ASTM E432-1991(2004) Standard Guide for Selection of a Leak Testing Method《渗漏试验方法的选择》.pdf

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1、Designation: E 432 91 (Reapproved 2004)Standard Guide forSelection of a Leak Testing Method1This standard is issued under the fixed designation E 432; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A num

2、ber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide2is intended to assist in the selection of a leaktesting method.3Fig. 1 is supplied as a simplified guide.1.2 The type of item

3、to be tested or the test system and themethod considered for either leak measurement or location arerelated in the order of increasing sensitivity.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 sta

4、ndard 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:E 425 Terminology Relating to Leak Testing43. Terminology3.1 DefinitionsThe definitions of terms relating to leaktesting which

5、 appear in Terminology E 425 shall apply to theterms in this guide.4. Selection of System4.1 The correct choice of a leak testing method optimizessensitivity, cost, and reliability of the test. One approach is torank the various methods according to test system sensitivity.4.2 The various testing me

6、thods must be individually ex-amined to determine their suitability for the particular systembeing tested. Only then can the appropriate method be chosen.For example, radioactive gases are not generally employed asa tracer for leak location because of the hazards associated withtheir use. However, s

7、uch gases are employed in leakagedetection equipment when they can be safely added to, andremoved from, a test chamber on a periodic basis.4.3 It is important to distinguish between the sensitivityassociated with the instrument employed to measure leakageand the sensitivity of the test system follow

8、ed using theinstrument. The sensitivity of the instrument influences thesensitivity that can be attained in a specific test. The range oftemperatures or pressures, and the types of fluids involved,influence both the choice of instrument and the test system.4.4 The sensitivity of various test systems

9、 differ. For ex-ample, a test utilizing a mass spectrometer leak detectornormally has an ultimate sensitivity of 4.4 3 1015mol/s whenthe procedure involves the measurement of a steady-state gasleakage rate. The sensitivity of the test may be increased underspecial conditions to 4.4 3 1019mol/s by al

10、lowing an accu-mulation of the leakage to occur in a known volume before ameasurement of leakage is made. In the first case, the sensi-tivity of the test equals the sensitivity of the instrument;whereas in the second case, the sensitivity of the test is 104times greater than that of the instrument.

11、If the test systemutilizes a mass spectrometer operating in the detector-probemode, the sensitivity of the test can be 102to 104smaller thanthat of the mass spectrometer itself.5. Leakage Measurement5.1 In general, leakage measurement procedures involvecovering the whole of the suspected region with

12、 tracer gas,while establishing a pressure differential across the system byeither pressurizing with a tracer gas or by evacuating theopposite side. The presence and concentration of tracer gas onthe lower pressure side of the system are determined and thenmeasured.5.2 A dynamic test method can be pe

13、rformed in the shortesttime. While static techniques increase the test sensitivity, thetime for testing is also increased.5.3 Equipment or devices that are the object of leakagemeasurement fall into two categories: (1) open units, which areaccessible on both sides, and (2) units that are sealed. The

14、second category is usually applied to mass-produced itemsincluding gas and vacuum tubes, transistors, integrated circuitmodules, relays, ordnance units, and hermetically sealed in-struments.1This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-tive Testing and is the direct respo

15、nsibility of Subcommittee E07.08 on LeakTesting.Current edition approved May 1, 2004. Published June 2004. Originallyapproved in 1971. Last previous edition approved in 1997 as E 432 - 91 (1997).2For ASME Boiler and Pressure Vessel Code applications see related Recom-mended Guide SE-432 in the Code.

16、3Additional information may be obtained from Marr, J. W., Leakage TestingHandbook, Report No. CR-952, NASA, Scientific and Technical InformationFacility, P. O. Box 33, College Park, MD 20740 (Organizations registered withNASA) or Clearing House for Federal, Scientific and Technical Information, Code

17、410.14, Port Royal Road, Springfield, VA 22151.4Withdrawn. Replaced by Terminology E 1316.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.3.1 Open or Single-Sealed UnitsEither evacuation orpressurization of one side of a unit that

18、is accessible on bothsides, may be employed to test for leakage across a unit.5.3.1.1 Systems Leaking to VacuumIn the order of in-creasing sensitivity for testing an evacuated system, the meth-ods include: flow measurement, absolute pressure measure-ment, the alkaline-ion diode halogen detector, and

19、 the heliummass spectrometer leak detector.(a) The first approach to the testing of units that may beevacuated is to determine if there is an inherent tracer in thesystem. This gas should be utilized if possible.(b) When one side is evacuated, leakage of the tracer intothe vacuum will reach the dete

20、ctor quickly if there is essen-tially no stratification. However, evacuation does not alwaysallow the most sensitive and reliable measurement. If theevacuated region is extremely large, high pumping speeds willbe required and the leakage gas will tend to follow streamlinesto the pump port. The amoun

21、t of tracer gas that reaches thedetector may then be substantially reduced depending on thelocation of the detector in the evacuated region.(c) When no inherent tracer is available, the next approachshould be to determine if there is a gage in the system thatmight be used for leakage measurement. Th

22、is gage might be anionization gage or, in some fortunate circumstances, a massspectrometer in the system as part of the analytical instrumen-tation. Consideration should be given not only to gages that arenormally used for leak detection, but to any gas concentrationdetection equipment that may be u

