1、Designation: E498/E498M 11Standard Practice forLeaks Using the Mass Spectrometer Leak Detector orResidual Gas Analyzer in the Tracer Probe Mode1, 2This standard is issued under the fixed designation E498/E498M; the number immediately following the designation indicates the yearof original adoption o
2、r, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.This practice has been approved for use by agencies of the Department of Defense.1. Scope*
3、1.1 This practice covers procedures for testing and locatingthe sources of gas leaking at the rate of 1 3 108Pa m3/s(1 3 109Std cm3/s)3or greater.The test may be conducted onany object to be tested that can be evacuated and to the otherside of which helium or other tracer gas may be applied.1.2 Thre
4、e test methods are described:1.2.1 Test Method AFor the object under test capable ofbeing evacuated, but having no inherent pumping capability.1.2.2 Test Method BFor the object under test with integralpumping capability.1.2.3 Test Method CFor the object under test as in TestMethod B, in which the va
5、cuum pumps of the object under testreplace those normally used in the leak detector.1.3 UnitsThe values stated in either SI or std-cc/sec unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents: therefore, eachsystem shall be used independently of
6、 the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health p
7、ractices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:4E1316 Terminology for Nondestructive Examinations2.2 Other Documents:SNT-TC-1A Recommended Practice for Personnel Qualifi-cation and Certification in Nondestructive Testing5ANS
8、I/ASNT CP-189 ASNT Standard for Qualification andCertification of Nondestructive Testing Personnel53. Terminology3.1 DefinitionsFor definitions of terms used in this prac-tice, see Terminology E1316, Section E.4. Summary of Practice4.1 The tests in this practice require a helium leak detectorthat is
9、 capable of detecting a leak of 1 3 109Pa m3/s(1 3 1010Std cm3/s).34.2 Test Method AThis test method is used to helium leaktest objects that are capable of being evacuated to a reasonabletest pressure by the leak detector pumps in an acceptable lengthof time. This requires that the object be clean a
10、nd dry. Also tocope with larger volumes or relatively “dirty” devices, auxil-iary vacuum pumps having greater capacity than those in themass spectrometer leak detector (MSLD) may be used inconjunction with the MSLD. The leak test sensitivity will bereduced under these conditions.4.3 Test Method BThi
11、s test method is used to leak testequipment that can provide its own vacuum (that is, equipmentthat has a built-in pumping system) at least to a level of a fewhundred pascals (a few torr) or lower.4.4 Test Method CWhen a vacuum system is capable ofproducing internal pressures of less than 2 3 102Pa(
12、2 3 104torr) in the presence of leaks, these leaks may belocated and evaluated by the use of either a residual gasanalyzer (RGA) or by using the spectrometer tube and controlsfrom a conventional MSLD, provided, of course, that theleakage is within the sensitivity range of the RGA or MSLDunder the co
13、nditions existing in the vacuum system.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.08 on LeakTesting Method.Current edition approved July 1, 2011. Published July 2011. Originally approvedin 1973. Last
14、previous edition approved in 2006 as E498 - 95 (2006). DOI:10.1520/E0498_E0498M-11.2(Atmospheric pressure external, vacuum internal). This document covers theTracer Probe Mode described in Terminology E1316.3The gas temperature is referenced to 0C. To convert to another gas referencetemperature, Tre
15、f, multiply the leak rate by (Tref+ 273)/273.4For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.5Available fromA
16、merican Society for NondestructiveTesting (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Unit
17、ed States.5. Personnel Qualification5.1 It is recommended that personnel performing leak test-ing attend a dedicated training course on the subject and passa written examination. The training course should be appropri-ate for NDT level II qualification according to RecommendedPractice No. SNT-TC-1A
18、of the American Society for Nonde-structive Testing or ANSI/ASNT Standard CP-189.6. Significance and Use6.1 Test MethodAis the most frequently used in leak testingcomponents which are structurally capable of being evacuatedto pressures of 0.1 Pa (approximately 103torr). Testing ofsmall components ca
19、n be correlated to calibrated leaks, and theactual leak rate can be measured or acceptance can be based ona maximum allowable leak. For most production needs accep-tance is based on acceptance of parts leaking less than anestablished standard which will ensure safe performance overthe projected life
