1、Designation: E 498 95 (Reapproved 2006)Standard Test Methods forLeaks Using the Mass Spectrometer Leak Detector orResidual Gas Analyzer in the Tracer Probe Mode1, 2This standard is issued under the fixed designation E 498; the number immediately following the designation indicates the year oforigina
2、l adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This specification has been approved for use by agencies of the Department of
3、 Defense.1. Scope1.1 These test methods cover procedures for testing andlocating the sources of gas leaking at the rate of 4.5 3 1014mol/s (1 3 109Std cm3/s)3or greater. The test may beconducted on any object to be tested that can be evacuated andto the other side of which helium or other tracer gas
4、 may beapplied.1.2 Three 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 TestMe
5、thod B, in which the vacuum pumps of the object under testreplace those normally used in the leak detector.1.3 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 a
6、nd health practices and determine the applica-bility of regulatory limitations prior to use. A specific hazardstatement can be found in 19.2.2. Referenced Documents2.1 ASTM Standards:4E 1316 Terminology for Nondestructive Examinations2.2 Other Documents:SNT-TC-1A Recommended Practice for Personnel Q
7、ualifi-cation and Certification in Nondestructive Testing5ANSI/ASNT CP-189 ASNT Standard for Qualification andCertification of Nondestructive Testing Personnel53. Terminology3.1 DefinitionsFor definitions of terms used in this stan-dard, see Terminology E 1316, Section E.4. Summary of Test Methods4.
8、1 These test methods require a helium leak detector that iscapable of detecting a leak of 4.5 3 1015mol/s (1 3 1010Stdcm3/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 accepta
9、ble lengthof time. This requires that the object be clean and dry andusually no larger than a few cubic feet in volume.Also to copewith larger volumes or relatively“ dirty” devices, auxiliaryvacuum pumps having greater capacity than those in the massspectrometer leak detector (MSLD) may be used in c
10、onjunc-tion with the MSLD. The leak test sensitivity will be reducedunder these conditions.4.3 Test Method BThis 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) o
11、r lower.4.4 Test Method CWhen a vacuum system is capable ofproducing internal pressures of less than 2 3 102Pa(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 convent
12、ional MSLD, provided, of course, that theleakage is within the sensitivity range of the RGA or MSLDunder the conditions existing in the vacuum system.5. Personnel Qualification5.1 It is recommended that personnel performing leak test-ing attend a dedicated training course on the subject and pass1The
13、se test methods are under the jurisdiction of ASTM Committee E07 onNondestructive Testing and is the direct responsibility of Subcommittee E07.08 onLeak Testing Method.Current edition approved Dec. 1, 2006. Published January 2007. Originallyapproved in 1973. Last previous edition approved in 2000 as
14、 E 498 - 95 (2000).2(Atmospheric pressure external, vacuum internal). This document covers theTracer Probe Mode described in Terminology E 1316.3The gas temperature is referenced to 0C. To convert to another gas referencetemperature, Tref, multiply the leak rate by (Tref+ 273)/273.4For referenced AS
15、TM 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 fromAmerican Society for NondestructiveTesting (ASNT), P.O. Box28518
16、, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.a written examination. The training course should be appropri-ate for NDT level II qualification according to Recommend
17、edPractice No. SNT-TC-1A 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). Test
18、ing ofsmall components can 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 performan
19、ce overthe projected life 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 t
20、he expected life ofthe device.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 t
21、ime as well as system sensitivityshould 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 whe
22、n there is noconvenient method 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 he
23、lium in the highvacuum chamber. 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 le
24、ak readilyenough since the 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 le
25、ak occursfrequently under 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
26、 is in proper design to eliminatethese 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
27、” pump (large vacuum systems).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.
28、Proper degreasing, vacuumbaking, 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 ther
29、e is a volume at each end 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 ti
30、mes are necessary, the connectionsto 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
31、not a part of the device 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
32、low enough pressure so that 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 us
33、ed in preference to vacuum 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 a
34、llowable sensitivity ofthe 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 MSL
35、D and tune theMSLD to achieve maximum sensitivity in accordance with themanufacturers instruction. Allow sufficient time for the flowrate 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 a
36、mbient tempera-ture for several hours.E 498 95 (2006)210. 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 pumps.NOTE 2This procedure will be automatic where the d
37、evice 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 be partially opened. Maximum testsensitivity will b
38、e 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 flow ofhelium is coming from the tip.10.3 Set the l
39、eak 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 detector output meter. If the probing rateis increa
40、sed, 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 amaximum signal occurs. The approximate leak size can bedet
41、ermined 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 the object to betested, spray the smallest amount o
42、f 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 (preferable) ortemporarily in such a manner as to a
43、llow 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 signal from the standard leak isbarely readable. This
44、 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 larger standard leak and farless test sensitivity or
45、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 sametechnique is continued until all leaks have been similarl
46、ytreated.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 first and would eliminatethe necessity for probing if
47、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 report or otherwise indicate the testresults as req
48、uired.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
49、 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 the vacuumchamber of the object to be tested and as far as practical fromthe inlet to the pumping system.13.3 Operate the equipment until equilibrium vacuum isreached in the vacuum chamber.13.4 Slowly open inlet valve to MSLD. Do not allow theMSLD pressure to exceed manufacturers recommendations.13.5 If inlet valve can be fully opened without exceedi
