1、Designation: E 499 95 (Reapproved 2006)Standard Test Methods forLeaks Using the Mass Spectrometer Leak Detector in theDetector Probe Mode1, 2This standard is issued under the fixed designation E 499; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase 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 Defense.1. Scope1.1 Th
3、ese test methods cover procedures for testing andlocating the sources of gas leaking at the rate of 4.5 3 1013mol/s (1 3 108Std cm3/s)3or greater. The test may beconducted on any device or component across which a pressuredifferential of helium or other suitable tracer gas may becreated, and on whic
4、h the effluent side of the leak to be testedis accessible for probing with the mass spectrometer samplingprobe.1.2 Two test methods are described:1.2.1 Test Method ADirect probing, and1.2.2 Test Method BAccumulation.1.3 This standard does not purport to address all of thesafety concerns, if any, ass
5、ociated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:4E 1316 Terminology for Nondestructive Examinations2.2 Ot
6、her Documents:SNT-TC-1A Recommended Practice for Personnel Qualifi-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, se
7、e Terminology E 1316, Section E.4. Summary of Test Methods4.1 Section 1.8 of the Leakage Testing Handbook6will be ofvalue to some users in determining which leak test method touse.4.2 These test methods require a leak detector with afull-scale readout of at least 4.5 3 1012mol/s (1 3 107Stdcm3/s)3on
8、 the most sensitive range, a maximum 1-min drift ofzero and sensitivity of 65 % of full scale on this range, and62 % or less on others (see 7.1). The above sensitivities arethose obtained by probing an actual standard leak in atmo-sphere with the detector, or sampling, probe, and not thesensitivity
9、of the detector to a standard leak attached directly tothe vacuum system.4.3 Test Method A, Direct Probing (see Fig. 1), is thesimplest test, and may be used in parts of any size, requiringonly that a tracer gas pressure be created across the area to betested, and the searching of the atmospheric si
10、de of the area bewith the detector probe. This test method detects leakage andits source or sources. Experience has shown that leak testingdown to 4.5 3 1011mol/s (1 3 106Std cm3/s)3in factoryenvironments will usually be satisfactory if reasonable precau-tions against releasing gas like the tracer g
11、as in the test area areobserved, and the effects of other interferences (Section 6) areconsidered.4.4 Test Method B, Accumulation Testing (see Fig. 2),provides for the testing of parts up to several cubic metres involume as in Fig. 2(a) or in portions of larger devices as in Fig.2(b). This is accomp
12、lished by allowing the leakage to accu-mulate in the chamber for a fixed period, while keeping it wellmixed with a fan, and then testing the internal atmosphere foran increase in tracer gas content with the detector probe. The1These test methods are under the jurisdiction of ASTM Committee E07 onNon
13、destructive Testing and are 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 E 499 - 95(2000).2(Atmospheric pressure external, pressure above atm
14、ospheric internal). Thisdocument covers the Detector Probe Mode described in Guide E 432.3The gas temperature is referenced to 0C. To convert to another gas referencetemperature, Tref, multiply the leak rate by (Tref+ 273)/273.4For referenced ASTM standards, visit the ASTM website, www.astm.org, orc
15、ontact 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 Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/w
16、ww.asnt.org.6Marr, J. William, “Leakage Testing Handbook,” prepared for Liquid PropulsionSection, Jet Propulsion Laboratory, NationalAeronautics and SpaceAdministration,Pasadena, CA, Contract NAS 7-396, June 1961.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, P
17、A 19428-2959, United States.practical sensitivity attainable with this method depends pri-marily on two things: first, on the volume between the chamberand the object; and second, on the amount of outgassing oftracer gas produced by the object. Thus, a part having consid-erable exposed rubber, plast
18、ic, blind cavities or threads cannotbe tested with the sensitivity of a smooth metallic part. Thetime in which a leak can be detected is directly proportional tothe leak rate and inversely proportional to the volume betweenthe chamber and the part. In theory, extremely small leaks canbe detected by
19、this test method; however, the time required andthe effects of other interferences limit the practical sensitivityof this test method to about 4.5 3 1013mol/s (1 3 108Stdcm3/s)3for small parts.5. Personnel Qualification5.1 It is recommended that personnel performing leak test-ing attend a dedicated