20、 of the component. Care must be exercised toensure that large systems are calibrated with reference leak ata representative place on the test volume. Leak rates aredetermined by calculating the net gain or loss through a leak inthe test part that would cause failure during the expected life ofthe de
21、vice.6.2 Test Method B is used for testing vacuum systems eitheras a step in the final test of a new system or as a maintenancepractice on equipment used for manufacturing, environmentaltest or for conditioning parts. As the volume tends to be large,a check of the response time as well as system sen
22、sitivityshould be made. Volume of the system in liters divided by thespeed of the vacuum pump in L/s will give the response timeto reach 63 % of the total signal. Response times in excess ofa few seconds makes leak detection difficult.6.3 Test Method C is to be used only when there is noconvenient m
23、ethod of connecting the leak detector to the outletof the high vacuum pump. If a helium leak detector is used andthe high vacuum pump is an ion pump or cryopump, leaktesting is best accomplished during the roughing cycle as thesepumps leave a relatively high percentage of helium in the highvacuum ch
24、amber. This will obscure all but large leaks, and thetrace gas will quickly saturate the pumps.7. Interferences7.1 Series leaks with an unpumped volume between thempresent a difficult if not impossible problem in helium leaktesting. Although the trace gas enters the first leak readilyenough since th
25、e pressure difference of helium across the firstleak is approximately one atmosphere, it may take many hoursto build up the partial pressure of helium in the volumebetween the two leaks so that enough helium enters the vacuumsystem to be detected by the MSLD. This type of leak occursfrequently under
26、 the following conditions:7.1.1 Double-welded joints and lap welds.7.1.2 Double O-rings.7.1.3 Threaded joints.7.1.4 Ferrule and flange-type tubing fittings.7.1.5 Casings with internal voids.7.1.6 Flat polymer gaskets.7.1.7 Unvented O-ring grooves.7.2 In general, the solution is in proper design to e
27、liminatethese conditions; however, when double seals must be used, anaccess port between them should be provided for attachment tothe MSLD. Leaks may then be located from each side of theseal and after repair, the access port can be sealed or pumpedcontinuously by a “holding” pump (large vacuum syst
28、ems).7.3 Temporarily plugged leaks often occur because of poormanufacturing techniques. Water, cleaning solvent, plating,flux, grease, paint, etc., are common problems. To a largeextent, these problems can be eliminated by proper preparationof the parts before leak testing. Proper degreasing, vacuum
29、baking, and testing before plating or painting are desirable.7.4 In a device being tested, capillary tubing located be-tween the leak and the leak detector can make leak testingextremely difficult as test sensitivity is drastically reduced andresponse time increased. If there is a volume at each end
30、 of thecapillary, each such volume should be attached to the leakdetector during testing. If this is impossible, the device shouldbe surrounded with a helium atmosphere while attached to theleak detector for a long time to assure leak tightness. Whenunusually long pumping times are necessary, the co
31、nnectionsto the leak detector (and all other auxiliary connections) thatare exposed to the helium should be double-sealed and thespace between the seals evacuated constantly by a smallauxiliary roughing pump to avoid allowing helium to enter thesystem through seals that are not a part of the device
32、to betested.TEST METHOD AHELIUM LEAK TESTING OFSMALL DEVICES USING THE MSLD8. Apparatus8.1 Helium Mass Spectrometer Leak Detector, having aminimum detectable leak rate as required by the test sensitivity.8.2 Auxiliary Pumps, capable of evacuating the object to betested to a low enough pressure so th
33、at the MSLD may beconnected.NOTE 1If the object under test is small and clean and the MSLD hasa built-in roughing pump, the auxiliary pumps are not required.8.3 Suitable Connectors and Valves, to connect to theMSLD test port. Compression fittings and metal tubing shouldbe used in preference to vacuu
34、m hose.8.4 Standard Leaks of Both Capsule Type (Containing itsown Helium Supply) and Capillary Type (an Actual Leak whichis Used to Simulate the Reaction of the Test System to HeliumSpray)The leak rate from the capsule-type leak should beadequate to demonstrate the minimum allowable sensitivity ofth
