss gross leaks Time consuming for step 1(bombing time and ventilation timemust be strictly respected)BEST PRODUCTS Standard needs (high throughput):DGC 1001 Other possibilities:ASM 142 or ASM 182 THelium Leak Detection TechniquesVACUUM TECHNOLOGYThe sniffing method is the easiest wayto detect a this method, Helium is introducedinto the component (or could alreadybe present as part of the product tobe tested). Helium leaking from the product tothe atmosphere is detected by"sniffing" the outside of the articleusing a sniffer probe attached to ahelium leak will detail two variants of thismethod in the following pages: sniffing test sniffing test with Sniffing testThe sniffing method involves pressurizing the tested part with Helium .)

9 Thedetector samples the Helium escaping from the part via a LDS (long distancesniffer) sniffer probe is moved over potential leak areas and the leak can Sniffing methodsHelium Leak Detection Techniques401 ApplicationsMainly used to leak test pressurizedsystems or systems usually filled witha control performed by themanufacturers and maintenance testsperformed by the applications: Refrigeration:air conditioning units Aeronautic: aircraft tanks Chemical industry:process lines, tubings Heavy industry: liquid natural gas carrier Other:telecommunication cables Can be also used to measurethe Helium concentration: Fluid or smoke circulationanalysis Geological or mining researchMain advantages Ability to locate the leak The system or piece to be testeddoes not need to be placed undervacuum. Very easy to perform Relatively inexpensiveNotes The sensitivity is limited by thehelium background (due to thehelium concentration = 5 ppm).

10 The response time will depend onthe length of the sniffer Sniffing test (continued)BEST PRODUCTS Basic needs:ASM 142 S (ASM 142) Specific needs (transportation):ASM 102 SHelium Leak Detection TechniquesVACUUM TECHNOLOGYThe tested part is pressurized with Helium and placed under a cover containinga sniffer Helium from the leak then accumulates over time inside the cover. Thedetector measures the concentration of Helium , but the leak cannot be to perform an industrial quality test in a production facility (when a hard vacuum test cannot be used):Test performed thanks to a dedicated leak test system (can be integrated into the production line)Some applications: Refrigeration: air conditioning units Mechanical industry: fire extinguishers Automotive: aluminium Sniffing test with accumulation402 Helium Leak Detection Sniffing test with accumulation (continued)403 Main advantages global test relatively inexpensive the system can be easily integratedin a production line (loading /unloading and interface withPLC/PC).