20、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 of the American Society for Nonde-structive Testing or ANSI/ASNT Standard CP-189.6. Significance and Use6.1 Test Meth
21、od A is frequently used to test large systemsand complex piping installations that can be filled with a tracegas. Helium is normally used. The test method is used to locateleaks but cannot be used to quantify except for approximation.Care must be taken to provide sufficient ventilation to preventinc
22、reasing the helium background at the test site. Results arelimited by the helium background and the percentage of theleaking trace gas captured by the probe.6.2 Test Method B is used to increase the concentration oftrace gas coming through the leak by capturing it within anenclosure until the signal
23、 above the helium background can bedetected. By introducing a calibrated leak into the samevolume for a recorded time interval, leak rates can be mea-sured.FIG. 1 Method AE 499 95 (2006)27. Interferences7.1 Atmospheric HeliumThe atmosphere contains aboutfive parts per million (ppm) of helium, which
24、is beingcontinuously drawn in by the detector probe. This backgroundmust be “zeroed out” before leak testing using helium canproceed. Successful leak testing is contingent on the ability ofthe detector to discriminate between normal atmospherichelium, which is very constant, and an increase in heliu
25、m dueto a leak. If the normally stable atmospheric helium level isincreased by release of helium in the test area, the referencelevel becomes unstable, and leak testing more difficult.7.2 Helium Outgassed from Absorbent MaterialsHeliumabsorbed in various nonmetallic materials (such as rubber orplast
26、ics) may be released during the test. If the rate andmagnitude of the amount released approaches the amountreleased from the leak, the reliability of the test is decreased.The amount of such materials or their exposure to helium mustthen be reduced to obtain a meaningful test.7.3 Pressurizing with T
27、est GasIn order to evaluate leak-age accurately, the test gas in all parts of the device mustcontain substantially the same amount of tracer gas. When thedevice contains air prior to the introduction of test gas, or whenan inert gas and a tracer gas are added separately, this may notbe true. Devices
28、 in which the effective diameter and length arenot greatly different (such as tanks) may be tested satisfactorilyby simply adding tracer gas. However, when long or restrictedsystems are to be tested, more uniform tracer distribution willbe obtained by first evacuating to less than 100 Pa (a few torr
29、),and then filling with the test gas. The latter must be premixedif not 100 % tracer.7.4 Dirt and LiquidsAs the orifice in the detector probe isvery small, the parts being tested should be clean and dry toavoid plugging. Reference should be frequently made to astandard leak to ascertain that this ha
30、s not happened.8. Apparatus8.1 Helium Leak Detector, equipped with atmospheric de-tector probe. To perform tests as specified in this standard, thedetector should be adjusted for testing with helium and shouldhave the following minimum features:8.1.1 Sensor Mass Analyzer.8.1.2 Readout, analog or dig
31、ital.8.1.3 Range (linear)A signal equivalent to 4.5 3 1011mol/s (1 3 106Std cm3/s)3or larger must be detectable.8.1.4 Response time,3sorless.FIG. 2 Method BE 499 95 (2006)38.1.5 Stability of Zero and Sensitivity A maximum varia-tion of 65 % of full scale on the most sensitive range while theprobe is
32、 active; a maximum variation of 62 % of full scale onother ranges for a period of 1 min.NOTE 1Variations may be a function of environmental interferencesrather than equipment limitations.8.1.6 Controls:8.1.6.1 Range, prefereable in scale steps of 33 and 103.8.1.6.2 Zero, having sufficient range to n
33、ull out atmospherichelium. Automatic null to zero is preferred.8.2 Helium Leak StandardTo perform leak tests as speci-fied in this standard, the leak standard should meet thefollowing minimum requirements:8.2.1 Ranges4.5 3 108to 4.5 3 1013mol/s (103to108Std cm3/s)3full scale calibrated for discharge
34、 to atmo-sphere.8.2.2 AdjustabilityAdjustable leak standards are a conve-nience but are not mandatory.8.2.3 Accuracy, 625 % of full-scale value or better.8.2.4 Temperature Coeffcient, shall be stated by manufac-turer.8.3 Helium Leak Standard,asin8.2 but with ranges of4.5 3 1012or 4.5 3 1013mol/s (10