35、e MSLD. The capillary type should be slightly smaller thanthe test requirement.8.5 Vacuum Gage, to read the pressure before the MSLD isconnected.8.6 Helium Tank and Regulator, with attached helium probehose and jet.9. Calibration of MSLD9.1 Attach the capsule leak to the MSLD and tune theMSLD to ach
36、ieve maximum sensitivity in accordance with themanufacturers instruction. Allow sufficient time for the flowE498/E498M 112rate from the capsule leak to equilibrate. The capsule leakshould be stored with the shutoff valve (if present) open, andthe leak should be allowed to equilibrate to ambient temp
37、era-ture for several hours.9.2 MSLD calibration shall be performed prior to and uponcompletion of testing.10. Procedure10.1 Evacuate the device to be tested until near equilibriumpressure is reached on the rough vacuum gage. Open the valveto the leak detector and close the valve to the roughing pump
38、s.NOTE 2This procedure will be automatic where the device is rela-tively small and clean and where an automatic MSLD is used withoutexternal pumps. Do not allow the pressure in the spectrometer tube toexceed the manufacturers recommendation. This means in some casesthat the MSLD inlet valve can only
39、 be partially opened. Maximum testsensitivity will be achieved with the inlet valve completely open and theauxiliary pump valve completely closed. However, testing at reducedsensitivity levels can be done as long as the inlet valve can be opened atall.10.2 Adjust the helium probe jet so that a small
40、 flow ofhelium is coming from the tip.10.3 Set the leak detector on the appropriate lowest range.10.4 Pass the tip of the helium probe by the end of thestandard capillary leak at a rate similar to the scan rate at whichthe object under test will subsequently be tested. Note thedeflection of the leak
41、 detector output meter. If the probing rateis increased, the test sensitivity will be decreased, and if theprobing rate is decreased, the test sensitivity will be increased.Consequently, when a leak is indicated during leak testing, itwill be necessary to move the probe slowly backward until amaximu
42、m signal occurs. The approximate leak size can bedetermined by multiplying the size of the standard leak by themaximum reading obtained from the located leak and dividingby the maximum reading obtained when the helium wasapplied directly to the standard leak.10.5 Starting at the most suspect part of
43、 the object to betested, spray the smallest amount of helium on the part that willgive a signal when sprayed on the capillary leak. If there aredrafts, work up opposite to the direction of air flow.10.6 When a leak is pinpointed, it should be first evaluatedif desired, then sealed either permanently
44、 (preferable) ortemporarily in such a manner as to allow repair at a later time,before proceeding to look for additional leaks. If the leak is solarge that the MSLD output saturates (that is, goes to the top ofthe highest range), it can be evaluated by reducing thesensitivity of the test until the s
45、ignal from the standard leak isbarely readable. This can be done by opening the roughingvalve and partially closing the MSLD inlet valve or byreducing the sensitivity of the leak detector itself if moreconvenient. If the unknown leak still produces an off-scalesignal, it will be necessary to use a l
46、arger standard leak and farless test sensitivity or to use a reduced percentage of helium inthe probe. (For instance, a probe gas concentration of 1 %helium and 99 % nitrogen would reduce the apparent sensitiv-ity by a factor of 100.)10.7 After the first leak has been found and sealed, the sametechn
47、ique is continued until all leaks have been similarlytreated.10.8 After all leaks have been found and repaired, it isdesirable to enclose the entire device in a helium envelope(which can be a plastic bag or a large bell jar) to determine thetotal device integrity.10.9 This step could also be done fi
48、rst and would eliminatethe necessity for probing if no leakage is shown. However, ifthere are any materials in the device that are pervious tohelium, doing this step first may build up the helium back-ground to such a degree that subsequent probing would beinsufficiently sensitive.10.10 Write a test
49、 report or otherwise indicate the testresults as required.TEST METHOD BHELIUM LEAK TESTING OFVACUUM EQUIPMENT AND SYSTEMS THAT HAVEINTEGRAL PUMPING SYSTEMS OF THEIR OWN11. Apparatus11.1 Helium MSLDSame apparatus as Section 8.12. Calibration of MSLD12.1 See Section 9.13. Preparation of Apparatus13.1 Connect inlet valve of MSLD to foreline of object to betested. If possible, insert a valve in the foreline between themechanical pump and the MSLD connection. All connectionsshould have as high a conductance as is practical.13.2 Attach the standard capillary leak to
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