23、sed for leakage measurementif it happens to be available. Equipment not originally intendedfor pressure measurement may be used; for example, it ispossible to detect the pressure rise in a leaking vacuum tube byoperating the grid at a positive and an anode at a negativepotential, and noting an incre

24、ase in anode current with time.(d) When there is no inherent tracer or gage within thesystem, a standard testing method must be chosen based on thesensitivity desired.5.3.1.2 Systems Leaking to AtmosphereThe choice of atesting method for systems leaking to atmospheric pressureshould be made in the s

25、ame manner as suggested for evacuatedsystems. In the absence of an inherent tracer or a gage, one ofthe standard methods of making leakage measurements againstatmospheric pressure must be chosen. These are, in the order ofincreasing sensitivity: flow measurement, pressure measure-ment, bubble testin

26、g (immersion), helium mass spectrometer,infrared analyzer, alkaline-ion diode halogen detector, andradioactive tracer. (Note that the helium mass spectrometerFIG. 1 Guide for Selection of Leakage Testing MethodE 432 91 (2004)2method may not be the most sensitive in this situation wherethe measuremen

27、t is to be made at atmospheric pressure.)5.3.2 Multiple-Sealed UnitsIn the testing of sealed units,applicable testing methods are, in the order of increasingsensitivity: bubble testing, flow measurement, pressure mea-surement, infrared analyzer, alkaline-ion diode halogen detec-tor, helium mass spec

28、trometer, and radioactive tracer. The lastfour methods are applicable to a back pressurizing testingprocedure.(a) Back pressuring, or bombing, is the usual procedureused for applying a tracer gas. If the leak in the unit isexceptionally large, any tracer gas in the unit will escaperapidly when it is

29、 subjected to reduced pressure. Consequently,high-sensitivity tests for this tracer will be ineffective if thetracer gas has already escaped from the system. It is thereforerecommended that all parts be tested for large leaks after thehigh sensitivity tests have been conducted. Tests for large leaks

30、involved relatively insensitive procedures. If liquids are em-ployed, the smaller leaks can easily become clogged and maynot be detected during a subsequent high sensitivity test.5.3.2.1 Evacuated Unit TestingWith evacuated units, thechoice of a testing procedure is relatively simple. If the systemi

31、ncludes a gage, this gage may be used to show the presence ofgas contamination. The back pressurizing procedure should beused in the absence of an internal gage. The units should bepassed through a bubble test after the back pressurizing test tolocate the exceptionally large leaks. If the unit can b

32、e openedto the atmosphere, a flow measurement procedure may be used.5.3.2.2 Units Sealed with AirTesting procedures for unitssealed with air may be divided into two categories: lowsensitivity testing by either bubble testing, flow measurement,or pressure measurement, and high sensitivity testing usi

33、ng theback pressurizing technique.5.3.2.3 Units Sealed With Tracer GasUnits sealed withtracer gas may be tested for leakage of the gas out of the unitby dynamic or static procedures. Generally, the partial pressureof tracer gas inside a unit will be higher than it would be if thetracer gas was force

34、d into an evacuated unit through a smallleak as is done in the back pressurizing procedure. Thus,pre-sealing with tracer gas leads to a more sensitive procedureinvolving fewer steps. As in the case with the other methods, afinal inspection must be conducted by means of a bubble testprocedure to loca

35、te exceptionally large leaks.6. Leak Location6.1 Leak location can be subdivided into a tracer probemode and a detector probe mode. The tracer probe procedure isused when the system is evacuated, and the tracer gas comesfrom a probe located outside the system. The detector probemode is used when the

36、 system is pressurized with tracer gasand testing is done at atmospheric pressure. Usually the tracerprobe technique is more rapid because the gas reaches thedetector at a higher concentration, despite any streamingeffects, than it does with a detector probe which detects tracergas which is highly d

37、iluted by atmospheric gases. In thedetector probe mode, a higher pressure differential across thesystem may be used, and therefore leaks of a smaller conduc-tance can be found. In using either mode it is important thatleak location be attempted only after the presence of a leak hasbeen verified.6.1.

38、1 Testing of Evacuated Systems (Tracer ProbeMode)In the location of leaks in evacuated systems, firstdetermine if there is an inherent detector within the system.This may be a pressure gage; preferably a gage that is specificfor some tracer gas which may be used. If such a gage does notexist, the me

39、thods to use in the order of increasing sensitivityare: sonic, pressure change, gage response, high-voltage dis-charge, alkali-ion diode leak halogen detector, infrared detec-tor, and mass spectrometer.6.1.2 Testing at Atmospheric Pressure (Detector ProbeMode)In testing a system that is leaking into

40、 atmosphere, thefirst consideration is whether or not the leaking fluid may beused as a tracer. This will always be the case when using eitherthe sonic method or the bubble-testing method. However, thetracer might be of a composition that will also prove satisfac-tory for use with the other testing

41、methods. In order ofincreasing sensitivity these methods for leak location are:chemical testing, gage response, infrared gas analyzer, massspectrometer, and alkali-ion diode halogen detector.6.1.2.1 When using liquid penetrants, the pressure may beatmospheric both inside and outside. Both surfaces m

42、ust beaccessible. Leaks are detected visually by fluorescence orcoloration.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity

43、 of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments

44、 are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not

45、received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E 432 91 (2004)3