35、7or 108Std cm3/s).38.4 Other ApparatusFixtures or other equipment specificto one test method are listed under that test method.9. Material9.1 Test Gas Requirements:9.1.1 To be satisfactory, the test gas shall be nontoxic,nonflammable, not detrimental to common materials, andinexpensive. Helium, or h
36、elium mixed with air, nitrogen, orsome other suitable inert gas meets the requirements. If the testspecification allows leakage of 4.5 3 1010mol/s (1 3 105Std cm3/s)3or more, or if large vessels are to be tested,consideration should be given to diluting the tracer gas withanother gas such as dry air
37、 or nitrogen. This will avoidexcessive helium input to the sensor and in the case of largevessels, save tracer gas expense (Note 2).9.1.2 Producing Premixed Test GasIf the volume of thedevice or the quantity to be tested is small, premixed gases canbe conveniently obtained in cylinders. The user can
38、 also mixgases by batch in the same way. Continuous mixing usingcalibrated orifices is another simple and convenient methodwhen the test pressure does not exceed 50 % of the tracer gaspressure available.NOTE 2When a vessel is not evacuated prior to adding test gas, thelatter is automatically diluted
39、 by one atmosphere of air.9.2 Liquid Nitrogen, or other means of cold trap refrigera-tion as specified by the maker of the leak detector.10. Calibration10.1 The leak detectors used in making leak tests by thesetest methods are not calibrated in the sense that they are takento the standards laborator
40、y, calibrated, and then returned to thejob. Rather, the leak detector is used as a comparator betweena leak standard (8.2) (set to the specified leak size) which ispart of the instrumentation, and the unknown leak. However,the sensitivity of the leak detector is checked and adjusted onthe job so tha
41、t a leak of specified size will give a readilyobservable, but not off-scale reading. More specific details aregiven in Section 11 under the test method being used. To verifysensitivity, reference to the leak standard should be madebefore and after a prolonged test. When rapid repetitive testingof ma
42、ny items is required, refer to the leak standard oftenenough to ensure that desired test sensitivity is maintained.11. Procedure11.1 General Considerations:11.1.1 Test SpecificationsA testing specification shall bein hand. This shall include:11.1.1.1 The gas pressure on the high side of the device t
43、obe tested; also on the low side if it need differ from atmosphericpressure.11.1.1.2 The test gas composition, if there is need to specifyit.11.1.1.3 The maximum allowable leak rate in standard cubiccentimetres per second.11.1.1.4 Whether the leak rate is for each leak or for totalleakage of the dev
44、ice.11.1.1.5 If an “each leak” specification, whether or not otherthan seams, joints, and fittings needs to be tested.11.1.2 Safety FactorWhere feasible, it should be ascer-tained that a reasonable safety factor has been allowed betweenthe actual operational requirements of the device and themaximum
45、 specified for testing. Experience indicates that afactor of at least 10 should be used when possible. Forexample, if a maximum total leak rate for satisfactory opera-tion of a device is 2.2 3 1010mol/s (5 3 106Std cm3/s)3, thetest requirement should be 2.2 3 1011mol/s (5 3 107Stdcm3/s)3or less.11.1
46、.3 Test PressureThe device should be tested at orabove its operating pressure and with the pressure drop in thenormal direction, where practical. Precautions should be takenso that the device will not fail during pressurization, or that theoperator is protected from the consequences of a failure.11.
47、1.4 Disposition or Recovery of Test GasTest gasshould never be dumped into the test area if further testing isplanned. It should be vented outdoors or recovered for reuse ifthe volume to be used makes this worthwhile.11.1.5 Detrimental Effects of Helium Tracer GasThis gasis quite inert, and seldom c
48、auses any problems with mostmaterials, particularly when used in gaseous form for leaktesting and then removed. When there is a question as to thecompatibility of the tracer with a particular material, anauthority on the latter should be consulted. This is particularlytrue when helium is sealed in c
49、ontact with glass or otherbarriers that it may permeate.11.1.6 Correlation of Test Gas Leakage with Other Gases orLiquids at Different Operating Pressures:11.1.6.1 Given the normal variation in leak geometry, accu-rate correlation is an impossibility. However, if a safety factorof ten or more is allowed, in accordance with 11.1.2, adequatecorrelation for gas leakage within these limits can usually beobtained by assuming viscous flow and using the equation:Q25 Q1N1/N2!P222 P12!/P422 P32!#E 499 95 (2006)4where:Q2= test leakage, Pam
